11-01-2009

Finalization of acoustic systems Radiotehnika 35AC-012 (S-90)

Radiotehnika 35AC-012, Radiotehnika S-90, Radio engineering 35AC-012, Radio engineering S-90

At the moment I am the happy owner of the Radiotehnika S-90 speakers.

Consideration of acoustics in normal condition

To begin with, the full name of acoustics should be specified - 35AC-012. From their issue, it immediately becomes clear that we are dealing with high-class acoustics, by Soviet standards, that is, acoustics with very high characteristics. It should be noted right away that by Soviet standards it was not the most best acoustics, but an ordinary ordinary workhorse. There were acoustics that had a more balanced sound, for example, the same Cleavers / Corvettes 35AC-008.

But as they say, we have what we have. Let's go back a little to the moment of their purchase. I took them from my friend for $ 50, when I came to him, at the sight of the decorative grilles protecting the sound-emitting heads, I wanted to cry, they were dented and very cruelly at that (mainly the grilles of the tweeter and mid-range speaker suffered). But this did not frighten me, since what was sold on our market cost at least $ 100, and the quality of the speakers deserved no more than 3, and in these speakers the speakers looked at 5. In general, I took these speakers to my home. When connected to an amplifier, the sound was quite decent. Nevertheless, two shortcomings should be noted, one of which is inherent in all 35AC-012, and, as it turned out, all of its 35AC clones, to one degree or another.

The first of the shortcomings that just killed me on the spot is an incomprehensible overtone during the operation of the woofer, very similar to the fact that something was stuck to the speaker at the back, and now this is something vibrating, as it turned out later, it was a drop of solder that stuck to diffuser on the back. The second drawback was precisely in the mid-frequency dynamics 15GD-11A - according to the old standard and 20GDS-1-8 according to the new one (these speakers came in a large number of modifications, for this reason it is extremely difficult to track which one you have). And again, a small digression, in which I will say that the differences in the standards are in the designation of power, that is, according to the old standard, the rated power of the speaker was indicated, and according to the new standard, nameplate power is indicated (from the sound engineering course:

1. The rated power of the speaker is such a power of the speaker, when summed up, it works with harmonic distortion levels not higher than the permissible
2. Passport power (often also called noise power): this is the level of power supplied to the speaker, at which the level of harmonic distortion is equal to ten times the level at rated power).

An additional division into the frequency ranges of the heads was also introduced, which was now indicated in the name of the speaker, in particular, this is the third letter.

So the disadvantage of this speaker is that it often starts to resonate at high volume and thereby spoils the sound picture, and as you know, the midrange speaker is crucial in shaping the sound picture.

Consider now in order all the speakers that we have available:

1)Low-frequency - 30GD2, aka 75GDN-1-4 (8):

Purpose - use in closed and phase-inverted remote acoustic systems of household radio equipment of the highest complexity group as a low-frequency link when working indoors. Loudspeaker head of electrodynamic type, low-frequency, round, with unshielded magnetic circuit. The diffuser holder is made of die-cast aluminum alloy. The conical diffuser is made of impregnated paper pulp. Suspension - torroidal shape - made of rubber. The centering washer is made of impregnated fabric.

I also want to add that the speakers have a relatively heavy dome and a rubber surround is used, which spoils the quality of the bass, it becomes more solid and booming than the speakers with a lighter mass of the moving part and foam rubber suspension. But it should be borne in mind that the bass is affected not only by the design, but also by the acoustic design itself, for this reason, these troubles can be slightly eliminated and the speaker will play decently. On the other hand, due to the rubber suspension, the speaker turned out to be very reliable and practically unkillable, and the foam rubber suspension soon crumbles due to the presence of sulfur in the air and the speaker needs to be repaired.

Purpose - use in closed and phase-inverted remote acoustic systems of household radio equipment of the 1st and 2nd complexity groups as a mid-frequency link when working indoors. Loudspeaker driver of electrodynamic type, midrange, round, with unshielded magnetic circuit. The diffuser holder is made of die-cast aluminum alloy. The conical diffuser and the spherical cap are made of impregnated paper pulp. Torroidal suspension - made of polyurethane foam. The centering washer is made of impregnated fabric.

Here is actually a photo of this miracle of technology:

It should be said that at a good volume it decently distorts the sound, but as practice has shown this problem very easy to solve and very simple.

Purpose - the use in closed acoustic systems of household radio equipment of the highest complexity group as a high-frequency link when working indoors. Loudspeaker head of electrodynamic type, tweeter, round, with unshielded magnetic circuit. Mounting flange and acoustic lens are made of plastic. The dome-shaped diaphragm with a suspension is made on the basis of polyethylene terephthalate.

In general, they sound good, only the filter tuning is close to resonant frequencies.

Upon closer examination of the acoustics (especially from the inside), you begin to be horrified by the build quality, for this reason we will begin to refine. We will refine it according to the simplest possible scheme, without interfering with the filters, since without specialized equipment there is nothing to do there. For those who are interested, here is the acoustics diagram:

Refinement 35AC-012

I will describe in order all the stages of improvement that my columns went through:
1. Disassembly:

• First of all, we take them to a secluded place (meaning a room) in which our experimental subjects will not be available to children (if any) and other family members. We lay the speaker system on our back and begin to disassemble it.
• Now remove the decorative trims from all the speakers and put them aside.

Here they are:

Then we get the speakers. ATTENTION When unscrewing the bass speaker (the tweeter and midrange speaker are attached with the same screws as the decorative trim, and the woofer is attached separately from the trim), be extremely careful, because if a screwdriver comes off, you will disfigure it. Then we solder the wires connecting the filter and the speakers with a soldering iron, and boldly hide the speakers in a secluded place.

• We remove the cover of the phase inverter and pull out the phase inverter itself, and this must be done as carefully as possible, since we are working with plastic, and it can easily break. Then we hide these details in a secluded place.
• Now we take on the regulator / regulators of the HF / MF links. To dismantle them, it is necessary to remove the decorative plug in the center of the regulator, then unscrew the opened screw and remove the regulator knob. After that, carefully pry off the remaining plastic lining with the help of two chisels and carefully remove it, then unscrew the 4 screws securing the attenuator itself and now it can be pushed out into the case. We push it out and solder it from the filter. We put it aside, in the future it will be necessary to conjure a little over it. By the way, the junction of the attenuator housing and the speaker housing is abundantly covered with a sealing viscous substance, I personally used it again when I assembled it in place, but you can use sealant or plasticine.
• We take out the bags of cotton wool, which, in theory, lie in your speaker system and set aside.
• We dismantle the panel with filters, it is screwed to the body, having previously unsoldered the wires from the output at the back of the speaker system. Putting it aside, as we will spend a lot of time working with them.
• Finally, remove the panel with terminals from the rear cover of the speaker and set it aside.

It seems like a lot of work has been done, but in fact it is just a drop in the ocean. More interesting and labor-intensive work lies ahead.

2. Restore appearance:

For this purpose, we take the gratings and speaker covers we removed earlier, level them, carefully sand, degrease and paint several layers of automotive paint (which is in spray cans) several times and leave to dry. I’ll make a reservation right away that I restored the gratings only for the reason that I have Small child, which can damage the speakers, otherwise the easiest solution would be to abandon the grilles as such, since they only bring minuses to the sound, think for yourself.

3. Refinement of the speaker cabinet:

It's actually very simple, and is carried out in several stages:

• If desired, the body can be strengthened. What will it give us? More precise and even bass, since the body panels will vibrate less and, accordingly, will introduce less overtones into the bass component of the sound. How to do it? This is purely everyone's business, because as many people as there are so many decisions. In general, everything consists in installing spacers, installing additional corners at the joints of the acoustic system walls, installing stiffeners on the speaker walls. Personally, I limited myself to pasting additional corners at the joints. You can also glue all the joints tightly. Unfortunately, I can’t show a photo, since the entire acoustic system is already dampened with foam rubber.
• Sealing all joints and seams. It is carried out very simply with the help of various materials. For example, I used plumbing sealant. The procedure is simple: we cover the joints with sealant and gently smear it with your finger, thereby tightly sealing possible gaps.
• In a hardware store we buy foam rubber 10 mm thick (I personally chose this thickness, do not take too much as you will strangle the case) and glue it to all walls except the front one with glue. Thus, we dampen the body, thereby increasing its virtual volume.

To do this, we buy terminal blocks with gold-plated connectors of a universal type in the store. Since the S-90 terminal block itself is large, and the new ones are small, we dismantle the connectors from the terminal blocks and install them on the body from the S-90 terminal block. After that, we lubricate the installation place with sealant (do not be sorry, then wipe off the excess) and put it all in place, tighten the screws. Here is a photo of what you should have:

5. We proceed to the alteration and installation of the filter in place:

• First of all, carefully examine the filter, pay attention to the fasteners of parts, since inductors were often fastened with metal screws, which immediately knocks down the filter setting.
• If there were problems in fasteners, bring it to the end by excluding metal parts from fasteners. There are also cases of assembling the filter on a metal plate, then transfer the filter to a plywood panel.
• We take a leaf, a pen in our hands and carefully redraw all the elements of the circuit, restoring the filter circuit itself, so to speak, because the parameters of the speakers varied and for this reason the filter circuit could be changed at the factory. By the way, we exclude the attenuator from the circuit, it just spoils the sound.
• Now we pick up a soldering iron (preferably 100 watts) and disassemble the filter, or rather, simply remove all the jumpers that were installed from the factory.
• Now we are assembling the filter, instead of jumpers we will now use an oxygen-free copper cable with a cross section of 4 mm 2, the cable can be bought at any car audio store. It should also be noted that you should not take a very expensive cable, as changes in sound quality will be insignificant, but the costs are simply enormous.
• After assembling the filter, we solder the wires that will go to the speakers based on: for the LF link 4 mm 2, for the MF link 2.5 mm 2, for the HF link 2 mm 2.
• We put the filter in place, after which we solder the terminal blocks to it (observe the polarity, otherwise you will lose the sound picture).
• The very last step is to run the wires to the speakers, fix them and cover the filter with foam rubber.

You will get something similar to these photos:

6. Attenuator setting:

• We remove all resistance from it.
• We put it in its place.
• We seal carefully.
• Additionally, we close it with foam rubber (I closed it only on the front wall)
• We install all the decorative panels to the end.

7. Installation of a phase inverter:

Everything is simple here, we put it back on the sealant, we carefully monitor that it is not pinched anywhere with foam rubber, as this will knock down its setting.

8. Install the overlay on the phase inverter:

We put it in the same way as it was removed, just put it on the sealant and on new screws, since the panel itself often rattles on the bass. Seal well the joint between the panel and the phase inverter.

9. Let's start installing the dynamic heads in place:

• A) Install the HF head:

1) We remove that parody of the sealant that stands on it (some kind of felting gum, felting cardboard, is behind it).
2) We cut out a new seal, a mouse pad is perfect, in particular a black porous base.
3) Solder the wires to the speaker and install it in place.
4) We put in place a decorative overlay (grille if desired) and tighten it tightly with screws.

• B) Install the midrange head:

1) We make a cylinder from foam rubber, of such a size that our box fits into it. We put this cylinder inside the column and pass a cable through it, which we bring out.

2) We pass the wire through the box (most likely we will have to expand the hole), after which we put the box in place, adjust the length of the wire and seal the hole into which the wire is passed.
3) Solder the wires to the speaker.
4) Now the crucial stage is the damping of the mid-frequency head. To do this, we sew a cylinder of foam rubber, of such a size that it fits tightly on the speaker frame and closes all the windows.

5) We fill the box with cotton wool, after fluffing it up.
6) We put the dynamic head, grille (optional) and frame in place and twist.

1) First, put back the bags with cotton wool that were removed during the disassembly of the speakers. Solder the wires to the head. I tied the wires that are soldered to the head to the frame so that they do not hit the diffuser, because there is a possibility that when you put the speaker in place, the wires will bend and fall into the diffuser holder window.

2) We make a gasket from a porous material, for example
apply window sealant and carefully place the speaker in place.
3) Tighten the fixing screws. Do not apply great efforts, then the speaker will be spring-loaded with a gasket and this will reduce the energy of vibrations transmitted to the case.
4) We put in place the grate (optional) and the decorative trim. If you nevertheless put a grate, then I advise you to cut out small triangles from the foam rubber and put it on the speaker at the place of its attachment, this will eliminate the vibration of the grate, and therefore remove the overtones at high volume.

I came up with this solution a long time ago, look at the photos in more detail:

Conclusion:

After the revision, all the listeners (there were not many of them, five people, but I asked for the most honest information from them) noted more gentle and soft basses, a much cleaner middle, the tops remained practically unchanged (it seemed to me that they became a little cleaner). Also, the acoustics began to quietly take higher volumes.

In conclusion, I would like to say that the proposed method is the cheapest, simplest and most accessible. All components, of course, can still be repeatedly modified or changed. For example, instead of foam rubber, you can use felt (natural), which in theory will give top scores than foam rubber, it is also a good idea to use vibromastics. Many advise replacing 15GD-11A with a 5GDSH broadband, for me this is a bad idea, but this is everyone's business. 10GD-35 - it is advised to treat with a notch filter, 15GD-11A to modify on the basis of halves from a tennis ball (by the way, the idea is quite interesting, I didn’t do it myself because I don’t have such speakers in stock).

Register .

As a child, one of my friends had Vega 50AC-106 speakers at home, then they sunk into the soul with their design, of course, because then, in the early 90s, for me, the boys, these speakers with their plastic overlays were something cosmic, riding perfection. Well, we didn’t really think about the quality of music then. Would like to have these. Time passed, but those columns remained in the memory, as did the desire to receive them. There are also opportunities to acquire them.

A small digression. This post does not claim to be the ultimate truth, nor does it claim to be some kind of audiophile frills, as well as the fact that the result obtained beats all records. Please do not argue on the topic “why did you bother with them, it would be better if you bought new normal ones”, I wanted exactly THAT columns, like a memory from childhood. For listening to music, I have Hifiman HE-400i headphones and homemade tube amplifier to them, this kit already claims some quality, although I'm not going to argue with audiophiles.

Anyone who is interested, please under the cat.

Purchase and initial inspection

With the purchase, everything turned out very simply, I found that same friend from childhood and it turned out that he still had those same speakers. Although they stand in a closet and have not been used for a dozen years. For a symbolic sum, we shook hands and the speakers moved to me. Immediately upon purchase, I was told that one tweeter burned out and needed to be replaced. Plus, the speakers were pretty dusty, and rust got out on the metal gratings. Next, the speakers were connected to the amplifier to test the performance. All the speakers turned out to be working except for one tweeter, which was confirmed by its dialing tester later. Of course, the sound of the speakers in the state as is did not please me. After the first turn on, the speakers were completely disassembled. The case is tested for the strength of the seams, often with old Soviet speakers side panels just glued on. I was lucky, all the joints were glued firmly, by the way, my cases were made entirely of plywood including the back wall, which is not often found in this model. Much more often, the side walls are made of plywood and the back is made of chipboard.

Next, the filter was completely disassembled to check its compliance with the original circuit, by the way, here it is:


Capacitors and resistors at face value coincided with the circuit. All the capacitors I had were metal-paper MBGOs, which in general is not so bad, because in real designs people also met electrolytes. By the way, after measurement, the capacitors showed deviations from the nominal value within 1%, which is just wonderful. But most of all I was interested in the inductance of the coils, but with them it was expectedly unlucky. NONE of the coils matched the circuit in inductance, and moreover, the coils did not match each other in pairs of speakers. For example, the inductance of the low-frequency coils was 0.85 mH and 0.64 mH, while according to the scheme it should be 2.8 mH. With MF and HF the story is exactly the same. Oh well, anyway, the scheme will be completely redone.

Work plan

After the initial inspection, a rough plan was drawn up:

1. Gluing all seams, joints and holes from the inside of the columns with sealant;
2. Gluing wooden spacers inside the body according to the front-back and left-right scheme;
3. Treatment of all walls with rubber-bitumen mastic to reduce resonances;
4. Pasting all walls with a layer of batting;
5. Replacement of tweeters with the manufacture of new podiums for them;
6. Complete alteration of filters with a change in the scheme and ratings of parts;
7. Replacement of all seals under the speakers;
8. Replacement of all wires;
9. Installation of ports with terminals;
10. Cleaning of panels and painting of gratings;
11. Reduction of resonances and bounce of front panels;

Well, once the plan is drawn up, you can get to work.

We cut, saw, wind, solder, paint and so on

The first step was to disassemble and clean the front panels. The metal grids are sanded, treated with a rust converter and painted. After that, the panels were assembled back, and the metal meshes were installed in plastic on a sealant in order to eliminate their rattling. Sealant is not visible from the outside.

Further, all the joints of the body, the holes were carefully smeared with building silicone sealant from the inside. This is done in order to eliminate any whistles from the outgoing air. There were no gaps in the body, but still. The next step was to glue two spacers of dry shtaketins with a section of 45x20 mm into the body, they were glued between the front-back walls and between the left-right walls, and the spacers were also glued together, so that a rigid cross was obtained. Thus, we increase the rigidity of the case, because the panels here are already quite large and the wall thickness is only 12 mm. After that, the body from the inside is completely smeared with two layers of rubber-bitumen mastic.

The next step was the insertion of ports with screw terminals for inserting wires into the case. (Photo didn't survive for some reason)

To upholster the case from the inside, ordinary batting was purchased from a fabric store, where it is somewhere 6-7 mm thick, so mats were made from batting folded into three layers. These mats were glued on all walls except the front, on the same rubber-bitumen mastic and additionally fixed in the corners with a furniture stapler.

After finishing work with the body, it's time to deal with the electrical part. Firstly, it was necessary to decide what to put in place to replace the native tweeters. I didn’t manage to find my native HF, and on the Internet they ask quite a lot for them, from 700 to 1000 rubles for an old HF, I think a lot. In addition, it is widely believed on the Internet that native 10GDV-2s are generally not particularly good. After reading the Internet and estimating the budget, as well as the expediency of buying expensive tweeters for these speakers, our 15GDV92-16, produced by the Novosibirsk NOEMA, were chosen. In terms of resistance and sensitivity, they are the same as 10GDV-2, and in terms of quality, they say, they are significantly superior. By the way, thanks to the NOEMA company for the prompt shipment and good packaging of the ordered speakers.

While the speakers were traveling through the Russian Post, I started reworking the filters. Again, at first I dug forums for a very long time, collected opinions and eventually found a scheme for reworking the filters of these columns, with good reviews and sufficient justification from the author.
The scheme was taken

Looking ahead a little, I will say that I liked the sound of the speakers with these filters.
As you can see, coils with a fairly high inductance are used here at LF and MF. It is not so easy to wind these on the “air”, because at the same time it must also have low resistance, which means you need to use a thick wire, the dimensions of the coils are not small. Therefore, it was decided to wind the coils on frames with transformer iron cores. A plumbing polypropylene pipe with a diameter of 40 mm was taken as a frame, strips of transformer iron, cut from old Soviet transformers, were tightly stuffed inside. The low-frequency coil is wound with a wire with a diameter of 1.6 mm along the varnish, and the midrange is 1.2 mm along the varnish. The HF coils were wound on native frames without cores, with a native wire, where it is somewhere 0.6-0.8 mm over the varnish. All coils were wound with careful control of the resulting inductance using an LC meter. This made it possible to achieve an almost perfect match of the inductance with the circuit. The capacitors in the filters were left with native MBGOs, all resistors were ordered with new ones with a power of 35 W, a resistance of 10 Ohms and 3.3 Ohms. 10 Ohm resistors were taken with a margin and with the help of a tester, the values ​​\u200b\u200bthat were closest to those indicated in the circuit were selected. The entire wiring of the filter is made with a rigid single-core installation wire with a cross section of 2.5 mm2. This section was chosen not so much from the desire to make the wire as thick as possible, but so that the wire would not hang out and reliable contact pads could be bent from it.

While fiddling with filters, and it took more than one day, the speakers came. Of course, their dimensions were different from the old ones, so we had to make new podiums for them. Well, after that it came to assembly.

The filters were installed in the housing, of course, they did not stand in the old place, I had to re-drill the holes and lower the filter below. The top of the filter was covered with batting; it was specially made longer on the back wall.

The phase inverter pipes had to be glued before installation, as they fell apart in their hands into two halves. They were inserted into the body on the sealant and glued with batting.

It's up to the speakers. The tweeters are fixed to the podiums through spacers. MF glasses are inserted into the housing for sealant. The glasses themselves are half filled with fluffy cotton wool. Seals made of automotive soundproofing material Splen are glued to the midrange and bass speakers. When pulling the speaker, it compresses the joint very well. The midrange speaker, when pressed, reluctantly goes inside and returns slowly, which indicates the tightness of the structure.

Unfortunately, the metal shiny caps on the bass and midrange speakers did not spare time, they were slightly peeled off. I had to paint them with acrylic spray paint. I tried to make it as neat and as thin as possible.

And at the end of the work with the case, the legs were cut out to replace the poor plastic relatives. I cut out the legs with a diameter of 7 cm from a sheet of soft rubber 4 cm thick. And let the audiophiles throw rotten eggs at me, but they work no worse than the spikes, which I refused after much thought.

After assembly, this is what happened:

After that, the entire body was covered with a colorless matte varnish.

Plastic cladding panels were glued on the inside with pieces of STP Aero automotive vibration isolation, which gave them weight and completely removed all sonority. Under the panels, Madeleine strips were glued onto the body, this is a special sealing anti-creak material, something like impregnated foam rubber. This is done in order to press the panels as tightly as possible to the body.

This work was completed. According to the results of listening, we can say that the speakers began to play much better than before the alteration, it became pleasant to listen to them. There will be no comparisons simply because I have nothing to compare with. There is Microlab speakers SOLO2 Mk2 converted to passives. The same tracks from the same amplifier reworked by Vega play much better, however, this is not surprising, the class of these microlabs is not at all high. Comparing Vega with Hifiman HE-400i headphones is at least stupid, these are things of completely different classes and different eras.

The set results have been achieved. I was nostalgic for the same speakers from my childhood, achieved a better and more pleasant sound and had a good time with my hobby. Now these speakers are at my house as the main ones, but it’s far from a fact that after a while they will not be replaced by something of a better quality, while it is likely that these may be other old Soviet speakers.

The budget of the whole event did not go beyond 5000 rubles, this includes the purchase of speakers, the purchase of speakers and the purchase of some materials. For the money to find something better and better sounding I think it is impossible. By the way, for the same S90 Radio Engineering, they ask us for 10,000 :) We promoted them on the Internet :)

Thank you all for your attention!

The first domestic speaker that meets the requirements for Hi-Fi equipment (the initial letters of the English words high fidelity - high quality, high fidelity of sound reproduction) was the S-90 35AC-012 speaker system: three-way, phase inverter type, 30GD-1 loudspeakers are used , 15GD-11, 10GD-35. Based on this model, acoustic systems 35AC-016 (with bass reflex), 35AC-018 (with bass reflex), 35AC-008 (closed), 35AC-015 (with passive radiator). All of them have similar parameters and differ in appearance. Currently, this one, to some extent, has ceased to satisfy the needs of lovers of high-quality sound reproduction. Taking into account the fact that a fairly wide range of expensive modern acoustic equipment, but not always of high quality, is presented on the current market, we will consider options for refining a pair of S-90 35AC-012 acoustic systems, released in 1985 by the Riga Radio Plant. A. S. Popov, equipped with newer, at that time, developments of LF, MF heads - 30GD-2 and 15GD-11A. principled circuit diagram and the layout of the AC filter parts are shown in Figure 1.

Rice. Fig. 1. Electric filter for acoustic system "S - 90" 35 AC-012: a - circuit diagram; b - the location of the elements on the board

Capacitors C1, C2, C4-7 are used type MGBO-2, C9, C8 - K73-11. The filter elements are mounted on 12 mm plywood with dimensions of 210 x 160 mm. The inductors are installed in a horizontal position and, moreover, L1, L2 and L3, L4 are placed close to each other, respectively. The filter itself is fixed on the back wall inside the speaker cabinet behind the woofer.

Frame

Carefully remove the protective grilles of the heads and the heads themselves, the filter and other elements that will restrict access to the inner surfaces of the housing walls. Carry out preventive maintenance. The joints of the walls and the seats under the woofer, midrange speakers are smeared from the inside with a silicone sealing mass. Seal with silicone (if necessary) the gaps between the rear, side, bottom and top walls on the outside of the case, having previously cleaned them of dust, dirt and glue. In order not to stain the veneer finish of the body with sealant, it is closed around the slots with paper construction tape. Excess sealant is removed. After it hardens, a shallow cut is made with a sharp knife under a metal ruler along the edges of the adhesive tape, at the points of its mating with the sealing compound. The tape is removed. The sealant is used to match the body color or transparent.

Among the many radio amateurs being finalized by the S-90, a common means of combating panel vibrations is to increase their rigidity by using additional "stiffening ribs" (slats), struts, etc. They also additionally cover the inner walls with a sound absorber. Which is not always justified, since such measures lead to a decrease in the internal volume of the case, which, in turn, reduces and even eliminates the efficiency of the phase inverter.

A simple increase in the rigidity of the walls by using additional "stiffening ribs" or thickening the panels only increases the resonant frequencies of the panels and changes the nature of the distribution of their vibrations and radiation, since the number of vibrating surfaces and their sizes change. The thickening of the panels, in addition, increases the weight and cost of decoration. Therefore, for the manufacture of decoration, it is more advisable to use materials with increased internal losses. vibrational energy during their deformation (increased "internal friction"), as well as sufficiently high elasticity. Such materials, called vibration damping or vibration absorbing materials, can be applied to conventional panels. Vibration-absorbing materials convert part of the oscillatory energy of vibrations into heat and increase the mechanical resistance of the panels, thereby reducing the amplitude of vibrations. Vibration damping is especially effective at resonant frequencies, when the amplitudes of vibrations and bending or shear deformations increase. The use of a vibration-absorbing coating on acoustic design panels leads to an increase in the overall rigidity of the panel, and therefore it seems possible to reduce the thickness of the panels by 1.5 - 2 times without fear of an increase in their vibrations. Therefore, a self-adhesive vibroplast with a thickness of 1.5 - 2 mm is applied to the inner surfaces of the walls of the speakers being finalized (a flexible and elastic vibration-absorbing material, which is a polymeric self-adhesive composition duplicated with aluminum foil, Fig. 2, is used to reduce vibrations of car body parts).

Rice. 2 Vibroplast

For a perfectly tight fit to the surface of vibration-isolating materials, the walls of the housing must be prepared from the inside. Namely, sand with medium grit sandpaper and prime, for example, with nitro-lacquer or PVA glue. After that, the necessary blanks are marked and cut out from a piece of vibroplast (on some materials there is a special marking in the form of molded squares 1 x 1 cm, which allows you to do without a ruler and marker). Bend the corner of the protective film on the workpiece and apply it to the intended place. Attach the edge of the material to the surface and gradually, gently smoothing it, while removing the film, stick the entire piece. The material is finally rolled with a roller, achieving maximum fit.

The sound-absorbing coating increases the sound absorption of low frequencies up to 500…1000 Hz. The degree of sound absorption should be proportional to the surface area of ​​the coating. If you mount it on the walls of the case not close, but at a distance of 20 - 50 mm from them, then the sound absorption at frequencies below 500 Hz increases. This condition 35AC-012 was fulfilled by the manufacturer - mats with cotton wool in sufficient quantities are located at a certain distance from the walls (approximately in the central part of the box). Therefore, additionally covering the walls with a sound absorber is not only useless, but also harmful. Rollers or cushions of sound-absorbing material suspended at the geometric center of the loudspeaker give the same results as placing it on the walls of the box.

Rice. 3. Sealing the seams of the bass reflex tunnels

The construction of the 35AC-012 phase inverter port has the shape of a curved tunnel of an unusual configuration in cross section. This is due to the goal of satisfying the following conditions: rigidity and the absence of resonant overtones in the material of the port. It consists of two glued plastic parts. The places of gluing look around. The cracks found during inspection are filled with dichloroethane. After that, at these points, both parts of the phase inverter port are tightened with clamps and dried - fig. 3. It will also be useful to paste over its walls with strips of vibroplast. After such processing, the plastic of the port becomes hard and deaf. It is recommended to install an Acoustic Impedance Panel (PAS) at the output of the bass reflex port. it technical solution, protected by the USSR author's certificate No. 577699, allows to reduce the acoustic quality factor of the loudspeaker head several times. The speaker system with such a PAS sounds more natural, without "mumbling".

The weakest link

The frequency response of the midrange driver 15A - 11A has a sharp drop above 4.5 kHz - fig. 4a, the acoustic quality factor is about 11.8. And the higher the quality factor of the oscillatory system, the stronger it emphasizes the frequencies coinciding with the resonant ones, or close to them. Which, in practice, excludes the possibility of obtaining a full-fledged undistorted sound when it is turned on through a midrange bandpass filter, if the necessary measures are not taken. To eliminate the first drawback, the following method is used.

Rice. Fig. 4. Medium-frequency dynamic head 15GD-11A (20GDS-4-8): a - frequency response of sound pressure; b) - dimensions and installation dimensions

Soak the dust cap of the head with nail polish remover, you can use solvents 646, 647 and others. Carefully remove it with a scalpel (Fig. 5, b). Remember that due to the strong action of the field of the magnetic system on a steel instrument, careless movements can damage the elements of the speaker! Then wipe with a cotton swab dipped in the same nail polish remover, the glue diffuser. Coated with glue "Moment" lower part horn and the top of the voice coil. Dry for 10 - 15 minutes. Again, coat both parts and immediately connect them, pressing lightly (Fig. 5, e). The horns are installed both new and extracted, in the above way, from old speakers (Fig. 5, c).

Rice. Fig. 5. Gluing the horn in 15GD-11A: a - dynamic head 15GD-11A; b - removing the dust cap; c - dynamic broadband head 10GDSH-1-4 (10GD-36K); g - high-frequency horns 10GDSh-1-4; e - stages of fitting the horn for 15GD-11A

The glued horn is designed for the 10GDSH-1 dynamic head. For our case, it should be adjusted. Fitting consists in cutting it, while measuring the frequency response of the speaker. To do this, place the speaker on the same axis as the microphone (preferably measuring), within 40 - 50 cm, in the room no closer than 1 meter from walls, furniture, etc. The microphone is connected to the appropriate port of the computer's video card, and the speaker to the amplifier computer speakers. Run the RightMark 6.2.3 program and measure the frequency response. Cut off the edge of the horn, about 1 cm. Measure the frequency response and compare it with the previous one. The operation is repeated until the most even frequency response is obtained in the middle frequencies, thereby increasing their range to 10 kHz (Fig. 6).

Rice. 6. The amplitude-frequency characteristic of the 15GD-11A head with an additional high-frequency horn

The second and subsequent cuttings should be carried out very carefully, cutting off no more than 3 mm. As a result, the side surface of the horn inside was about 7 mm (from the dust cap to the trim edge) - fig. 5, e. Trimming is performed with nail scissors, since they turned out to be the most acceptable tool for this type of work, they have miniature rounded cutting surfaces. The cut edge, to stiffen, is impregnated with BF-2 glue with slightly diluted ethyl alcohol.

To eliminate the second disadvantage, acoustic damping of the head using PAS is used. Damping the heads with sound-absorbing material is less effective and, moreover, contributes to an increase in resonant frequency. In order to increase the effectiveness of the PAS action on a mobile system operating in acoustic design heads, damping fabric should be placed as close as possible to the diffuser. It is most rational to arrange the PAS in the holes of the diffuser holder. To do this, eight identical elements are cut out of thick cardboard with a thickness of approximately 2 mm (Fig. 7, a). The total area of ​​the holes for the head 15GD-11A should be 22 ... 28 cm 2. One side of each element is smeared with glue moment. After 5 minutes, they are glued onto a cotton fabric stretched with the help of an embroidery hoop. After 30 minutes, the fabric is trimmed around the elements. The PAS elements are slightly bent and glued into the windows of the diffuser holder (Fig. 7. b). Places of gluing are additionally smeared with glue. It is important that the fabric in the holes of the elements is stretched, otherwise there will be no effect from the use of PAS! The use of PAS, i.e. acoustic damper, allows you to slow down the natural oscillations of the diffuser, as a result, the "after-sound" time will be significantly reduced and the sound quality of the speaker will noticeably increase.

Rice. 7. Head 15GD-11A: a - PAS element; b - PAS in the windows of the diffuser holder

The damping effect of the PAS for the dynamic head 15 GD-11A is graphically shown in Figure 8.

Rice. 8. Damping action PAS for head 15GD-11A

The effectiveness of the use of PAS was tested by employees of the Berd Radio Plant. In particular, the harmonic coefficients of the mid-frequency driver 15GD-11A with and without PAS were measured. The measurement results shown in Table 1 show that PAS can significantly reduce the harmonic distortion in the frequency range in which the human ear is most sensitive.

Table 1. Harmonic coefficients of the head 15GD-11A

frequency Hz	Harmonic coefficient, %

A rubber-fabric suspension, to restore elasticity, is impregnated with an aerosol "Air conditioner and tensioner for drive belts". After such a refinement, the frequency range of the head has significantly increased, up to 10 kHz (!), The linearity of the frequency response of sound pressure has improved and, most importantly, the sound quality of the speaker system as a whole.

Crossover filters

In passive crossover filters, their design plays an important role, as well as the choice of specific elements - capacitors, inductors, resistors, in particular, the mutual placement of inductors has a great influence on the characteristics of speakers with filters; closely spaced coils. For this reason, it is recommended to place them mutually perpendicular, only such an arrangement allows minimizing their influence on each other. Inductors are one of the most important components of passive crossover filters. It is not recommended to place the coils closer than 100 mm to each other. The simplest way to refine the filter 35AC - 012 (Fig. 1, b) is to reinstall the coils L1 and L3 perpendicular to the base and to each other. For this arrangement, plastic corners are used, cutting out from cases of old equipment or boxes. Pay special attention to the base material on which the filter parts are placed. It must be dielectric! In some acoustic systems, 35AC-1, "S-90" 35AC-212, the predecessors of "S-90" 35AC-012, the filter parts are mounted on a steel plate, the magnetic properties of which negatively affect the inductors and, of course, sound quality.

The 10GD-35 high-frequency head is shunted with a notch filter tuned to its main resonance frequency of 3 kHz. It is a high quality series LC circuit. The capacitance of the circuit capacitors is 6.6 μF (MBGO and MBM with a tolerance of ± 10% from the nominal value), the coil inductance is 0.43 mH, its winding contains 150 turns of PEV-1 wire 0.8 mm, wound on a frame with a diameter of 22 and a length 22 mm with a cheek diameter of 44 mm. The use, for these purposes, of the filter elements of the acoustic system 10AC - 401 will significantly reduce the costs and labor intensity of the work. The product of the capacitance of the capacitor in microfarads and the inductance of the inductor in mH should be equal to 2.82 (http://www.radiolamp.ru/acoustics/3/). If 2.82: 6.6 = 0.43 mH, then for a circuit with an inductance of 0.5 mH, it is easy to calculate the capacitance of the capacitor: 2.82: 0.5 = 5.6 uF. Just need to pick up the capacitors to the required capacity - 5.6 microfarads.

Another refinement option is unwinding from an inductor of 0.5 mH, extra turns to the required 0.43 mH. It is convenient to use the RLC - meter. In place of the filter resistor of the acoustic system 10AC - 401 (previously removed as unnecessary), a 2 μF capacitor is reinstalled, and in its place a 4 μF capacitor of the same type, MGBO, is attached. MBM capacitors are soldered to the terminals of the capacitors to set the capacitance of the required value of 6.6 μF (Fig. 9). As a result of the described refinement, overtones, rattling and characteristic "hissing" of the 10GD-35 head are eliminated.

Rice. 9. The filter of the acoustic system 10AS - 401, converted into a notch filter for the HF head 10GD-35

conductors

Connecting cable speaker and amplifier, contributes to the sound of the system. Mainly due to the fact that the cable has a certain resistance. The influence of this resistance not only affects the sensitivity of the speakers, but also affects the power distribution between the radiators in the column. To eliminate this effect as much as possible, the cross-sectional area of ​​the wire should be as large as possible, and the length should be as small as possible. In addition, it is necessary that the length and cross section of the wire be the same for all speakers. It is also impossible to exclude the fact that the conductor has a certain inductance, and two closely spaced conductors form a capacitance. In this regard, the twin wire can be considered as an LC filter. low frequencies. That is, the longer the wire, the stronger the high frequencies will be damped. In practice, the influence of the wire inductance appears only when the cable length is over 50 m. Also, when a current of low-frequency sound signals of a high level flows through an acoustic wire, a strong magnetic field is formed around the cable conductors. This field affects the currents flowing through these conductors. sound signal mid and high frequencies, resulting in the sound of the speaker system becoming less clear and transparent. The solution to these problems is to ensure the flow of currents of the low-frequency components of the signal and the currents of its mid-, high-frequency parts along physically separated conductors. To do this, an additional pair of sockets (screw clamps) is installed in the acoustic system, to which the input of the filters of the midrange and high-frequency loudspeakers is connected. Thus, the input of the woofer filter is then connected to a separate pair of input terminals. Such a connection is called "bi-wiring" (bi-wiring), i.e. in two pairs of wires to one speaker. The use of two- and three-pair communication cables with a load allows you to significantly reduce the total cross section of the conductors without increasing the mutual influence of the loudspeakers. Such acoustics with a double set of terminals can also be connected to separate amplifiers, which will already be called "bi-amping" (bi-amping), i.e. two amplifiers per channel. In the latter case, they also get rid of the electrical interaction of the emitter sections. As screw terminals, instrument threaded terminals are used. The material of the stud is brass, the thread is M6 x 0.5, the lamb is covered with ABC plastic.

The most important criterion for choosing a conductor for an AU is its electrical power. The electrical power P supplied to the loudspeaker is understood as the power dissipated by a resistance equal in value to the nominal electrical resistance R n, at a voltage equal to U at the loudspeaker terminals: P = U2 / R n. In the practice of designing domestic speakers, two types of power were usually used - nominal (electrical power, limited by the occurrence of distortions exceeding a given value) and nameplate (the highest electrical power at which the loudspeaker can work satisfactorily for a long time on a real sound signal without thermal and mechanical damage, usually 1.5 ... 2 times higher than the rated power). According to the technical documentation "S-90" 35AC-012, the rated power P nom. \u003d 35 W, passport R pass. = 90 W. The manufacturer of these types of dynamic heads allows their operation with a voltage not higher than 11 volts. In this case, the current I flowing in the voice coil of the woofer will be 2.8 A, and in the voice coil of the midrange loudspeaker - 1.4 A. To calculate the conductor cross section, it is necessary to proceed from the indicated current values.

Note. The calculation is made in a simplified form, provided that there is only active resistance in the circuit, at which the cosine of the phase shift angle of the current and voltage φ is equal to zero. In real electrical circuit loudspeaker always has inductive and capacitive resistances, called reactive, which introduce temporary changes in current and voltage values.

Musical works are variable in nature, both in terms of signal level and frequency, so a current of 2.8 A can theoretically take place, but not constantly and in very short time sections of the musical path, for example, when a bass drum is "thumping". The internal installation of "S-90" 35AC - 012 is made of tinned copper stranded wire in PVC insulation with a cross section of 1 mm 2, which corresponds to the calculated data, since the current density in the copper conductor becomes 6 - 10 amperes per square millimeter. Note that the voice coils of the loudspeakers are wound with a wire of a much smaller cross section: 30GD-1 - 0.1 mm 2, 15GD-11A - 0.02 mm 2, 10GD-35 - 0.005 mm 2. The total cross section of the wires of all coils is 0.125 mm 2 , eight times thinner than the internal mounting wire of the speaker! In the power circuits of power amplifiers of the "S-90" era, with a nominal power of 25 to 50 W per channel, fuses (fuses) for a current of 2 to 3 A were provided, and this, first of all, to power the circuit and then the load.

The real sound signal is impulsive. On a signal with steep fronts, even at frequencies in the audio range, the skin effect (from the English skin - outer layer, sheath) is largely manifested - the effect of current displacement to the surface of the conductor, which leads to an increase in the effective resistance of the connecting cables. .

Low-frequency signals propagate almost throughout the entire volume of the conductor, and the propagation of high-frequency signals occurs mainly in a thin near-surface layer. This skin effect dramatically increases the resistance of the conductor and slightly reduces its inductance. Figure 10 shows the frequency dependence of the impedance of copper conductors of various diameters 1 m long. At f 100 kHz, inductance plays a dominant role. A copper wire with a diameter of 0.16 mm up to a frequency of 20 kHz does not change its resistance, but has a relatively large value, almost 1 ohm. Significantly reduce the conductor resistance and leave it unchanged in the entire band audio frequencies will allow the use of several core insulations with a diameter of not more than 0.16 mm. A bundle of enameled wires intertwined in a special way (from German Litzen - strands and Draht - wire) is called a litz wire.

Rice. 10. Frequency dependence of the impedance of copper conductors of circular cross section 1 m long

Thus, speaker cables should not only have a minimum resistance and inductance, but also have a minimum skin effect. Connecting loudspeakers, especially MF - HF, is best done with a litz wire or copper wire coated with a thin layer of silver. Silver has the highest conductivity among all metals, and its thin layer, in which, due to the skin effect, most of the current flows, has a strong influence on the active resistance of the conductor.

When choosing a mounting wire, it is also necessary to take into account the principle of connecting acoustics through 2 pairs of contacts, which, of course, proportionally distributes power between LF and MF - HF channels. With equal sensitivity of the heads, the maximum noise (passport) power at the crossover frequency, in our case, is 500 Hz for the LF channel - 56% of the total power, and for the MF-HF - 44%. Between the midrange and tweeters, the power at a cutoff frequency of 5000 Hz is distributed by 41.5% and 2.5%, respectively. Such a division of power cannot be considered unconditional, but gross errors in the calculations can be avoided. Speaker heads differ both in sensitivity and in the value of the nominal electrical resistance(Table 2). The difference in each of these parameters leads to the need for an appropriate choice of voltage supplied to the head to obtain a uniform frequency response for pressure. And the voltage supplied to the head is one of the dominant indicators that affect the power.

Table 2. The main parameters of the heads used in the acoustic systems "S - 90" 35AC - 012

Head name according to GOST 9010-78

According to OST 4. 383.001-85. Modern counterpart

Limiting noise (passport) / limiting long-term / limiting short-term power, W

Rated power, W

Rated resistance, Ohm

Frequency range, Hz

Frequency response unevenness, dB

Standard sound pressure, Pa

Main resonance frequency, Hz

Level of characteristic sensitivity, dB/mW

Overall dimensions (in plan), mm

Height, mm

Weight, kg

Note. Information about the parameters is taken from many sources, not always exhaustive, and sometimes contradictory (indicated in brackets).

It should be noted that, in home acoustic design, the influence of conductors on sound quality is negligible compared to other factors. It is necessary to pay attention to more important elements, the acoustic properties of the room, the correct placement of equipment. Information about the exclusivity of oxygen-free copper cables, from wires with the "orientation" of the surface layer of the conductor, which affects the passage of the sound signal in one direction or another, is nothing more than advertising.

Electrical part improved system

The circuit diagram is shown in Figure 11,a. The filter uses capacitors with a maximum operating voltage of 160 V: K73-11 (C1, C10, C11); K73-16 (S2-4); MBGO-2 (C5 - 9); MGBO-2 and MBM (S13) connected in parallel. Installation is carried out with a single-core copper wire with a cross section of 1 mm 2 (extracted from a communication cable with air insulation of each core) and a MGSHV wire (flexible multi-wire, conductive conductors made of tinned copper wire, wrapped with electrical insulating silk with PVC insulation, for intra- and inter-unit installation of various electronic equipment and appliances for Rated voltage up to 1000 V alternating current frequencies up to 10,000 Hz), with sections of 1.5 mm 2 (for a low-frequency link) and 0.5 mm 2 (only in the mid-high-frequency filter). The connection between the terminals, the divider, the filter and the high-frequency head is carried out with a LEPShD 500 x 0.05 wire (round wire 0.98 mm 2 with a core twisted from 500 copper wires with a diameter of 0.05 mm, insulated with a polyurethane-based varnish, with a two-layer natural silk winding recommended for the frequency range 250…500 kHz, with electrical resistivity, at 20˚C, 0.0158…0.018 Ohm/m). The playback level control can be omitted.

Rice. Fig. 11. Electric filter of the acoustic system "S - 90" 35 AC-012 after completion: a - circuit diagram; b - the location of the elements on the board

All elements are placed on the plywood of the native filter "S - 90" 35 AC - 012, (Fig. 11, b). Particular attention should be paid to the relative position of the inductors. Details must be rigidly fastened. Connections are made with as short wires as possible, avoiding sagging. Filter elements must not touch. If necessary, for tight mounting, use sealant, ties, insulating tape, etc. Otherwise, as a result of vibrations of the case and air vibrations inside the speaker, the filter parts will rattle and emit unpleasant overtones. The filter is attached to the bottom wall inside the case, thereby minimizing the effect on the inductors of the magnetic field of the woofer.

Installing speakers

Before installation, first of all, the woofer and tweeter heads (the midrange head has already been brought back to normal) are inspected for the integrity of the structures, especially in the places of gluing, the absence of mechanical damage to parts, the integrity of the suspensions of the woofer. It can be rubber or polyurethane (35AC - 018). The suspension, made of not very high quality rubber, hardens over time. Polyurethane is destroyed by impurities of sulfur contained in the air. The problem of suspensions is eliminated by replacing them. Alternative solution for a rubber suspension that is not damaged, it can be impregnated with an air conditioner and a drive belt tensioner. Replacing suspensions is a very time-consuming job that requires some knowledge and skills. Places of peeling of the centering washer or suspension from the diffuser holder are smeared with glue with the simple name 88, after which the glued surfaces are pressed. It is also necessary to make sure that the voice coil does not touch the elements of the magnetic system. Restoration of the appearance of the diffuser is carried out by simply painting it with a black marker filled with alcohol ink (it says: "alkohol" on it). Some "finishers" use printer ink. This is not the right solution, since it has the properties of quick burnout and rinsing with ordinary water. At the tweeter, the acoustic lens is removed to release the domed cone with the voice coil. Carefully remove it and make sure the integrity of the voice coil. Very often, its turns are separated from the frame during operation. If the specified defect is found, the diffuser with the voice coil is replaced with a new one. For prevention, the voice coil is coated with BF-2 glue, slightly diluted with ethyl alcohol. It is advisable to test the heads with the measurement of the frequency response of sound pressure. Loudspeakers that cannot be repaired are replaced with new ones.

Another effective way reducing vibrations, and therefore unwanted overtones, lies in the "soft" fastening of the heads. They are mounted on rubber gaskets. It is necessary that the fastening elements do not come into contact with the diffuser holder. To do this, select a tube of the required diameter, for example, PVC, with a snug fit to the walls of the speaker mounting holes, while ensuring the free entry of screws. If necessary, the holes are drilled to the desired size. Under the nets with decorative rims, rubber washers are also placed at the holes. It should be noted that the bass and midrange heads are mounted in recesses. Therefore, it is necessary to put rubber bands in four places around each speaker, for example, from a bicycle tube, to prevent the side parts of the diffuser holders from touching the case.

Facing and decorative elements have a significant impact on the frequency response of speakers. A decorative material that covers the opening of the phase inverter, especially the passage, can have a significant impact due to high oscillatory air velocities. Grilles and blinds can sometimes cause resonant phenomena and in frequency response loudspeaker, additional peaks and dips will appear. The front part of the head 10GD-35, around the acoustic lens, is pasted over with felt or thick cloth. This will ensure both its soft fastening and the minimization of diffraction, the manifestation of the reverberation effect. sound waves, which, in turn, will weaken the resonant phenomena between the head and the grate. Acoustic system 35AC-1 has a removable decorative panel. In the technical documentation specified by the AU, it is recommended to remove the panel when listening to high-quality programs, when working at maximum permissible powers. Figure 12 shows the frequency response graphs of the sound pressure of loudspeakers 15GD-11A and 10GD-35 in an open version (white curve) and closed with decorative nets (green curve), provided for by the design of the S-90 35AC-012 speaker system. No special differences are observed. Conclusion: in this device, there is no special need to remove protective decorative nets, since their presence does not affect the frequency response of the heads in the operating frequency range. You should be guided by subjective assessments after listening to a real sound signal through a speaker system with and without decorative grids.

Rice. 12. Frequency response of loudspeaker sound pressure: a - 15GD-11A; b - 10GD-35

The described refinement methodology sound speakers"S - 90" 35 AC - 012 will also be useful for reworking loudspeakers and other models, as well as making speaker systems with your own hands.

Literature

1. Aldoshina I. High-quality acoustic systems and emitters, M.: Radio and communication, 1985.
2. Ephrussi M. M. Loudspeakers and their application - M .: Energy, 1976. - 64 - 66 p.
3. Young N. Acoustic damping of loudspeakers. Radio, No. 4, 1969.
4. Sysoev N. Sound improvement 35AC-012 (S-90). Radio, No. 10, 1989.
5. Burko V. Household acoustic systems. Operation, repair - Minsk: "Belarus", 1986.
6. Maslov A. Once again about the alteration of the loudspeaker 35AC-212 (S-90). - Radio, 1985. No. 1, S. 59.
7. Popov P. Improving the sound quality of loudspeakers - Radio, No. 6, 1983.
8. Shorov V. Improving the sound of the 25AC-309 loudspeaker - Radio, No. 4, 1985.
9. Gorshenin D. Comparison of capacitors in AC crossover. Radio, Nos. 8, 9, 10, 2009.
10. Kunafin R. And again 35AC ... - Radio, 1995, 5, p. 19, 20.
11. Afonin S. Creation of acoustic systems at home - M .: Eksmo, 2008.
12. Bystrushkin K. Acoustics with which we live. "Stereo & Video" N 11 1997.
13. Petrov A. Sound circuitry for radio amateurs, St. Petersburg: Science and Technology, 2003.
14. Brans J. Electronic design: methods of dealing with interference, M.: "Mir", 1990.
15. Sapozhkov M. A. Acoustics: reference book - M .: Radio and communication, 1989.

Publication date: 05.02.2015

Readers' opinions

• Vladimir / 12/14/2018 - 01:17
  Good day everyone! Luck smiled on me today! I stumbled upon your article and realized that I went on a crazy path. I have never, professionally, been involved in radio electronics, but it was useful to improve it. I used articles that are full on the net and are not supported by deep knowledge. Vladimir, I have a not very modest request to you. I'll leave my phone number (0675202057), please drop an SMS with information that will give you the opportunity to chat. Unless, of course, you have the opportunity and desire. For me, an amateur, it is easier to explain the essence of the problem. Thank you.
• [email protected] / 10.09.2018 - 07:31
  Dear author, hello friends! I have had S90 since 1982 and only now I realized that they are buggy, medium and high. I spent the evening, it was found that 2 technological errors were made during the assembly of the speakers: The first and it is the most intricate, 15GD-11A is placed in a cap, its rear is airtight and he does not breathe, hence there are so many complaints about this speaker, everyone changes it to something else. EVERYTHING IS SIMPLE! under the midrange speaker from the back, place 4 bushings 5 ​​mm high (you can use 4 nuts for 10). Glue the nuts on the plasticine and then install the midrange speaker and it will sing perfectly and will not interfere with the HF head. Remove ALL props from the HF head on the front side, for some reason the mesh is made of steel and attracts the tweeter with a magnet (this is not correct). Eliminate these 2 technological errors of the manufacturers and YOU will say. What wonderful designers came up with S90 !!!
• Author / 25.07.2018 - 18:35
  Sorry, part 4 at the following link: http://www..html Part 5 is under development, coming soon.
• Andrey / 23.07.2018 - 23:33
  Where is part 5 from? If only 3 parts of revision 35ac-12. Maybe I missed something, throw a link about part 5.
• Author / 23.07.2018 - 19:19
  Be guided by the recommendations from the 5th part of the article on the replacement of elements and their relative positions. A notch filter can be installed in the high-frequency part of the filter. If you don’t modify the midrange head, then perhaps that’s all.
• Andrey / 22.07.2018 - 23:57
  Good afternoon. I have this question. There are columns Orbita 35as-016 with regulators. I can send a photo of how they are located inside the filter. How and what can I improve. I can hold a soldering iron. And read the diagrams a little. Maybe someone will tell you what to do and according to what scheme. Thank you.
• Rush / 26.05.2018 - 02:42
  Excellent! Only pasting the case with a 3mm vibration isolator has already made the sound cleaner and more pleasant. What is good is that in the S-90f everything that is possible in the filter has already been removed. It remains to make a PAS for the count .. I glued this thing https://www.ulmart.ru/goods/3774803. The result is very noticeable and pleasing. Thank you!
• Alexander B. / 22.05.2018 - 15:44
  Thank you for your reply.
• Author / 22.05.2018 - 15:17
  Aldoshina I. in her book noticed that additional wall stiffeners and spacers do not eliminate resonances, but distribute them over new surfaces of the same stiffeners and spacers. But the application of a material with increased internal friction to the surface of the walls makes it possible to use the material for thinner walls. In fact, the vibroplast virtually thickens the walls, thereby reducing unwanted resonances. Making a PAS for the midrange head is the first thing to do. The game is worth the candle.
• Alexander B. / 21.05.2018 - 15:48
  Vladimir, good afternoon. Thank you for your article. I would like to consult with you and ask a few questions. I have S-90F (91g.) After reading your article, I also decided to improve the system, but since I'm not an electronics, to a minimum. to newer ones with the same rating (without changing the filter scheme) 5. Replace the acoustic terminal 6. Put on spikes. In this regard, the question 1. Should I put a spacer between the rear and front walls? 2. Is it possible to make a PAS on the midrange and not change the filter circuit (I'm not friends with this)? Is the game worth the candle for such a minimal improvement?
• Author / 16.05.2018 - 20:52
  Two native cotton mats are enough.
• Victor / 16.05.2018 - 20:11
  Hello Vladimir. In the process of working on the columns, a question arose. Maybe it’s worth pasting over the vibroplast with thin felt (1-1.5 mm) or batting in 1 layer? And then something confuses the "aluminum" inner surface of the box.
• Author / 04/01/2018 - 13:46
  Probably to weaken the resonance phenomena in oscillatory circuit coil-capacitor and frequency response equalization. There is a whole article on the use of resistors in a filter in conjunction with coils and capacitors.
• Anton / 31.03.2018 - 18:35
  Hello! Please tell me why you need a 75 Ohm resistor R1 (100 Ohm in some circuits), which is parallel to the L2 coil in the RF head filter? Is it necessary to put it on?
• Author / 29.03.2018 - 09:09
  It is enough to cover the suspension on one side, evenly, avoiding streaks. The diffuser, of course, must be closed. Find coils from 35AC-212 (012) and wind up to a tedious size - it will be easier, better and more reliable.
• Yuri.B. / 29.03.2018 - 08:33
  As for the coil, I am working on options from what is: there are two sounders from tube TV but the cross section "w" of the core is more than about 5-6 cm2. Wire from the OS of the same phone. but it seems to be thinner. As an option, is it possible to connect two coils in series 2.5 + 0.25 = 2.75 if I find the same crossovers? And the question about the air conditioner is to handle suspensions on both sides and you should probably cover the diffuser (cut out a circular template from paper or cardboard) ?.
• Author / 28.03.2018 - 15:46
  Resistors can be connected in series or in parallel. In this case, the total power is equal to the sum of the powers of the resistors used. If you decide to modify your speaker according to the methodology from the Radio magazine article No. 4 for 1985, then in the diagram in fig. 3, it is necessary to install a resistor R3 with a nominal value of 15 ohms - this is to attenuate the signal of the 6GDV-4-8 head by half (i.e., by 3 dB). I wonder where you will get the L3 Coil?
• Yuri.B. / 28.03.2018 - 10:53
  Dear Vladimir, thanks again! You probably confused me with another Yuri, who is ahead of me in correspondence with you. About the failure of the frequency response, you probably had a conversation with him. To clarify, I added the letter "B". My question is, is it possible to add a resistor in series, otherwise I don’t have a 10-ohm PEV type? And the second question is whether the filter should be upgraded in the future according to your recommended article by J. Radio 1985 No. 4 (you have a typo not for 1984). Of course, I will carry out the modernization in stages, comparing it with another column (I put music of different genres and balance alternately left and right). And a question for the future - on Arcturus 004 there are a couple of second exits for AC - I never used it. How would you recommend using it? Maybe you can make a separate entrance for the same 25AC309? Sincerely, Yuriy.B.
• Author / 27.03.2018 - 19:59
  The 25AC-309 filter for the midrange head has a cutoff frequency of only low frequencies. There are no restrictions on the upper frequency range. What do you want to improve? The sensitivity of the 6GDV-4-8 head is two times higher (by 3 dB) than that of the 5GDV-1. Therefore, the signal must be attenuated twice. To do this, the resistor R3 (5.1 ohms) is replaced by a resistor with a nominal value of 12 ohms or close to it. If your circuit has a resistor R3 - 3.3 ohms, then replace it with 10 ohms. That's the whole improvement. Check the polarity of the heads. You wrote about the dip at 3000 Hz. If you measure two heads at once, MF and HF, then a failure occurs when they are connected incorrectly. The polarity of the RF head connection should be reversed.
• Yuri / 27.03.2018 - 17:40
  Vladimir - thank you so much! Tell me about the filter upgrade. Should the midrange cutoff be increased? What changes need to be made based on the details of the old filter is desirable. And how to tie a new tweeter? Can you conveniently reset to my email. -I will write. Regards, Yuri.

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Music lovers are constantly arguing about which speaker system to choose for comfortable listening to music at home. And this is no accident: the entire contingent was divided into two camps. The former believe that it is worth shelling out a tidy sum for buying a cool Hi-Fi (or even better Hi-End) system in order to be happy and forget about headaches about this topic for the rest of your life. But there are those who are not ready to give up their entire life's savings for expensive acoustics (instead of a car or an apartment), which is why they consider the best option to purchase simpler equipment or to refine the good old classics to good sound.

In this article, we will talk about one of the most popular audio systems from the times of the USSR, which could not leave indifferent any of its owners. The S90 speakers, whose technical characteristics are able to excite the mind to this day, have become one of the highest achievements of the Soviet company Radiotekhnika.

Speaker models

The very first thing worth mentioning is the real and full name of the speaker model - 35AC-012. An important factor is the fact that this acoustics was produced in several variations. The most popular of them are S90 and S90B. There were also models S90i, S90D and S90f, but they were not widely used and are now almost never found.

The model with the postfix "B" differed from the usual "nineties" in a wider range of reproducible frequencies. Also a significant difference was the introduction of an indicator of electrical overload of the speakers. The recommended power rating of a high-quality amplifier for these speakers is in the range of 20 to 90 watts. It is also worth noting that Radiotekhnika S90, S90B (and other modifications) were the first models of acoustic systems that met international requirements for Hi-Fi category equipment.

Design

The case, in which the S90 speakers are enclosed, is, in fact, a non-separable rectangular box made of fine wood veneer. The walls of the speakers are 16 mm thick, the front panel is made of plywood 22 mm thick. The internal joints of the walls of the case are connected by special elements that increase the rigidity and strength of the structure, but do not interfere with high-quality sound.

Looking at the device from the front, the speakers are arranged in the following order (from top to bottom): tweeter, midrange speaker and woofer. Also on the front panel of the S90 speaker you can see the frequency response graph (amplitude-frequency response) and the phase inverter hole. While the frequency response is located above or below (depending on the acoustic model), the phase inverter is always located at the bottom. This was done for reasons of proper design for better sound and giving the speakers good bass.

S90 speakers: specifications

If we take the usual S90 as an example, then they are equipped with dynamic direct-radiation heads. More precisely, a high-frequency head 10GD-35, a mid-frequency head 15GD-11A and a low-frequency head 30GD-2 (in later models - 75GDN-1-4).

Equipped with two step playback level controls for adjusting the midrange and treble in the ranges from 500 to 5000 Hz and from 5 to 20 kHz. Each knob moves in three fixed positions. In the "0" position, there is no obstruction to the signal from the crossover filter, and it is fed directly to the corresponding head. When using the "-3 dB" and "-6 dB" positions, the signal is attenuated by 1.4 and 2 times, respectively, with respect to the "0" position. By switching the selected knob, you can make changes in the timbre of the sound.

The nominal power of the S90 speakers is 90 watts, while the nominal power is 35 watts. The indicator of the nominal electrical resistance in this speaker system is at around 4 ohms, and the frequency range available for playback ranges from 31.5 Hz to 20 kHz. The nominal sound pressure of the S90 is 1.2 Pa. I would like to note the rather impressive dimensions of one column - 71.0 x 36.0 x 28.5 cm, and the total mass of the entire system reaches 30 kg.

Speaker layout and connection to the sound source

In order to understand whether it is worth refining any speaker system, you need to study all the data and aspects of the equipment. Below is the electrical diagram of the S90 speakers. Even a novice radio amateur can figure it out, you just need to have at least basic knowledge.

Another important point is correct connection acoustic system. After all, if something goes wrong, even when connecting, you can, unwittingly, disable the equipment. You don't have to be a pro to figure out how to hook up your S90 speakers. The main thing is to have at least 20 watts with an amplifier (in this case, most likely, the sound will not be loud enough for large rooms), but not more than 90 watts. In case of exceeding allowable value amplifier power, the user runs the risk of being left without acoustics due to its breakdown. To connect, you will need ordinary acoustic wires, which must be connected to the terminals on each speaker and on the amplifier. The main condition for connection is polarity.

Refinement 35AC-012

As it becomes clear from the description above, in itself it has good technical characteristics and is capable of “building up” even small public spaces. But for home use, the most sophisticated music lover will prefer to modify the S90 speakers with their own hands. And all because, assembled more than twenty (or even thirty) years ago, the acoustic systems of the Radiotekhnika company already in those years did not have a high build quality and materials used.

Parsing

In the event that the acoustics were purchased in a used condition and this moment well worn by life, it is worth giving importance appearance. To do this, you need to disassemble the S90 speakers, after putting them on the “back”.

When removing the speakers, you need to take into account that the treble and midrange heads are attached to the case using the same screws as the lining. The woofer is attached separately, and you need to be as careful as possible so as not to damage it when unscrewing it.

Treble/midrange controls are much easier to dismantle than you think. All you need to do is carefully remove the decorative caps that are in the center of each knob. After that, using a screwdriver, it is necessary to unscrew the screw that has opened to the eye, and remove the regulator knob itself. The plastic lining must be carefully lifted from both sides with the help of flat objects and removed, and the four screws remaining under it must be unscrewed. After that, you can push the S90 column inside, not forgetting to unsolder it from the filter.

Cotton bags inside the case must be removed. Again, if the previous owner of the speakers did not forget to return them to their place in case of parsing.

You should first unsolder the panel with filters from the output from the back of the speaker, after which it must be dismantled by unscrewing the screws. Now you can remove the panel with the terminals attached to it.

Appearance and body

If the speaker grilles and decorative trims are “tired”, then it is worth straightening and painting them, having previously sanded and degreased them. This will give a fresh look to the speakers. The body of the S90 will loosen over time and can be strengthened as desired. This will result in a better sounding woofer.

It can be done different ways, including the installation of spacers and additional corners inside. It is also necessary to pay attention to sealing all joints and seams with ordinary plumbing sealant. In addition, you can glue the inner walls of the case (except the front) with foam rubber, which will increase the volume of the latter.

Terminals and filter

Knowledgeable radio amateurs are advised to replace the standard speaker terminals with universal-type terminals with gold-plated connectors. The installation place must be lubricated with sealant and put the panel with the terminals in place.

Considerable attention should be paid to the sound filter. If it was attached to the body with metal screws, then the filter setting will go astray. There are cases when the filter was assembled on a metal plate. This should be fixed by transferring all the nodes to the plywood panel. The circuit of the filter itself could be changed at the factory due to different speaker parameters, so you should make sure that everything is assembled according to GOST. If there are jumpers in the filter, then they must be removed and replaced, for example, with an oxygen-free copper cable with a cross section of 4 mm 2. It is worth removing the attenuator from the circuit, as it simply distorts the sound, and replacing the wires used to connect the speakers to the filter.

For woofers, a wire with a cross section of 4 mm 2 is suitable, for midrange speakers - with an area of ​​2.5 mm 2, for tweeters - with an area of ​​2 mm 2. After such simple actions, the filter must be returned to its place and closed with foam rubber.

Speakers and other "little things"

For speakers, new seals should be cut. This can be done with the help of cheap or simply obsolete mouse pads. This is the easiest option. After that, it is worth returning them to their seats and putting decorative trims and nets.

Before installing the regulators in place, you will have to unsolder all the resistances from them. When installing them in place, it is imperative to apply a sealant, as well as when installing a phase inverter.

Through such simple manipulations, the S90 speakers acquire a new life. The sound quality becomes an order of magnitude higher, despite the small costs. As a result, we can say that if there is no money for expensive 2.0 format acoustics, you can use this option and become the happy owner of the time-tested AS Radiotekhnika S90. If it happens that only half of the speakers are available, do not be upset. After all, it is noteworthy that the S90 column, a photo of which can be found on almost any website of acoustic lovers from the times of the USSR, can work alone and give a good result.