The passive radiator was first described by Harry Olson ( Harry Olson) in the 1935 patent "Loudspeaker and method of sound transmission". In the home audio market acoustic systems with a passive radiator have received relatively moderate distribution, and in car audio they have not been used at all. But recently, two well-known manufacturers of audio equipment for the automotive industry Boston Acoustics and Eathquake began to use passive radiators, adopting the experience of using them from home audio equipment systems.

Externally, passive radiators look deceptive, because they look like and even move like a regular subwoofer. But it seems so only from the outside of the speaker system. As the name suggests, there is no "drive" in these emitters. In other words, there is no voice coil, magnet, centering and end washers, flexible lead and connection terminals. Passive radiators are essentially unconnected speaker drivers, so they are paired with a connected woofer in the same cabinet. Systems with passive radiators refers to a type of housing with a hole or port, i.e. there is a phase inverter type. Mathematically, they are identical, only a diaphragm is used instead of a port. The main two parameters in passive radiators should be noted: the weight and rigidity of the diaphragm.

Weight is a key design element and must be accurately calculated to correct operation phase inverter, since it can change the resonant frequency and, accordingly, the setting of the entire case. The rigidity of the diaphragm is determined by a combination of the elasticity of the suspension material and the volume of air inside the housing chamber.

Passive radiators are tuned to resonate at a frequency below the operating woofer's linear response range. Working range passive radiator lies between values ​​1/4 octave above and below the resonance value. This means that the combination of a woofer and a passive radiator can expand the bass range by about half an octave. Of course, this principle applies when there is correct setting emitter. The slope of the frequency response is quite steep - 18 dB / octave.

Both diffusers: active and passive can move in phase, with a relative oscillation shift, up to antiphase. Keeping the oscillations of both cones in phase would be ideal in order to amplify the output of the woofer, but in its physics this kind of resonant system is impossible.

Predominantly common are systems with a passive radiator larger than the active speaker diameter. This allows a relatively smaller diameter woofer to improve performance in the upper and mid-bass ranges. In this case, the lower playback range is also extended, but a different cabinet design is required.

Like any design solution, a passive radiator has some disadvantages. In the foregoing, it was noted that the radiator is able to reproduce tones in antiphase, that is, with a shift of 180 ° relative to the acoustic oscillations of the speaker. Depending on the produced frequency, the relative position of the passive radiator and the active one - in frequency response multiple failures may occur. The longer the range, where the full frequency response does not include any sudden changes or breaks, the human ear will not detect these dips.

Another internal problem is the large slope of the frequency response. The frequency response drops sharply below the tuning frequency of the passive radiator. Additionally, the elastic properties of the air in the speaker housing no longer restore the movement of the radiator and especially the low-frequency driver below the resonance of the passive radiator. In this mode, even the possibility of damage to both the active low-frequency driver and the passive radiator is not ruled out.

Currently, there are promising developments of passive radiators that have an adjustable set of cone weights for easier tuning. Also important right choice Woofer with a low total quality factor (Q TS \u003d 0.2-0.4) and the corresponding housing design.

The history of the origin of the tunnel phase inverter dates back to 1930 from the Stromberg-Carlson acoustic labyrinth ( Stromberg Carlson). This labyrinth consisted of a long tube, at one end of which a speaker head was mounted, while the other end was left open. The cross-sectional area of ​​the open part was equal to the area of ​​the head. 1960s experiments to change the speed of sound depending on the interior coating various types damping materials and variation in tube shape have set the modern standard for this type of hull design.

The tunnel phase inverter is a long chamber on the back of the loudspeaker.

At the opposite end of the tunnel, there is a passage or hole (mainly the size of the diaphragm of the speaker head) that goes out to the outer side of the case. Properly designed tunnel phase inverter eliminates phase cancellation sound waves dynamics. Despite this, these devices are not yet widely used in caraudio due to their size and complexity of placement. The design consists of an elongated circuit made to eliminate the standing waves and resonances typical of other speaker cabinets. Standing wave suppression protects the driver from the harmful effects of reflected waves, which cause distortion and damage to the cone.

The length of the tunnel disrupts the synchronized movement of air inside the chamber, which weakens the oscillations of the frontal wave. By changing the length of the tunnel, the chamber is tuned, similarly to the tuning of a pipe of a cathedral organ open at one end. This is based on the phenomenon of phase shift of acoustic wave oscillations. The phase shift of the rear sound wave (woofer) amplifies the frontal wave at low frequencies, where the latter begins to weaken due to an increase in air resistance in this range.

The damping of the tunnel phase inverter, unlike the air resistance of a closed case, does not restrict the movement of the diffuser. As a result, it is also more efficient than a resonant phase inverter. The fidelity and linearity of the frequency response also have high performance. The design of the cases of such phase inverters requires compliance with the calculations and accurate settings. Commonly used speaker heads have low total (Q ts =0.2-0.4) and electrical (Q es =0.3-0.4) quality factor at a low self-resonant frequency. The path length of the rear acoustic wave is individual for a given case and is determined fractional part wavelength on resonant frequency woofer. For example, if the resonant frequency of the used tunnel bass reflex speaker is 40 Hz, the wavelength will be approximately 8.61 m. The channel inside the tunnel should be 1/4, 1/2 or 3/4 of this value and equal to 2.15, 4, 31 or 6.46 m, respectively. Due to these values, the tunnel is often folded into a maze for greater compactness. Reducing the actual length is facilitated by the correct filling with damping material, such as wool.

In a sense, fourth-order acoustic design (passive radiator bass reflex and tunnel bass reflex) is not convenient enough for component use in car audio, but represents an alternative to existing subwoofer enclosures.

In this article, we will see how to make a subwoofer with our own hands, without delving into the bowels of electroacoustics, without resorting to complex calculations and delicate measurements, although some will still have to be done. "Without much difficulty" does not mean "a blunder on a brick, drive, grandma, mogarych." These days on home computer it is possible to simulate very complex acoustic systems (AS); see the link at the end for a description of this process. But working with a ready-made device on a whim gives something that you can’t get by any reading and viewing - an intuitive understanding of the essence of the process. In science and technology, pen-tip discoveries are rare; most often, the researcher, having gained experience, "inside" begins to understand what's what, and even then he looks for mathematics suitable for describing the phenomenon and deriving design engineering formulas. Many great ones recalled their first unsuccessful experiences with humor and pleasure. Alexander Bell, for example, at first tried to wind the coils for his first telephone with a bare wire: he, a musician by education, simply did not know yet that the wire under current should be insulated. But Bell did invent the telephone.

About computer calculations

Do not think that JBL SpeakerShop or other acoustic calculation program will give you the only possible best correct option. Computer programs are written according to well-established proven algorithms, but non-trivial solutions are impossible only in theology. “Everyone knows that this is not the way to do it. There is a fool who does not know this. He is the one who makes the invention.”- Thomas Alva Edison.

SpeakerShop appeared not so long ago, this application was developed very thoroughly and the fact that it is used very actively is an absolute plus for both developers and amateurs. But in some ways, the current situation with him is similar to the story of the first photoshops. Who else used Windows 3.11, remember? - then they just went crazy with the processing of pictures. And then it turned out that in order to take a good picture, you still need to be able to take pictures.

What is it and why?

A subwoofer (simply - a subwoofer) in a literal translation sounds curious: a podgavkivatel. In reality, this is a bass (low-frequency, woofer) speaker that reproduces frequencies below approx. 150 Hz, in a special acoustic design, a box (box) of a rather complex device. Subwoofers are also used in everyday life, in high-end floorstanding speakers and inexpensive desktop speakers, built-in and in cars, see fig. If you manage to make a subwoofer that correctly reproduces bass, you can safely take on, because. low-frequency reproduction is perhaps the fattest of the whales on which all electroacoustics stands.

It is much more difficult to make a compact low-frequency speaker link than midrange and high-frequency (mid- and high-frequency), firstly, due to an acoustic short circuit, when sound waves from the front and rear radiating surfaces of the speaker (loudspeaker head, GG) cancel each other out: LF waves - meters, and without proper acoustic design GG, nothing prevents them from immediately converge in antiphase. Secondly, the spectrum of sound distortion at low frequencies extends far into the best audible region of the midrange. In essence, any broadband speaker is a low-frequency link, in which midrange and high-frequency emitters are built. But from the point of view of ergonomics, an additional requirement is imposed on the subwoofer: the subwoofer for the home should be as compact as possible.

Note: all types of acoustic design of the LF GG can be divided into 2 large classes - some dampen the radiation from the rear of the speaker, the second turn it in phase by 180 degrees (turn the phase) and re-radiate from the front. A subwoofer, depending on the properties of the GG (see below) and the required type of its amplitude-frequency characteristic (AFC), can be built according to a scheme of one class or another.

A person distinguishes the direction to sounds below 150 Hz very poorly, so in an ordinary living room a sub can be placed anywhere in general. MF-HF speakers (satellites) acoustics with a subwoofer are very compact; their location in the room can be chosen optimally for this room. Modern housing with an excess of space and good acoustics, to put it mildly, does not differ, and it is not always possible to “stick” at least a couple of good broadband speakers in it correctly. Therefore, making a subwoofer on your own allows you not only to save a very substantial amount of money, but still get a clean, true sound in this Khrushchev, Brezhnevka or modern new building. The subwoofer is especially effective in full surround sound systems, as putting 5-7 columns on a full page each is too much for the most “fancy” users.

bass

Bass reproduction is not only technically difficult. The narrow, in general, low-frequency section of the entire spectrum of sound waves is heterogeneous in its psychophysiological effects and is divided into 3 areas. To choose the right bass speaker and make a subwoofer box with your own hands, you need to know their boundaries and meaning:

• Upper bass (UpperBass) - 80-(150 ... 200) Hz.
• Medium bass or midbass (MidBass) - 40-80 Hz.
• Deep bass or sub-bass (SubBass) - below 40 Hz.

top

middle

On midbass, the main task when creating a subwoofer is to ensure the highest return of the GG, the given shape of the frequency response and its maximum uniformity (smoothness) in the minimum volume of the box. frequency response, to the side low frequencies close to rectangular, gives a powerful, but harsh bass; Frequency response, evenly falling - clean and transparent, but weaker. The choice of one or the other depends on the nature of the listened to: rockers need a “angrier” sound, and more gentle for classics. In both cases, large dips and bursts in the frequency response spoil the subjective perception with formally identical sound technical parameters.

Depth

The subbass has a decisive influence on the timbre (color) of the sound of musical instruments only for wind organs in halls specially built for them. Strong sub-bass components are characteristic of the sounds of natural and man-made disasters, strong explosions and the voices of certain animal species (lion's roar). Over 90% of people either do not hear subbass at all, or hear it indistinctly. For example, if the sounds of a tropical hurricane and a nuclear explosion are fundamentally different in nature and are filtered out from everything except for sub-bass, then hardly anyone can tell from them what is really going on there. Therefore, a home subwoofer is almost always optimized for mid-bass, and the rest of the sub-bass, which happens, masks the room's own noise. For what it, by the way, is very suitable and how it is very useful.

Subbass in the car

The effect of noise masking is especially needed in a cramped and noisy car interior, so auto subwoofers are optimized for sub-bass. Sometimes for the sake of this, Hi-Fi lovers at speed give the entire trunk to the subwoofer, putting there 15 "-18" monster speakers with 150-250 watts of peak power, see fig. However, a quite decent subwoofer in a car can be made without sacrificing useful volume in the back, see below.

Note: the peak power of the speaker is often identified with the noise, which is not true. At peak power, the sound is distorted, but still distinct, i.e. distinguish in meaning. Noise power is defined as that which a speaker can operate for a certain amount of time (usually 20 minutes) without burning out or being mechanically damaged. In this case, the sound is most often incoherent wheezing, which is why such power is called noise. But in some types of acoustic design, the noise power of the speaker may be lower than the peak, see below.

What speaker do you need?

A complete calculation of the acoustic design is carried out according to the so-called. Thiel-Small parameters (PTS). Since we decided to spend time and effort tuning the subwoofer, we only need the full quality factor of the head at its own resonant frequency Qts, because it is on it that the optimal variant of acoustic design is selected. Depending on the value of Qts, the dynamics are divided into 4 groups:

• Qts<0,5 – «безразличные» сверхнизкодобротные. Очень дорогие, очень низкая отдача, но способны воспроизводить подбасы вплоть до 20-15 Гц. Настройка сабвуфера с такими без звукомерной камеры и специальной измерительной техники невозможна, т.к. резонансный пик не выражен.
• 0,5
• 0,7
• Qts>1 - high quality. High return, low price, harsh sound in suboptimal design. It is difficult to get a smooth frequency response. Compact, available in diameters (down) up to 6” (155 mm). Optimal for a desktop subwoofer or a TV (not a home theater!).

measurements

In speaker manufacturer's specifications, Qts may be referred to as Qp or simply Q, but it is not always present there, and public databases like WinISD are full of errors. Therefore, we will most likely have to determine the value of Qts at home.

Training

First of all, we select and prepare a room for acoustic measurements. It should have as many curtains, curtains, carpets on the floor and walls, upholstered furniture as possible. Rigid horizontal surfaces (table) need to be covered with something fluffy; It will not be superfluous to throw more pillows everywhere. The corners distort the sound field especially strongly, incl. hard furniture with walls, they need to be curtained with something, for example, with clothes on hangers. Next, we connect long wires to the speaker and hang them in the geometric center of the ceiling (under the chandelier, if any) with the front side of the diffuser down at a height of 2/3 of the ceiling height from the floor.

Now you need to assemble the measurement circuit, as shown at the top in Fig. We still need the lower circuit to measure the impedance (impedance) of the speaker Z. This one differs from the measuring circuit usually used by amateurs without a transformer with quite professional accuracy: in common circuits on bridge diodes, approx. 1.5 V even with tester input resistance of 10 MΩ. The operation of this circuit is based on the fact that the impedance of the transformer and R2, on the one hand, is much greater than the impedance of the GG; on the other hand, it is much less than the output impedance of the audio frequency power amplifier, and on the fact that the lousiest digital multitester at the 200 mV limit has an input impedance of more than 1 MΩ. However, if the measurement signal is supplied from an audio frequency generator (AFG) with a standard 600 ohm output, this circuit is not suitable for measuring Z.

Procedure

From the computer with the GZCH emulation program, the measuring signal is fed from the output of the sound card. You need to “drive” it within 20-100 Hz at first with a discrete (step) of 10 Hz. If the GG resonance is not visible, it is unsuitable for a subwoofer. Or the seller shamelessly deceived you by selling for 100 rubles. indifferent GG at the price of $200.

When the boundaries of the resonant peak are determined, we “pass” it already with a discrete of 1 Hz and build the frequency response. If the GG is high- or medium-quality closer to the upper limit of Qts, you get a graph like the one in pos. I fig. In this case:

• According to the f-le (1) on pos. II find U(F1,F2);
• According to the schedule, we find F1 and F2;
• Using f-le (2), we check whether the calculated frequency of natural resonance in free space F's coincides with the measured Fs. If the discrepancy is more than 2-3Hz, see below;
• Using f-le (3) we find the mechanical quality factor Qms, then f-le (4) electrical Qes and, finally, f-le (5) the required total quality factor Qts.

If the quality factor of the GG is closer to low or such that it is generally good, the resonance curve will be noticeably asymmetric, and its peak will be flat, blurry, pos. III, or the check on f-le (2) will not converge even with repeated measurements. In this case, according to the graph, we determine the points of the greatest slope of the tangents to the concave "wings" of the A1 and A2 peaks; mathematically, in them the second derivative of the function describing the resonance curve reaches a maximum. For Umax then we take, as before, its value at the top of the peak, and for Umin - calculated from the f-le at pos. III new value U(F1,F2).

System Structure

Have you measured? Is the speaker suitable? Do not rush to choose a design. First you need to choose a block diagram of the entire sound system, because. its electronic part can bear a share of the cost no less than a good bass speaker. A sound system with a subwoofer can be built according to one of the following. diagrams, see fig.

Note: the equalizer and the infra-low frequency Finch filter (rumble filter) in all circuits are switched on before the inputs of the stereo channels.

Pos. 1 – system with passive power filtering. Plus - you don't need a separate bass amplifier, it connects to any UMZCH. Huge disadvantages, the first, mutual electric leakage of channels in the subwoofer over the midrange: for LC filters that reduce it to an acceptable value, you will need a decent case, which, in order to buy their components, will first have to be filled with about a third of money (in 100 ruble bills). Secondly, the output resistances of the low-pass filters of the low-pass filter, together with the input GG of the speaker, form a tee, and each UMZCH channel will theoretically spend a quarter of the power on heating its neighbor with its low-pass filter. Really - more, because. on power and losses in filters are significant. However, the power filtered system is applicable to low power subwoofers with independent sound drivers, see below.

Pos. 2 - passive filtering into a separate bass UMZCH. There are no power losses, the mutual influence of the channels is weaker, because characteristic resistances of filters are kilo-ohms and tens of kilo-ohms. Currently, it is practically not used, because. It turns out to be much easier and cheaper to assemble an active filter on microcircuits than to wind passive coils.

Pos. 3 – active analog filtering. The channel signals are added by a simple resistor adder, fed to the analog active low-pass filter, and from it to the bass UMZCH. Channel interference is negligible and imperceptible under normal listening conditions, the cost of components is low. The optimal circuit for a homemade subwoofer for a novice amateur.

Pos. 4 - full digital filtering. The channel signals are fed to the splitter R, which divides each of them into at least 2 equal to the original ones. One signal from a pair is fed to the MF-HF UMZCH (possibly directly, without a high-pass filter), and the rest are combined in adder C. The fact is that with resistor addition at the lower frequencies of the midbass and in the subbass, electrical interaction of signals in the low-pass filter is possible, several distorting the overall bass. In the adder, the signals are added in a digital or analog way, excluding their mutual influence.

From the adder, the general signal is fed to a digital low-pass filter with built-in analog-to-digital (ADC) and digital-to-analog (DAC) converters, and from it to the bass UMZCH. The sound quality and channel isolation are the highest possible today. The cost of microcircuits for this entire economy turns out to be feasible, but working with ICs already requires some amateur radio experience, and even more if you buy not a ready-made set (which is much more expensive), and the system components are selected independently.

Decor

On fig. the most commonly used acoustic design schemes for home subwoofers are given. Labyrinths, horns, etc. do not meet the requirements of compactness. Beginners prefer schemes in green, doable ones in yellow, and unsuitable ones in red. Who is more experienced may be surprised: the 6th bandpass is for dummies? No worries, this great bass acoustic on trumpets can be set up over the weekend. If you know how.

Shield

Making a subwoofer in the form of an acoustic screen (shield, pos. 1) at home is feasible if the GGs are built into the wall sheathing, because. their sizes are commensurate with the lengths of sub-bass waves. Hence the dignity - there are no problems with the sub-bass, as long as the speakers pull it. Another is the utmost compactness, the subwoofer does not occupy usable space at all. But there are also serious disadvantages. The first is a large amount of construction work. The second - the acoustic screen does not affect the frequency response of the GG. “Humpbacked” will sing like that, so you can only put expensive low-quality and indifferent speakers on the shield. A sub-minus, so to speak - their return is small and the shield is not able to increase it in any way.

closed box

A huge plus of a closed box (pos. 2) - deep damping of the GG; for inexpensive, high-response, high-quality speakers, this is the only acceptable type of acoustic design. But this plus entails a minus: with deep damping, the noise power of the GG often turns out to be lower than the peak, especially for expensive powerful heads. The coil is already smoking, but the wheezing is still not audible. An overload indicator is needed, but the simplest ones without a separate power supply distort the signal.

An equally fat plus is an extremely smooth, smoothly falling frequency response and, as a result, the clearest and most lively sound. For this reason, high-end powerful high-quality GGs are produced specifically for installation in closed boxes or 4th order bandpasses (see below).

Minus - of all speakers of equal volume, a closed box has the highest lowest reproducible frequency, because. it increases the resonant frequency of the speaker and is not able to increase its output at frequencies below it. Those. in terms of compactness, the subwoofer in a closed box passes with a big stretch. To some extent, this disadvantage can be reduced by filling the box with padding polyester: it perfectly absorbs the energy of sound waves. The thermodynamic process in the box then changes from adiabatic to isothermal, which is equivalent to an increase in its volume by 1.4 times.

Another significant disadvantage is that only a passive subwoofer can be made in a closed box, because. the electronics in it are very hot even placed in a fenced off compartment. If you come across old AC 10MAS-1M, drive them at half power for half an hour and touch the case with your hand - it will be warm.

FI

Note: FI is equivalent in everything to a passive radiator (PI) - instead of a pipe with a port, they put a bass speaker without a magnetic system and with a weight instead of a coil. There are no “non-tuning” methods for calculating PI, therefore, in industrial production, PI is a rare exception. If you have a burnt bass speaker lying around, you can experiment - the setting is done by changing the weight of the load. But keep in mind - it is better not to make active PI for the same reason as a closed box.

About deep cracks

Acoustics with deep slots (pos. 4, 6, 8-10) are sometimes identified with PHI, sometimes with a labyrinth, but in fact it is an independent type of acoustic design. The advantages of a deep gap are many:

There is only one drawback to a deep gap, and that is for beginners: it is not customizable after assembly. As it is done, so it will sing.

About antiacoustics

bandpasses

BandPass in translation is the passage of the band, the so-called speakers without direct emission of sound into space. This means that bandpass speakers do not emit midrange due to its internal acoustic filtering: the speaker is placed in a partition between resonating cavities, ports of pipes or deep slots that communicate with the atmosphere. Bandpass - acoustic design specific to subwoofers and does not apply to completely separate speakers.

Bandpasses are divided according to the magnitude of the order, and the order of the bandpass is equal to the number of its own resonant frequencies. High-Q GGs are placed in bandpasses of the 4th order, where it is easy to organize acoustic damping (pos. 5); low- and medium-quality - into bandpasses of the 6th order. Contrary to popular belief, there is no tangible difference in sound quality between those and those: already on the 4th order, smoothing of the frequency response at low frequencies up to 2 dB or less is achieved. The difference between them for an amateur is mainly in the complexity of the settings: to fine-tune the 4th bandpass (see below), you will have to move the partition. As for bandpasses of the 8th order, they have 2 more resonant frequencies due to the acoustic interaction of the same 2 resonators. Therefore, the 8th bandpass is sometimes called the 6th order bandpass of class B.

Note: idealized frequency response at low frequencies for some types of acoustic design are shown in fig. red. The green dotted line is the ideal frequency response from the point of view of the psychophysiology of hearing. From where it can be seen that there is still enough and enough work in electroacoustics.

Amplitude-frequency characteristics of the same loudspeaker head in different acoustic design

Auto subwoofers

Car subwoofers are usually placed either in the cargo compartment, or under the driver's seat, or behind the back of the rear seat, pos. 1-3 in fig. In the first case, the box takes up useful volume, in the second case the subwoofer works in difficult conditions and can be damaged by feet, in the third case, not every passenger will be able to endure a powerful bass right next to their ears.

Recently, a car subwoofer is increasingly being made of the stealth type, built into the rear wing niche, pos. 4 and 5. Sub-bass of sufficient power is achieved by using special auto-speakers with a diameter of 12 ”with a rigid cone, little susceptible to the membrane effect, pos. 5. How to make a subwoofer for a car by molding a wing niche, see next. video.

Video: do-it-yourself car subwoofer "stealth"

It just doesn't get easier

A very simple subwoofer that does not require a separate bass amplifier can be made according to a scheme with independent sound emitters (IS), see fig. In fact, these are two channel woofers GG, placed in a common long case, installed horizontally. If the length of the box is comparable to the distance between the satellites or the width of the TV screen, the "spreading" of the stereo is hardly noticeable. If listening is accompanied by viewing, then it is completely imperceptible due to involuntary visual correction of the localization of sound sources.

According to the scheme with independent OUTs, you can make an excellent subwoofer for a computer: a box with speakers is placed in the far upper corner under the tabletop. The cavity below it is a resonator tuned to a very low frequency, and an unexpectedly good sub-bass cuts through from a small box.

FI for a subwoofer with independent OUT can be calculated in the speaker shop. In this case, the equivalent volume Vts is taken twice as much against the measured one, the resonant frequency Fs is 1.4 times lower, and the total quality factor Qts is 1.4 times greater. The material of the box, as elsewhere, is MDF from 18 mm; for subwoofer power from 50 W - from 24 mm. But it is better to place the speakers in a closed box, in this case it can be done without calculation: the length inside is taken at the installation site ranging from 0.5 m (for a computer) to 1.5 m (for a large TV). The cross section of the box inside is determined based on the diameter of the speaker cone:

• 6 "(155 mm) - 200x200 mm.
• 8 "(205 mm) - 250x250 mm.
• 10" (255 mm) - 300x300 mm.
• 12" (305 mm) - 350x350 mm.

In the worst case (under-table computer subwoofer with 6" speakers), the volume of the box will be 20 liters, and the equivalent with filling - 33-34 liters. With an UMZCH power of up to 25-30 W per channel, this is enough to get a decent midbass.

Filters

LC filters in this case are better to use type K. They need more coils, but in amateur conditions this is not essential. K-filters have low attenuation in the stopband, 6 dB / oct per link or 3 dB / oct per half link, but a completely linear phase response. In addition, when operating from a voltage source (which is UMZCH with great accuracy), the K-filter is not very sensitive to changes in the load impedance.

At pos. 1 fig. schemes of K-filter links and calculation formulas for them are given. R for LF GG is taken equal to its impedance Z at the cutoff frequency of the LPF 150 Hz, and for the HPF equal to the impedance of the satellite z at the cutoff frequency of the HPF 185 Hz (formula in pos. 6). Z and z are determined according to the scheme and formula in fig. above (with measurement schemes). Working diagrams of filters are given in pos. 2. If you prefer to buy capacitors rather than winding coils, exactly the same parameters can be made up of P-links and half-links.

Data and diagrams for the manufacture of filters for a simple subwoofer with independent radiators

The attenuation of the low-pass filter in the stopband is 18 dB / oct, and the high-pass filter is 24 dB / oct. Such a frankly non-trivial ratio is justified by the fact that the satellites are unloaded from the bass and give a cleaner sound, and the rest of the bass reflected from the HPF is sent to the bass speakers and makes the bass deeper.

Data for the calculation of filter coils are given in pos. 3. They need to be arranged mutually perpendicular because K-filters work without magnetic coupling between the coils. When calculating, they are set by the dimensions of the coil and, according to the inductance found in the order of calculating the filter, the number of turns is determined. Then, using the stacking factor, find the diameter of the wire in the insulation, it should be at least 0.7 mm. It turns out less - we increase the size of the coil and recalculate.

Setting

Setting up this subwoofer comes down to equalizing the volumes of the woofers and satellites, respectively. cutoff frequencies. To do this, first prepare the room for acoustic measurements, as described above, and a tester with a bridge and a transformer. Next, you need a condenser microphone. For a computer one, you will have to make some kind of microphone amplifier (MUS) with a bias applied to the capsule, because. a conventional sound card cannot simultaneously receive a signal and emulate a GZCH, pos. 4. If there is a condenser microphone with a built-in MCC, at least an old MKE-101, excellent, its output is connected directly to the primary (smaller) winding of the transformer. The measurement procedure is simple:

1. The microphone is fixed opposite the geometric center of the satellites at a horizontal distance of 1-1.5 m.
2. The subwoofer is disconnected from the UMZCH and a 185 Hz signal is applied.
3. Record the voltmeter readings.
4. Without changing anything in the room, they turn off the satellites, turn on the sub.
5. A 150 Hz signal is applied to the UMZCH, the readings of the tester are recorded.

Now you need to calculate the equalizing resistors. Equalize the volume by muffling the louder links in a series-parallel circuit (pos. 5), because. it is necessary to keep the previously found values ​​of Z and z unchanged in absolute value. Calculation formulas for resistors are given in pos. 6. Power Rg - not less than 0.03 of the power of the UMZCH; Rd - any from 0.5 W.

Too simple

Another option for a simple, but already real subwoofer is with a paired woofer GG. Pairing woofers is a very effective way to upscale their sound. The design of the subwoofer on a pair of old 10GD-30 is given in fig. below.

The design is very perfect, bandpass of the 6th order. Bass amplifier - on TDA1562. You can use other high-quality GGs with a relatively small diffuser stroke, then you may have to make adjustments by selecting the length of the pipes. It is produced at control frequencies of 63 and 100 Hz next. way (control frequencies are not resonant speakers!):

• Prepare the room, microphone and instruments as described above.
• Served on UMZCH alternately 63 and 100 Hz.
• Change the length of the pipes, achieving a difference in voltmeter readings of no more than 3 dB (1.4 times). For gourmets - no more than 2 dB (1.26 times).

The tuning of the resonators is interdependent, so the pipes must be moved according to: the short one is pushed out, by the same amount, in proportion to its original length, the long one is pushed in. Otherwise, you can completely upset the system: the peak of the optimum setting for the 6th bandpass is very sharp.

1. A dip between 63 and 100 Hz - the baffle must be moved towards the larger resonator.
2. Dips on both sides of 100 Hz - the baffle is shifted towards the smaller resonator.
3. Surge closer to 63 Hz - you need to increase the diameter of the long pipe by 5-10%
4. A surge closer to 100 Hz is the same, but for a short pipe.

After any of the fitting procedures, the subwoofer is reconfigured. For its convenience, a complete assembly on glue is not done at first: the partition is tightly smeared with plasticine, and one of the side walls is placed on double-sided tape. Make sure there are no gaps!

Tubes for resonators

Ready-made bent pipes for acoustics are sold in music and radio stores. You can make a telescopic acoustic pipe with your own hands from scraps of plastic or cardboard pipes. In both cases, 2 pieces of fishing line must be firmly glued across the inner mouth: one is tight, the other is a loop protruding outward, see fig. on right. If the pipe needs to be moved apart, a pencil is pressed on a tight fishing line, etc. If shortened - pull the loop. Tuning a resonator with a pipe is thus accelerated many times over.

Powerful 6th order

Drawings of the bandpass of the 6th order under 12 ”GG are given in fig. This is already a solid floor structure for power up to 100 watts. It is configured like the previous one.

Subwoofer drawings 6th order bandpass for 12″ speaker

4th order

Suddenly, a 12 ”high-Q GG will be at your disposal, it will be possible to make a 4th order bandpass of the same quality, but more compact, see fig. dimensions in cm. However, setting it up will be much more difficult, because. instead of manipulating the tube of a larger resonator, you will have to immediately move the baffle.

Subwoofer bandpass 6th order for 12″ speaker

Electronics

The bass UMZCH for a subwoofer is subject to the same as for filters, the requirement for full linearity of the phase response. The UMZCH, made according to the bridge circuit, satisfies it, it also reduces the nonlinear distortions of the integral UMZCH with a non-complementary output by an order of magnitude. UMZCH for a subwoofer with a power of up to 30 W can be assembled according to the scheme in pos. 1 rice; 60-watt according to the scheme in pos. 2. It is convenient to make an active subwoofer on a single chip of a 4-channel UMZCH TDA7385: a couple of channels are sent to the satellites, and the other two are switched on by a bridge circuit to the subwoofer, or, if it is with independent OUT, they are allowed to go to the woofers. The TDA7385 is also convenient in that it has common inputs for the St-By and Mute functions for all 4 channels.

According to the scheme in pos. 3 makes a good active subwoofer filter. The amplification of its normalizing amplifier is regulated by a variable resistor of 100 kOhm over a wide range, so in most cases the rather dreary procedure for equalizing the volumes of the subwoofer and satellites disappears. Satellites in this version are included without HPF, and potentiometers for presetting the volume with slots for a screwdriver are built into the MF-HF amplifiers.

You might want to design a slotted subwoofer from scratch instead of fiddling with reconfiguring prototype subwoofers to fit your speaker. In this case, follow the link: //cxem.net/sound/dinamics/dinamic98.php . The author, we must give him his due, was able to explain at the level “for luminous dummies” how to calculate and make a high-class subwoofer using modern software. However, in a big case, not without a miss, therefore, when studying the source, keep in mind:

And still…

Making a sub yourself is exciting, useful for developing intelligence and skill, besides, a good bass speaker costs one and a half times cheaper than a pair of a lower class. However, at control auditions, both seasoned experts and casual listeners "from the street", all other things being equal, clearly prefer sound systems with full channel separation. So think about it first: won’t you still have a couple of separate columns in your hands and wallet?

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What I love about Kicker is its out-of-the-box approach. While everyone is resting and riveting subwoofers in bass-reflex cases, these car audio oldies just remember that there are other types of design. A passive radiator (also known as a passive radiator) has much in common with a phase inverter, but is devoid of many of its shortcomings. And after all, nothing new, Harry Olson described his principle in his patent already in 1935 ...

Design

I will not get ahead of myself and first of all "a meeting on clothes". Kicker CWTB10 is very compact - the length of the case does not exceed 44 cm. The outer diameter, respectively, like that of a typical ten, is slightly less than 28 cm. There is also an 8-inch model in the series, it is even more compact.

I would like to emphasize that the subwoofer is positioned by the manufacturer as universal - it can be used not only in a car, but also, say, in boats, open SUVs or ATVs. The case is made of thick impact-resistant plastic and is completely sealed.

Threaded holes are provided for mounting the subwoofer, and several brackets are included for horizontal or vertical mounting.

I got a model with a nominal impedance of 2 ohms for the test, but in general the Kicker CWTB10 also has a 4-ohm version. It is better to connect a 2-ohm one to some kind of bass monoblock, but a 4-ohm one can also be used with multi-channel amplifiers by connecting a subwoofer to a pair of channels in a bridge.

Now, actually, to the acoustic design - a passive radiator. The shape of the body here does not play the most important role, but in our case it is made in the form of a pipe, at the ends of which there is a diffuser. Dynamics actually owns only one of them. The second exactly the same diffuser and on exactly the same suspension - this is the passive radiator.

How does a passive radiator work?

It was not in vain that I mentioned at the very beginning that a passive radiator has much in common with a phase inverter. For those who do not know how a phase inverter works, I will briefly tell you.

As the speaker cone moves back and forth, it alternately compresses and decompresses the air inside the cabinet. Accordingly, this air will alternately tend to go out through the port, then be sucked back through it. But the trick is that the air inside the port has a certain inertia, and all these vibrations will "get" to the exit from it with some delay.

At a certain frequency (this is what is called the port tuning frequency), it will turn out that the air at the outlet of the port will oscillate synchronously with the diffuser itself. That is, the radiation from the diffuser and from the port will add up. Actually, this is the effect of acoustic amplification.

A passive radiator works in exactly the same way. Only instead of a port with an air mass inside it, just a diffuser on a suspension works here. In fact, a passive radiator is exactly the same speaker, only without a magnetic system. And if the setting of a conventional phase inverter port can be changed by its proportions and dimensions, then in a passive radiator the setting is changed by the mass of the diffuser and the elasticity/viscosity/stiffness of its suspension.

What are the advantages of a passive radiator over a conventional bass reflex port?

And you look at the dimensions of the case, and the question will disappear by itself. In the case of the Kicker CWTB10, the internal volume is something like 27 liters. If you try to calculate a regular port for such a case (for example, in JBL Speakershop or in BassPort), then the program will give you very inconvenient sizes for it. Either the cross section will be too small, or the length is insane.

And with a passive radiator, you can make any area and any setting. Do you think it will be possible to make a regular port of the same section with a low setting? Here I am about the same.

How is it arranged inside?

The speakers are attached through the "paws" of the protective grill. To get to the screws, you just need to remove the plugs from them.

By the way, these are not some self-tapping screws for you, everything is serious - with embedded nuts implanted into the body.

Inside the body is filled with fluffy synthetic winterizer. In short, it, firstly, creates the effect of "increasing" the internal volume, and secondly, to some extent damps the vibrations of the air inside it.

The speaker itself is without extra labels and other embellishments. Although the Comp R series indicated on the front side hints at its relationship with the separate subwoofer speaker Kicker 43CWR104. Most likely, this is it, only in a simplified version - without decorative overlays and with simpler cable connection terminals.

And here is what is on the other side of the case. From the outside it looks like a speaker, but inside it doesn't look like a speaker at all. Rather, it looks like a speaker without a motor.

Where a coil is usually attached to the diffuser, a metal washer is fixed - it adjusts the weight of the moving system.

measurements

For interest, I took an impedance curve not only for the entire subwoofer, but also separately for the speaker. Judging by the nature of the curves, the passive radiator is tuned somewhere around 35 Hz, which is very close to the Fs of the speaker itself.

Measured speaker parameters in the subwoofer Kicker CWTB10:

• Fs (natural resonant frequency) - 35 Hz
• Vas (equivalent volume) - 19.5 liters
• Qms (mechanical quality factor) - 8.97
• Qes (electric quality factor) - 0.51
• Qts (full quality factor) - 0.49
• Mms (effective mass of the moving system) - 159 g
• BL (electromechanical coupling coefficient) - 11.1 T m
• Re (voice coil DC resistance) - 1.8 ohm
• dBspl (reference sensitivity, 1m, 1W) - 84.2 dB

However, the speaker parameters are so, more for interest. We have a ready-made subwoofer, so I will appreciate its work as an assembly.

To begin with, I shoot the frequency response of the radiation of the diffuser itself. Pay attention to the dip just in the passive radiator tuning zone - about 35 Hz:

The fact is that when the subwoofer operates at this frequency, the passive radiator enters into resonance and itself begins to compress and decompress the air in the case, and for the speaker, the air in the case becomes elastic. Which, in turn, limits the course of its diffuser.

It turns out that the subwoofer almost does not work at these frequencies? Of course not, it’s just that near the tuning frequency of the passive radiator, it’s not the speaker that works, but the radiator itself:

And this is how they work together:

Unfortunately, I cannot show the overall frequency response, since it is correct to make measurements at lower frequencies only in the near field (it should not be taken into the MTUCI anechoic chamber because of one measurement). But even a cursory analysis of the frequency response of the speaker and the passive radiator makes it clear that the subwoofer should work very tasty in the car. Which, in fact, was confirmed in practice.

Trial in the case and conclusions

A small experiment in the car showed that it is not necessary to prematurely judge the capabilities of this sub by its size. A passive radiator when properly configured (and here it is configured correctly) is a big power. In terms of impact and bass depth, the Kicker CWTB10 is certainly not inferior to the average 12-inch subwoofer.

By the nature of the bass, I will say one thing - this is Kicker. Dense, weighty, juicy. For club music - generally a godsend. Interestingly, with an increase in volume, the bass does not begin to put pressure on the ears, but it begins to be perceived tactilely - the bass rhythm is perceived by blows to the chest as if it were a heavy rubber ball. And this is from some dozen there!

In open space (and with such a performance of the Kicker CWTB10, you can safely use it even on a boat, even on an open SUV), the bass quite naturally loses in depth, but almost does not lose in pressure. I would even say that it becomes even more dense and collected in its structure. And again, the very thing for rhythmic club music.

In general, a correctly calculated passive radiator is not some kind of "fasik on a pipe" for you. This will be tougher.

• Compact, easy to install
• Can be used in open SUVs, boats, ATVs, etc.
• Quality performance
• Surprisingly high bass response for a 10-inch caliber
• On club music, the bass is simply gorgeous

• gravitates towards rhythmic music

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On room acoustics, we found that any room is a kind of resonator that dramatically affects the character of the sound of the system. Now it's time to talk directly about the sources of this very sound, that is, about the acoustic systems.

In order to properly understand the processes occurring in a box on the wall of which one or more speakers are mounted, you need to carefully read a couple of books, each of which contains more formulas than in the entire school physics course. I will not get into such a jungle, so this material is not worth it as an exhaustive analysis or guide to building audiophile speakers. However, I really hope that it will help novice music lovers (and some chronic ones too) to properly navigate the variety of acoustic solutions, each of which, of course, its developers call the only correct one.

Some time after the invention in 1924 of an electrodynamic radiator with a conical diffuser (okay, just a speaker), its wooden frame performed primarily decorative and protective functions. It is understandable - after many years of listening to records through mica membranes and bells of gramophones, the sound of the new device and without any acoustic refinement seemed just the apotheosis of euphony.

Gramophone membranes were most often made of aluminum or mica.

However, recording technologies were rapidly improving and it became clear that it was extremely problematic to reproduce the audible range more or less plausibly with a speaker simply mounted on some kind of stand. The fact is that the dynamic head left to itself is in a state of acoustic short circuit. That is, the waves from the front and rear surfaces of the diffuser, radiated, of course, in antiphase, freely overlap each other, which most sadly affects the efficiency of work, and especially the bass transmission.

By the way, in the course of this story, I will most often talk about low frequencies, since their reproduction is a key moment in the operation of any speaker cabinet. RF drivers, due to the small length of the emitted waves, do not need to interact with the internal volume of the column at all, and most often are completely isolated from it.

Soul wide open

The easiest way to separate the speaker's front and rear radiation is to mount it on a shield as large as possible. From this simple idea, the first acoustic systems were actually born, which were a box with an open back wall, since for compactness the edges of the shield were simply taken and bent at a right angle. However, in terms of bass reproduction, the success of such designs was not too impressive. In addition to the imperfection of the body, the problem was also in a very small diffuser suspension course, according to modern concepts. In order to somehow get out of the situation, the speakers were used as large as possible, capable of developing an acceptable sound pressure with a small amplitude of oscillation.

PureAudioProject Trio 15TB with 15" woofers on 3-layer bamboo panels

Despite the apparent primitiveness of such structures, they also had some advantages, and so specific and interesting that the adherents of open speakers have not died out so far.

To begin with, the absence of any obstacles in the path of sound waves is the best way to increase sensitivity. This moment is especially valuable for audiophile tube amplifiers, especially single-ended or devoid of feedback. Paper cones of large diameter, even at a power of about four or five watts, can create a rather impressive, and at the same time surprisingly open and free sound.

With a height of 1.2 m in the world of open acoustics, Jamo R907 are considered almost compact

As for the back radiation, in order not to introduce distortions into the direct sound, it must arrive at the listener with a noticeable delay (over 12-15 ms) - in this case, its influence is felt as a slight reverberation, which only adds air to the sound and expands the musical space . The subtlety is that in order to create this very “noticeable delay”, the speakers, of course, must be located at a fair distance from the walls. In addition, the large area of ​​the front panel and the impressive size of the bass drivers have a corresponding effect on the overall dimensions of the speakers. In a word, owners of small and even medium-sized living rooms, please do not worry.

By the way, a special case of open systems is acoustics built on electrostatic emitters. Only due to the almost weightless diaphragm of a large area, in addition to all the advantages described above, electrostats have the ability to delicately transmit even the sharpest dynamic contrasts, and due to the lack of signal separation in the midrange and treble zones, they also have an enviable timbre accuracy.

open decoration

Pros: High-end open speakers are a great way to get a real kick out of listening to purist tube single-ended speakers.

Minuses: It is better to forget about fat compression basses right away. The entire sound path must be subordinated to the idea of ​​open acoustics, and the speakers themselves will have to be chosen from an extremely limited number of proposals.

locked in a box

With the growth of power and the improvement of the parameters of amplifiers, the ultra-high sensitivity of acoustics has ceased to be the main stumbling block, but the problems of uneven frequency response, and especially the correct reproduction of bass, have become even more relevant.

A giant step towards progress in this direction was made in 1954 by the American engineer Edgar Vilchur. He patented a closed-type speaker system, and it was by no means a gimmick in the style of the current patent trolls.

Patent application of Edgar Vilchur for AU in a closed format

By that time, a phase inverter had already been invented and, of course, the speaker was also repeatedly tried on to a box with a bottom, but nothing good came of it. Due to the elasticity of the closed volume of air, it was necessary either to lose a significant part of the energy of the diffuser, or to make the housing prohibitively large in order to reduce the pressure gradient. Vilchur decided to turn evil into good. He greatly reduced the elasticity of the suspension, thus shifting the control of the movement of the diffuser to the volume of air - a spring much more linear and stable than a corrugation or a rubber ring.

In a closed box, the movements of the diffuser are controlled by air - unlike paper or rubber, it does not age or wear out

So it was possible not only to completely get rid of the acoustic short circuit and increase the output at low frequencies, but also significantly smooth out the frequency response throughout its entire length. However, there was also a minor moment. It turned out that damping by a closed volume of air leads to an increase in the resonant frequency of the moving system and a sharp deterioration in the reproduction of frequencies below this threshold. To combat such a nuisance, it was necessary to increase the mass of the diffuser, which logically led to a decrease in sensitivity. Plus, the absorption inside the "black box" of almost half of the acoustic energy could not help but contribute to the reduction of sound pressure. In a word, a new type of speaker required amplifiers of quite serious power. Fortunately, at that time they already existed.

Subwoofer SVS SB13-Ultra with closed acoustic design

Today, the closed design is used mostly in subwoofers, especially those that claim serious musical performance. The fact is that for home theaters, the energetic development of the lowest bass is often more important than dynamic and phase accuracy throughout the low-frequency range. But by combining a relatively compact closed subwoofer with decent satellites, you can achieve a much more correct sound - albeit not filled with ultra-deep bass, but extremely fast, collected and clear. All of the above can also be attributed to full-range speakers, "closed" models of which occasionally appear on the market.

closed box

Pros: Exemplary attack speed and resolution in the low frequency range. Relative compact design.

Minuses: A sufficiently powerful amplifier is required. Super-deep bass on the verge of infrasound is very difficult to achieve.

Case - pipe

Another way to curb the anti-phase rear radiation was the phase inverter, in Russian literally “phase unfolder”. Most often, it is a hollow tube mounted on the front or rear surface of the case. The principle of operation is clear from the name and is straightforward: since it is difficult and irrational to get rid of the radiation from the back side of the diffuser, it means that it must be synchronized in phase with the frontal waves and used for the benefit of listeners.

The amplitude and phase of air movement in the phase inverter change depending on the frequency of the diffuser oscillations

In fact, an air pipe is an independent oscillatory system that receives an impulse from the movement of air inside the housing. Possessing a completely defined resonance frequency, the phase inverter works the more efficiently, the closer the cone oscillations are to its tuning frequency. Sound waves of higher frequencies simply do not have time to move the air in the pipe, and lower ones, although they have time, but the lower they are, the more the phase inverter phase shifts, and, accordingly, its efficiency. When the phase rotation reaches 180 degrees, the tunnel begins to frankly and very effectively muffle the sound of the bass driver. This explains the very steep drop in speaker sound pressure below the bass reflex tuning frequency - 24 dB / oct.

In the fight against turbulent overtones, phase inverter designers are constantly experimenting

In a closed box, by the way, at frequencies below the resonant frequency response decay is much smoother - 12 dB / oct. However, unlike a blank box, a box with a pipe in the side wall does not force designers to go to any tricks in order to minimize the resonant frequency of the speaker itself, which is rather troublesome and expensive. It is much easier to set up a phase inverter tunnel - just select its internal volume. This is true in theory. In practice, as always, unforeseen difficulties begin, for example, at high volume levels, the air leaving the hole can make noise almost like wind in a stove chimney. In addition, the inertia of the system often causes a drop in attack speed and poor articulation in the bass. In a word, the space for experiments and optimization before the designers of phase inverter systems is simply incredible.

Phase inverter

Pros: Energetic feedback on low frequencies, the ability to reproduce the deepest basses, relative simplicity and low cost of manufacture (with a fair amount of calculation complexity).

Minuses: In most implementations, it loses to a closed box in terms of attack speed and clarity of articulation.

Let's go without a coil

Attempts to get rid of the genetic problems of the phase inverter, and at the same time save on the volume of the case without compromising the depth of the bass, prompted the developers to replace the hollow pipe with a membrane driven by vibrations of the same working volume of air. Simply put, another low-frequency driver was installed in a closed box, only without a magnet and a voice coil.

A passive radiator can double the effective surface of the diffuser, or even triple it if they are installed in pairs in one column.

The design was called "passive radiator" (Passive radiator), which is often not too well translated from English as "passive radiator". Unlike a subwoofer tube, a passive cone takes up much less space in the cabinet, is not as critical to location, and besides, like the air inside a closed box, it dampens the main driver, smoothing its frequency response.

Subwoofer passive radiator REL S/5. The main driver is directed to the floor

Another plus is that with an increase in the area of ​​​​the radiating surface, a smaller oscillation amplitude is required to achieve the desired sound pressure, which means that the consequences of the non-linear operation of the suspension are reduced. Both diffusers oscillate in phase, and the resonant frequency of the free membrane is tuned by precise adjustment of the mass - a weight is simply glued to it.

Passive radiator

Pros: Compact body with impressive bass depth. The absence of phase inverter overtones.

Minuses: An increase in the mass of the radiating elements leads to an increase in transient distortion and a slowdown in the impulse response.

exit from the labyrinth

Acoustics, armed with phase inverters and passive radiators, reproduce deep basses thanks to resonators working with the mediation of air inside the speakers. However, who said that the volume of the column cannot play the role of a low-frequency radiator by itself? Of course it can, and the corresponding design is called an acoustic labyrinth. In fact, it is a waveguide, with a length of half or a quarter of the wavelength, at which it is planned to achieve system resonance. In other words, the design is tuned to the lower boundary of the speaker frequency range. Of course, using a full wavelength waveguide would be even more efficient, but then for a frequency of, say, 30 Hz, it would have to be made 11 meters.

The acoustic labyrinth is a favorite design of DIY acousticians. But if desired, the case of the most cunning form can be ordered ready-made

In order to accommodate even a twice as compact design in a column of reasonable dimensions, baffles are installed in the case, forming the most compact curved waveguide, with a cross section approximately equal to the diffuser area.

The labyrinth differs from the phase inverter in the first place by its less “resonant” (that is, not accentuated at a certain frequency) sound. The relatively low speed and laminar nature of air movement in a wide waveguide prevents the occurrence of turbulence, which, as we remember, generates unwanted overtones. In addition, in this case, the driver is free from compression, which increases the resonant frequency, because its rear radiation encounters practically no obstacles.

Schematic for case calculation at dbdynamixaudio.com

There is an opinion that acoustic labyrinths create less problems with standing waves in the room. However, with the slightest miscalculation in design or manufacture, standing waves can occur in the waveguide itself, which, unlike a phase inverter, has a much more complex resonance structure.

In general, it must be said that a competent calculation and fine tuning of an acoustic labyrinth are very difficult and time-consuming processes. It is for this reason that this type of cabinet is rarely found, and only in speakers of a very serious price level.

acoustic maze

Pros: Not only good response, but also high tonal bass accuracy.

Minuses: Serious dimensions, very high complexity (read - cost) of creating a properly functioning structure.

Hey, on the ferry!

Horn - the most ancient and, perhaps, the most provocative type of acoustic design. It looks cool, if not outrageous, it sounds bright, but at times ... In old films, the characters sometimes shout something to each other, and the characteristic coloring of such a sound has long become a meme in both the music and cinema worlds.

Avantgarde Acoustics Trio with 2.25 m Basshorn XD low frequency horn array

Of course, the current acoustics have gone very far from a tin funnel with a handle, but the principle of operation is still the same - the horn increases the resistance of the air to better match the relatively high mechanical resistance of the moving speaker system. Thus, its efficiency increases, and at the same time a clear directionality of radiation is formed. Unlike all the structures described earlier, the horn is most often used in high-frequency speaker units. The reason is simple - its cross section increases exponentially, and the lower the reproducible frequency, the larger the size of the output hole should be - already at 60 Hz a bell with a diameter of 1.8 m is required. It is clear that such monstrous structures are more suitable for stadium concerts, where they really can be found periodically.

The main trump card of horn playback adherents is that acoustic amplification allows, for a given sound output, to reduce the membrane travel, which means to increase sensitivity and improve musical resolution. Yes, yes, again a nod to the owners of tube single-cycles. In addition, with proper calculation, bells can play the role of acoustic filters, sharply cutting off sound outside their band and allowing you to limit yourself to the simplest, and therefore minimally distorting electric crossovers, and sometimes even do without them.

Realhorns systems - special acoustics for special occasions

Skeptics do not get tired of reminding about the characteristic horn coloring, especially noticeable on vocals, and giving it a characteristic nasality. It is really not easy to overcome this trouble, although judging by the way the best examples of High-End horns play, it is quite real.

mouthpiece

Pros: High acoustic efficiency, which means excellent sensitivity and good musical resolution of the system.

Minuses: Characteristic difficult-to-remove coloring of sound, childish sizes of medium- and even more so low-frequency structures.

Circles on the water

It is by this analogy that the easiest way to describe the nature of the radiation of counter-aperture acoustic systems, first developed in the Soviet Union in the 80s of the last century. The principle of operation is not trivial: a pair of identical speakers are mounted so that their diffusers are located opposite each other in a horizontal plane and move symmetrically, either compressing or expanding the air gap. As a result, circular air waves are created that radiate evenly in all directions. Moreover, the characteristics of these waves during their propagation are distorted minimally, and their energy decays slowly - in proportion to the distance, and not to its square, as in the case of conventional speakers.

Duevel Sirius combines elements of horn and contra-aperture designs

In addition to the range and circular orientation, counter-aperture systems are interesting for their surprisingly wide vertical dispersion (about 30 degrees versus the standard 4-8 degrees), as well as the absence of the Doppler effect. For speakers, it manifests itself in signal beats caused by a constant change in the distance from the sound source to the listener due to the oscillation of the cone. True, the real audibility of these distortions still causes a lot of controversy.

The mutual penetration of the concentric sound fields of the right and left speakers creates a very extensive and uniform zone of surround perception, that is, in fact, the issue of precise positioning of the speakers relative to the listener becomes irrelevant.

Italian-Russian counter-aperture acoustics Bolzano Villetri

A characteristic feature of counter-aperture is that the sound coming to the listener from virtually all directions, although it creates an impressive presence effect, cannot fully convey information about the sound stage. Hence the stories of listeners about the feeling of a piano flying around the room and other wonders of virtual spaces.

Contraperture

Pros: A wide zone of spectacular surround perception, naturalistic timbres due to the non-trivial use of wave acoustic effects.

Minuses: The acoustic space differs noticeably from the sound stage conceived when recording a phonogram.

And others...

If you think that this list of speaker design options is exhausted, then you greatly underestimate the design enthusiasm of electroacoustics. I described only the most popular solutions, leaving behind the scenes a close relative of the labyrinth - a transmission line, a bandpass resonator, a case with an acoustic impedance panel, load pipes ...

Nautilus from Bowers & Wilkins is one of the most unusual, expensive and authoritative speakers in terms of sound. Type of design - loading pipes

Such exoticism is quite rare, but sometimes it materializes in a design with a truly unique sound. And sometimes not. The main thing is not to forget that masterpieces, like mediocrity, are found in all designs, no matter what the ideologists of a particular brand say.

Adapted from Stereo & Video Magazine, June 2016