16/09/2013 , Posted in

Exists whole line principles by which all subwoofers can be classified for, or listening room. Below we list the main ones, in each case, indicating the advantages and disadvantages of each type.

Built-in amplifier

Depending on the presence or absence of a built-in amplifier, there are Active and Passive subwoofers.

Active subwoofers are currently the most common and, by and large, are the best choice for use in or. Active subwoofers are, quite simply, the most flexible and easy to install. However, they don't necessarily sound the best. The simplest active subwoofer carries an amplifier, a crossover frequency control (LPF or HPF - Low Pass Filter or High Pass Filter), a phase switch and two types of input connections. The presence of a built-in amplifier necessitates a separate power cord from the 220V outlet to the subwoofer. The crossover frequency control allows you to limit from above the range that the subwoofer will play. A phase control (more often a switch) will allow you to better integrate the subwoofer with the rest of the speakers in your system. It is designed to invert or smoothly change the phase of the audio signal input to the subwoofer. For his correct installation you will most likely have to listen to the system play in both modes (0 and 180) and choose the one with the most pleasing and deep bass. Well, and, of course, an active subwoofer needs to be signaled from the corresponding line output of your AV receiver or processor.

Active subwoofers LJAudio and SVSound

Advantages of active subwoofers:

• Very easy to use (as well as AV receivers compared to a set of separate components);
• Easier to install and configure due to the fact that everything you need is already built into them;
• As a rule, they are less expensive (like AV receivers compared to an AV processor + multi-channel amplifier set).

Disadvantages of active subwoofers:

• The built-in amplifiers on most, though not all, subwoofers are relatively inferior;
• Less convenient in terms of installation, tk. always need to pull 2 ​​cables (power and signal);
• If something bad happens to the amplifier, it is not so easy to find a replacement or repair it;
• Manufacturers do not always sell spare parts for older models;
• Some active subwoofers do not turn on automatically if a low-level audio signal is supplied to them (the auto-off / on system does not work well).

Passive subwoofers originally designed to be used with external amplifier. The amplifier can be used as a dedicated (best option) or integrated (for example, you can use the free channels of the AV receiver). Important point is that since the subwoofer initially requires more power to reproduce low-frequency sounds, the amplifier must be powerful enough. In addition, if the subwoofer does not have a built-in high-pass filter (and a passive subwoofer usually does not), the signal must be filtered on the AV receiver side before it reaches the subwoofer.

Passive subwoofers PRO, RBH and JBL

Advantages of passive subwoofers:

• External amplifiers are usually more solid, they have the right massive power supplies, high-quality wiring of signal circuits;
• Able to digest more power and give out more dB;
• A multi-channel amplifier can make several passive subwoofers play in your ;
• Passive subwoofers are simpler and cheaper to manufacture;
• The internal useful volume of the case is larger with the same dimensions, which allows for more flexibility in the placement of the speaker and phase inverter ports;
• If the amplifier starts to act up, it can easily be replaced with any other;
• Less fire hazardous (electrics and wooden case are separated in space);
• One of the main advantages is great installation flexibility. You can mount the amplifier in a rack along with the rest of your DC equipment, and run only one regular speaker wire to the subwoofer. You don't need to feed them!
• Long acoustic (speaker) wires are usually cheaper than special subwoofer cables of the same length;
• Speaker wires (can be completely flat) are much easier to hide than subwoofer cables.

External subwoofer amplifier

Disadvantages of passive subwoofers:

• Significantly more difficult to organize and install;
• External amplifiers can be more expensive than built-in ones.

Emitter directivity

Depending on which direction the speaker is looking, subwoofers can be divided into:

Radiating down (DownFiring). This type of subwoofer has a speaker installed in the bottom wall of the case and directed to the floor. Subwoofers of this type look more like some kind of furniture than a speaker system. They don't need a protective grill. They can play even more efficiently than their relatives, so you should avoid installing them in the corners of rooms and in close proximity to walls (applies to the option with one subwoofer in the system). Otherwise, the sound may be too boomy.

Down Firing subwoofers Yamaha and Atlantic Tech

Radiating forward (FrontFiring). The speaker of this type of subwoofer is mounted on one of the front walls of the case and is directed parallel to the floor plane. These types of subwoofers require a protective grill to protect the speaker from damage, and are more like a conventional speaker system.

Front Firing Earthquake and Rhythmic Audio subwoofers

Type of acoustic design

This classification is the most extensive and is deeply rooted in the Acoustics section of the science of Physics. As a minimum educational program, we will talk a little about the purpose and function of any acoustic design dynamics. The speaker emits sound not only forward, but also backward. The front and rear sound waves are opposite in phase. In this regard, there is a term “acoustic closure” in which the waves on both sides of the speaker cone add up and (if they are completely opposite in phase) cancel each other out. In theory, you should not hear sound from a bare speaker at all, in practice, the sound will be, but very far from the original. The case (box) of the speaker system, in which the speaker is installed, allows this circuit to be eliminated and to give the sound waves the required parameters in terms of dynamics and frequency response.

We will omit further theory and try to briefly review the most common types of acoustic design, not forgetting to talk about the advantages and disadvantages of each of them.

Closed box (ZYa, Closed case,Enclosure). The speaker is installed in a closed, airtight housing. This solution completely isolates the rear sound wave of the speaker from the front.

Advantages:

• Ease of design and production (only two parameters need to be taken into account: the volume of the box and the quality factor of the speaker);
• Relatively small body volume;
• Excellent impulse response (response to a short-term signal, the ability of the component to accurately reproduce short-term musical events);
• There is no need to use a subsonic filter (LPF), because there is a natural tendency of the AP to suppress frequencies below the resonant frequency of the speaker;
• Fast, natural, smooth, bouncy, crisp, controlled and warm are a number of subjective characteristics often used to describe the bass produced by a good subwoofer of this type.

Flaws:

• Relatively high lower frequency limit, rarely below 30 Hz (-3 dB level);
• The lowest efficiency in comparison with other types of acoustic design.

Phase inverter(FI, Ported, Vented, Bass-Reflex). The speaker is installed in a housing that has a tunnel that continues inward in the form of a pipe, box or slot for a certain length. This tunnel is called the bass reflex port. Due to it, the internal volume of the box communicates with the surrounding space. The length and area of ​​the tunnel are critical important parameters for the correct operation of this type of acoustic design. Both the speaker and the phase inverter port work in tandem, forming a second oscillatory system that radiates (already in phase with the speaker cone) additional sound energy of the rear wave. The speaker, as a rule, is installed in the front wall of the case. The phase inverter port is most often located on the same wall, less often on the perpendicular (in the case of a downward looking speaker) wall of the case and tunes the device to maximum output in a certain (rarely wider than 1-2 octaves) frequency range. In this range, the speaker operates with minimal load, vibration and distortion (most of the sound is emitted by the port), allowing the subwoofer to handle more maximum power. Above the tuning frequency, the tunnel becomes less and less "transparent" to sound vibrations, and the speaker works as if in a closed box. Below the tuning frequency, the opposite happens: the inertia of the port gradually disappears, and at the most low frequencies the speaker works almost without load, as if it were taken out of the case. The amplitude of oscillation increases rapidly, and with it the risk of spitting out the speaker cone or damage to the voice coil from hitting the magnet. This feature necessitates the use of infra-low frequency filters (subsonics) in bass-reflex subwoofers.

Advantages:

• Lower frequency response border, quietly located in the region or even below 20 Hz (at the level of -3 dB);
• Allows you to supply more power due to the smaller amplitude of the oscillation of the speaker cone, especially in the area and above the tuning frequency;
• More productive, surpassing on average 3dB in sound pressure level of their counterparts in a closed box;
• Deep, powerful, full, loud, inspiring, stunning and earth shaking - such epithets often accompany the description of the low-frequency effects reproduced by this type of subwoofer.

Flaws:

• Requires a larger case;
• It is more difficult to get the desired result in design and production;
• They require an additional infra-low-frequency filter (sabsonic) or volume limitation, tk. there is a high probability of damage to the speaker at frequencies below the tuning frequency;
• Impulse characteristics are worse than WL, which affects the subjective perception of bass notes, especially in music;
• The diameter of the port must be relatively large in order to avoid unwanted overtones of the air passing through it. This entails the need to increase the length of the tunnel, which, in turn, entails the need to increase the body itself. The result may be a box of completely obscene dimensions;
• Resonant, stuffy, sluggish, single-note, slow and inaccurate are often subjective epithets regarding bass from failed subwoofers of this type.

Most subwoofers on the consumer electronics market are bass-reflex. Devices of this type allow you to get the deepest and loudest bass, albeit in some places due to the quality of reproduction of especially subtle and exacting musical details.

Bandpass loudspeaker 4th order (band passVented\Sealed, Bandpass, PSU). The 4th order bandpass is characterized by a speaker, the front and rear parts of which are installed in two separate chambers of a single housing. Moreover, the rear part of the speaker is in a closed box, and the front in a box with a port (tunnel) or vice versa. The case of such a subwoofer is created like a closed box, but with the addition of an acoustic filter (port). This filter, working in tandem with the front sound wave of the speaker, limits the bandwidth of the device, simultaneously raising the sound pressure level in this frequency range.

Advantages:

• A fairly low frequency response limit is achievable (at the level of -3 dB), but only due to lower returns and a higher level of distortion;
• Extremely high sound pressure levels are achievable at the cost of higher tuning frequency and narrow bandwidth;
• Less total speaker travel required, less chance of damaging it;

Flaws:

• It's hard to get everything right. The result strongly depends on the accuracy of the obtained volumes of both chambers, as well as on the tuning frequency;
• Prone to one-note bass, especially if not well constructed;
• To achieve a wide bandwidth, you will have to put up with low sensitivity and the presence of distortion in a certain range;
• Weak impulse responses;
• Bandwidth and sensitivity are inversely related.

Bandpass subwoofers Lanzar and Sonance

Most often, subwoofers of this type are found in automotive installations aimed at participating in car audio competitions in the maximum sound pressure (SPL) category.

6th order strip loudspeaker (band passVented). Bandpass of the 6th order is characterized by a speaker, the front and rear parts of which are installed in two separate chambers of a single housing. Moreover, both the rear and front of the speaker are in a box with a port (tunnel). Each camera is tuned to its own calculated frequency. The resulting frequency response, in theory, should be better than all the previously described design options. The rights to this type of acoustic design and the secrets of the principles of calculating the case are owned by Bose. They explain the theory this way: “The woofers sit between two separate acoustically elastic volumes inside Bose's patented 'Acoustimass' module. When the speaker cone moves, it excites the air in the chambers. The air in the chamber, acting as an acoustic spring, interacts with the air in the tunnel and produces more low-frequency sound when less power amplification. The system is more sensitive and requires a smaller amplitude of oscillation of the speaker cone, which, in turn, gives rise to less distortion. Even if distortion was somehow created, thanks to the patented technology, it will remain captive to the acoustic volumes of the cabinet and never reach your ears.”

Advantages:

• Great sensitivity;
• Less fluctuation of the cone - the minimum level of audible distortion.

Flaws:

• The total volume of the two chambers results in a rather bulky box;
• Difficult to construct. The result strongly depends on the accuracy of the implementation of the calculated parameters;
• There are no clear formulas for calculating the volumes and sizes of ports due to a patent owned by Bose;
• The speaker can fail quite easily as a result of constant high pressure, which entails overheating of its parts;
• Weak impulse responses.

EBS (ExtendedBassShelf, Extended Bass Shelf). EBS is a type of bass-reflex speaker cabinet design. The difference is that the working volume of the case is purposely chosen to be 25-75% larger than the optimal calculated one, and the port is tuned to a frequency close to the resonant frequency of the speaker. As a result, we get a decent increase in the lower cutoff frequency of the subwoofer. If you measure the frequency response of such a device, the same “Shelf” becomes visible, located immediately above the tuning frequency.

Advantages:

• Low frequency response (-3 dB), easily reaching values ​​far below 20 Hz;
• Infra-low, earth-shaking bass;
• Increased output below 25 Hz at the expense of reduced output above 30 Hz (Frequencies depend on internal volume parameters and port tuning frequency).

Flaws:

• Giant body size;
• The speaker is able to withstand 25-50% less maximum power before it starts to break down;
• Lack of presence effect, lack of attack - such epithets are found when describing EBS;
• The overall effect of the bass is greatly softened. Signals at frequencies between 40 and 60 Hz are extremely low in level;
• It is more difficult to “sell”, because most people are weakly receptive to sounds at such low frequencies;
• It takes 8 times more power (as well as the volume of air moved) to make a sound at 20 Hz as loud as at 40 Hz.

Infinite screen (Infinite baffle, IB). IB is a type of open speaker design in which the screen separating the front and rear sound waves is presented as an infinite plane. This design involves mounting the woofers in a very large isolated working volume, the dimensions of which allow us to neglect the drag force created by compressing air in other types of design. This type of design does not affect changes in the resonant frequency of the speaker, which inevitably happens in other cases. Often, the room next to the home theater room (basement, attic, cellar, pantry, garage, etc.) is used as an “isolated” volume. Unlike their bass-reflex and closed counterparts, IB-subwoofers are distinguished by the absence of extraneous overtones, which are so often created by bass-reflex ports and the walls of the OH cabinet. As IB supporters say: "Listen to the bass, not the body (Hear The Bass, Not The Box)".

Advantages:

• The lowest frequency response limit (at the level of -3 dB), reaching a value of 5 Hz;
• Extremely infra-low, earth-shaking and breath-taking bass;
• The absence of extraneous overtones and sound color;
• Saving inner space– there is no need to install large boxes in the room;
• The secrecy of the installation is a godsend for the interior designer.

Flaws:

• Always a complex custom installation project. IBs are not industrial grade;
• Availability of an appropriate adjacent room for the installation of speakers;
• In an adjacent room, there will be as much bass as in your cinema (there is a question of additional soundproofing);
• More speakers are required because their maximum power is reduced by 50% (no acoustic air resistance, it is easier to damage the speaker);
• Complicated calculation and tuning, requiring professional calibration equipment and equalizers.

Options for organizing IB subwoofers

These subwoofers are only found in the homes of advanced home theater enthusiasts, who are rightly referred to as "Bass Heads". These guys know no compromises and build subwoofers, allocating an entire adjoining room for them, mount several pairs of 15-18" speakers, supply 3-4 kW of amplifying power - all for the sake of achieving that very presence effect. And, apparently, not in vain, because the LFE channel of the soundtrack of a number of films contains low-frequency effects that go down to 5 Hz!

A real example of the frequency response of an IB subwoofer (red graph)

Passive radiator (PI, Passive Radiator, PR). A passive radiator is always used in combination with an active one and serves as a replacement for the phase inverter tunnel. A passive radiator speaker is most similar to a bass reflex speaker in terms of its acoustic characteristics, however, with increased sensitivity. Passive radiators are often made in the form of a conventional speaker, which does not have a magnet and coil, or simply in the form of a flat diaphragm on a suspension. The radiator must be larger or at least the same size as the active speaker.

Advantages:

• Absence of overtones and sound coloration created by the phase inverter port;
• Ease of setup. By a simple addition or by subtracting small values ​​of the mass of the PI, the tuning frequency of the body can be changed to a value from 0.1 to 15 Hz. Easily achievable fine tuning;
• Possibility of tuning small cases to a lower frequency - no restrictions on the length of the tunnel;
• There is less threat of speaker failure at infra-low frequencies, there is no need to use a subsonic.

Paradigm, Definitive Tech and Mirage Passive Radiator Subwoofers

Flaws:

• There may be distortion due to the “ping-pong” effect (in short, fluctuations in the PI can cause fluctuations in the main speaker);
• Slightly higher lower frequency response of the subwoofer compared to the FI;
• The steepest rolloff (36 dB/octave) is below the tuning frequency;
• More expensive to manufacture (PI costs more than a plastic FI pipe).

Transmission line (TL, Labyrinth, Transmission Line, TL). The speaker is installed in the case, inside which an acoustic labyrinth or a long pipe is organized, which is called the transmission line. The length of such a labyrinth depends on the resonant frequency of the speaker and the material from which the damping composition is made, covering the walls of the entire labyrinth. TL can narrow and expand or remain with the same cross-sectional area along its entire length, and also have a number of bends and turns to reduce the final dimensions of the speaker cabinet. The length of the transmission line corresponds to 1/4 wavelength of the resonant frequency of the speaker. The labyrinth is usually filled with various types of damping material, which helps to absorb most of the return energy. sound wave and allows you to use a shorter TL while maintaining the target speaker frequency.

Advantages:

• Excellent impulse response, equal (and often superior) to closed designs (ZYa) and significantly superior to bass-reflex designs (FI);
• A priori, a more rigid body design eliminates the distortions introduced by its walls;
• Low frequency response slope (around 10 dB / octave or less), which leads to an increase in the return in the deep bass zone;
• Less coloration in upper bass notes due to reduced impedance peaks;
• Liver, clearer and deeper bass.

Transmission Line PMC and Earthquake subwoofers

Flaws:

• The complexity of design and construction;
• Not all speakers will perform well in the maze, and there are no specific recommendations for their choice;
• There are no clear design methods and calculation formulas for creating TL, by and large it is always a trial and error method;
• The size of the case can be impressive.

Rarely found in home theaters. For the most part, labyrinth-based speakers are the lot of Hi-Fi and Hi-End enthusiasts.

Isobaric (Compound, Isobaric) with two speakers. Two loudspeakers are installed together in a case having a closed space of a certain volume between them. The speakers must work with each other in phase. The volume of space enclosed between the speakers should be as small as possible for the cones to move freely. In the process of modeling a case of this type, half the internal volume of the sound box is taken, which allows any subwoofer to be made twice as compact as any other type of acoustic design.

Advantages:

• doubled smaller sizes enclosures for any speaker with respect to WL - the main plus;
• Improved response at the lowest frequencies;
• Thicker, faster, clearer and more natural are the epithets used to describe the bass reproduced by the isobaric.

Flaws:

• The operation of the internal speaker requires additional amplification power of the same magnitude, which is wasted;
• The sensitivity of the system is lower by 3 dB compared to the CL due to the mass of the diffusers doubled and the internal volume reduced by half;
• The sensitivity of the system is 6dB lower compared to two OHs of the same volume and with the same speakers.

Currently, subwoofers of this type are extremely rare and only where there are big problems with the space for their installation, and the bass is required rather clear than loud.

Pull/Push (push/Pull) with two speakers. In a closed case with a single internal volume, two speakers are installed in a special way. The best option is when the speakers are installed in the same plane of the case, with one directed outward, and the second directed inward. The connection to the amplifier is carried out in antiphase, when in reality the operation of the speaker cones turns out to be in phase. Odd harmonics, according to Vance Dickason's theory, cancel themselves out. And if you believe the company, M&K, specializing in the production of Push / Pull subwoofers, this approach allows you to get rid of even even harmonics. One way or another, harmonic distortions born from the anomalies of the dynamics and its constituent parts, are reduced due to similar inverted anomalies of the second speaker. The sound, as the supporters of this type of design say, is as natural and natural as possible due to the corrections made by the speakers in relation to each other. Often there is a Push / Pull design option, when both speakers look outward, which looks more aesthetically pleasing and familiar. Although in this case the effect of distortion reduction is weakly expressed, all other advantages of the approach remain. The size of the cabinet should be twice as large as it was calculated for a single speaker. The system turns out to be more sensitive (by 3 dB) compared to a half-volume sound system and one speaker on board with a completely similar frequency response curve. The subwoofer becomes able to withstand twice the power.

Advantages:

• Better sensitivity;
• Doubled maximum power;
• No harmonic distortion;
• Appropriate ability to generate high sound pressure levels (SPL).

Flaws:

• A single large subwoofer enclosure that can be both ugly in appearance and difficult to construct and move around.
• The frequency response, by and large, corresponds to two separate subwoofers in cases half the size, however, here you do not have the opportunity to space them apart. different parts rooms when setting up, which is often extremely necessary.

Push/Pull subwoofers from Blue Sky, MK Sound and 3D DIY model

Companies that have excelled in push/pull subwoofer technology, such as MK Sound and Ken Kreisel (the founder of MK), today offer subwoofers and speakers that look great with unrivaled performance and sound. This is confirmed by the use of their products in the leading film studios in Hollywood and recording studios in London. We only add that Ken Kreisel is the inventor of subwoofers as such and satellite-subwoofer systems.

Loudspeaker size (speaker)

Very often, subwoofers are divided into classes according to the size (usually diameter) of the working surface of the installed speaker cone. The loudspeakers (woofers) used in the construction of subwoofers are, as a rule, the largest in size, because they must move large amounts of air to create low frequency sound waves. To get the same volume level one octave lower (eg 30 Hz instead of 60 Hz) you need four times as much power. The lower resonant frequency speaker, the lower frequency sounds are able to reproduce the loudspeaker with a given level of distortion. The resonant frequency of a speaker (denoted Fs) is determined by a combination of the mass of its moving parts (cone, protective cap, coil and its base) and the flexibility of the suspension. Under normal conditions, we need more powerful amplifier to “drive” the subwoofer speaker rather than a conventional speaker system. However, it is important to remember that although you must have an amplifier with a headroom to avoid distortion (clipping), the main task is still to match the subwoofer with the main speakers. At any volume level, the subwoofer should not stand out and be localized, but only invisibly expand the boundary of the system's sound down the frequency response curve.

The most common speaker sizes for use in subwoofers are 8″, 10″, 12″, 15″ or 18″(we are talking about the diameter of the round diffuser). Although an 18″ subwoofer is capable of reproducing bass at the lowest frequency and at maximum volume, the largest driver is not always the best. the best choice for optimal reproduction of bass notes. Larger woofers are more difficult to control and tune. There are 10″ subwoofers on the market these days that can move as much air as the old 15″ models could move. This is made possible by a very long-throw 10″ driver cone, designed to maintain linearity throughout its entire travel, and a high-power Class D digital amplifier capable of driving such a woofer in a small cabinet.

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, passive radiator speakers 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. The operating range of a 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 works with the correct setting of the 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 frequency produced, the relative position of the passive radiator and the active one, several dips can be observed in the frequency response. 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. A properly designed tunnel bass reflex eliminates the phase mutual damping of the speaker's sound waves. 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 at the resonant frequency of the 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 it provides an alternative to existing subwoofer enclosures.

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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 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 resistance direct current) - 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. Passive radiator at correct setting(and here it is set up correctly) - great 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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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 in terms of sound acoustic systems. 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.