On this page we will briefly go over the elements that make up any woofer and midrange speaker. This will help you better understand the structure of the subwoofer and more fully imagine the process of sound reproduction.

So, what is a subwoofer or low-frequency speaker? A subwoofer is a device that converts the signal frequency into air vibrations, which we perceive as sound.

The operating principle is as follows - the signal from the amplifier is transmitted through wires to a coil, which, when interacting with a magnet, moves and moves the speaker diffuser, which creates sound waves (air vibrations).

Now that's enough definitions, let's look at the pictures.

Components

Below are the main elements that make up the subwoofer.

Suspension— attaches the diffuser to the basket. Together with the length of the coil winding, it affects the stroke of the speaker, and elasticity and strength depend on the material.

Mounting ring- acts as a seal; in some models it can attach the suspension to the basket.

Wire output— a modern solution is to route the wires from the coil along the centering washer, which eliminates the possibility of damage and extraneous sounds during operation.

Terminal— acoustic wires from the amplifier are connected to the terminal block; in some models they may be absent, offering the owner a direct connection or a connection through the housing terminal.

Voice coil- located in the gap between core And top flange, where a magnetic field is formed. The coil is a cylinder ( sleeve), on which a thin copper wire is wound ( coil winding). Sleeve connected to diffuser, due to which it is set in motion.

Basket is the speaker housing and frame for all elements.

Dust cap- prevents dust from entering the voice coil gap.

Diffuser- the area that creates air vibrations that we hear as sound.

Centering washer— centers and holds the coil in the gap.

Magnetic system. Magnet It is made from special alloys or magnetic ceramics - specially pressed and “sintered” powders. The power of the speaker depends on the mass and material of the magnet.

Magnet located around core and secured between top And lower flanges. All this together makes up the subwoofer's magnetic system.

Ventilation holes And air exhaust channel used to remove heat and protect the coil from overheating. Cooling can be passive or active, both options are used in speakers. With passive cooling, heat is dissipated due to the heat transfer of materials, and with active cooling, hot air is removed due to the movement of the diffuser, respectively, when accelerating or increasing the range of motion, the cooling intensity also increases.

Conclusion

These were the main elements that make up the subwoofer; low-frequency and most mid-frequency speakers have this principle. High-frequency ones are built somewhat differently.

The combination, materials and interactions of all these elements determine the characteristics of the subwoofer, and of course the sound character and quality of the speaker.

Video about what a subwoofer consists of

I hope after this material you understand what a subwoofer consists of and how it works.

Speaker systems that are designed to reproduce sound frequencies ranging from 20 to 120 Hz are called subwoofers. The operating principle of this device is to convert electrical signals into acoustic ones. When potential consumers ask what a subwoofer is, the explanation presented above is sometimes not enough. For this reason, specialists have to describe in more detail the technical characteristics of the presented device.

Device types:

• Active;
• Passive.

In fact, it is not so difficult to explain what an active subwoofer is, because it is a model that includes a power amplifier in its design, as well as an active crossover. Such devices are capable of receiving and subsequently converting signals related to the line level. Active subwoofers can be connected without problems between the signal source itself, as well as wideband speakers. This type of connection is called end-to-end by specialists. The corresponding subwoofers often have additional capabilities in order to adapt to specific conditions of use. In this situation, we can talk about the steepness of the cut, adjusting the frequency response, the position of the cut points of the crossover itself, etc.

Quite common autonomous active subwoofers are characterized by the fact that they combine in one design not only a subwoofer with a crossover filter, but also a power amplifier of very high quality in terms of its functionality. This type of subwoofer is equipped with linear inputs, which serve to connect to a pre-amplifier, which is very important from a technical point of view. The design also includes linear outputs. They produce a signal that goes to the power amplifier. For ease of use, stand-alone models also include a special regulator in their design, which is designed to control the subwoofer signal. The crossover frequency is also in the vast majority of cases adjustable on the device.

Absolutely logically, motorists are wondering what a passive subwoofer is, which is also very popular among buyers. It should be understood that such models consist not only of a body, but also a speaker. This allows them to connect to a power amplifier without any problems. To put it as simply as possible, a passive subwoofer is one or even several low-frequency heads that were placed in a housing. These heads must be connected to an external amplifier.

There are several options for connecting a passive subwoofer. One of the most famous schemes involves supplying a signal from a stereo amplifier. Subsequently, these same signals are sent not only to the subwoofer, but also to the main speakers. To be fair, it should be noted that this connection option is far from the most desirable. The fact is that this circuit provides for supplying the output signal from the power amplifier to the input of the subwoofer itself. This circumstance leads to the fact that the crossover filter removes low frequencies from the signal. The main speakers subsequently receive the filtered signal.

Types of acoustic design

The simplest type of acoustic design for a subwoofer is a traditional closed box, but this option is definitely not the only one. A fairly well-known type is the bass reflex. In this case, one of the walls of the subwoofer contains a tunnel with a clearly defined diameter and length. An almost identical option is a passive radiator. However, this type of acoustic design contains an additional speaker instead of a tunnel. True, it is not equipped with a magnetic system and voice coil. Another very interesting option is a labyrinth. The back wall of such a subwoofer is designed to work with a zigzag sound guide.

A closed box is a type of design that does not provide for the presence of additional emitters. The box is completely sealed, and on one of its walls there is a woofer. Depending on its design, the quality of the final sound may vary.

Bandpass. This type of design is a bass reflex box. In the middle of this structure there is a special wall that separates the chambers, which differ in different volumes. As for the speaker, it is located directly on the partition between the cameras. It should immediately be noted that this design is characterized by a fairly high efficiency of its operation. As for the name Bandpass, its origin is easy to explain. The fact is that such a housing can without any problems significantly limit the frequency response that the subwoofer has.

Distinctive features of car subwoofers

Knowing thoroughly what an active and passive subwoofer is, it becomes clear that such devices can be installed not only in vehicles, but also in the home. However, the difference lies in the installation process. Home models are very easy to install, but in the case of automobile analogues, certain requirements must be met. It is no coincidence that drivers are actively interested in what a car subwoofer is and its basic technical properties. These models are distinguished by their small volumes, thanks to which they can be easily placed in the trunk.

Main problems

Before you learn about what an active car subwoofer is, it is necessary to consider certain theoretical problems that may subsequently arise. First of all, it should be noted the need to use additional electronics. Initially, the sound quality of the bass may be quite low. Of course, it is important to know what a passive car subwoofer is, but the possible disadvantages should never be ignored. For example, not in all situations the sound of the presented device may coincide with the most basic speakers. It is better to know these and other purely theoretical shortcomings in advance and minimize the likelihood of occurrence during operation.

A fairly common problem is also the situation in which subwoofers are forced to reproduce rather deep bass during their operation. Due to high-quality controllability, this goal is still achieved, but the level of sensitivity of the device increases. This situation causes most subwoofers to sound somewhat slow or exaggerated. It is not uncommon for important parts to be lost.

We should also not forget that subwoofers in certain situations can fill the vehicle with low-frequency energy. As a result, many resonance phenomena occur inside the machine. In order to avoid such consequences, it is necessary to pay special attention to the correct placement of the subwoofer inside the car. If you miss this fact, then there will be a high probability that the so-called “musical results” will not be at the highest level. If you install two subwoofers at the same time, you can somewhat mitigate the problem associated with excitation of car interior frequencies.

Reasons for hearing the subwoofer and not the bass

The highest quality subwoofers are characterized by the absence of cabinet vibration. However, quite often the walls of the housing also emit sound. Other elements and panels may also experience vibration. As a result, the overtones become even more high-frequency. It happens that the problem arises simply because the amplifier filters were configured with some errors.

Among other things, unwanted overtones may well be a logical consequence of air turbulence. Experts clearly know that at fairly low frequencies, the diffuser stroke in most cases is quite significant. When exposed to high temperatures, it can even reach several centimeters. It is clear that in such a situation the air movement will be very significant, and this already leads to turbulence.

The subwoofer manufacturer must have a positive reputation and good reviews. Otherwise, consumers risk purchasing a subwoofer whose housing is characterized by poor quality assembly. That is why before buying a subwoofer you need to study it very carefully. Without exception, all panels of the device must be adjusted in such a way that even minimal gaps are completely absent. As you know, the smallest hole will automatically have a negative impact on the final sound.

A subwoofer is an acoustic system that converts low-frequency sound waves. Localization of low frequencies is very poor, as a person can hardly determine where the sound is coming from. For this reason, for any audio system, one subwoofer is enough, which must be installed in the right place.

You can install the compact device somewhere under the table, so its functionality will not suffer at all. True, when standing waves occur in a small space, it depends on the placement of the subwoofer how effectively they can be dealt with.

Listening to most music does not require purchasing a subwoofer, since they do not contain bass. The equipment is suitable for those who:

• likes to listen to heavy music, like rock;
• watches blockbusters with powerful special effects.

It is in these cases that the subwoofer is able to show itself in all its glory by adding volume to the sound and specific resonance.

Types of subwoofers

All low-frequency systems are conventionally divided into two groups in relation to the presence of an amplifier:

• active;
• passive.

The former already have a built-in power amplifier, which helps match the different parameters of the subwoofer and the sound source. The latter are not equipped with an amplifier, so they require external connection of equipment. Of course, you can do without an amplifier, but in this case the subwoofer will produce distorted sound waves, often expressed as an unpleasant wheeze.

In a professional environment, it is believed that a passive subwoofer is capable of conveying a deeper sound of low waves, giving a specific coloring. But to achieve such an effect, you will need to configure the equipment, which not everyone can fully achieve. For ordinary people, it is better to give preference to an active subwoofer, since it can be directly connected to the sound source.

Types of subwoofer designs

There are several types of subwoofers, differing in their design. So, for example, in a horn device used at concerts, the horn is folded. In closed boxes there is no additional emitter, and the woofer is built into one of the walls of the sealed case.

The bass reflex is a cylindrical ventilation tube built into the housing. This allows sound to be emitted from the rear of the diffuser. With this component, the efficiency of the subwoofer can be significantly increased, which is accompanied by an expansion of the spectrum of reproduced low frequencies.

A passive radiator has a similar purpose as a bass reflex, only an additional diffuser without a voice coil and a magnetic system is installed in the housing instead of a tube. By varying the parameters of the diffuser, you can change the lower limit of reproduced frequencies.

The bandpass is a box with a bass reflex, divided in the middle by a wall. The speaker in such a subwoofer is inserted into the partition between two chambers, due to which the frequency can be limited. The efficiency of such a device is higher than that of simple boxes with a bass reflex. There are three types of bandpasses:

• fourth category (two cameras with a built-in bass reflex in the top);
• sixth category type A (two cameras and two bass reflexes, each of them in its own chamber);
• sixth category type B (two cameras and two bass reflexes, with the top one being common to both cameras).

A quarter-wave resonator is a tunnel with a certain cross-section and length. The output of this design is 40% higher than that of bass-reflex ones, and up to 300% than that of closed boxes.

How to choose a subwoofer?

There are several factors to consider when purchasing a subwoofer:

• price of the device;
• the area of ​​the room in which the device will be installed;
• intended installation location;
• sound preferences;
• range of output frequencies;
• maximum sound pressure;
• compatibility with other elements of the system.

Subwoofers are considered good, the price of which starts from 10,000 rubles. When purchasing a device, you can get excellent upper and mid-low frequency ranges, but it is effective to install the equipment in a room not exceeding 20 sq.m.

Subs costing more than 20,000 rubles are intended for large areas. They are preferred by true audio connoisseurs. When choosing, you should focus on the power of the system, since the higher it is, the better the sound will be transmitted. True, you should not purchase a subwoofer with a power of up to 1 kW for a small room.

As for the frequency range, it is better to give preference to devices whose lower limit starts at least from 60 Hz. The rule works here: the lower the frequency limit, the better the bass you can get. There is no point in chasing the upper limit, since any speakers already voice the range from 350 to 2000 Hz. It is worth remembering that the more limited the sound range of a subwoofer, the better quality it will transmit it.

When installing a subwoofer indoors, you should choose a location near a long wall, away from a corner. The sound pressure should be from 100 dB, and as the indicator increases, the power of the sounds produced also increases. Another parameter is the presence of regulators built into the subwoofer. The necessary ones include Level, Cutoff Frequency and Phase.

Connecting a subwoofer

Any low-frequency speaker system is connected either via low- or high-amplitude inputs. When connecting via high-amplitude inputs, you need to connect the device to an amplifier or receiver using connectors for a second pair of speakers (if the amplifier has this capability).

When using high-amplitude outputs, the following connection procedure is allowed: the signal is transmitted to the subwoofer from the outputs to the front pair of the receiver, as a result of which high frequencies are automatically cut off and redirected to the front speakers. True, the subwoofer amplifier in this case does not perform its function. The methods described above are very rare and are used only when it is not possible to connect through low-amplitude inputs or if a passive subwoofer is used.

To connect to low-amplitude inputs, RCA connectors are used, which are marked Sub out or Pre-out, which means the same thing. If the receiver or amplifier has only one input, connection is possible to the left input connector labeled Mono or marked L. The second subwoofer is connected exclusively through low-amplitude outputs.

Thus, if you want to add low frequencies to your speaker system, adding volume, you need to add a subwoofer to it. One device is quite enough, since a person is not able to distinguish where low-frequency sound comes from. True, a lot depends on what design the subwoofer has and what parameters it has. To ensure that everything is connected correctly, it is recommended that you read the instructions for use in advance, which will greatly simplify the setup process and will not affect the quality of the transmitted signal.

The difference between an active subwoofer and a passive one

The difference between an active subwoofer and a passive one is obvious, since both devices perform different functions. A subwoofer is a low-frequency speaker designed to reproduce a wide range of frequencies, working in conjunction with any type of speaker system.
Knowing how an active subwoofer differs from a passive one, you can safely make your choice in favor of one speaker or another.

Types of subwoofers

For a subwoofer to work, three elements need to interact. This is the housing itself, the subwoofer and the amplifier.
Depending on this layout, subwoofers are divided into two types:

• Active subwoofer;

Main differences between subwoofers

A passive subwoofer is a low-frequency speaker enclosed in a special acoustic housing. For it to work, you must connect to an external amplifier.
It can also be connected using an electronic frequency separation filter. This arrangement allows you to achieve deeper bass and significantly expand the frequency spectrum.

Note: it is worth considering that at higher volumes, linear sound distortion is significantly reduced, so it is advisable to listen to songs at an average sound volume.

A low-frequency subwoofer is usually complemented by a home theater system or a car speaker system. This allows you to achieve rich bass and separate sound.
An active subwoofer can significantly reduce the load on the receiver in a home theater system. When choosing a subwoofer, you need to take into account the properties of the space where it will be installed.
A bass reflex subwoofer has deeper bass and is designed for a larger room size. In a confined space, such as a car, this type of subwoofer may begin to resonate.

Advantages and disadvantages

Each type of subwoofer has its own advantages and disadvantages, due to its design features. A passive subwoofer has deeper and richer bass compared to an active one.
This is due to many different factors:

• No air overheating inside the case;
• Possibility of connecting additional electronic filters (see);
• The external power amplifier has a large number of settings;
• Due to the absence of foreign components in the housing, the power and depth of the bass becomes more saturated;
• Lower cost compared to an active subwoofer with similar technical characteristics.

• Can be used as a portable device if there are outputs for additional speakers;
• Various execution options.

When choosing between an active and passive subwoofer, you should decide directly where it will be used and what sound characteristics are needed.

The effect of the enclosure on the sound of the subwoofer

The subwoofer housing is the main element of the speaker system. Thanks to it, you can create directional, dull or diffuse bass.
There are several main types of housing:

• A closed-type enclosure is a box in which the speaker is located in a closed space. In this case, the vibrations of the speaker dampen the pressure that arises inside due to the vibrations of the diffuser.
  The subwoofer in a closed housing provides deep, rich bass. The inside of the case is lined with special sound-insulating materials, which absorbs heat and creates air pressure inside.
  The power of such a subwoofer directly depends on the internal volume of the case. But there is one drawback: the efficiency of this type of subwoofer is the lowest;
• Housing with bass reflex. There is a special hole made in it for air exhaust.
  This allows you to direct the sound wave and significantly increase the power of the subwoofer. Thanks to this, even at the lowest frequencies the speaker operates with virtually no significant load.
  A low-frequency sound wave occurs due to air injection. This type of cabinet produces very sharp and powerful bass;
• Bandbass body. The speaker is located in the partition between the two chambers. This type of enclosure combines the previous two and significantly improves sound quality and efficiency.
  The main idea is that you can simultaneously adjust the upper and lower bass levels. This allows you to make the bass more rich and natural. But this type of subwoofer is the most expensive because it is very difficult to manufacture.

Each type of subwoofer is designed for a specific type of room. At the same time, due to the internal properties of the case and the size of the speakers, the sound directly depends.
Both subwoofers have their advantages and disadvantages, so before choosing, it is better to consult with specialists.
A passive subwoofer produces a larger frequency range than an active one. But problems may arise with its connection, since it is necessary to select the right power amplifier and connect electronic sound filters.
An active subwoofer just needs to be connected to a power source and an audio signal sent to it. You can even do this yourself, as the kit also includes instructions.
When going to the store to make a purchase, you need to understand that the price of a quality device will be high. Of course, it is advisable to look at photos and videos regarding the operation of different types of subwoofers in order to decide on your choice.

From time to time, bandpass subwoofers come into our field of vision. Otherwise - bandpasses...

Most often, it should be noted, in the form of finished products. Much less often - as an element of a system built according to an individual project. The basics (the very basics) of the theory and practice of this type of design were published in our country a long time ago, about 15 years ago. There is an opinion (from the author) that it would be necessary to clarify something in this matter, or else, you see, and remind, not forgetting about the “newly discovered circumstances...”

1. Relatively narrow frequency range.

2. Increased complexity of manufacturing and configuration.

We see more advantages.

1. Availability of an internal low-pass filter.

2. Ability to reproduce low bass.

3. Acoustic amplification.

4. The speaker is protected from external influences.

The first minus and the first plus are two sides of the same coin, which confirm the well-known wisdom that every thing is good in its place. That is, the bandpass is of little use for the role of a broadband bass radiator (in a three-way acoustic system, say), while in the position of a subwoofer it would be very useful. The second drawback was a factor that significantly limited the spread of band-pass designs. Moreover, the problem is not even in manufacturing; after all, the difference between PP and FI is only in the presence of an additional inner wall. The difficulty is that during the fine-tuning process, one of the walls will probably have to be moved, changing the “front” volume. In a single production this is indeed inconvenient, but when preparing a series (even a small one) - what is the problem?

Now about the positives. As you can imagine, the presence of a natural low-pass filter was responsible for some of the popularity of bandpasses in the past, when passive filters were considered a natural way to separate frequency bands. A passive low-pass filter, tuned to a frequency typical for subwoofers, involves the use of large and expensive coils. As we moved towards dedicated bass amplifiers and active filters, this factor became irrelevant. However, considering that in our industry most truly musical amplifiers are equipped with second-order filters, the presence of an additional (acoustic) low-pass filter will be very useful.

The ability to reproduce low bass is a good thing, but not for us. Let's say, a subwoofer for a home theater in a home theater can play bass from 50 Hz, in a design with FI - from 32, and in a PP design - from 25, and if you sacrifice the uniformity of the frequency response, you can reduce the frequency limit to 20 Hz. However, in our industry there seem to be no problems with low bass; the subwoofer in the ZYA plays (in theory) from 0 Hz. We have other problems - with the uniformity of the mid-bass, since the transition from free field to compression mode occurs at 55 - 70 Hz (-3 dB rise frequency). All subwoofers with FI provide a rise, starting from this frequency and downwards; a SF, tuned exactly to the transition frequency, will give a straight-line response, but, naturally, without any rise. With all other settings, the VZ will give either a rise in the mid-bass region of 70 - 50 Hz, or, even worse, a decline at the same frequencies.

So, a fourth-order bandpass (we will only talk about it below; we will avoid unnecessary complications) can give a rise exactly where it is needed, near the upper limit of its operating band, and in salon conditions maintain an attractive shape of the frequency response. I think this alone is enough to take a closer look at it. Well, the last of the above advantages is also worth something.

So, let's start taking a closer look. Let's take some unnamed speaker, we are not interested in its characteristics for the time being. For now, we are building the characteristics in a free field, it’s more clear. Let's see how the frequency response changes depending on the size of the “rear” (that is, closed) volume.

Rice. 1. Change in characteristics depending on the size of the closed volume

Rice. 2. Change in characteristics depending on the size of the front volume

Rice. 3. Change in characteristics depending on the air mass inside the port

Rice. 4. Variation of characteristics depending on the bandwidth

As you can see, even when the volume changes more than three times (by 10 dB), the bandwidth changes insignificantly. However, as the volume decreases, the rise in the characteristic shifts to the lower limit of the passband. But we don't need this. Therefore, the guideline will be simple, the first volume should correspond to a ground cell with a Butterworth quality factor or slightly lower, say, from 0.62 to 0.72 (green curve on the graph). To avoid bulky boxes, we must immediately focus on heads with a quality factor at least 25% lower than this indicator, that is, no higher than 0.47 - 0.5.

Now notice that all curves pass through some point. This is the resonance frequency of the port and the front volume, we will call it the center frequency. In this case, it is 38 Hz, this choice is typical for a home subwoofer; in our field, the center frequency must be chosen significantly higher.

The upper frequency limit most depends on the size of the second (front) volume.

By reducing this volume, we extend the frequency range upward, while simultaneously obtaining a boost in the characteristic. The shape of the high-frequency part of the characteristic is due to the resonance of the bass reflex with joint elasticity due to the rigidity of the suspension, the elasticity of the rear air and the elasticity of the front volume air. A 3 dB boost (orange curve) is obtained when the high resonance frequency is an octave higher than the center frequency. The air mass inside the port affects the lower frequency limit and at the same time the shape of the characteristic.

The performance in this area is due to the resonance of the combined air mass inside the port and diffuser with the joint elasticity of the suspension and rear volume. Luckily, we don’t need a lot of mass; it’s enough to move the lower resonance 1/3 octave away from the center frequency (brown curve). To understand the nature of the bandbass, it will be useful to see how the shape of the characteristic will change if we maintain the port setting, but at the same time change both the mass of air inside it and the volume of the front chamber.

The graphs are shown in an idealized form, which is obtained without taking into account leakage (as well as non-rigidity) of the housing. If this is taken into account, the central part of the graphs will never reach the 0 dB level. However, in the theory available today, losses are not taken into account.

Now let's move on to practice. Let's select two heads from test No. 2 for this year. Their parameters meet the Qts criterion<0,5. Как показало моделирование, чтобы избежать провала характеристики на суббасовых частотах, надо, чтобы частота резонанса головки в ЗЯ (заднем объёме) была не выше 50 Гц. Потому добавляем ещё один критерий: Fs <35 Гц. Вот что мы выбрали:

Head No. 1. Fs = 31.6 Hz; Vas = 29.3 l; Qts = 0.480.

Head No. 2. Fs = 33.4 Hz; Vas = 22.0 l; Qts = 0.454.

To calculate the PP of fourth-order design, you can use many of the ready-made programs: not all of them give the expected results, but the old JBL Speakershop (aka Bass Box) in this case gives quite correct ones. If, as already mentioned, we ignore possible housing leaks. But for meaningful calculations it is advisable to have some starting points. For example, for the first head, first calculate the volume of the cell in which the Butterworth (or slightly lower) quality factor is achieved. For Butterworth we get 24.7 liters. If, after installing the head in such a box, we measure the impedance characteristic, it will look something like in Fig. 5:

Rice. 5. Characteristics of the impedance of head No. 1 in the GZ

Now we need to determine the anterior volume. A good starting point would be 1/3 of the rear, in this case 8.2L. As a result of the simulation, the refined value of the front volume is 8.06 liters, which is almost the same. During the calculation, we obtain a free-field characteristic as shown in Fig. 6. The graph shows the approximate position of the port resonance frequency.

Rice. 6. Characteristics of the PP subwoofer in a free field

However, we are much more interested in the characteristics of the subwoofer in a car showroom environment. If we superimpose the standard transfer function of “AutoSound” on the previous graph (it was published in its entirety in No. 8/2000), we get the picture depicted in Fig. 7.

Rice. 7. Characteristics of the PP subwoofer in a typical cabin. Head No. 1, cutoff frequency 100 Hz

As you can see, the maximum amplitude spread over the entire operating range from infrasound to 95 Hz is less than 2 dB. A similar characteristic can be obtained using the SG, but on the bandpass side there is also a constant acoustic gain of 3 dB plus an effective roll-off slope of 18 dB/oct on top.

To complete the picture, you can look at Fig. 8 impedance characteristic. The port's tuning frequency is 64.3 Hz, the lower resonance is tuned an octave lower, the upper one about 2/3 of an octave higher.

Rice. 8. Characteristics of the impedance of the subwoofer PP. Head No. 1, cutoff frequency 100 Hz

What happens if we make a mistake with the volume of the front drawer during manufacturing? Say, by 10% (Fig. 9)?

Rice. 9. Front drawer volume detuning by ±10%

Nothing particularly scary. The upper frequency limit changes by 5%, but the shape of the frequency response does not change radically. But it is not recommended to make a big mistake in realizing the air mass inside the port; the consequences are shown in Fig. 10.

Rice. 10. Port mass detuning by ±10%

A deviation of the air mass inside the port by 10% in each direction (that is, a 5% change in the tuning frequency) leads to a deviation of the frequency response by 1 dB in one direction or the other.

With head No. 2, although not quite identical, a similar set of characteristics is achieved. In this case, we set the first volume to a quality factor of 0.66; for this you will need a box (part of a box) with a volume of 21 liters. The resonance frequency in such a cell would be equal to 48.8 Hz. As a result of modeling, the front volume was chosen to be 7.3 liters. The calculated frequency response is shown in Fig. eleven.

Rice. 11. Characteristics of the PP subwoofer in a typical cabin. Head No. 2, cutoff frequency 100 Hz

Unevenness over the entire range is no more than 2 dB, the upper limit frequency is about 95 Hz. The slope of the decline is the same 18 dB/oct. If we now turn to the impedance characteristic (Fig. 12a), it will be easy to see that the characteristic frequencies here are almost the same as in the case of head No. 1.

Rice. 12. Impedance characteristics of the PP subwoofer. Head No. 2: a) cut-off frequency 100 Hz; b) cut-off frequency 80 Hz

If we need to work in a narrower band, the settings will change in a predictable way (Fig. 12b). To get an upper frequency limit of 80 Hz instead of 100 Hz, we will need to lower the center frequency and the upper resonance frequency by about 10%. In this case, the frequency response takes the form as in Fig. 13.

Rice. 13. Characteristics of the PP subwoofer in a typical cabin. Head No. 2, cutoff frequency 80 Hz

The unevenness increased to 3 dB, although unlike FI, which tend to focus on the lower bass, in the PP design the decline begins around 30 Hz, where, in fact, the informative bass ends. True, in order to narrow the strip at the top, the front volume had to be increased to almost 10 liters. Paradoxically, in our conditions, bandpass design works better over a wider band.

There's just a little bit left to add. That the bandpass, for all its apparent “technocraticism,” emits like a closed box, and therefore its transient characteristics are more interesting than those of the FI. For the same reason, its bass (properly tuned) turns out to be more collected, which is important for SQ installations. Finally, in terms of total volume, the bandpass does not lose that much to phasics; we can say that the amount of loss is equal to the value of the front volume. This is the price for uniform acoustic amplification, in other words, for increased efficiency.

From the history of the bandpass

To avoid the impression that bandpasses were just invented, here are two illustrations with dates. The first is a US patent issued in the name of a man with the noble French surname d'Alton. He came up with a bandpass as a narrowband emitter, hoping to assemble broadband acoustic systems of great efficiency from many of them, tuned to different frequencies, in the manner of a church organ.

The idea is outlandish and, as history has shown, of little use, but the nobleman understood both the device and, as far as can be judged from the lonely graph, the characteristics, in principle, correctly.

Twenty years later, when the speaker (that is, the direct radiation electrodynamic loudspeaker) finally replaced other means of sound emission, another patent appeared. It already states in plain text that this is a way to expand the frequency band downward using a separate, relatively narrow-band acoustic unit. That is, exactly what we today call the word “subwoofer”.

Moreover, Henry Lang's explanations already include sound pressure curves very similar to those discussed in today's publication. “The process began” from that moment.