Subwoofer housing - closed box (ZY)
As part of the general topic of choosing a subwoofer, let's consider this design or type of housing as a closed box (BY).
A closed box is the simplest and most widely used subwoofer design. It is a sealed box, that is, its name speaks for itself.
What kind of music is ZY suitable for?
The ZYa subwoofer is distinguished by fast and collected bass, punches well, has almost no delays and has a relatively even and smooth sound.
An example of the frequency response of a ground cell in a car interior
Based on these characteristics, a closed box is well suited for many and varied genres - popular, club and rock music, classical and various instrumental - jazz, acoustic compositions, etc.
ZY is not suitable for genres that have a lot of bass, where low frequencies are the basis of the composition. You shouldn't choose it for dubstep, rap, r&b and the like.
Choosing a speaker for the radio
To select a subwoofer speaker for a closed box, you need to start from. Usually this data is indicated in the accompanying documentation, but if you don’t have it, then the parameters can always be found on the Internet.
In order to understand whether the speaker is suitable for the radio, it is enough to carry out simple calculations. Need to divide by and if the value turns out to be less than 80, then such a sub is suitable for the subwoofer and will sound optimally in such a housing.
For example, the same speaker RE Audio SX PRO 15D2 Fs = 27.8 Hz, a Qts = 0.38.
Fs/Qts = 27.8 / 0.38 = 73.2 This sub is quite suitable for a closed box.
If the value for your speaker is more than 80, then you should find a different design for it using.
Features of manufacturing a closed box
This housing primarily requires tightness and absence of vibrations. As a material for manufacturing, choose plywood or MDF with a thickness of 18 mm or more. If the walls are thin, they will rattle and vibrate, causing unnecessary waves to be transmitted into the cabin, which, when mixed with the sound waves of the playing speaker, will ultimately deteriorate the purity and quality of the bass. This is one of the reasons why ready-made subwoofers with thin cabinet walls made of low-quality material are not even considered for purchase.
See the table for verified box volumes.
Table of cell volumes for different speaker sizes
The net volume for the radio is the internal volume of the housing minus the volume occupied by the speaker.
More accurate results need to be calculated using the parameters of a specific model.
The more sealed the ZYa subwoofer, the higher its efficiency and better quality sound.
Example of subwoofers with rubber rims
Advantages and disadvantages of ZY
Pros:
- ease of calculation (you only need to calculate the volume);
- relative simplicity of design and manufacture;
- small dimensions;
- wide range of music genres, fast and clear bass without delays.
Minuses:
- low efficiency (loudness);
- not suitable if you need a lot of bass.
Nuances
Despite the high requirements for tightness, some audiophiles drill a hole no larger than 2 mm in the housing. to equalize internal air pressure at different temperatures.
High-quality sound cannot be imagined without good transmission of low tones. Unfortunately, the standard speakers installed in cars by default do not cope well with this task. Need a subwoofer.Not every car enthusiast has a subwoofer, but probably everyone can imagine what it looks like: a hefty speaker that takes up half (at best) of the trunk. Why does the subwoofer have to be big? Strictly speaking, for high-quality transmission low frequencies a large diffuser size is not needed - any good headphones are able to convey the “low” in all its richness, despite the size of the diffuser being tens of times smaller than that of a subwoofer. The problem is the sound pressure created by the speakers. It is not difficult to create sound pressure in a small volume between the ear and the headphones; it is another matter when we are talking about at least the volume of air inside the car. And here, the lower the frequency, the slower the diffuser moves and the more difficult it is to create the necessary sound pressure. A diffuser with a small diameter must have a very large stroke so that as the volume increases, the sound pressure at lower frequencies remains the same as at high frequencies - so that the “lows do not sag.” And if you want to listen to music very loudly, and even with enhanced bass, then no standard speaker will cope - you need to increase the size of the diffuser.
Another feature of the subwoofer - both in stereo systems and in surround sound systems - is that there is always one (this is also known to many, although not everyone knows why this is so). The fact is that a person has difficulty determining the direction of a low-frequency sound source. Because the sound wavelength is comparable to the distance between the ears, both of our methods for determining the direction of the sound source do not work. The attenuation of the sound is indistinguishable (the wave simply bends around the head and sounds in both ears with the same intensity), and it is also impossible to determine the direction by the phase shift (the peak of the signal arrives in both ears at the same time). Therefore, one subwoofer is quite enough - if there is no high-frequency signal going to it, it will not be possible to determine where it is installed.
Why do many small subwoofers cost more than larger ones? What is the difference between expensive and cheap models, besides power? Firstly, in a combination of power (preferably more), sound pressure (also more) and size (smaller). The requirements are mutually exclusive, therefore, the closer a manufacturer manages to bring its product to an unattainable ideal, the more expensive materials and engineering solutions are used in it. Secondly, in terms of sound quality: in the pursuit of power, many manufacturers leave the issue of quality “behind the scenes” - after all, it requires the use of high-quality (and therefore expensive) materials for the diffuser and subwoofer housing.
Characteristics of subwoofers.
View. There are active and passive. Everything is simple here - the active one already contains an amplifier and can be directly connected to the audio system. The undoubted advantage of an active one is that the manufacturer has already selected an amplifier suitable for it in all respects, and you don’t have to rack your brains about it. The downside is that, as a rule, this is a single-channel amplifier, and if you want not just to add a subwoofer to a standard audio system, but to build a high-quality speaker system from scratch, you will have to buy another amplifier. But the most significant disadvantage of active subwoofers is that the amplifier in them is a “pig in a poke” and manufacturers often skimp on it. If you need not only loud, but also high-quality sound, then when buying an active subwoofer you should not rely on cheap products from little-known manufacturers. And for expensive models, it is advisable to find out the frequency characteristics of the amplifier: amplitude-frequency response, distortion coefficients, signal-to-noise ratio, etc. If this information is not in the instruction manual, then most likely the manufacturer saved on the amplifier, and the quality of its output signal far from ideal. Besides, active subwoofers(other things being equal) are larger in size than passive ones (in the same case there is an amplifier, which is also sometimes quite large) and it will be more difficult to find a place for it in the car.
The passive subwoofer does not have an amplifier; you will need one before connecting it. And in general, all its pros and cons are the pros and cons of active ones.
For assembling a high-quality audio system, a passive subwoofer is clearly preferable. You might even be better off choosing among subwoofer speakers.
For an existing speaker, installing an active one is much faster and easier.
Power. Separate rated power And maximum. No matter how many watts are drawn on the box or enclosure of the subwoofer, you should definitely find out what its rated power is - the one at which it can operate for an hour without the risk of damage. It is this power that should be used when selecting a subwoofer, since there is no standard procedure for measuring maximum power.
Maximum power is the power of a short-term (up to 2 seconds) signal that the subwoofer can withstand without damage. If the maximum power of the amplifier is higher than the maximum power of the subwoofer, you should refrain from listening to music at close to maximum volume - especially music with sudden and prolonged changes in volume.
What should the power of the subwoofer be relative to the power of the amplifier? There is no consensus here; all options have their ardent supporters and opponents.
For sound purity, it is better if the power of the amplifier is greater than the power of the subwoofer. Only with this combination should you remember that maximum power You can't use a subwoofer.
A combination in which the amplifier is weaker than the subwoofer, if the system is properly configured, is considered safer - but only if properly configured. This combination is dangerous because the amplifier, under extreme loads, enters clipping mode and begins to produce a high-power high-frequency signal at the output, which is very dangerous for the speakers. The first sign of amplifier “clipping” is wheezing, crackling and clicking that appears in the sound of the subwoofer. But, unfortunately, due to the volume of the sound, the owner of the audio system often does not notice these signs until it is too late. Properly functioning amplifier overload protection, adjusting its sensitivity and filters, the presence of a filter or external crossover between the amplifier and the subwoofer - they can protect the speaker from the effects of the “clip”, but this requires the correct selection of components and their settings.
Impedance or subwoofer input impedance. Must be exactly supported by the amplifier. If you connect a subwoofer with an impedance of 2 Ohms to an output designed for at least 4 Ohms, then the output stage of the amplifier may burn out, unable to withstand twice the current. If, on the contrary, you connect an 8 ohm subwoofer to an output designed for a maximum of 4, then the sound of the speaker will be much quieter than if the connection were made correctly.
If the subwoofer supports connecting two speakers with a minimum impedance of 2 ohms, then when connected “in a bridge” (if the amplifier allows such a connection), the minimum impedance of the connected subwoofer doubles - less than 4 ohms cannot be connected.
Sometimes, to increase the sound pressure, two subwoofers are connected to the amplifier at once. Then their total impedance is calculated using a formula corresponding to the type of connection.
Speaker diameter. There is an opinion that the more the better. Not necessary. Speaker diameter should only be considered in conjunction with power and sensitivity. If two subwoofers of the same power and sensitivity have different diameters, it is better to take the one that is smaller. Another thing is that speakers with high power and sensitivity usually have a larger diameter. But the volume of the machine is not so large and an 8-10 inch speaker may be quite enough to create good sound pressure. But what if you plan to use your car audio system as a mobile audio system for outdoor audio? Once you open the trunk, the requirements for sound pressure will increase significantly. This is where diffusers of 12-15 inches or larger come in handy. With the appropriate power, of course.
Case material– another topic for heated debate among adherents of certain materials. Some argue that nothing can be better than pure wood; others prefer plywood covered with felt or carpet. However, most mass-produced models are made of MDF and plastic.
In general, the main purpose of the housing in any of the designs is to absorb “unnecessary” sound, so the higher the sound-absorbing characteristics of the material, the better it is suitable for the subwoofer housing.
The rigidity of the material is also important, especially in “closed box” type structures.
MDF and chipboard, due to their high density and weak resonant qualities, are well suited for any type of subwoofer; dense plywood 10-12 mm and wood are a little worse. Metal and aluminum dampen sound the worst, so it is highly desirable that such enclosures be covered with felt or other sound-absorbing material (preferably on both sides). Another reason why metal is not the most the best choice subwoofer housing: it can begin to resonate on its own, then you can forget about the purity of the sound. Some manufacturers (for example, Bell-Audio) use special multilayer plastic in their cases, but cases made of ordinary plastic with not the best performance are much more common, so it is better to refrain from buying a subwoofer (especially a powerful one) in a plastic case.
Sensitivity– for a subwoofer – a synonym for sound pressure. Shows how loud (in dB) a 1 W signal applied to the input will sound at a distance of 1 m from the speaker. For devices of comparable power, the higher the sensitivity, the louder the sound.
Type of shell. All types of enclosures essentially solve one problem: what to do with the sound generated behind the diffuser. This sound is generated in antiphase to the main one, and, adding to the main one, dampens it due to the ability of long sound waves to bend around obstacles (if there is no body).
 |  |
Sealed (closed box) is the simplest type of enclosure. It simply dampens the sound behind the diffuser, for which purpose the insides of the sealed box are often lined with sound-absorbing material. In addition, due to the tightness of the housing, an air cushion is created behind the diffuser, smoothing out sudden movements of the diffuser and allowing it to withstand greater power. The advantages are simplicity, low cost and greater resistance to peak loads. The downside is that a considerable part of the power is wasted: the sound behind the diffuser is simply muffled, so with the same power, subwoofers in such enclosures sound quieter.
 |  |
There is a hole in the bass reflex housing, the distance from which to the speaker is selected in such a way that the sound wave from the rear side of the diffuser reaches the hole in the same phase as from the front side. The sound is not muffled, power is spent more efficiently. The downside is that the wavelength depends on the frequency, and if the wavelength deviates from the calculated one, the sound will be distorted. In addition, speakers in such enclosures are more susceptible to damage under heavy loads - this is especially true if the amplifier does not have an ultra-low-pass filter (subsonic).
 |  |
Band-pass housing combines bass reflex and sealed. Unlike previous enclosures, this enclosure works as a bandpass filter - the best sound will be received by those frequencies whose wavelengths are close to the distance from the speaker to the hole. This solution can be used to increase the bass depth of a speaker with low sensitivity. At the same time, such a case is much larger than a sealed or bass reflex case.
Minimum and maximum frequency reproduced by the subwoofer. The frequencies at which the sound pressure drops critically for mid-range speakers are below 100 Hz. That's why maximum frequency subwoofer must not be lower than this threshold. More often it is much higher; You can adjust the cutoff level yourself using a low-pass filter, which should be on any active subwoofer or subwoofer amplifier. What frequency to set depends on the capabilities of the audio system and everyone's personal preferences, but the general principle is simple - give the subwoofer only what the rest of the audio system does not pull out.
The era of cassette car radios and the “tinny” sound pouring into the ears of passengers and drivers of cars from homemade speaker systems or speakers from NONAME. Very quickly, car enthusiasts appreciated the benefits of digital sound and the advantages of high-quality audio equipment, in particular subwoofers. These devices complemented the standard acoustics with powerful bass, which made it possible to enjoy rich sound that caused a friendly run of “goosebumps” on the skin. In our rating of the best active and passive subwoofers for cars, we tried to cover the most interesting (according to reviews from car enthusiasts and experts) models in different price categories.
How to choose a subwoofer
Selecting a subwoofer wisely is not only a question of the quality of the speaker or the power of the amplifier. Its design itself has a noticeable “sharpening” for specific styles of music- for example, subwoofers with a bass reflex are perceived by ear as having a sharper attack (the rear volume does not dampen the movement of the diffuser, and also acts as a sound source), therefore they have long been loved for the synthetic “tink-tink”, while a softer and more natural-sounding attack Subwoofers with a closed rear volume will allow you to enjoy not only the blues, but also many rather extreme styles of instrumental music on the move. A Band-pass type case, where the diffuser works on the internal volume on both sides, and all the sound comes out through a hole in the box, gives maximum efficiency, but with a pronounced “hump” in the region of a certain frequency band - such a subwoofer can only be recommended for certain tastes , so in any case you need to listen to a specific instance.
Which subwoofer is better - active or passive? Here the question is solely about budget and requirements: of course, an active subwoofer is easier to connect and install, but sound quality will most likely have to be sacrificed - it’s not for nothing that most high-end products are passive, the amplifier for them is already selected for a specific installation.
Closed enclosure, bass reflex or bandpass? But we’ll answer this question simply - choose a subwoofer by at least listening to it in a car of similar volume, and not in a store: the difference will be very strong. And, of course, listen to exactly the music that you like - then you can understand exactly how suitable it is.
Which brand's car subwoofer is better? Over the years, the domestic car audio equipment market has developed a group of favorites whose products are always popular. Car subwoofers from companies such as Sony, Alpine, Pioneer, Helix, JBL, Kicx, Yamaha and other famous manufacturers have long proven themselves to be the best.
At the time of purchasing a subwoofer head, I was completely unprepared for this process and had to be satisfied with the choice that the sales consultant advised me. Another thing is that the assortment of 10" subs was not rich, and the prices in that store were lower than on sites on the Internet, and I decided to buy one of the most expensive ones that were there.
As a speaker, I bought (by mistake, bought as Free Air) a JBL GTO 1002D, whose recommended volume in a closed box is 21.25 liters.
Diameter, mm - 250
Rated power - 250 W
Maximum power - 1000 W
Reproducible frequency range - 25-400 Hz
Resistance - 2 x 2 Ohm
Sensitivity - 91 dB
Installation depth - 116 mm
Description of JBL GTO-1002D:
The new JBL basket allows for maximum movement of the subwoofer cone while simultaneously reducing its mounting depth, which greatly expands the options for choosing where to install the subwoofer. In addition, a completely new basket design ensures that the motor drive assembly is centrally positioned in the voice coil gap, ensuring long term service and fidelity of reproduction.
Rubber suspension with high sealing bead. The large suspension roller is optimized to create maximum diffuser area, while providing excellent diffuser edge suspension and linearity during large movements, high controllability and stability at the extreme points of movement.
Each GTO subwoofer features a specially designed spider centering washer with a non-linear response that provides better control at the extreme points of diffuser displacement compared to a conventional spider centering washer, which has a linear characteristic. This can significantly reduce distortion at high radiated power. Ventilated pole pieces provide additional cooling for the electric drive unit. This allows you to significantly expand the thermal capabilities of the subwoofer and increase its maximum permissible input power.
10, 12 and 15 inch subwoofers (25 cm, 30 cm and 38 cm, respectively) can have two 2 ohm voice coils. This allows for the most flexible approach to optimizing system settings. The two voice coils can be configured using proprietary metal jumpers as one 1 ohm coil, two 2 ohm coils, or one 4 ohm coil. All subwoofers are pre-configured with a single 4 ohm impedance voice coil, making them easy to use in standard applications.
In short, in a word, a simple, inexpensive, unpretentious sub, suitable in terms of parameters for the system that I decided to build for myself. There are a lot of subs for 21 liters, in the future I can change them to a more expensive one if it makes sense. If your ears can hear the difference.
Calculation of housing dimensions and assembly
The available length of the subwoofer along the shelf turned out to be around 65 cm, the required height of the internal volume was about 15 cm, the available width of the box was 35 and 18 cm on different sides.
The exact dimensions will be adjusted after final calculations and by strengthening the box from the inside with layers of 10mm plywood and gluing the box with layers of sound insulation. If the volume is significantly exceeded, it is enough to insert a partition into the narrow end at the calculated distance, which will limit the volume (which was done subsequently).
In this form, a prototype box was assembled from 10 mm plywood.
The picture shows the subwoofer housing with the bottom removed.
From the inside it is reinforced with a frame into which self-tapping screws are screwed and a second layer of 10 mm plywood. After this, the walls are covered with a 5mm polyurethane foam seal. All joints are coated with Moment glue.
The box is closed with a bottom lid that resembles, you can see for yourself what. :-) It is still closing, because after sealing the joints, the lid will also be seated onto the screws.
The top cover has a different geometry than the “coffin-shaped” bottom. This is due to the peculiarities of how the box is connected to the rear parcel shelf of the car. More precisely, with a connection to the rear shelf reinforcement, made of plywood, which is pre-attached to the rear shelf and increases its rigidity.
The shelf amplifier is attached to the rear shelf at 5 points with 8mm bolts and washers, and it is planned to attach the subwoofer body itself to it. This was done not only for reasons of strength, but so that the connection was detachable and it was possible to dismantle the box without any problems, unload it to another place, and fill the trunk with potatoes or firewood. :-)
The upper part of the shelf turned out to be more or less flat, there are no protruding parts such as nuts. This is done so that there are no problems with fastening to the rear parcel shelf of the car.
The studs that secure the sub to the shelf are secured to the shelf using steel plates and welding. This is necessary in order to fix them from the inside.
The sub's body is properly varnished. So that it does not absorb moisture. In this form, all the walls were finally assembled and pulled together with self-tapping screws, every 5 cm, and the joints were coated with Moment glue. Residual glue leaked out of the seams when tightened. This created some illusion of tightness.
The connectors are placed on the outer wall of the subwoofer housing, but the sound pressure does not reach them, because there is another wall inside, at a distance of about 3 cm from the side. It was then sealed and glued thoroughly. That is why there is no point in bothering with gluing the plastic and the outer wall.
The terminal connectors are removable and dismountable.
In the final version of the subwoofer and amplifier assembly, the shelf will look like this
And this side will be visible when opening the trunk.
If you look from below, this is what it looks like.
After assembly, I began to check the operation of the subwoofer and discovered two holes through which air was passing. Both are from old screws. Sealed it.
Next, I missed all the joints where there were suspicions and began to check the tightness by pressing on the speaker and releasing. A bubble appeared in one place where I had just coated. I coated this area more thoroughly inside and out and let it dry.
I can’t say that I’m sure that the joint is 100% tight, but if air comes out, it’s not so intense that it can be noticed.
Listening to low-frequency sounds at high volumes did not produce overtones identifying the passage of air through the cracks in the structure. We will assume that everything is fine and move on.
It's time to cover the surface with carpet. The carpet was purchased inexpensively at the Rus Trade auto store. There was also purchased glue that is sprayed from a bottle. This one, gatt, was expensive, around 250 rubles per bottle.
I started gluing from the shelf reinforcement, glued the lower part in one piece, wrapped the rest on top and fixed it there.
Around the hole for the speaker I made a circle of foam rubber, covered with carpet, in order to press the shelf amplifier to the metal of the rear shelf.
This is what a sheathed shelf amplifier looks like
The seal protrudes slightly beyond the edges of the hole.
This is what a subwoofer covered in carpet looks like.
Now let's connect it to the rear parcel shelf amplifier.
All the holes match, the structure fits together quite tightly and the carpet acts as a seal that reduces vibrations of the shelf amplifier relative to the subwoofer.
After final assembly, I connected the sub again with two windings to the outputs of the music center, first adjusted the balance in antiphase at low volume, then connected it normally and pumped the sub at frequencies from 20 to 50 Hz. In a room of 20 square meters, the resonance was at a frequency of 28 Hz, such that the glass was shaking.
I think that the car should have enough power to spare, no matter how much they scold the 10" subs. Moreover, the speaker really plays into the interior without sending unnecessary waves through the trunk.
Installation
The installation process itself involved dragging the subwoofer box from the house to the car, catching the puzzled looks of the neighbors. It turned out to be heavy, about 15kg, maybe more.
Together with my father-in-law, we installed the shelf amplifier, then the subwoofer itself.
After tightening the nuts, I tugged at the box, tapped it, it seemed that it was sitting quite firmly, the strength of the shelf amplifier was enough to distribute the load over the rear shelf, even when fastened at 5 points. Although, perhaps, I’ll screw the amplifier in a couple more places when I soundproof the bottom of the shelf.
This is what this whole structure looks like in the trunk.
That is, the sub does not take up space on the floor, but it can interfere with the installation of large loads. But it can be easily removed and transferred to the salon or taken home. This is one of the advantages for which the entire design was developed.
Now it was time to test it in action.
