Calculation of the hull Closed box (CL)

Before you start designing and assembling the box, you need to decide on the choice of speaker. We recommend choosing 10-12 inch imported speakers, as they are most often used in car subwoofers and are best suited. We described in detail how to choose a speaker for a subwoofer in a previous article. The design of the box is also important: the quality and volume of low-frequency sound depends on it.

What types of subwoofer boxes are there?

There are several types of subwoofer boxes. The sound quality directly depends on the design of the box, which you will receive at the output. Below are the most popular types of subwoofers:

A closed box is the easiest to manufacture and design; its name speaks for itself. The woofer is housed in a sealed wooden housing, which improves its acoustic performance. Making a subwoofer in a car with such a housing is quite simple, but it has the lowest efficiency.

A 4th order bandpass is a type of subwoofer whose body is divided into chambers. The volumes of these chambers are different; in one of them there is a speaker, and in the second there is a bass reflex (air duct). One of the features of this type of subwoofer is the design's ability to limit the frequencies that the cone reproduces.

The 6th order bandpass differs from the 4th order by the presence of another bass reflex and another camera. There are two types of 6th order bandpasses - the first has one bass reflex, and the second has two (one of them is common to both cameras). This type of box is the most difficult to design, but produces maximum efficiency.

A bass reflex is a subwoofer with a special tube in the housing. It vents air and provides additional sound from the rear of the speaker. In terms of complexity in manufacturing and sound quality, this type is a cross between a closed box and a bandpass.

If you want to get the highest quality sound, you can opt for bandpasses. But this type of design has many details that must be carefully designed and calculated. All this can be done using a special program WinlSD, which will not only determine the optimal size and volume of the subwoofer, but also create a 3D model of it, and also calculate the dimensions of all parts.

Unfortunately, this program requires at least minimal knowledge in this area and the average car enthusiast is unlikely to be able to do everything correctly the first time. Moreover, in order for the program to work correctly, it needs some speaker parameters, which are also not known to everyone. If you do not plan to take part in car audio competitions, we advise you to discard the bandpasses.

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A bass reflex will be the most optimal solution for a homemade subwoofer. This type of box is good because the tube (bass reflex) allows for better reproduction of the lowest frequencies. In fact, this is an additional sound source that contributes to the sound of the subwoofer and increases efficiency.

What materials do we need to assemble the subwoofer?

The material for making the subwoofer box must be durable, dense and well insulating sound. For this Multi-layer plywood or chipboard is perfect. The main advantages of these materials are their affordable price and ease of processing. They are quite durable and provide good sound insulation. We will make a subwoofer from 30 mm thick multilayer plywood.

To make a subwoofer box we will need:

Wood screws (approximately 50-55 mm, 100 pieces)
Soundproofing material (Shumka)
Drill and screwdriver (or screwdriver)
Jigsaw
Liquid nails
Sealant
PVA glue
Carpet, approximately 3 meters
Klemnik

Subwoofer box drawings

In this article we will make a box for a subwoofer with a 12-inch speaker. Recommended box volume for one 10-12 inch speaker is 40-50 liters. Calculating a box for a subwoofer is not difficult, here is an approximate diagram with the dimensions of the panels.

It is worth paying attention to the minimum distance from the walls of the case to the speaker. It, like the volume of the entire box, is calculated based on the inner surface.

Video instruction: how to make a drawing for a subwoofer yourself

Assembling a subwoofer box with your own hands

You can start assembling. We use a 12-inch Lanzar VW-124 speaker.

Its diameter is 30 cm, and the first thing you need to do is cut a hole for the speaker. The minimum distance from the center of the diffuser to the subwoofer wall is 20 cm. We measured 23 cm (20 cm + 3 cm plywood width) from the edge of the panel and cut a hole with a jigsaw. Next, we cut a hole for the bass reflex slot; in our example, it has a size of 35*5 cm.

Instead of a slot, you can use a classic air duct - a tube. Now we assemble the bass reflex slot and attach it to the front panel of the subwoofer. We go along the joints with liquid nails and tighten them with self-tapping screws.

It is important to tighten the screws very tightly so as not to leave any voids. They will create resonant vibrations that will ruin the sound of the subwoofer.

Next, we assemble the side walls of the box, having previously lubricated them with liquid nails, and tighten them tightly with self-tapping screws.

On the back cover of the box you need to cut a small hole for the terminal block. We connect all parts of the body. We make sure that we cut and fastened all the parts correctly.

We insert the speaker. Let's look and admire.

Let's move on to the interior decoration of the box. The first thing you need to do is seal all the joints and cracks with epoxy glue or sealant. Next, using PVA glue, we glue soundproofing material onto the entire inner surface of the box.

Now we cover the entire outer plane of the box with carpet, including the bass reflex slot. You can attach it with epoxy glue or using a furniture stapler.

Next, insert and screw the speaker tightly. The subwoofer is almost ready, all that remains is to stretch the wires from the speaker to the terminal block and connect the amplifier.

We bought an additional amplifier, but you can also make it yourself. This is quite difficult, as it requires knowledge and practice in the field of radio engineering. You can also use ready-made kits and circuits for radio amateurs, like Master-KIT, and assemble the amplifier yourself. The only thing requirement for the amplifier - its maximum power must be less than the maximum power of the speaker.

See also a video report on making a homemade subwoofer for 2 speakers

Making a stealth subwoofer with your own hands

Tired of carrying a huge box in your trunk? Then the stealth subwoofer is just made for you. This unique type of case is more practical than the classic box. It doesn't sit in a square box in the middle of the trunk and takes up less space. Often, stealth is installed in the inner part of the wing, sometimes in a niche instead of a spare wheel. The minimum volume of the box that requires a 10-12 inch speaker for normal operation is 18 liters.

To make a passive stealth subwoofer we will need:

subwoofer;
protective grille and socket for connection to the amplifier;
wire for connecting the speaker to the outlet;
multilayer plywood or chipboard (thickness 20 mm);
a small piece of fiberboard;
epoxy glue;
brush;
fiberglass;
mounting tape;
polyethylene film;
wood screws;
drill, jigsaw.

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After choosing the place where the stealth will be installed, we empty the trunk and begin manufacturing the body. You can remove the trunk trim where the subwoofer will be installed to place it even closer to the fender. First of all, lay a plastic film on the floor of the trunk. It performs two functions at once: it protects the trunk lining from epoxy glue and allows us to make a mount to which we will screw the bottom of the subwoofer. Next, we cover the inside of the wing with mounting tape in two layers.

We cut the fiberglass into small pieces, approximately 20x20 cm. We put pieces of fiberglass onto masking tape and glue them with epoxy glue. It is better to overlap the fiberglass fabric so that there are no obvious joints and seams.

We sculpt layers of fiberglass on top of each other, simultaneously lubricating them with epoxy glue, until the thickness of the sheet reaches 10 mm (about 4-5 layers).

The material will harden in approximately 12 hours. To speed up the process, you can use a lamp. Now we cut out the bottom of the subwoofer and glue it to our body. The joint is treated with sealant or glued with epoxy resin.

In this particular case, the shape needs to be adjusted to the trunk hinges so that our homemade subwoofer does not interfere with its closing. After we cut off all the excess, we cut out the side walls and the top cover from chipboard. We make the rounded part from plywood, we did it “by eye”.

To make it easier to give the plywood a rounded shape, you must first wet it, give it the desired shape, secure it and let it dry.

Chipboard sheets must be glued with epoxy glue or sealant, and then fastened with self-tapping screws. We also glue the fiberglass box using epoxy resin, and when it dries, we fasten it with self-tapping screws.

For better sealing you can glue the seams again. We applied another layer of epoxy glue and pressed the structure with sand to help the glue adhere better.

Next we can measure the front panel and cut it out. Using a jigsaw, cut out a circle for the speaker. In order to securely attach the front panel to the body, you need to tighten it with self-tapping screws on all sides. That is, you need to install bars on the entire inside of the panel, at a distance slightly greater than the thickness of the plywood (in our case, we attached the bars at a distance of approximately 25 mm from the edge of the panel). Thanks to this, we will be able to secure the front part at the top, bottom, sides, and most importantly - securely attach it to the rounded element.

Cut a hole in the end for the socket.

In the end, it was decided to add two more layers of fiberglass and epoxy glue to the curved part of the body for the stealth subwoofer.

We carry out the final assembly: install the socket and connect the speaker to it, but do not screw it in yet. Next There are two options - paint the subwoofer, or cover it with carpet. Painting is a little more difficult, since you must first level the surface. For this we used universal putty.

We level everything with sandpaper, prime and paint. The subwoofer is ready!

Subwoofer housing calculation

Calculating the housing for a subwoofer is not easy for every motorist, even one who is very passionate about music and understands various acoustic subtleties. A subwoofer is a complex and independent acoustic system designed to create high-quality sound inside a car.
However, few motorists know how to design a subwoofer housing correctly and without problems.

Hull and its calculations

So, directly the algorithm for calculating the subwoofer housing:

There are four main types of subwoofer enclosures available today;
Housing 3Ya is a closed type structure. This type, from the point of view of design and manufacturing, is the simplest. However, it has practically no efficiency. On top of that, it is leaky;
The phase inverter (PI) has a complex calculation principle, but it has a high efficiency;
The 4th and 6th order bandpass is the most difficult option from the point of view of design and practical manufacturing, but it has the highest efficiency within the range of low sound frequencies and at the same time completely suppresses high frequencies.

Note. Objectively, each of the options described above has a number of characteristic advantages and disadvantages, however, the choice must be made in accordance with the recommendations of the design program.

Program WinlSD 0.44

Before moving directly to the design process, you need to create an audio speaker in the database using the WinlSD 0.44 program:

First, you need to move the computer mouse cursor to the New tab, after which you need to check Owndrivers and click on New again. After that, download the parameters selected in accordance with your own wishes and capabilities. At the end, just click OK, Close;
Then you need to create a project based on the speaker and previously specified dimensions;
Next, you need to repeat the above procedure many times, changing the type of case, having tried all four variations.

Direct algorithm for creating the housing itself for a car subwoofer

Here's what you need to know:

The most optimal shape would be a truncated pyramid, since it is the most universal;
The slope of the rear wall should be approximately 23 degrees, since the vast majority of modern passenger cars have an interior with the rear seat backs tilted at exactly this angle;
It is imperative to calculate the volume of the case in accordance with the dimensions of the free space of the trunk (see).

Creating a closed enclosure

Let's start:

All walls of the 3Ya case (closed type case) must be made of chipboard, and the front wall must be 23 mm thick, and the side wall must be 220 mm thick;
Now you just need to cut out the walls of the specified size from chipboard with an accuracy of a millimeter, and then you can proceed to the direct assembly of the body;
The connection should be made using glue and specialized screws with their further screwing in at a distance of 5 cm from each other;

For the self-tapping screws, you need to create holes exactly 3 mm in size using drills, and for the heads of the self-tapping screws, you will need to create the corresponding recesses using a 10 mm drill;
Now it's time to mark the holes for the acoustic terminal using a simple compass;
Next you need to create the corresponding holes using an electronic jigsaw.

Note. If the acoustic terminal is constantly under high pressure conditions, then various kinds of overtones will regularly emanate from it. In order to avoid the effect described above, it is necessary to simply shield the acoustic terminal using a small box.

Let's continue:

Before proceeding to screwing the pre-prepared screws, it is necessary to coat the entire surface of the joints with glue;
The parts of the body that protrude after gluing just need to be carefully cut off using a plane;
In a similar way, it is necessary to mark and cut the corresponding holes already on the front wall in order to ensure high-quality installation of the car speaker;
Nitrolacquer for furniture must be applied to a wooden body in order to preserve the properties of anti-moisture and anti-condensation processes;
To create a beautiful appearance, it is recommended to cover the outer part of the body with carpet (see);
Now all that remains is to simply connect the acoustic terminal and the subwoofer speaker.

Note. It is extremely important to familiarize yourself with all stages of the instructions and understand the design program, as this will allow you to perform independent installation and individually design the box directly to the dimensions and capabilities of the luggage compartment of your car. Also, during absolutely all stages of work, a high degree of attentiveness and accuracy is important, because any inaccuracy will certainly affect the final result.

Self-construction instructions in combination with photo and video materials will allow you to complete the work quickly and efficiently. The price of the issue is minimal and is ten times different from the operation performed in the workshop.
It is quite possible to build a housing with your own hands. The main thing, we repeat, when creating and constructing for the first time, is to carefully read the detailed practical instructions.

Acoustic design in the form of a closed box can be considered as an extreme case of a bass reflex box with an infinitesimal opening. An equivalent acoustic circuit of a low-frequency head in a closed box can be obtained if in the circuit of Fig. 3 discard the elements related to the inverter. The corresponding frequency response of the loudspeaker coincides with equation (17) with y3 = y4 = 0.

Among the many types of frequency responses that can be obtained for a closed box loudspeaker. Of greatest interest are the smooth second-order Butterworth frequency responses. These characteristics are formed under the condition that the relationships between the head and box parameters, expressed by equation (27) at f b / f s = 0, are satisfied. A feature of loudspeakers with second-order Butterworth frequency characteristics is the fact that the cutoff frequency f 3 (29) coincides with the resonant frequency of the head in box f c .

The graphical representation of equations (27) and (29) forms a nomogram for calculating loudspeakers with acoustic design in the form of a closed box. In Fig. 17 in a rectangular coordinate system shows the dependences of the ratios V as /V, f 3 /f s, f c /f s as a function of Qt. The method for calculating the acoustic design of a loudspeaker with a known cutoff frequency or with a box of known dimensions is completely similar to the method for loudspeakers in the form of a bass reflex box. The nomogram was built for a loudspeaker without losses in acoustic design (Qb = infinity), however, it can be used with almost satisfactory accuracy provided Q b >10.

Partial filling (up to 20% of the volume) of a closed box with absorbing material in order to suppress standing waves and improve the unevenness of the frequency response at medium frequencies has little effect on Qb. In addition to smoothing the frequency response, attenuation is also useful in the sense that by changing the law of compression and rarefaction of air during vibrations in the sound-absorbing material, the effective volume of the box increases (the measured ratio Vas/V decreases). This makes it possible to obtain a frequency response with a lower cutoff frequency, or the same cutoff frequency in a smaller design, compared to an unfilled box. Excessively dense filling of the box with absorbent material leads to the opposite result - a decrease in the effective internal volume due to mechanical displacement of air and, at the same time, an increase in losses in the box. Current trends in closed box loudspeaker construction are to use drivers with low resonant frequencies and greater flexibility in the moving system. For such loudspeakers, the Vas/V ratio is greater than or equal to 3, and the cutoff frequency is 2 times or more the natural resonant frequency of the head in free air.

Closed box and bass reflex box are currently the most common types of loudspeaker acoustic designs. A comparative analysis shows that each of them has its own advantages and disadvantages.

The advantages of a loudspeaker with a closed box include a smooth decline in the frequency response towards low frequencies (12 dB per octave for a closed box and 18 dB per octave for a bass reflex box). A smoother roll-off of the frequency response results in less transient distortion.

The advantages of a loudspeaker made in the form of a bass reflex box include the following.

All other things being equal, in the region of the lowest frequencies the efficiency of the loudspeaker is 3 dB higher than for a closed design. This efficiency gain can be translated into an advantage in cutting frequency or design volume. Thus, with the same efficiency and volume of design, a loudspeaker in the form of a bass-reflex box will have a lower cutoff frequency, and with equal efficiency and cutoff frequencies, a smaller volume of design.

Due to better matching of the loudspeaker head with the environment, the amplitude of the moving system in the region of the loudspeaker resonance frequency turns out to be many times smaller than that of a closed box. This means that with equal radiated power, a loudspeaker in the form of a bass reflex box has less nonlinear distortion.

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 a speaker is suitable for a radio cell, 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. For manufacturing materials, 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 the better the sound quality.

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.

Cons:

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.

The proposed method for calculating a bass reflex is based on the simplest measurements carried out with a very specific instance of a loudspeaker installed in an acoustic bass reflex and on a nomographic determination of the dimensions of the latter.

First of all, guided by Fig. 1 and the table, it is necessary to make a “standard volume” - a sealed plywood box, all joints of which are carefully adjusted, glued and coated with plasticine to avoid air leaks.

Compact speakers for high-quality sound reproduction

Closed box calculation (Version 2)

Bass reflex calculation

Due to frequent letters asking for help in calculating this or that acoustic design, I am writing this article. I won’t calculate the design for anyone, I don’t always have time. I created this site specifically for those who are interested in acoustics and want to understand it. I’d rather lay out ready-made options and examples of calculations for the lazy, and then figure it out yourself, use your brain. So.

In the low frequency range, the performance of the loudspeaker does not depend on the shape of the box or the type of bass reflex, but is determined only by two parameters of acoustic design - the volume of the bass reflex box V and frequency of its adjustment Fb. The calculation of acoustic design basically comes down to finding these quantities.

FAQ on speakers and subwoofers

In connection with multiple questions about how to calculate housings for speakers, I am posting several articles related to the calculation of acoustic design for speakers. Don't forget that acoustic design is important for LF heads. And so we begin....

Lately we have been hearing a lot of questions about speakers and subwoofers. The vast majority of answers can be found in the first three pages of any book written by professionals. The material is addressed primarily to beginners, lazy ;) and rural home-made workers, prepared on the basis of books by I.A. Aldoshchina, V.K. Ioffe, partly Ephrussi, magazine publications in Wireless World, AM and (a little) personal experience. Information from the Internet and FIDonet was NOT used. The material in no way pretends to cover the problem completely, but is an attempt to explain the basics of acoustics at a glance.

Most often the question sounds something like this: “I found a speaker, what should I do with it?”, or “Comrade, they say there are such subwoofers...”. Here we will consider only one option for solving this problem: Using the existing speaker, make a box with optimal low-frequency parameters, as far as possible. This option is very different from the task of the factory designer - to tighten the lower frequency of the system to the value required according to the specifications

Sound at the end of the tunnel

“Volodya, when you’re in the warehouse, grab the ports for the phasics...”
(overheard in one of the Moscow installation studios)

When AutoZvuk was still small and sat under the wing Salon AB, the first two parts of a trilogy about subwoofers have been published - about what to expect from different types of acoustic design and how to choose a speaker for a closed box.

A significant portion of those who, contemplating life, decided to treat the bass armament of their car with understanding, could, in principle, get by with this. But not all. Because there is at least one more, extremely popular type of acoustic design, which is not inferior in popularity to a closed box.

Bass reflex in Russian literature, bass reflex, ported box, vented box in English - all this is, in fact, a sound engineering implementation of the Helmholtz resonator idea. The idea is simple - a closed volume is connected to the surrounding space using an opening containing a certain mass of air. It is precisely the existence of this mass - that same column of air that, according to Ostap Bender, puts pressure on any worker, and produces miracles when a Helmholtz resonator is hired to work as part of a subwoofer. Here, a sophisticated thing named after a German physicist takes on the prosaic name of a tunnel (in bourgeois port or vent).

Charging....

Then he began to calculate the volume of the violin box, and this work was long and exciting. …. The volume cannot be reduced - the violin will wheeze and begin to drone dully. If you increase it, it will squeal piercingly, the bass will become dull and weak.…
(A.A. Weiner, G. A. Weiner Visit to the Minotaur)

The article found out what is good and what is bad about different types of acoustic design. It would seem that now “the goals are clear, let’s get to work, comrades..” But that was not the case. Firstly, the acoustic design, in which the speaker itself is not installed - just a box assembled with varying degrees of care. And often it is impossible to assemble it until it is determined which speaker will be installed in it. Secondly, and this is the main fun in designing and manufacturing car subwoofers - the characteristics of a subwoofer are worth little outside the context of the characteristics, at least the most basic ones, of the car where it will work. There is also a third thing. A mobile speaker system that is equally suited to any music is an ideal rarely achieved. A competent installer can usually be recognized by the fact that, when “taking readings” from a client ordering an audio installation, he asks to bring samples of what the client will listen to on the system he ordered after its completion.

As you can see, there are a lot of factors influencing the decision and there is no way to reduce everything to simple and unambiguous recipes, which turns the creation of mobile audio installations into an activity very much akin to art. But it is still possible to outline some general guidelines.

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