Do-it-yourself active home subwoofer. Do-it-yourself subwoofer: from entry-level to high-end Subwoofer circuit diagram 2.1

This article will focus on a subwoofer based on the well-known and common speaker 75GDN.

dynamic head

So, I got the 75GDN dynamic head almost for nothing, though in not very good condition and in poor appearance, the entire speaker was covered with gunpowder, the dust cap was cut out of cardboard, and not very evenly.

I had experience in repairing speakers, so I simply could not leave it in this state, I decided to make a small upgrade.
So, I disassembled the speaker. I will not describe all the details of this process, this is done with the help of a solvent, an improvised tool, such as a screwdriver, tweezers and straight arms.

In the speaker basket, for better cooling of the coil, 8 holes with a diameter of 8 mm were made. Then the basket was sanded, the places where the centering washer and suspension were glued were sealed with electrical tape and painted. Gold-plated clips were also supplied.

The speaker cone was cleaned of dust and glue residue, sanded, and a new, flat field-protective cap was glued (cut out of cardboard). After that, the head was reassembled. The speaker cone was covered with a layer of PVA glue and also painted. A decorative sticker on the cap was made from a colored adhesive film.

With the speaker finished, you can take on the manufacture of the box.
subwoofer cabinet

The body is made of furniture, laminated chipboard 16mm thick. There are two baffles inside. The side walls are recessed to improve the appearance and ease of pulling the subwoofer. The front wall is thickened, 32 mm thick, glued from two chipboard boards. Also, a hole was made in the front of it, where the indicator board is located, and a recess was made for the head to fit. The walls of the case are interconnected with screws and glued with PVA glue, also along the entire perimeter inside the beam 20x20mm. An additional, separate compartment is made in the side wall, where the amplifier is located. Net volume is about 40l.

Inside the sub is pasted over with foam rubber 10 mm thick, medium density. It is better to tune the phase inverter by ear, since the TC parameters of the speakers may differ. Its inner diameter is 70mm, the length of the port can vary from 18 to 25 cm, tuned to a frequency of 30-40 Hz.

In principle, the box came out quite strong and deaf, although it might be worth making the side walls a little thicker, for example 18mm.
The top of the sub is covered in black carpet.

Electronics

Amplifier

The amplifier circuit is shown below.

You can read about the operation of the scheme in the article " car amplifier monoblock" or directly in the article of the author of the circuit, in the magazine "Radio". The only thing that has changed is the printed circuit board. The amplifier does not require adjustment, everything works from the first start.

Voltage converter and stabilizer

The voltage converter and stabilizer circuit also remained unchanged. The only thing that has changed is the circuit boards and added another 15V voltage regulator to power the output power indicator. The converter and stabilizer are mounted on two boards with dimensions of 160x85mm and 45x50mm, respectively.

I will not delve into the operation of the circuit either, however, from the experience of the previous article, I will tell you again about the winding of the transformer, since many questions arose due to the lack of a photo.

The transformer is wound on a ferrite ring with dimensions 40x25x11. First, all the sharp edges of the ring are rounded with a file and wrapped with rag tape.

The primary winding is wound with 5 strands of wire 0.8-0.9mm and contains 2x6 turns. First, the first half of the winding is wound, it is evenly divided throughout the ring.

Then the second.

At the ends, the cores are twisted and 4 outputs come out. We bend these conclusions under the holes in the board and wrap the primary winding with the same electrical tape.

Now you can take on the secondary winding, in my version it is wound with 1.5mm wire and contains 2x16 turns, it is wound in the same way as the primary winding. As a result, we get 4 more outputs of the secondary winding.

We bend it under the board and wrap it with electrical tape. The transformer is ready, we clean the leads and solder them onto the printed circuit board.

Also, it may be worth introducing output chokes into the circuit for each power arm, they can be wound on ferrite rods 2 cm high and 8 mm in diameter and contain 6-8 turns of 1.2-1.8 mm wire. The input inductor is wound on a ferrite ring from a computer power supply with two 1mm wires and contains 10 turns evenly distributed on the ring.

The assembled stabilizer board looks like this:

Filter block

All the same, 100 times checked by me filter scheme:

Power output indicator

The output power indicator is assembled on the LM3915 chip according to the following scheme.

S1 switches the indicator operation mode, when the contact is closed, the "column" mode, when the contact is open - "wave". Trimmer resistor R5 can be set to the desired level of the indicator. In principle, any LEDs can be used.

Construction and installation

Since there was not so much space for electronics, it turned out to be not so easy to "shove" it there, I had to be philosophic. Therefore, all boards, connectors and control knobs are fixed on an 8mm MDF plate. The radiator, power and REM terminals, input jacks, as well as filter block regulators are displayed on the outside. Externally, this plate, together with the radiator, is painted black. From the inside, in the place where the transistors should be attached, a rectangular hole was made in the plate. A duralumin plate was cut through this hole in order to "build up" the radiator to right level and it was convenient to mount transistors. This plate is screwed to the radiator with two bolts, between the plate and the radiator, of course, a layer of thermoplastics. The bolts are deliberately left longer, because later a duralumin plate sits on them, which presses all the transistors to the radiator. (The photo shows the first version of the amplifier, one TDA7294 without transistors. The circuit did not show itself, because another PA was later implemented)

The converter board is attached to the MDF plastic using duralumin corners, two small ones are directly screwed to the board and the plate, and two large ones are removed from the board and with the help of 2 extensions made of copper wire do not allow the board to swing.

A plastic corner was made for the power amplifier board, which supports one part of it, however, it is mainly held by the output transistors and the microcircuit, which are strongly pressed against the radiator with a duralumin plate. Between the radiator, microcircuit and all output transistors, there must be a dielectric plate and, of course, thermal paste, transistor cases and microcircuits are isolated from the radiator.

The stabilizer board is attached to two plastic corners, and the filter board is held with the help of duralumin plastic, to which three regulators are screwed.

The wires from the power terminals to the PN board are as thick as possible, at least 4-6 sq. mm. An 8-pin connector is used to connect the indicator board and the subwoofer operation indicators. Also, for convenience, you can introduce a 2-pin connector for connecting a dynamic head.

The output power indicator board and power indicators are fixed in the allotted place, the holes for the wires are sealed with plasticine after installation. The indicators are covered with a tinted glass plate.

final result

Satisfied with the end result at the time. The subwoofer played very soft, pleasant and deep BASS and could create quite good sound pressure for a 10. However, he was not sued to play with me for a long time, because after buying a car it was planned to build another system with a different subwoofer. This subwoofer was sold and until now it pleases the new owner.

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It all started with the fact that a year and a half ago I bought a twelve-inch woofer in order to assemble a car subwoofer. But there was not enough time, and the speaker stale in my apartment. And now, a year and a half later, I finally decided to assemble, but not a car, but an active home subwoofer. In this article I will describe step-by-step instructions for calculating and assembling subwoofers of this type.

1. Calculation and design of the case (box) of the subwoofer

To calculate the subwoofer enclosure, we need:

• Thiel-Small parameters for loudspeaker,
• Program for calculating acoustic design

1.1 Measurement of the Thiel-Small parameters for a loudspeaker

Usually these parameters are indicated by the manufacturer in the loudspeaker's passport or on their website. But now most of the loudspeakers sold in the markets (including my loudspeaker) do not have these parameters specified or do not correspond to them (despite numerous attempts, I have not been able to find my speaker on the Internet, and the Thiel-Small parameters have already and there was no question.) Therefore, we will have to measure everything ourselves.

For this we need:

• Computer or laptop with a GOOD (that is, with a linear frequency response) sound card,
• A software sound generator that uses the headphone output of a sound card (I personally like the program,
• AC voltmeter with the ability to measure voltage of the order of 0.1 mV,
• drawer with phase inverter,
• Resistor 150-220 Ohm,
• Connectors, wires, etc……..

1.1.1. First, let's check the linearity of the frequency response of the sound card. Exists a large number of programs that automatically measure the frequency response in the range of 20-20000 Hz (when the headphone output is connected to the microphone input of the sound card). But here I will describe manual method measurement of frequency response in the range of 10-500 Hz (only this range is important for measuring the Til Small parameters of a low-frequency radiator). If an AC voltmeter with the ability to measure voltage of the order of 0.1 mV is not at hand, do not worry, you can use a regular inexpensive multimeter (Tester). Typically, such multimeters measure AC voltage with an accuracy of 0.1V and DC voltage with an accuracy of 0.1 mV. To measure an alternating voltage of the order of several mV, you just need to put a diode bridge in front of the multimeter input and measure in voltmeter mode constant voltage in the range up to 200mV.

First, connect a voltmeter to the headphone output (Either to the right or to the left channel).

Turn off all sound effects and equalizers, open the speaker properties and set the volume level to 100%.

Open the program, press “Options”, in “Tone Interval” select “Frequency”, and set the step to 1Hz.

Close "Options", set the volume level to 100%, set the initial frequency to 10Hz and press "Play". With the “+” button, we begin smoothly, in 1 Hz steps, to increase the generator frequency to 500 Hz.

At the same time, we look at the voltage value on the voltmeter. If the maximum amplitude difference is within 2dB (1.259 times), then such a sound card is suitable for measuring speaker parameters. For me, for example, the maximum value was 624mV, and the minimum value was 568mV, 624/568 = 1.09859 (0.4dB), which is quite acceptable.

1.1.2. Let's move on to the long-awaited Thiel-Small parameters. The minimum parameters by which you can calculate and design acoustic design (in this case, a subwoofer) is:

• Resonance frequency (Fs),
• Total electromechanical quality factor (Qts),
• Equivalent volume (Vas).

For a more professional calculation, you will need even more parameters, such as mechanical quality factor (Qms), electrical quality factor (Qes), sensitivity (SPL), etc.

1.1.2.1. Determining the resonant frequency (Fs) of a loudspeaker.

We collect such a scheme.

The speaker must be in free space as far away from walls, floor and ceiling as possible (I hung it from a chandelier). We open the NCH Tone Generator program again, insist on the volume as described above, set the initial frequency to 10Hz and begin to gradually increase the frequency in 1Hz steps. At the same time, we again look at the value of the voltmeter, which will first increase, reach the maximum point (Umax) at the natural resonance frequency (Fs), and begin to decrease to the minimum point (Umin). With a further increase in frequency, the voltage will gradually increase. The graph of the dependence of voltage (active resistance of the speaker) on the frequency of the signal looks like this.

The frequency at which the voltmeter value is maximum is the approximate resonant frequency (at a step of 1 Hz). To determine the exact resonant frequency, it is necessary in the region of the approximate resonant frequency to change the frequency in steps no longer by 1 Hz, but by 0.05 Hz (accuracy 0.05 Hz). We write down the resonant frequency (Fs), the minimum value of the voltmeter (Umin), the value of the voltmeter at the resonant frequency (Umax) (in the future they will be useful for calculating the following parameters).

1.1.2.2. Determination of the total electromechanical quality factor (Qts) of a loudspeaker.
Find UF1,F2 using the following formula.

By changing the frequency, we achieve the values ​​of the voltmeter corresponding to the voltage UF1, F2. There will be two frequencies. One is below the resonant frequency (F1), the other is above (F2).

You can check the correctness of the calculations with this formula.

If the difference between Fs' and Fs does not exceed 1 Hz, then you can safely continue measurements. If not, then you need to do everything first. We find the mechanical quality factor (Qms) using this formula.

The electrical quality factor (Qes) is found using this formula.

Finally, we determine the total electromechanical quality factor (Qts) using this formula.

1.1.2.3. Determine the equivalent volume (Vas) of a loudspeaker.

To determine the exact equivalent volume, we need a prefabricated, durable, sealed bass reflex box with a hole for our speaker.

The volume of the box depends on the diameter of the speaker, and is selected according to this table.

We fix the speaker to the box and connect it to the circuit described above (Fig. 9). Again, open the NCH Tone Generator program, set the initial frequency to 10Hz and use the “+” button to start smoothly, in 1Hz steps, to increase the generator frequency to 500Hz. At the same time, we look at the value of the voltmeter, which again begins to increase to the frequency FL, then decrease, reaching the minimum point at the frequency of the phase inverter (Fb), increase again and reach the maximum point at the frequency FH, then decrease and slowly increase again. The graph of the dependence of voltage on the frequency of the signal has the form of a two-humped camel.

And finally, we find the equivalent volume (Vas) using this formula (where Vb is the volume of the box with the phase inverter).

We repeat all our measurements 3-5 times and take the arithmetic mean of all parameters. For example, if we got the Fs values, respectively, 30.45Hz 30.75Hz 30.55Hz 30.6Hz 30.8Hz, then we take (30.45+30.75+30.55+30.6+30.8)/5= 30.63Hz.

As a result of all my measurements, I received the following parameters for my speaker:

• Fs=30.75Hz
• Qts=0.365
• Vas=112.9≈113 L

1.2. Modeling and calculation of the subwoofer case (box) using the JBL Speakershop program.

There are several options for acoustic design, of which the following options are most common.

• Vented box-box with phase inverter,
• Band-pass 4th, 6th and 8th order,
• Passive radiator - a box with a passive radiator,
• Closed box - a closed box.

The type of acoustic design is selected based on the Thiel-Small parameters of the loudspeaker. If Fs/Qts<50, то такой громкоговоритель можно использовать исключительно в закрытом оформлении, если Fs/Qts>100, then exclusively in Vented box or Band-pass or Closed box. If 50

First, download and install the program. This program is written for Windows XP and does not work on Windows 7. To make the program work on Windows 7, you need to download and install virtual machine Windows Virtual PC-XP Mode (you can download it from the official Microsoft website), and run the installation of JBL Speakershop through it. You also need to open JBL Speakershop through a virtual machine. After opening the program, we see this interface.

Press "Loudspeaker" and select "Parameters--minimum", in open window write, respectively, the value of the resonant frequency (Fs), the value of the equivalent volume (Vas), the value of the total electromechanical quality factor (Qts) and press “Accept”.

At the same time, the program will offer two optimal (with the most even frequency response) options, one in a closed design (Closed box), the other in a Vented box (box with a phase inverter). Press “plot” (both in the Vented box and in the Closed box) and look at the frequency response graph. We choose the design, the frequency response of which is most suitable for our requirements.

In my case, this is the Vented box, because at low frequencies (20-50Hz), the Closed box has a much larger amplitude drop than the Vented box (Figure above).

If the volume of the box suits you optimally, then you can build a box with such a volume and enjoy the sound of the subwoofer. If not (with too large volumes), then you need to set your own volume (the closer to the optimal volume, the better) and calculate the optimal tuning frequency of the phase inverter.

To do this, in the Vented box area, click “Custom”, in the window that opens, write your volume of the box, click “Optimum Fb” (in this case, the program will calculate the optimal tuning frequency of the phase inverter, at which the frequency response of the acoustic design will be the most linear) and then “Accept”.

Press “Box” and select “Vent…”, in the window that opens, in the “Custom” area, write the diameter of the pipe (Dv), which we will use as a phase inverter. If we use two phase inverters, then we put a dot on “Area” and write the total cross-sectional area of ​​\u200b\u200bthe pipes.

Press “Accept” and in the “Custom” area on the line Lv the length of the phase inverter pipe will appear. Now that we know the internal volume of the box, the diameter and length of the phase inverter pipe, we can safely proceed to the design of the acoustic design, however, if you really want to know the optimal aspect ratio of the box, you can press “Box”, select “Dimensions…”.

1.3. Designing the case (box) of the subwoofer

To obtain high-quality sound, it is necessary not only to correctly calculate, but also carefully manufacture the acoustic design case. After determining the internal volume of the box, the length and diameter of the phase inverter pipe, you can safely proceed to the manufacture of the subwoofer case. The material of the box must be sufficiently strong and rigid. The most suitable material for acoustic cabinets high power is a twenty-millimeter MDF. The walls of the box are attached to each other with self-tapping screws, and the gaps between them are smeared with sealant or silicone. After the box is made, holes are made for the handles, and the outer surface is finished. All irregularities are leveled with putty or epoxy (I add a little PVA glue to the putty, which prevents cracks from appearing over time and reduces the level of vibrations). After the putty dries, the surfaces must be sanded until perfectly smooth walls are obtained. The finished box can be either painted or covered with a self-adhesive decorative film, or simply glued on with a thick fabric. From the inside, a sound-absorbing material consisting of cotton wool and gauze is glued to the walls of the box (in my case, I glued the batting). As a phase inverter, you can use a plastic sewer pipe or a paper rod from different rolls, as well as a ready-made phase inverter that can be bought at almost any music store.

The housing of the active subwoofer consists of two compartments. The loudspeaker itself is located in the first compartment, and the entire electrical part (signal conditioner, amplifier, power supply ......) is located in the second. In my case, I placed the adder unit and the filter unit in a separate compartment from the power amplifier unit, power supply unit and cooling unit. From the inside, I glued foil to the walls of the compartment of the adder unit and the filter unit, which I connected to ground (GND). The foil prevents external fields and reduces noise levels.

If you use my printed circuit boards, then these compartments should have the following dimensions.

2. The electrical part of the active subwoofer

Let's move on to the electrical part of the active subwoofer. The general scheme and principle of operation of the device is represented by this scheme.

The device consists of four blocks assembled on separate printed circuit boards.

• Adder block (Summators),
• Filter unit (Subwoofer driver),
• Power amplifier block,
• Power supply (Power supply) and cooling unit (Heatsink fun).

First, the audio signal enters the Summators block, where the signals of the right and left channels are summed. Then it enters the filter unit (Subwoofer driver), where the subwoofer signal is formed, which includes a volume control, subsonic filter (low-pass filter), bass booster (volume increase at a certain frequency) and Crossover (low-pass filter). After formation, the signal enters the power amplifier unit (Power amplifier), and then to the loudspeaker.
We will discuss these blocks separately.

2.1. Block of adders (Summators)

2.1.1.Scheme

First, consider the adder circuit shown in the figure below.

Sound signal with external devices(computer, CD player……..) goes to the adder block, which has 6 stereo inputs. 5 of them are ordinary line inputs, differing from each other only in the type of connector. And the sixth is a high-voltage input, to which you can connect the speaker output (for example, music Center or car radio that do not have a line-out). Each input has a separate op amp combiner that shifts the right and left channel signals, which prevents the sound signal from one external device to another, while allowing you to connect several external devices to the subwoofer at the same time. And there are also outputs (5 outputs, the 6th simply did not fit on the board, and therefore did not install), which make it possible to apply the same signal that enters the subwoofer to the input of a broadband stereo system. This is very convenient when the sound source has only one output.

2.1.2.Components

TL074 (5 pcs.) were used as operational amplifiers. Resistors are rated for 0.25W or higher (resistance ratings are shown in the diagram). All electrolytic capacitors have a voltage rating of 25 volts or higher (capacitance ratings are shown in the diagram). As non-polar capacitors, you can use ceramic or film capacitors (film is better), but if you really want to, you can put special audio capacitors (capacitors designed for use in high-quality audio systems). Chokes in the power supply circuit of operational amplifiers are designed to suppress the “noise” coming from the power supply. Coils L1-L4 contain 20 turns wound with copper wire with a diameter of 0.7mm, on the core of a gel pen (3mm). RCA, 3.5mm audio jack, 6.35mm audio jack, XLR, WP-8 connectors are also used.

2.1.3.Printed circuit board

The printed circuit board is made according to . After soldering the parts, the printed circuit board should be coated to avoid oxidation of the copper.

2.1.4. Photo of the finished adder block

The adder unit is powered by a bipolar ±12V power supply. The input impedance is 33kΩ.

2.2 Filter block (Subwoofer driver)

2.2.1.Scheme

Consider the subwoofer driver circuit shown in the figure below.

The summed signal from the adder block enters the filter block, which consists of the following parts:

• Volume control (volume regulator),
• Infra low pass filter (subsonic filter),
• Bass amplifier of a certain frequency (bass booster),
• Low pass filter (crossover).

Volume control takes place at two levels. The first is when the signal enters the filter block, which reduces the level of the own “noise” of the adder block, the second when the signal leaves the filter block, which reduces the level of the own “noise” of the filter block. The volume is adjusted using a variable resistor VR3. After the first level of volume control, the signal enters the so-called “bass booster”, which is a device that increases the amplitude of signals of a certain frequency. That is, if the bass booster tuning frequency is inserted, for example, at 44Hz, and the gain level is at 14dB, then the frequency response looks like this ( Row1).

Row2- tuning frequency=44Hz, gain level=9dB,
Row3- tuning frequency=44Hz, gain level=2dB,
Row4- tuning frequency=33Hz, gain level=3dB,
Row5- tuning frequency=61Hz, gain level=6dB.

The tuning frequency of the bass booster is inserted using a variable resistor VR5 (within 25 ... 125Hz), and the gain level with a resistor VR4 (within 0 ... + 14dB). After the bass booster, the signal enters the subsonic filter, which is a filter that cuts off unwanted, ultra-low signals that are no longer audible to humans, but can severely overload the amplifier, thereby reducing the actual output power of the system. The cutoff frequency of the filter is adjusted using a variable resistor VR2 within 10…80Hz. If, for example, the cutoff frequency is inserted at 25Hz, then the frequency response has the following form.

After the infra-low-pass filter, the signal enters the low-pass filter (crossover), which cuts off the upper, unnecessary for the subwoofer (mid + high) frequencies. The cutoff frequency is adjusted using a variable resistor VR1 within 30 ... 250 Hz. The slope of the attenuation is 12 dB / octave. The frequency response has this form (at a cutoff frequency of 70 Hz).

2.2.2.Components

TL074 (2pcs), TL072 (1pc) and NE5532 (1pc) were used as operational amplifiers. Resistors are rated for 0.25W or higher (resistance ratings are shown in the diagram). All electrolytic capacitors have a voltage rating of 25 volts or higher (capacitance ratings are shown in the diagram). As non-polar capacitors, ceramic or film capacitors (preferably film ones) can be used. Chokes in the power supply circuit of operational amplifiers are designed to suppress the “noise” coming from the power supply. Three double (50kOhm-2pcs, 20kOhm-1pcs) and two quad variable (50kOhm-6pcs) resistors are also used. Two dual resistors can be used as quad variable resistors.

2.2.3.Printed circuit board

Files printed circuit board in *.lay and *.pdf formats can be downloaded at the end of the article.

2.2.4. Photo of the finished filter unit

The filter unit is powered by a bipolar ±12V power supply.

2.3. Block power amplifier (Power amplifier).

2.3.1.Scheme

An Anthony Holton amplifier with field-effect transistors in the output stage is used as a power amplifier. There are a lot of articles describing the principle of operation, assembly and tuning of the amplifier on the Internet. Therefore, I will limit myself to embedding the schematic and my version of the PCB.

2.3.2.Printed circuit board

PCB files in *.lay and *.pdf format can be downloaded at the end of the article. The power amplifier unit is powered by a bipolar power supply with a voltage of ± 50 ... 63V. output power amplifier depends on the supply voltage and the number of pairs field effect transistors(IRFP240+IRFP9240) in the output stage.

2.4. Power supply and cooling unit (Power supply)

2.4.1.Scheme

2.4.2.Components

As a power transformer, you can use both a ready-made and a home-made transformer with a power of approximately 200W. The voltages of the secondary windings are shown in the diagram.

The diode bridge Br2 is designed for a current of 25A. Capacitors C1 ... C12, C29 ... C31 must have a rated voltage of 25V. Capacitors C13…C28 must have a nominal voltage of 63V (when the supply voltage is below 60V), or 100V (when the supply voltage is above 60V). As non-polar capacitors, it is better to use film capacitors. All resistors are rated at 0.25W. The R5 thermistor is smeared with thermal paste and attached to the amplifier heatsink. The operating voltage of the fan is 12V.

2.4.3.Printed circuit board

PCB files in *.lay and *.pdf format can be downloaded at the end of the article.

3. The final stage of subwoofer assembly

List of radio elements

1. About computer calculations
2. What is it and why?
3. What speaker do you need?
4. System structure
5. Registration
6. Auto subwoofers
7. It just doesn't get easier
8. Too simple
9. Powerful 6th order
10. 4th order
11. Electronics
12. How to calculate a subwoofer?

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

About computer calculations

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

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

What is it and why?

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

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

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

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

bass

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

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

top

middle

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

Depth

FI

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

About deep cracks

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

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

About antiacoustics

bandpasses

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

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

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

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

Auto subwoofers

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

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

Video: do-it-yourself stealth car subwoofer

It just doesn't get easier

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

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

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

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

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

Filters

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

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

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

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

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

Setting

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

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

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

Too simple

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

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

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

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

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

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

Tubes for resonators

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

Powerful 6th order

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

Subwoofer drawings bandpass 6th order under 12? speaker

4th order

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

Subwoofer bandpass 6th order under 12? speaker

Electronics

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

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

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

And still…

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

From that article you will learn how to make an amplifier for car subwoofer medium power.

In the presented amplifier, as in many industrial production amplifiers, there are no various protections. But this does not affect the reliability of the amplifier. This device is able to work for a very long time if no one closes anything.

To achieve a cutoff of the order of 100 Hz (all frequencies above are absent), a second-order filter is introduced into the circuit.

This is a conventional push-pull converter, push-pull boost. The master oscillator is built on the TL494 chip.
Next is a small driver on direct conduction transistors. This part discharges the capacitance of the gates of the field-effect transistors after the latter are closed.

As you know, if a certain voltage is applied to the gate of a field-effect transistor, in this case it is a control pulse, then the latter will open. And if you remove the voltage at the gate, the transistor will still remain open.

Therefore, some circuits are supplemented with a separate driver, which can close the transistor in time. Although many dedicated PWM controllers have a fairly powerful built-in output stage for this purpose, the TL494 is not one of them.
It is fashionable to use literally any pnp transistors in the driver. Our KT3107 are also great.
Field-effect transistors, as always, are n-channel - in this case IRFZ44, but others are possible. When selecting transistors, you need to pay attention to the documentation. The calculated key voltage should be at least 40 V, and the current strength should be at least 30 A. The ideal option would be 60 V keys with a current of 50-60 A.

The primary winding has 2 x 5 turns wound with a bundle of 5 wires 0.7 mm each. Secondary winding 11 turns, 6 cores of 0.33 mm. Naturally, for each core there will be different winding data, so the calculation must be done independently.
The idling of the inverter turned out to be no more than 50 mA, and with the connected filter and amplifier about 250 mA, given that no signal was applied to the input of the amplifier. Idling is minimal.

The amplifier works in class A-B, and the radiator is needed quite large considering the power. Be sure to isolate the cases of field-effect transistors and amplifier microcircuits from the radiator using heat-conducting gaskets and insulating washers.

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