Subwoofer for the home, for the family. Part 1 - general information. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Speakers

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Comrade Kostyan (akustik13@yandex.ru), who ate a dog (frrr!, meow) while building subwoofers and amplifiers for them, shared with us some initial information regarding his craft. In fact, he knows much more, but not a single threat of being severely scratched broke his stubbornness and forced him to reveal all the secrets...

Assembling a home subwoofer will require you to:

1. FREE TIME CAR (from a week to a month)
2. MONEY (the steeper the sub the more)
3. PATIENCE AND CARE - I.E. WISHES

This is enough!!!!!!!!!!!

Let's start!

Selecting a dynamic head

First you need to successfully select a dynamic head (popularly, a speaker).

We select according to the following criteria:

• the diameter of the speaker is at least 20 cm, otherwise the bass will not be enough, and the price for them goes off scale for 5-6 thousand rubles.
• we choose a speaker with a rubber suspension, which should ensure the cone moves FORWARD by 1,5-2 cm (or more) without any overtones.
• resistance should not be less than 3 ohms. If it is 2 ohms according to the passport, then there may be problems with the selection of an amplifier.
• determine the power of the speaker. For an apartment, it is required to keep within the interval of 80-150 "honest" watts.
• we must not forget about the sensitivity of the speaker, it should not be less than 90dB. The sensitivity of the speaker determines how effectively it manages the power given to it by the amplifier. In other words, the sound pressure that a driver creates at a distance of 1 meter when a 1 W signal is applied to it.

However, sometimes the indicator of the sensitivity of the speaker, indicated in his passport, is not entirely adequate to the real state of affairs. The thing is that the power is created by a voltage that depends on the nominal resistance of the driver. If it is equal to 4 ohms (which is typical for car acoustics), then a voltage of 2 V is supplied. But 8-ohm home speakers require 2,83 V. You can play on this difference, which many manufacturers do by indicating the absolute sensitivity of the woofer, that is, measured with an input voltage of 2,83 V. Acceptable sensitivity for a subwoofer is 90 dB, but, as they say, the more the better , higher output speakers place lower demands on the power of the amplifiers. This is clearly illustrated in this table:

As you can see, even a 3 dB difference is very significant and allows you to save twice on the power of the amplifier. But do not rush to rub your hands. It also has its own pitfalls. Subwoofers with high sensitivity often suffer from higher cutoff frequencies, which means that saving on amplifier power can easily be lost at the deepest bass frequencies. I have a sub with a sensitivity of 91dB

• it is required to determine the equivalent volume i.e. with body volume.
• make sure that when moving the diffuser, the wires from the coil to the terminal block do not touch the frame.

According to these criteria, you can choose to choose a high-quality speaker for the subwoofer.

Types of subwoofers

What should be the acoustic design of the woofer depends on many factors. Each type of subwoofer box, whether fully sealed (sealed), bass-reflex (ported) or band-pass (band-pass), has its own advantages and disadvantages. In addition, much depends on the specific platform for building an audio complex. And yet: is there an unquestionably better type of bass cabinet? The answer is negative. Agree: if there was, then why do we need all the others? On the contrary, closed boxes are installed with approximately the same regularity as phase inverters.

Before we turn to subwoofer enclosures, let's talk about why they are needed in principle. The whole problem is that the rear of the speaker generates as much sound as its front, but with the opposite directionality. Purely hypothetically, if these two components affect the auditory organs with equal intensity, then they will be neutralized, and you will not hear anything at all. In practice, speakers devoid of proper acoustic design will radiate high and medium frequencies, but not the bass we need. This is because the sound wave emanating from the rear of the head has to make a longer path to the listener's ear. As a result, the high and mid frequencies are amplified, while the low ones, on the contrary, are weakened. In a word, "corpusification" is indispensable. What are the boxes made from? Experienced installers have a variety of preferences, but most agree on one thing: without wood, in one form or another, good bass cannot be achieved. The two most common materials today are medium particle board (MDF) and plywood. These materials are distinguished by optimal acoustic characteristics, are sufficiently durable, easy to process and affordable. Chipboard is even more affordable, inferior in its characteristics (sound insulation, density, strength) to the two previous materials. Various types of plastic or plexiglass are more often used when there is a lack of space or for demonstration purposes, but this is already a certain concession from the side of music.

Fully enclosed boxes (sealed boxes)

A type of subwoofer enclosure that is reasonably effective at blocking the propagation of sound waves emanating from the rear of the loudspeaker. The "stuffy" air inside the box in this case acts like a spring, controlling the vibrations of the diffuser. Fully enclosed boxes are easier to design than, say, bass reflex and bandpass subwoofers. They are not too picky about the displacement required for optimal driver performance, and are more forgiving of erroneous data provided by the manufacturer in the product's accompanying documents. The airbag protects the speaker from low-frequency impulse noise, which sometimes occurs when the system is turned on, infrasonic energy is supplied to it, or simply when driving on rough roads. This is the preferred option if you need to take up a minimum of space in the trunk or cabin, since it is believed that the volume of a fully closed case may be insignificant to reproduce "deep bass", although in this case you need to know when to stop. When the volume decreases below acceptable limits, significant losses of the low-frequency component occur. With an increase in volume, the return in the region of infrasonic frequencies will increase, but then the effect of saving space is leveled. In any case, in terms of output, such a subwoofer will be inferior to larger-sized counterparts of the bass-reflex or bandpass variety. At the same time, compared to them, the frequency response of closed cases in the decay region is smoother.

Bass reflex subwoofers (ported)

Bass reflex cabinets, unlike fully enclosed ones, use the sound coming from the rear of the speaker for the benefit of powerful bass, since the resulting sound pressure is the sum of the emissions of the cone and port. Accordingly, the use of this acoustic design allows you to increase the efficiency of the bass head. At the same time, phase inverters are more complex to manufacture and more picky in terms of calculating the working volume, setting the port to the optimal frequency, matching the radiation resistances of the diffuser and the phase inverter pipe, etc. Therefore, it is better to double-check the parameters indicated by the manufacturer. But well-done work, as a rule, is rewarded according to merit. It is believed that a bass-reflex subwoofer is capable of reproducing bass a whole octave below the case. True, there is one "but": in this case, the box itself should be five times larger. So the use of a case with a phase inverter is often due to the customer's willingness to part with a certain volume of the cargo compartment.

Bandpass subwoofers

This type of acoustic design can be called a hybrid of the two previous ones, since in its design it has the characteristic features of both. A typical strip subwoofer consists of two chambers, one of which does not have access to the outside, and the second one has it in the form of a phase inverter tunnel. Through it, the bass in a concentrated form is fed out. In a concentrated one, because the speaker is mounted in a wall separating two volumes filled with air, and the vibrations of the diffuser meet resistance both from the front and from the rear. As a result, the energy that is supplied to the loudspeaker is not dissipated, but is spent more rationally than in closed and bass-reflex boxes.

Such a cunning design of the bandpass causes, on the one hand, its higher sound pressure (up to 6 dB compared to closed cases), and on the other hand, it tends to work in a narrow low-frequency band. But strips are good because they give you the right to choose, since by changing the volume of the chambers you can either increase the amount of sound pressure created by the woofer or expand the boundaries of the frequency range. However, in order to successfully manipulate the volumes, as well as adjust the phase inverter tunnel in accordance with acoustic conditions, one must have extensive installation experience. Here, the "course of a young fighter" will clearly not be enough. We evaluate our experience and decide how we will design the speaker.

Author: Kostyan, akustik13@yandex.ru; Publication: radiokot.ru

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