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Choice and installation of autoacoustics, ch.2 (subwoofer)

InfoAdvisor.net already told about Basic Elements of automobile acoustics. Also, one of important components of high-quality sounding is good reproduction of low frequencies. Such device as a subwoofer also intends for these purposes just. It represents the separate speaker system for reproduction of low frequencies (20-100gts).
Сабвуфер In the material "Choice and Installation of Autoacoustics, P.1 (Loudspeakers)" of InfoAdvisor.net told about Basic Elements of automobile acoustics. Naturally, one of important components of high-quality sounding is good reproduction of low frequencies. Such device as a subwoofer also intends for these purposes just. It represents the separate speaker system for reproduction of low frequencies (20-100gts). As the human hearing practically does not distinguish the direction of low-frequency waves, a subwoofer it will be possible to arrange enough in many places of the car.

Subwoofer case

For reproduction of low frequencies the subwoofer needs to be placed in acoustic registration. Let's consider that this such and for what it is necessary. Let's take the simplest fluctuation of a membrane of the loudspeaker. When the diffuser sharply moves forward, for a moment it before itself(himself) creates air compression. Then this air will sharply be unclenched and will cause again air compression, but already at some distance from the previous. These compression and discharges of air are also sound waves which we hear. Now we will return to our case when the loudspeaker made fluctuation and squeezed before itself some volume of air. During this moment from its rear party there is absolutely antiput phenomenon – air discharge. Waves of low frequency well bend around obstacles, as a result of interaction of a rear and frontal wave we will receive sharp decrease in sound pressure. This phenomenon is called acoustically short circuit.
That it did not occur, it is necessary to separate waves of frontal part from waves the rear. It can be made or by means of the big screen, or placing our loudspeaker in any case. This screen or the case will also be acoustic registration. Actually there are many various acoustic registrations, but it is possible to carry the infinite screen (free-air), the closed box, the phase inverter to the main. Now is more detailed about each of them.

Infinite screen or free-air
Оформление сабвуфера - бесконечных экран (free-air) In this type of registration it is meant that waves of frontal and rear part of the loudspeaker will be divided by infinitely big screen. In practice mean rather big case by such screen, in which elasticity of the concluded air much less elasticity of subweight of the diffuser. The main advantage of this registration – simplicity of installation and naturalness of a bass. But InfoAdvisor.net would like to note that thus it is necessary to pay off with various reproduction of compositions at change of free volume of a luggage carrier and not really high level of sound pressure.

The closed box
Сабвуфер в закрытом корпусе Treats the simplest type of acoustic registration. The fluctuations radiated by rear part are in the closed space therefore, eventually, they are extinguished, passing into heat. For improvement of attenuation of waves, the case becomes covered with sound-absorbing material inside.
Despite simplicity, this type of acoustic registration has many pluses. First, it is simplicity in production and calculation. Secondly, fluctuations of the loudspeaker restrain elasticity of air volume of the case that reduces probability of mechanical damage at extreme operating modes. Thirdly, the loudspeaker which is in competently designed closed case, has very good pulse characteristics. If you the admirer of styles of music in which very high-quality transfer of the lowest frequencies is required, for example, the jazz or the blues, most likely, is your choice.
Minus registrations – low efficiency. Therefore it is better to be prepared for big energy consumption at once.

Phase inverter
Фазоинвертор The phase inverter on a design reminds the closed box, however it is not completely tight. The internal volume of air contacts external space by means of a special tunnel, usually round or squared, called by the phase inverter. Such design uses energy from the back party of the diffuser and as a result of a wave radiated by the diffuser and the phase inverter are in an identical phase. Such effect is reached in quite narrow range of frequencies, but the efficiency considerably increases in it. Actually it can seem strange, but in the range of setup of the phase inverter the most part of a sound is radiated by a tunnel, and fluctuations of the diffuser are minimum that favorably affects viability of a head. In this range of frequencies is admissible to bring the greatest possible power without extra risk of mechanical damage of a head.
It is worth carrying to pluses of this registration that thanks to phase inverter radiation the sound pressure of all design increases twice, the low level of distortion, because of the small course of the diffuser and lower frequency of reproduction in comparison with the closed box.
It is worth referring complexity of calculation of this registration, considerable volume of the case and possibility of emergence of aerodynamic noise to minuses at the big levels of a sound arising because of an air turbulence at the exit of port.
Фазоинвертор At a choice of acoustic registration it is necessary to remember that for each type it is necessary to choose the loudspeaker possessing certain characteristics. Often producers specify the recommended registrations on packings of loudspeakers.
Now some words about ready case subwoofers which enough in our market is presented. Such subwoofers are divided on active and passive. Active, unlike passive, the amplifier who is built in the case and the crossover and everything already contains that it is necessary for him is to connect the power supply and chains of an entrance signal. Plus such subwoofers, of course, the low cost and simplicity in installation so, even without possessing professional skills, it is possible to install the case in independently. Minuses – poor quality of components will undoubtedly affect quality of a sound.

Installation of a subwoofer

Варианты установки сабвуфера в седанInstallation of a subwoofer in cars with a body a sedan
As the most widespread place it is possible to consider the back shelf of the car. Here it is possible to use all 3 types of acoustic registration.
In case of use of "the infinite screen" in the back shelf it is necessary to cut out an adjusting opening. It is also necessary to increase rigidity of the shelf. It becomes by means of the sheet MDF which is cut out by the sizes of the back shelf and is fastened to it by bolts. Thus it is necessary to close up all cracks connecting salon to a luggage carrier compartment.
Pluses: simplicity of installation, and, therefore, and low cost. It is worth carrying to minuses of such installation that characteristics of a bass will depend considerably on extent of filling of a luggage carrier.
That to avoid it, it is possible to apply acoustic registration like "the closed box". Thus the loudspeaker is located in the closed box which fastens to the back shelf. The internal volume of such box usually is in limits of 15-30 liters. Minus: loss of net volume of a luggage carrier, and also high cost of installation as it is necessary to make the subwoofer case to prepare the back shelf for installation and to fit all design material.
Installation of the phase inverter differs in nothing from the closed box, the truth thus the internal volume of the case will be a little more, about 20-40 liters. The tunnel of the phase inverter is mounted near the loudspeaker.
The space behind an armrest of a back seat behind which in many cars there is a window for transportation of long subjects can become one more installation site of a subwoofer. In it it is possible and to remove the subwoofer loudspeaker. InfoAdvisor.net pays your attention that thus diameter of the diffuser should be chosen proceeding from the window sizes. At installation in this place acoustic registration like phase inverter or the closed case will approach. Minus: useful space of a luggage carrier all too which it is necessary to leave also the high cost of installation.

Installation of a subwoofer in cars with a body a hatchback and the versatile person
Сабвуфер в хетчбэке If you the owner of the car with a body a hatchback or the versatile person then any types of acoustic registration, except, of course, free-air will approach as to achieve full sound insulation of the leaning-back back shelf it is almost unreal.
The place for installation of a subwoofer can be found in a luggage carrier, behind a surface in a wing niche. Thus compactly made subwoofer will not stir in case of need loading of large-size subjects, however, of a bass at the filled luggage carrier will be.
In cars with such type of a body the subwoofer is installed, as a rule, by the loudspeaker towards a luggage carrier. In addition, in cars with a body the hatchback can be changed the direction of radiation, having arranged a subwoofer the loudspeaker up, having used reflection of sound waves from back glass.

So, if you already came to a conclusion that want to install the full-fledged speaker system on the basis of separate a component, it will also be useful to learn more about amplifiers and crossovers. Just about it the following article "Choice and Installation of Autoacoustics, ch.3 (Crossover and Amplifier)".
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