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Choice and installation of autoacoustics, ch.3 (crossover and amplifier)

After the quantity of components of autoacoustics and a place of their arrangement is defined, it is necessary to think of their connection to an audiosignal. For this purpose we need two types of devices. One of them the amplifier who serves for strengthening of low level of a signal, and another – the crossover which serves for division of frequencies according to channels of acoustics.
In the previous articles "Choice and Installation of Autoacoustics, P.1 (Loudspeakers)" and "Choice and Installation of Autoacoustics, ch.2 (Subwoofer)" on the pages, those components of autoacoustics thanks to which correct installation actually and the full-fledged acoustic picture is created were discussed.
After the quantity of components of autoacoustics and a place of their arrangement is defined, it is necessary to think of their connection to an audiosignal. For this purpose we need two types of devices. One of them the amplifier who serves for strengthening of low level of a signal from a linear exit of the head device, and another – the crossover which serves for division of frequencies according to channels of acoustics.


Активный кроссовер Ready automobile crossovers represent the case, small by the sizes, approximately 12kh6kh4sm (GKHSHKHV) in which various filters for a transmission of a signal of certain frequencies are assembled.
So filters of low frequencies pass signals below some certain frequency (frequency undressed) practically without change and considerably weakens a signal above it. Such filter can be necessary, for example, for allocation of a signal of a subwoofer, adjusted on section frequency in 80-100 Hz.
By analogy high-frequency filters pass signals of high frequencies, and low frequencies will be considerably weakened. Such filter can be installed for allocation of a signal for the high-frequency twitter which is adjusted, for example, on the frequency of 2-4 kHz.
Also there are strip filters. They pass frequencies only in the certain range and weaken everything that above and below this range. Such filters can be necessary for allocation of a signal for the mid-frequency loudspeaker of 3-band system. The lower frequency of such filter can be about 700-800 Hz, and the top about 5 kHz.
Crossovers are divided on active and passive. Distinction between them that the first usually consist from active (demanding the power supply) a component, such as operational amplifiers, microcontrollers etc. Passive consist of passive elements which do not need the power supply. Generally it is resistors, condensers and coils.
Active crossovers are set only in front of the amplifier. Passive can be established both in front of the amplifier, and just before the loudspeaker.
Пассивный кроссовер It is worth carrying to pluses of passive crossovers that, using only two channels of the amplifier, it is possible to divide signals for two or even for three-lane system. Besides, undoubted advantage is the low price. Minus – impossibility of control without intervention in an electric circuit. At active crossovers various regulators and switches thanks to what it is possible to change characteristics of the crossover smoothly are brought to the case. It is necessary to distinguish the high price, need of use of certain amplifiers for each channel from minuses, and also the distortions brought by active elements.
Depending on quantity of strips of system respectively is selected two or the three-lane crossover. A crossover choice – business quite not simple, but its wrong control can spoil considerably sounding of all system therefore it is better to entrust this work to professionals.


Трёхканальный усилитель Often the regular amplifier of the head device has not really high-quality amplifier even if the radio tape recorder has quite high cost.
Reasons here a little. The compartment for the radio tape recorder has the limited sizes therefore it is impossible to install in the case of the head device the amplifier of big power. For the same reasons there is a problem of dispersion of heat of elements of the amplifier. Therefore for a qualitative sound the external amplifier will be better to get.
Proceeding from number of channels, the amplifier can be single-channel, i.e. is capable to strengthen only one channel, two-channel – to strengthen a stereosignal, three-channel – strengthening of a stereosignal and the channel of a subwoofer, four-channel – for strengthening of a signal of frontal and rear acoustics, and also to five or six channel. Treat key parameters of the amplifier:
Двухканальный усилитель
  • Power which should be chosen 10-20% less than the power of loudspeakers not to put them out of action. It is necessary to pay attention to RMS power as peak or maximum power has nothing in common with high-quality sounding and only shows peak and instant values at very big level of distortions;
  • Loading resistance for which the amplifier can work. Do not connect at all amplifiers who are intended for work with loudspeakers as an impedance of 4 or 8 Ohms, to the loudspeakers having smaller resistance. The amplifier can put it out of action;
  • Relation signal/noise. This parameter shows, what quantity of extraneous noises appears in an output signal in comparison with an entrance signal. Such noise often can be heard as hissing in nizkokachestvenno equipment which will be clearly audible in silent musical compositions. It is measured parameter in dB. Better that this parameter equaled 98 dB and more.Усилитель
Many amplifiers have possibility of bridge inclusion. Thus two channels of the amplifier connect for connection of one loudspeaker. Thus the power given by the amplifier increases twice. Such connection is often used for connection of a subwoofer.
Also enough amplifiers already with the built-in crossovers is now presented, however use of external modules provide big flexibility at setup of all speaker system.

Now we will talk about installation
Установка усилителя As overall dimensions of the case of the amplifier are not great, about 40х30х5 (SHKHGKHV) of cm, installation sites can be quite a lot. For example, it is the lower part of the back shelf where the amplifier it is possible to fasten by means of bolts or self-tapping screws. It is also possible to hide the amplifier in a wing niche. In case of production of the case for a subwoofer to order, it is possible to cut effectively the amplifier in the same case. The only thing, on what pays your attention: the amplifier is a device which allocates quite large number of heat therefore completely it is impossible to isolate it from surrounding space by no means.

Let's sum up the results
Акустическая система If you want to install the speaker system in the car, using a minimum of means, for this purpose you need to get broadband loudspeakers, having established them in a regular place and to use the regular amplifier from the radio tape recorder. Further the speaker system can be improved, having added to it an active case subwoofer.
If you the admirer of music where accurate localization of tools, a volume sound scene and acting out of fine details then it should be taken into account option of installation of the two-way speaker system with use of passive crossovers and external amplifiers is important. As the back to establish a subwoofer in the closed registration.
The two-way speaker system with a subwoofer like phase inverter will be suitable for fans of a dance music. As a rear-fill to install pair of loudspeakers to the back shelf.
Well, and if you decided "to load" your car on full that played not only qualitatively, but also is loud, then your choice – installation of the three-lane speaker system with active crossovers, rear loudspeakers for a rear-fill, a subwoofer and some external amplifiers.
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