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What is it: Crossover
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These pages were created
in order to help people with limited knowledge of electronics and who may need to
understand the basics of loudspeaker systems design. We think that this may be helpful
for a lot of potential users, such as musicians, DJs and others who have to deal
with loudspeakers but do not have technical background. Spectrum of sound frequencies from 20 Hz to 20 kHz are accepted as audible and are suppose to be reproduced by the loudspeakers. The ratio between lowest audible frequency (20 Hz) and highest audible frequency (20 kHz) is 1:1000. None of the existing speaker drivers can cover the full range of sound frequencies with acceptable quality. Quality of sound reproduction is determined by a number of factors including flatness of the frequency magnitude, harmonic distortions, phase distortions and many more parameters which can be measured and recorded. Drivers, used for sound reproduction in loudspeaker systems, are designed for optimal performance in limited frequency range. In order to design and build a system capable of reproduction of the full sound range with acceptable quality, the designer must divide full frequency range into a few narrow bands and each frequency band will be reproduced by the dedicated driver. That is exactly what crossover does. This is a very important task because sound quality of the whole sound system depends on the finite component: the loudspeaker. Drivers used for reproduction of the low frequencies must have large physical dimensions and must be capable of moving a large amount of air in order to reproduce low frequencies with satisfactory sound levels. At the same time, high frequency drivers must be as small as possible* and their diaphragms have very short travel distances. Let's assume that we do not need a crossover, but we will use 2 separate amplifiers to drive low and high frequency drivers. In that case, full sound spectrum is applied to each driver. The low frequency driver will reproduce some part of the high frequency band but the results will be disastrous: high frequencies will be modulated by the low frequencies and we will have an unacceptable level of distortions. The same applies to the high frequency driver, but here we will have even more problems because high frequency drivers are not capable of accepting a lot of power and will be physically damaged. This is just the tip of an iceberg, because, in the real world all these problems are much more complicated. So, we need a device which will separate full sound spectrum into two or more bands and each band will be reproduced by the proper driver. This task can be performed by either active or passive crossover. Passive crossover consists of passive components (inductors, capacitors, resistors) and are installed after the power amplifier, just before the drivers. Active crossover uses active components (IC's, transistors, vacuum tubes) and are installed before the power amplifier. In this case, you will need two or more power amplifiers in the system. Each power amplifier will feed a signal to a dedicated driver or a group of drivers. (*) There are certain rules which govern physical dimensions of the drivers. |
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