Crossover 102 - Electronic Crossovers - Page 2

Why do I need to Bi-amp?
Full range sound systems quite frankly just do not have enough power amplifier headroom to successfully Mic the drum kit and bass guitar, as well as all of the remaining stage instruments and vocals. There are a couple of reasons for this. First of all individual musical waveforms consist of a fundamental frequency upon which the higher harmonics ride. In other words the highs frequencies are modulated by, or they ride on the fundamental as super-impositions on a composite waveform. The combined waveforms of the individual musical instruments create an even more complex composite electrical signal when mixed together. This very complex composite waveform has an in initial leading edge or transient spike that can be +12 to +20 dB above where the signal levels off at the crest or average of the waveform.

Complex musical waveform


Also, there is a great deal more power used to reproduce low frequencies than high frequencies. Some people think that this is due to the differences in efficiency between the woofer and compression driver. But, the difference in their sensitivities is narrowed due to the fact that the high frequency driver is more sensitive, and the voltage to it must be attenuated or reduced to match the levels between the two transducers at the crossover point. There are others that think it takes more energy to reproduce the low frequencies, because they know that low frequency acoustical sound waves are very large, and they reason that you must push or shovel more air from the low frequency transducer. Actually it requires more energy for low frequency reproduction because we humans are nearly deaf when it comes to the perception of low frequencies. The threshold of human auditory hearing at 40 Hz is about +44 dB greater than the threshold for 4 kHz. Our ears just aren't flat, and that's a fact. The frequency response of our ears is dynamic also, in that it changes with the level of perception. Even at the loud level of a Rock & Roll performance, the low frequencies require 3 to 10 times (10 to 20 dB) more voltage than the high frequencies. See the Fletcher/Munson equal loudness contour curves below:



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