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.
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| 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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