Yamaha P-2200 - Manual (Page 40)

APPLICATIONS
BIAMPLIFICATION AND TRIAMPLIFICATION
Biamplification, or "biamping," triamplification, or
"triamping," all refer to the use of separate power
amplifiers to cover separate portions of the audio
spectrum.
The traditional, non-biamplified speaker system is
diagrammed in Figure 64A. The crossover network,
which routes the high and low frequencies to their
respective speakers, is located in the circuit between the
power amplifier and the speakers. A large system may
contain many power amplifiers, crossovers, and speakers.
Figure 64B diagrams a biamplified speaker system,
showing the crossover located in the circuit before the
power amplifiers, and showing a separate power
amplifier for the high and low frequencies. A triamplified
system has an extra crossover section, another power
amplifier, and a woofer, midrange and tweeter.
The crossover for a biamplified system is a low level
crossover since it processes low power signals. It may
also be called an active or electronic crossover since it is
usually an active device (using transistors, tubes, and/or
IC's). Some low level crossovers are passive (no transis-
tors, tubes, or IC's). All high level crossovers used in non-
biamplified speaker systems are passive, and they must
process the full power of the power amplifier.
There are any number of good reasons for taking a
biamplified or triamplified approach to a professional
sound system. One reason is that a biamplified system
can actually provide more headroom per watt of
amplifier power than a system with a traditional (high
level) passive crossover.
Fig. 64A - System using Conventional, Passive/High-Level
Frequency Dividing Networks.
Fig. 64B - Biamplified System using Yamaha F1030
Electronic Frequency Dividing Network.
Headroom
Program material (music or speech) is made up of
many different frequencies and their harmonics. Most
music, especially popular music, is bass heavy; that is,
the low frequency material contains much more energy
than the high frequency material. When both high and
low frequency material, such as a flute and a bass guitar,
are present in a program, the high energy bass fre-
quencies can "use up" most of the power in a power
amplifier leaving none for the high frequencies. The
result can be severe clipping (distortion) of the high
frequency material. With an electronic crossover, the
high frequency material can be routed to its own power
amplifier, avoiding the clipping problem. This results in
an effective increase in headroom that is greater than
would be obtained by simply using a larger, single
power amplifier.
Figure 65A shows a low frequency waveform from a
power amplifier output. The peak-to-peak voltage of
the waveform is 1 2 1 volts, corresponding to 43 volts
RMS. If this voltage were applied to an 8-ohm speaker
load, the power level would be 230 watts, which is equal
to the peak output of Yamaha's P-2200 professional
power amplifier into an 8-ohm speaker load just before
clipping occurs.
Figure 65B shows a high frequency waveform from a
power amplifier output. The peak-to-peak voltage, RMS
voltage, and power into an 8-ohm speaker load are less
than shown in Figure 65A and correspond to a 1 6 watt
output into an 8-ohm load. The levels of these high and
low frequency waveforms are typical of musical content.
Figure 65C shows the effect of adding the signals of
Figure 65A and Figure 65B, corresponding to a low fre-
quency note and a high frequency note being played at
the same time. Note that the total peak-to-peak voltage
(which would be 153 volts if it were not clipped) is
greater than the peak-to-peak voltage of either signal by
itself. For an amplifier to produce this voltage into an
Fig. 65 - Advantages of Biamplification