As you might expect, "Bi-Amplification" means "two
amplifiers". One amplifier is connected to the woofer section
of a loudspeaker while the other is connected to the combined
mid and tweeter section. The Bi-Wire loudspeaker connection makes
the Bi-Amplification hookup very easy.
- Unfortunately, with the arrival of Bi-Wiring,
the exact meaning of Bi-Amplification has become blurred. I prefer
the old original meaning. The original concept places a "crossover"
between the preamplifier and the power amplifiers. With this
arrangement each amplifier operates over a restricted frequency
range. This restricted range presents each amplifier with a much
simpler job and each amplifier is less likely to injure the sound
in some way. The newer Bi-Amp concept simply uses two power amplifiers
without a crossover. In this arrangement each amplifier must
still work with the full frequency range, even though output
current will flow over a restricted range. Unless one uses an
external crossover ahead of the amplifiers, we don't feel the
benefit justifies the extra cost.
- The crossover consists of a LPF (Low Pass Filter) and a HPF
(High Pass Filter). As its name implies the LPF passes frequencies
below a cutoff and rejects frequencies above the cutoff frequency.
Likewise, the HPF passes frequencies above its cutoff. In the
Bi-Amplification connection the external Crossover frequency
is set to match the speaker requirements.
Not for novices
- In spite of any initial trepidation, connection of a basic
audio system is very simple. Conventional speaker designs, where
there is only one connection for the amplifier, make connection
a nearly errorless process. Other than causing a short circuit
or intermittent connection, not much can go wrong while connecting
a speaker. The big decision is whether the terminals twist or
press before accepting the wire. Bi-Amplification is not so simple.
- The speaker's built-in crossover is designed to match the
efficiency of all the individual drivers (tweeters, midranges,
and woofers are often called "drivers", much as you
are sometimes referred to as "people"). When using
the Bi-Amplifier connection you must directly deal with some
of these issues.
Here are the steps to connect speakers in the Bi-Amplification
- Turn everything OFF and wait at least 30 seconds for
the power amplifiers to shut down.
- Set all the sections of your crossover to the frequency required
for your speakers. The speaker owners manual will usually give
the crossover frequencies. If your speaker is a three-way (woofer,
midrange, tweeter) design, the Bi-Wire connection separates the
woofer from the combined midrange and tweeter section. Therefore,
you should use the lower crossover frequency specified by the
- Connect the preamp output to the electronic crossover. "Y"-cables
may be necessary.
- Connect each output of the crossover to its amplifier channel.
- If present, remove the bi-wire links from each speaker.
- Connect each amplifier channel to its respective speaker
section. Make sure that the correct frequencies pass through
from the crossover, to the amplifiers, then on to the speaker
sections and that you observe proper phasing.
- Set the level controls on the crossover and power amplifiers
such that a fixed level signal at any frequency will arrive at
all speaker terminals at the same level.
This is a very important point, let's clarify it: If a 1 Volt
100 Hz signal on the left channel input to the crossover causes
a 2 Volt signal at the output terminals of the left low frequency
amplifier; then a 1 volt 1000 Hz input to the right channel crossover
should result in a right high frequency amplifier output of 2
If your amplifiers are identical, it is usually sufficient
to set all the amplifier level controls the same. Most crossovers
also have level controls that can be set the same.
Above, we've shown our preferred setup using one stereo amplifier
per speaker. This arrangement allows minimum speaker wire length.
If your amplifiers are not identical, use the more powerful amplifier
for the low sections and the cleaner (better sounding) amplifier
for the high sections.
If you have sufficient will and the instrumentation to make
these level measurements, avoid taking them at the crossover
frequency. A good choice of frequencies would be half and double
the crossover frequency. Please note that few consumer or professional
grade digital voltmeters have a frequency response good enough
for this task. Always check the meter specs before using your
meter for audio. Most meters roll off beginning at 1000 Hz or
have a frequency response of ±3 dB (or worse).
If you are an expert
- In our opinion, the best method of connecting your speakers
is to supply one amplifier per voice coil and eliminate the speaker's
built-in crossover. If your speaker is a three-way design, then
you must "Tri-Amplify" your speaker.
- This technique, however, is not for the feint of heart because
you must be prepared to modify your speakers and take some measurements.
Individual driver efficiency varies. The original speaker crossover
equalized these variations. After eliminating the original crossover,
these sensitivity variations must be accounted for by your crossover
or amplifiers. Another loose end is the fact that some speaker
designers deliberately connect the midrange out of phase.
- For anyone willing to take the trouble to devote one amplifier
to each voice coil, the sonic rewards are outstanding. We can
recall an unforgettable lesson many years ago when a manufacturer
had two versions of the same loudspeaker. One version used the
traditional set-up, the other was Bi-Amplified using built-in
amplifiers. Even though the amplifiers used for the Bi-Amplified
version were nothing special, the self amplified version always
sounded better than the passive version, even when driven by
our best amplifier using our best speaker wire.
- A word of caution: While we enjoy the results of this technique
very much, you may not. There will be many obvious improvements
in the sound, everything will be clearer and tighter. Everyone
will appreciate these benefits. The possible down side is associated
with the imaging characteristics of your speakers. Part of the
physics of crossovers is a slight time delay as the signal travels
through the frequency selective networks. Depending on the design
of the original speaker crossover and the new external crossover,
the relative time delays between drivers may change after the
modification. Because of the change in relative delays, the imaging
characteristic of your speaker may change slightly. Only you
will know if the result is good, bad, or insignificant.
- Porvided by
- David Mann Audio