Biamplification vs. Bridging
Power Amplifiers - page 2
Conservatively, let's only add 1 dB for the improvement in
woofer output due to elimination of the woofer series inductor
in the passive crossover. The tweeter is capable of an average
output from 6-8 dB in excess of the woofer, and the phenomenon
of masking will allow the tweeter to cover up the woofer clipping
by at least half of that, or 3-4 dB of additional output before
the output becomes noticeably distorted. Again, that is a conservative
number. That's at least another 4 dB total increase on top
of the nominal text book 6 dB for biamplification, or a total
increased SPL over the single channel use of 10 dB.
As far as reliability is concerned, the tweeter is only
exposed to 100 watts of power capability, not 400 watts,
and the same goes for the woofer. Accidents or sudden overloads
are much less likely to damage a driver, and the amplifier
is likely to be less stressed than when in bridge mode operation,
which does add some extra operating stress.
One thing that can be done with most amps used for biamplification
is to double up on each band (channel), or load two biamp
capable 8 ohm nominal rated speaker systems off of one amp.
The load on the amp would then only be a four ohm load per
channel. Two woofers can operate off of the low frequency
amp channel, and two tweeters off of the high frequency channel.
That extra speaker could provide an additional 3-6 dB more
SPL, or more crowd coverage, all the while biamped and playing
clean and loud. A bridged amp that is only rated down to
four ohms per channel, eight ohms bridged, could only have
one single 8 ohm speaker connected while in bridge mode.
Obviously, with biamplification, you can also mix and match
amp capabilities to the drivers. If you have two power amps
with different power ratings, use the bigger amp for the
woofers, and a smaller amp for the tweeters, and as long
as the tweeter amp was at least 1/3 to ½ the power
rating of the woofer amp, you would still enjoy that increased
output advantage over bridging. Remember, we still had about
3-4 dB of excess tweeter output, left over after the masking
effect was overcome, so the tweeter amp does not have to
have the same power capabilities as the woofer amp to keep
up.
Biamplification does require an electronic crossover to
operate properly, while most pro amps come already equipped
for bridged operation. Some users may not want to deal with
the additional complexity of an electronic crossover, most
such stand-alone crossovers need to be adjusted, and the
crossover settings are not always obvious or easy to make
correctly for best sound. Peavey offers a pair of simple
solutions to the electronic crossover "blues".
The new CS®-800S has provisions for different input
modules to be inserted, and one of those that is available
is the Peavey X1 crossover module. It has made biamplification
a breeze for anyone. With it's crossover point cleverly set
to a specific point, with jumper adjustment of polarity and
mode, it can be used with a wide variety of Peavey sound
reinforcement speaker systems. All EQ and crossover adjustments
have already been made, and in most cases, equal gain for
both amp channels will get you within a few clicks of nominal
levels for the proper balance of highs to lows. The real
plus is that the crossover output is defaulted to the two
channels of the CS®-800S with the X1 module installed,
so no extra patch cables are needed!
The speaker systems that work extremely well with the X1
are: The Peavey SP-2 series, the SP-4 series,
the SP-5 series, the new SP-1G, the Impulse 500,
the DTH 2 series, and the DTH 4 series. By following
the set chart in the owner's manual, and using a simple system
of movable jumpers on the crossover module, any of these
speakers can be used with this crossover module, and biamplified
precisely and correctly. Many other similar two-way sound
reinforcement speakers can be used with the X1 module, where
the jumper adjustments allow for fine tuning of another similar
type of biamp capable speaker system. A similar type would
be a 15" woofer in combination with a constant directivity
horn driven by a 2" diaphragm compression driver tweeter.
The X-1 also has provisions for use as a subwoofer crossover,
with the same easy hookup and set-up. And for that really
all out stack, it has provisions for triamplification, with
the subwoofer output going to another amp used in conjunction
with the CS®-800S. Oh, and to make things even easier,
the polarity of the subwoofer and the upper range output
are both connected in the same (positive) polarity, and the
blend between the sub and the top range cabinet is always
correct! No frequency response suck-outs or bumps!
Now for the very best part: this X1 module for the CS®-800S
only costs $74.99 retail!
The other electronic crossover option that is relatively
painless is the tried and true Peavey PL-cans. These
$40 retail crossovers plug into the crossover island on the
CS®-series, CS® X models and most prior models. For
use with the mainstream Peavey speaker systems, the PL-1200EQ
is the recommended model, while the PL-800EQ can also
be used. For subwoofer biamping, there is a 150 Hz crossover
version, the PL-150, for use with subwoofers; or if
you prefer a lower subwoofer crossover frequency, a PL-100.
In most cases, they can be hooked up all positive polarity,
and levels adjusted, and you are up and running in bi-amp
mode. Patch cables are required to get in and out of the
crossover island jacks on the CS®-series amps.
So if you want to get the most from your system, and maximize
the output SPL of your components, consider the minimal investment
in a Peavey crossover module to put you into the biamp arena.
For those fans of bridged amp operation, there are a few
tricks that may be of some help to you. There is one thing
that a bridged amp that is capable of 2 ohm music operation
can do that a biamped set-up can not do, and that is to drive
a pair of speakers, one off of each channel, and then drive
a subwoofer in bridged mode at the same time! All the speakers
need to be an 8 ohm load. The sub should be an add-on type,
one that has an inherent acoustic roll-off of the highs,
or a built-in low-pass filter. A sub that dos not fit into
either of these categories can be used by placing an inductor
in series with the sub, to help roll-off the highs. This
arrangement will have the subwoofer operating with 6 dB more
gain than the two full range speakers, but this is usually
not a problem, as most people run their subs at a level that
is hotter than a flat match to the upper range speakers,
and most subs are not as sensitive as the full range cabinets
either, so the net result is a decent balance, and certainly
not a problem for DJ, reggae or disco use if it is a little
on the hot side.
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