I'm finally getting around to biamping my B&W 801 Matrix Series III
speakers. Since I'm not ready to completely replace the existing
crossovers, my plan is to use a line-level crossover before the amps in
addition to the existing crossovers in the speakers. That just leaves
the questions of:

What frequencies to use?

The existing crossover is at 380 Hz. My thoughts are to either put the
crossovers one octave away at 190 Hz (200 Hz) and 760 Hz (800 Hz), or
put them at 380 Hz and adjust the Q. I have no idea which would sound
better, which makes me think an adjustable crossover would be better at
this point.

What crossover to use?

I'm considering:
* 6dB/octave passive line-level crossover (PLLXO)
* Ashly XR2001 24dB/octave active crossover
* TDM 24CX-3 24dB/octave active crossover

I'd like to use the 24dB/octave Marchand XM46 PLLXO, but its
frequencies aren't adjustable.

Eventually, my plan is to remove the existing crossovers completely and
replace them all with a DEQX, but that's still a long way off. This is
an interim solution where cost is definitely a factor.

I could build a 6dB/octave PLLXO. Building a 24dB/octave one is beyond
my skills.

The amps are two "identical" Conrad-Johnson MF-200s. I have to put
identical in quotes because the amps definitely sound different despite
being the same models.

Any thoughts, ideas, suggestions, warnings?

So far even without an additional crossover, with one amp for the highs
and one for the lows, the system sounds markedly better. I suspect the
difference is that the reduced current requirements keeps the amps in
their class A region, but I can't say for sure. It does sound better
though.


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wrote:

I'm finally getting around to biamping my B&W 801 Matrix Series III
speakers. Since I'm not ready to completely replace the existing
crossovers, my plan is to use a line-level crossover before the amps in
addition to the existing crossovers in the speakers.

It looks like you are trying to biamp a three way speaker. Do you
intend on using one amp for the woofer, another amp for the mid/tweeter
and use the existing passive crossover between mid and tweet?

That *may* work, but would depend on the topology of the crossover
circuit. I'd talk to B&K and see what they recommend.

Or maybe I'm misunderstanding what you're trying to do. Generally, you
want to use either the passive crossover that's already in the box, or
an active crossover, but not both.

What frequencies to use?

The existing crossover is at 380 Hz.

I'd start at the same frequency. And not go more than half an octave or
so in either direction.

My thoughts are to either put the
crossovers one octave away at 190 Hz (200 Hz) and 760 Hz (800 Hz), or
put them at 380 Hz and adjust the Q. I have no idea which would sound
better, which makes me think an adjustable crossover would be better at
this point.

This makes no sense whatsoever.


What crossover to use?

I'm considering:
* 6dB/octave passive line-level crossover (PLLXO)
* Ashly XR2001 24dB/octave active crossover
* TDM 24CX-3 24dB/octave active crossover

24db/octave is best because the output signals are in phase throughout
the crossover region. I've had good experience with Ashley gear. Not
cheap by consumer standards.

So far even without an additional crossover, with one amp for the highs
and one for the lows, the system sounds markedly better.

Huh? I don't get it. How are you using a different amp for highs and
lows without an active crossover? Are you paralleling the output of
two amps? That's a big no-no.



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Walt wrote:
Or maybe I'm misunderstanding what you're trying to do. Generally, you
want to use either the passive crossover that's already in the box, or
an active crossover, but not both.

I'm using both, so I'm adding an additional active crossover in
addition to the existing passive crossover.

You look at the existing speakers as being two-way with a 24 dB/octave
crossover at 380 Hz. I'm adding additional crossovers at 760 Hz for the
low pass and 190 Hz for the high pass. In theory, I'd get the benefits
of reduced power requirements and less IM distortion while still
keeping all the tweaking that went into the original crossover.

Mark


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wrote:
Walt wrote:
Or maybe I'm misunderstanding what you're trying to do. Generally, you
want to use either the passive crossover that's already in the box, or
an active crossover, but not both.

I'm using both, so I'm adding an additional active crossover in
addition to the existing passive crossover.

You look at the existing speakers as being two-way with a 24 dB/octave
crossover at 380 Hz. I'm adding additional crossovers at 760 Hz for the
low pass and 190 Hz for the high pass. In theory, I'd get the benefits
of reduced power requirements and less IM distortion while still
keeping all the tweaking that went into the original crossover.

Mark


Walt is right, you should use either a passive crossover or an
electronic crossover, NOT both. Using two crossovers will create holes
in the frequency response. Even if they were to be at identical
frequencies and slopes so you didn't get holes in the frequency
response, you would gain nothing by so doing.

Bi-amping with passive crossovers gains you nothing as the only benefit
to the power amp is a reduced loading in the treble or bass. However,
any even half-decent power amp used for the bass should not show *any*
improvement from the small loss of treble load, and similarly, any power
amp used for treble won't show an improvement for not driving bass
current, unless the design is very badly flawed.

Active operation with an electronic crossover, however, offers great
advantages in being able to shape the crossover region more accurately
than is possible with passive components, and a considerable increase in
available power output, as each amplifier is being asked to supply a
lower voltage than when driven by a full-range signal.

S.


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