Bi-amping + speaker crossovers = redundant?

I use three way tri amped system. My system was built that way, however, you can do it yourself. You can use an external xover such as the Bryston 10b xover. Pre out to cross over the to three matched amps amps to the speakers. The volume control is at the preamp and used for all channels.

OK, I finally thought of how it would work. Signal to one pre section, then to the electronic crossover , the signal is split and the level balanced with its volume controls, then out to each of the amp sections, not using the second pre stage. But you will still have the problems Drew described. Last winter I considered something like this; I have 6 identical mono amps and speakers that are tri wirable with easily removable crossovers. I gave up when I started to discover SOME of the problems Drew spoke of. These projects are best left to the technically gifted who enjoy the construction as a pleasure in itself.

This will get complicated as the electronic crossover will have to be placed between the signal source and the two amps if it is to divide the frequency between them. I am having a little trouble visualizing the exact configuration and I have a fairly complex system. The signal cannot pass through the 'Master" amp to the "Slave" amp as it will not be the full range signal, only the partial signal. There is no way I know of to place the crossover between the amps and the speaker as it acts on the signal, not the amp output. It will feed two separate signals to the two amps and you are back with two volume controls. There is a reason why, despite their many drawbacks, almost all speakers are passive. KISS rules again!

08-24-10: Mhedges writes
> There are commercial external crossovers for this exact purpose. I am using the now discontinued NHT X2 crossover to biamp my speakers. It is a good piece but would not be suitable for this application since it is really designed for biamping speakers with built in subs and only has low pass and high pass filters up to about 200 hz.

The problem there is that you need to duplicate the intended transfer functions of the current speaker level networks.

Most commercial solutions are not plug-and-play solutions for that.

Electrical cross-over slopes vary from the speaker's stated acoustic cross-over slopes which result from a combination of the electrical networks and driver's inherent band-pass functions, points and slopes are asymmetric to get proper summation with offset drivers, rising response and resonances are compensated for, there's usually a shelving low-pass for baffle step compensation, and the response may be intentionally non-flat to compensate for the decreased directivity above the tweeter cross-over point.

Simple cross-overs which only provide high-pass and low-pass won't do all that.

Where you have a programmable DSP unit (DCX) or plug-in cards providing the components surrounding an op-amp (the Marchand units) you need to measure the existing cross-over functions (using a program like ARTA) and duplicate the transfer function.

>One solution would be to use Harrison Labs PFMOD in line crossovers. These plug in between the amp and preamp and will provide the high and low pass filtering necessary.

That's unlikely to work well.

>The amp that you use on the tweeter needs to have no DC offset or turn on "thump" or you will kill the tweeter in a hurry since there is now no capacitor to protect it from DC

No. A small turn on transient won't run the tweeters out to their mechanical limits and a few milliwatts dissipated due to slight DC offsets won't hurt anything.

When I built my Linkwitz Orions I hung my oscilloscope off my intended tweeter amplifier that had a thump on power up, noted that the turn-on transient magnitude was less than the AA battery I used to check driver polarity, and didn't worry about it.

It's been seven years and well over a thousand power cycles since then without issue.

If you're really paranoid you can put a capacitor in series with the tweeter that are big enough to make a pole two octaves below the electrical cross-over point; or derive one of the cross-over poles from a smaller capacitor although good film capacitors cost more than replacement dome+coil assemblies for nice tweeters.

Thank you very much for your replies. Now I understand. The setup I had considered would create more problems than it would solve.

Proper biamping does NOT send the full range signal to the tweeter or the woofers. What is done is the signal is filtered at the line level before amplification, which in theory should cause much less distortion than filtering the amplified signal.

There are commercial external crossovers for this exact purpose. I am using the now discontinued NHT X2 crossover to biamp my speakers. It is a good piece but would not be suitable for this application since it is really designed for biamping speakers with built in subs and only has low pass and high pass filters up to about 200 hz.

One solution would be to use Harrison Labs PFMOD in line crossovers. These plug in between the amp and preamp and will provide the high and low pass filtering necessary.

Waryn - do you know what the crossover frequency is of your speakers?

Biamping can be done with integrated amps but you will need the "master" amp (meaning the one you want to use to control volume) to have seperate pre outs to connect to the other amp.

The amp that you use on the tweeter needs to have no DC offset or turn on "thump" or you will kill the tweeter in a hurry since there is now no capacitor to protect it from DC.

Hope this helps - it is a little complicated but certainly doable.

Mark

If you send the full range signal to the tweeters with tone controls setting the bass as low as it goes...you will blow your tweeters. No question, don't do it. Tweeters just cant move that much (excursion).

I second Stan's comments. You need to keep the low frequencies out of the tweeters, or you will destroy them. You need to keep the high frequencies out of the woofers, or (at best) you'll mess up the frequency response in the crossover region. Tone controls on the integrated amps are unlikely to accomplish these things adequately. And at best you'll wind up with a very crude approximation of what the speaker designer intended his crossover network to accomplish, which will undoubtedly sound poor. There is also the practical issue of having two separate volume controls, as Stan mentioned.

Finally, to the extent that low frequencies are not kept out of the power amplifier section of the integrated amp that feeds the tweeters, using a more powerful amp on the woofers will be pointless. How loud you can turn up the volume will be limited by the clipping point of the lower powered amp, if the lower powered amp is allowed to see most or all of the bass content of the signal.

Oftentimes simpler is better!

Regards,
-- Al

My speakers are two-way. My idea was to connect one integrated amplifier to the tweeters, and another one (more powerful) to the woofers. The article about bi-amping (thanks for the link!) does not seem to address such a possibility, hence my confusion.

It certainly is possible but unless the speakers are two way then you will still need to leave part of the crossover in place.

Any decent external active crossover will also have volume control for the outputs so you can match everything up. Once you get that set you can change the volume with your preamp as normal.

Here is a link with a lot more info on biamping:

http://sound.westhost.com/bi-amp.htm

Mark

NO! The crossovers determine how much power each section of the speaker gets, if you have no crossover the tweeter and mid gets as much power as the woofer, a sure recipe for disaster. What you are looking for is an external electronic crossover which attenuates the signal before the amp sees it. You can also remove the crossover from the cabinet to improve the sound. Even if what you propose was possible the amps would require rebalancing every time you changed the level.