Bi-amping 989s??

[Studley]

Is it possible to modify quad 989s so they can be bi-amped? I don't know enough about their crossover set-up to answer this, assuming they have crossovers?? Anybody?

[david yost]

Probably, but why would you want to?

[Studley]

Because the received wisdom is that bi-amped (active) systems are intrinsically superior to traditional set ups. As I understand it this is basically because you are asking the amplifiers to perform much less onerous tasks; they don't have to deal with the full frequency range and the attendant difficulties that come with that configuration.

[I_Forgot]

Originally posted by Studley
Because the received wisdom is that bi-amped (active) systems are intrinsically superior to traditional set ups. As I understand it this is basically because you are asking the amplifiers to perform much less onerous tasks; they don't have to deal with the full frequency range and the attendant difficulties that come with that configuration.

The amps aren't the problem. In conventional speakers you have a passive crossover network that sends the highs to the tweeter, etc. Getting a passive crossover to work properly is very difficult because it depends on both the electrical and mechanical characteristics of the drivers, both of which vary from unit to unit as the drivers are manufactured.

When you biamp a system you eliminate the passive crossover between the bass and mid/treble and use an active network before the amplifier. The active network can more easily be made to behave as you want, and is less dependent on the electrical and mechanical characteristics of the drivers than a passive crossover.

In the case of a Quad ESL there isn't really a crossover in the conventional meaning of the word. It uses delay lines and resistors that work with the capacitance of the speaker panels to control the frequencies sent to each section of the speaker.

I suppose you could go into the speaker and start hacking out some of the connections to the bass panels, then bring the connections out of the speaker. Outside the speaker you'd need an active crossover and amp plus the step-up transformers required to drive the speaker panels. Don't forget to terminate the ends of the delay lines you just cut free of the bass panels otherwise the delay lines for the rest of the speaker will not perform properly.

If you really want to do some biamping for your quads, get separate bass drivers and an active crossover set to about 100-150 Hz and drive those with the low bass. You will extend the low frequency response of the system and increase the maximum SPL at the same time because the ESL will no longer be trying to reproduce very low frequencies which it can't do well anyway.

I_F

[Studley]

I_F

Many thanks for that. You have confirmed my suspicion re their crossovers being different to conventional ones.

I have thought about the active crossover + powered sub-woofer option before, for precisely the reasons you mention and to ease the burden on my amps. I would like to get the Supratek Cabernet Dual preamp at some point and that should work great with such a set up.

[Zombie]

The active crossover (or high-pass filter) has to be VERY good not to loose the transparency of the ESL...

[Studley]

Agreed. I've been told the Ground Sound ones are good.

Any alternatives?