How to allocate power for bi-amping

[lehelke3]

Hello all, quick question. I'm thinking of using my two Rotel amps to bi-amp a pair or CL3 speakers. I got a 130WPC and a 200WPC Rotel stereo amps.
Should I use the one with more power for the woofers or the panel. Which one is more power hungry ?

 

[JonFo]

Should I use the one with more power for the woofers or the panel. Which one is more power hungry ?

Use the more powerful one for the panels, as they have the most demanding impedance curve, and you need all the voltage the amp can muster.

130wpc is enough for the woofer and would be more than enough if you got rid of the power-sucking coil in the passive crossover. But that's a bigger task.
Try the bi-amping, I think you'll hear some improvements.

 

[Tosh]

I wouldn't like to argue with JonFo, but back when I went active xo on the bass of my SL3, it was still appreciative of a bigger amp on the bass, while the ESL is an easy load (current-wise). Try them both and use the better-sounding amp on the ESL!

 

[lehelke3]

I tried with just the 1582 (200WPC) and bass distorts if I go 75 or higher especially with dance or trance beats.

So I am feeding the woofer with 1552 (130WPC) and panel with bigger amp


Sound is not necessarily louder but it's stronger and more well rounded
Not sure how to describe

I was surprised that it didn't get significantly louder .....

 

[Brandon Hartwick]

If you're bi-amping with 2 differently rated amplifiers ideally you'd have gain controls to level match the panels and woofers.

But the panels usually use more power than anything else.

 

[lehelke3]

So if no gains not recommended to use different power ratings amplifiers ?

 

[Brandon Hartwick]

So if no gains not recommended to use different power ratings amplifiers ?

You might have a volume difference between the woofer and the panel, that's all. But it might also not be noticeable, you be the judge.

 

[Tosh]

Think about the combo load in a passive hybrid: An ESL via a transformer which would like to see voltage, and in parallel a series inductor and woofer which want current.
When you bi-amp, the top amp is happy to not drive the passive xo in the bass, and the top end is glorious. But the bass amp is still strangled by the series coil in the passive bass xo, so it loses control of the woofer.

JonFo, Brandon, and I all use at least an ACTIVE xo on the bass, if that tells you anything.

 

[rluciano]

So if no gains not recommended to use different power ratings amplifiers ?

It is not the power rating, but the gain of the amplifier that matters. PS Audio makes amps with power ratings into 8 ohms from 140 watts to 700 watts per channel some class AB; some class D, but all have 30.5 dB of gain. So you could pair any two of those without issue. On the other hand you could have two 100 watt per channel amplifiers one with 16 dB of gain and another with 26 dB of gain. The latter will produce twice the output with the same input.

 

[Leporello]

Hello all, quick question. I'm thinking of using my two Rotel amps to bi-amp a pair or CL3 speakers. I got a 130WPC and a 200WPC Rotel stereo amps.
Should I use the one with more power for the woofers or the panel. Which one is more power hungry ?

Bear in mind that with the 130W and 200W both driven to just below clipping, the level difference would be about 1.9 dB. In other words, for lack of any other information, it shouldn't make a heck of a lot of difference. I'm unfamiliar with "CL3" speakers. Is this a Martin Logan model?

Having no way to adjust the levels between the bass and treble amps in a biamp setup is really not an option, unless they miraculously matched. There are a lot of variables in play here. Bottom line, I have to agree with other posters: you'll have to play it by ear.

To set the levels between the amps you can either do it by ear, or if you have a response plotting setup such as REW, go for a smooth transition at the crossover point. If you're contemplating ear splitting levels you might want to determine which amp clips first with the type of music you typically listen to, and allocate the amps accordingly. But if the only difference between them is the power rating I doubt you're going to hear much of a difference.

Typically, most of the power spectrum of most music is concentrated at the lower frequencies, so that's what I would try first. On the other hand, a dynamic loudspeaker--the woofer--is typically more sensitive, i.e. converts the watts into more radiated acoustic power, than an esl panel. Again, experimentation is in order, but I doubt you'll hear a night and day difference between the two possibilities.

 

[Leporello]

So if no gains not recommended to use different power ratings amplifiers ?

If no gains, not recommended to use even power amps of the same ratings, unless the gains of the amps and acoustic efficiencies of the speakers were serendipitous, which has approximately a zero probability. But gains are easy enough to arrange. Wire potentiometers in an enclosure with RCA cables if you have to. Balanced inputs would be trickier, but still possible. It may be ugly, but you wouldn't have to adjust them very often. You could hide it behind your equipment rack. Put it in whichever leg needs gain reduction.

BTW what sort of crossover are you using? If you're just feeding the original low pass and high pass passive crossover legs full range, then you would have a fighting chance with amps of the same, or close to the same (as you are) power ratings. That assumes the voltage gains of the amps are the same, or similar, which may not be a valid assumption. But you're losing at least part of the advantage of a biamp setup doing that. An electronic crossover, and bypassing the original crossover, is highly recommended.

 

[Leporello]

I tried with just the 1582 (200WPC) and bass distorts if I go 75 or higher especially with dance or trance beats.

So I am feeding the woofer with 1552 (130WPC) and panel with bigger amp


Sound is not necessarily louder but it's stronger and more well rounded
Not sure how to describe

I was surprised that it didn't get significantly louder .....

What do you mean by "go 75 or higher"? Does the Rotel have a power meter? 200WPC should be more than adequate for any ML hybrid in any room at any sane level. Are you sure it's the amp that is distorting? My experience is, the Ascents driven with 200WPC played much louder than the CLS II's I'm using now, and I couldn't be in the room with the amp clipping into either speaker. Maybe you're just asking too much out of a hybrid ESL.