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Biamp Top/Bottom Balance

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xenonaut

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I have a question about biamping and hope that someone can offer some insight.

Quick background for context:
I currently have a Musical Fidelity 3.2CR amp driving my SL3s. I tried biamping with my old Adcom 545 on the bottom, and noticed that the MF 3.2 sounded better when driving just the panels than it did driving panels and woofers. I don't feel like the Adcom is up to the level of the MF, so I thought I'd get another 3.2CR and biamp with the matched pair of MF amps.

Assumptions:
My understanding is that the panels are easier to drive than the woofers. When driving both panel and woofer with the same amp/channel (conventional, non-biamp setup), it seems like the woofer would use more of the energy (from the shared signal) than the panel, and the balance between panel and woofer would work out naturally (as designed by M-L, presumably). However, biamping means that the panel and woofer are no longer sharing the same signal (clearly a benefit in some respects, BUT...)

Formulating the actual question:
If I drive the panel and the woofer with identical amps (or with different channels of one stereo amp), do I end up with a top/bottom imbalance because I am feeding exactly the same power to different loads? Are my panels going to be (relatively) louder than my woofers with such a setup? Do I need to feed my panels less power to keep them in line with the woofers?

The Management Summary version:
Does vertical biamping make any sense (for hybrid electrostats), or does it result in too much power at the panel relative to the woofer?

Thanks in advance for any input anyone may have.

Cheers,

Hal
 
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aliveatfive

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IMHO -

Electrostatic panels are not easy to drive. They can present a horribly low impedance load to the amplifier. Your amp must be very stable to power them properly. Sometimes they are required to drive loads as low as 1 ohm. The primary reason for using equivalent amps on top and on bottom are for maintaining a balance between panels and woofers without using an additional electronic crossover.
 

JonFo

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First a couple of clarifications:

The panels are much more difficult to drive, as their impedance curve drops really low at high frequencies, additionally, they present a largely capacitive load on the amp.
The woofer on the other hand, presents a fairly consistent impedance and a traditional resistive load on the amp.
To drive the ESL’s, you need an amp that delivers high current. Your MF 3.2 can deliver 75amps peak to peak current, which is a decent rating, but no where near the 240amps a Sunfire can deliver. The question to ask MF would be, how many amps can they deliver into 2 Ohms?

You can easily use non-matching amps for panels and woofers, however, there are some caveats. First and foremost is level matching. You don’t want one amp driving its section louder than the other. Some test discs and an SPL meter will help here.
Meeting this requirement is sometimes difficult as not all amps have volume controls. For instance the GFA-545 does not, and neither does the MF 3.2, so you have a problem right there.

If you used an Active crossover in front of the two amps, you could use the gain settings in the x-over to match. But that would require bypassing the passive X-overs in the SL3. A bit of simple wiring changes, but not for the timid.

You correctly surmise that if you use passive crossovers and biamp each input, your best choice is to do vertical biamping with same model amps on each channel. This addresses the level matching issue.

Personally, I do active x-overs and use different model amps (but same vendor) for panels and woofers. This works much better than the passive designs.
IMHO, any biamping, whether passive or active, yields better results than one amp.
 

JonFo

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aliveatfive said:
IMHO -

Electrostatic panels are not easy to drive. They can present a horribly low impedance load to the amplifier. Your amp must be very stable to power them properly. Sometimes they are required to drive loads as low as 1 ohm. The primary reason for using equivalent amps on top and on bottom are for maintaining a balance between panels and woofers without using an additional electronic crossover.
:) LOL, good to see two replies come out at the same time and actually agree :D
 
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xenonaut

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Top/Bottom Balance

Hi Guys,

Thanks for the responses.

Does it really require more current to drive the panels at mid- and high frequencies than it does to get solid bass out of the woofers? I was thinking of one of the forum members here (Spike, maybe?) using AES SixPac tube monoblocks on panels and a larger Classé for bass...

But I don't think that whether it is the tops or bottoms that are harder to drive is of critical importance to the question. In any event, if the loads are different for panel and woofer, and I vertically bi-amp, aren't I guaranteed an imbalance, because I am feeding identical current to different loads (which is presumably not the case, when you do not bi-amp, as the woofer and panel interact in sharing the current)?
 

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xenonaut said:
Hi Guys,

Thanks for the responses.

Does it really require more current to drive the panels at mid- and high frequencies than it does to get solid bass out of the woofers? I was thinking of one of the forum members here (Spike, maybe?) using AES SixPac tube monoblocks on panels and a larger Classé for bass...
I think that’s because SS amps have better damping factors than tubes that people use them on woofers . And yes, the panels draw lots of current.

xenonaut said:
But I don't think that whether it is the tops or bottoms that are harder to drive is of critical importance to the question. In any event, if the loads are different for panel and woofer, and I vertically bi-amp, aren't I guaranteed an imbalance, because I am feeding identical current to different loads (which is presumably not the case, when you do not bi-amp, as the woofer and panel interact in sharing the current)?
The key here is the passive crossover is designed to ‘balance’ the load between ESL and woofer. So whether it’s one amp or two, the crossover is providing level and phase balance between the two halves (as long as it’s the same model amp).
What bimaping enables is for the amp driving the ESL to basically not have to deal with the demands of the bass (and the loads of that part of the Crossover) and can deliver its full capability to the upper ranges. And, as this is where an ESL is the most difficult to drive, you come out ahead in terms of current headroom when playing at moderate to loud levels.
 

Spike

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xenonaut said:
I was thinking of one of the forum members here (Spike, maybe?) using AES SixPac tube monoblocks on panels and a larger Classé for bass...
Sorry for getting back on this board kinda late (from a ski trip) but it does look like I have to chime in for this thread since my name was called...

But I don't think that whether it is the tops or bottoms that are harder to drive is of critical importance to the question. In any event, if the loads are different for panel and woofer, and I vertically bi-amp, aren't I guaranteed an imbalance, because I am feeding identical current to different loads (which is presumably not the case, when you do not bi-amp, as the woofer and panel interact in sharing the current)?
I agree with JohnFo that the built-in passive crossover takes care of distributing the right amount of energy to the panel and woofer. If you passively bi-amp with 2 different amplifiers, both amplifiers will drive full-range signals to the speaker interfaces, but the excess energy (outside of the effective frequency range) is converted into heat by the crossover circuitry. This heat dissipation process is not as efficient as actively bi-amping with an electronic crossover, but it is still much more efficient than the amplifier having to drive an actual (speaker) load. The trick is to present the same balanced signals at both speaker interfaces, and this can be achieved by having a good quality attenuator at the bigger (solid-state) amplifier to dial-down the gain to match with the tube counterpart.

Spike
 

aliveatfive

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Spike said:
Sorry for getting back on this board kinda late (from a ski trip) but it does look like I have to chime in for this thread since my name was called...


I agree with JohnFo that the built-in passive crossover takes care of distributing the right amount of energy to the panel and woofer. If you passively bi-amp with 2 different amplifiers, both amplifiers will drive full-range signals to the speaker interfaces, but the excess energy (outside of the effective frequency range) is converted into heat by the crossover circuitry. This heat dissipation process is not as efficient as actively bi-amping with an electronic crossover, but it is still much more efficient than the amplifier having to drive an actual (speaker) load. The trick is to present the same balanced signals at both speaker interfaces, and this can be achieved by having a good quality attenuator at the bigger (solid-state) amplifier to dial-down the gain to match with the tube counterpart.

Spike

The power of the amp does not determine the gain. A tiny single-ended triode amp can have more gain that a 500 wpc solid-state device. To obtain proper balance, you should probably use a sound-level meter and test tones.
 

Spike

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aliveatfive said:
The power of the amp does not determine the gain. A tiny single-ended triode amp can have more gain that a 500 wpc solid-state device.
Agreed that the power output does not determine the gain factor of the amp. I was stating the use of attenuator in my own set-up.
To obtain proper balance, you should probably use a sound-level meter and test tones.
Or read the spec. For example, my Classe' has 26db gain vs 19db gain for the AES SixPacs. There's a 7db differential that I have to dial down to make the Classe' match with the SixPacs. I can achieve this attenuation with a fixed 7db attenuation adaptor or with by a RadShack SPL meter as suggested.

Spike
 
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