Details for bi-amping

JeffreyBehr, I think he means that he wants to use a pair of monoblock solid state amps for the lows, and a pair of monoblock tube amps for the mids/highs.

You are of course making a good point that what needs to be matched is gains, not sensitivities. More likely than not the solid state amps, presumably being more powerful, will have higher gain, and therefore their inputs will probably be the ones having to be attenuated.

I second the comments about biamping being more complex an undertaking than is often anticipated, with there being a substantial possibility of disappointing results.

One of the most common misconceptions about passive biamping (i.e., biamping without an active line-level crossover) is that it makes sense to use a powerful solid state amp on the bottom, and a much less powerful tube amp on top. In addition to the possibility of that resulting in a sonic mismatch, what is commonly not realized is that much of the power capability of the solid state amp will not be utilizable, because how much of its power capability can be utilized will be limited by the clipping point of the lower powered amp. In a passive biamp arrangement, the mid/hi amp(s) have to output just as large a voltage swing as the bass amp(s).

Regards,
-- Al

"...what is commonly not realized is that much of the power capability of the solid state amp will not be utilizable, because how much of its power capability can be utilized will be limited by the clipping point of the lower powered amp."

Maybe so, but one still has more power available than if using only one pair of amp channels of whichever you had first, because each amp channel's power is not consumed driving a full-range signal.

Do understand that 'after filtering' (by the crossover's filters) is as effective in power saving as prefiltering, in that, for instance, the upper-frequency amp simply isn't able to/doesn't have to deliver current required by low-frequency signals. Said another way, if one starts this biamping (NOT 'bi-amping') process with a 50WPC tubed amp and adds a 100WPC amp for the bass, the 50WPC amp no longer has to consume the power of its powersupply driving low frequencies into the 'bottom half' of the speaker. So maybe we don't have 150WPC available, but we do have lots more than 50WPC available.

Passive biamping can be very effective, but it also can be excessively complex if one starts with the wrong amps and especially if one can't balance levels correctly.
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The amount of relative power of amps used in a biamp setup is very much related to the crossover point.
Take a crossover of 10khz. How much power, as a %age of total does music contain above the crossover? Maybe 10% or 15%?
Likewise, if you crossed over at 100hz, you may need MORE power to the mid/hi amp than the bass amp. Above crossover may end up as 80% of total power needed.
Depending on crossover point, it may actually be appropriate to mate a relatively small amp on 'top' with a more powerful amp for the lows....

3 way designs would just complicate the heck out of it!
As an example:: The Braun Tri-Amp.....maybe early late '70s / early '80s? had three amps per speaker. 55watts=bass 35watts=mids 15watts=highs. Wacky expensive for me at the time, I looked but didn't touch!

The OTHER issue I never see addressed is what I call latency. How long does it take a signal to get thru amp 'a' vs amp 'b'? What is the effect at crossover if one amp is a hi feedback design (for bass=hi df) vs an amp with less feedback used above crossover? How will those distortion products interact at crossover +- 1 octave?

Excellent points, Magfan. To further clarify my point about power, though, what I was basically saying is that for passive biamping voltage swing capability needs to be considered as well as power capability, particularly if there is a large disparity in the power capability of the two amps.

Using your extreme hypothetical example of a 10kHz crossover, the amount of power that would have to be provided by the high frequency amp is extremely small. However, if say a 50W amp were used for the highs and a 500W amp were used for the lows, the 500W amp would in effect be no more powerful than, for example, perhaps 75 or 100W. Asking it to provide more power than that would cause the OTHER amp to clip, resulting in lots of extraneous non-musical high frequency energy going into the tweeter.

Good point about latency, aka propagation delay. You're right, that never seems to be addressed. Not sure how it would play out quantitatively under typical circumstances.

Best regards,
-- Al