When Bi-amping is there change in sensitivity

I'm not sure that the level control on the tube amp will be able to do the job. My suspicion would be that even with it set to its maximum setting the 500W amp would still have a higher gain. If so, you would still have to provide a means of reducing the gain of the 500W amp, such as a passive attenuator in series with its input.

Yes, an active crossover would presumably provide the necessary gain adjustment, and would also keep low frequencies out of the high frequency amp, resolving the problem I mentioned of not being able to utilize all of the power capability of the high powered amp.

I have no experience with active (or passive) biamping, but those who do generally recommend removing the crossover from the speakers, which would seem logical. However before proceeding down that path you would want to obtain detailed information on the technical characteristics of the crossover in the speakers, and make sure that the active crossover you choose would be able to emulate (match) those characteristics. Some speakers have complex crossover characteristics that may not be matchable by most or all active crossovers.

Another question I had was if the transients in the mid-high frequencies require as much headroom as the transients in the bass region. Would a 80wpc amp be able to give enough power to provide clean high volume sound (mid-high only) with a moderately affecient speaker, say 89db sensitivity?

It depends on the frequency of the crossover point. It has been mentioned in past threads here that a crossover frequency of 350 Hz will typically result in an equal division of power between the low frequency and mid/hi frequency sections. The higher the crossover point, the lower the amount of power that will be required for the mid/hi section.

Regards,
-- Al

>03-18-12: Gago1101
>Another question I had was if the transients in the mid-high frequencies require as much headroom as the transients in the bass region.

Yes provided that you are passive bi-amping (although I'd argue active bi-wiringis a more useful description of what's going on). Both amplifiers see the same input signal and (assuming you don't change the tap on an ampliier with transformer coupled outputs) will clip almost exactly where they would have when running the entire speaker full-range.

Active (real) bi-amplification lacks this drawback but takes a line level cross-over which in hi-fi applications must be designed for the drivers and enclosures in question and means it isn't a viable DIY proposition for most people.

>Would a 80wpc amp be able to give enough power to provide clean high volume sound (mid-high only) with a moderately affecient speaker, say 89db sensitivity?

Probably.

Issues about wether it's actually beneficial or not aside, I am intrigued by a couple of the technical matters discussed so far. Great info from Al (as always) and Drew, BTW.

Is it not true that of great importance is each amp's input sensitivity? And is there a correlation between an amp's power rating and it's input sensitivity as Al suggests? That has not been my experience.

Also, while I understand that each amp would see a full range signal at it's input, I don't understand why the amp would not still benefit from not having to DRIVE a full range signal. What am I missing?

Thanks, Frogman.

Is it not true that of great importance is each amp's input sensitivity? And is there a correlation between an amp's power rating and it's input sensitivity as Al suggests? That has not been my experience.

In referring to sensitivity I was referring to the sensitivity of the speaker, which is what I thought the OP was asking about. Now that you mention it, though, I'm not completely certain that I was interpreting the question as it was intended.

In any event, I certainly agree that in general there will not be a high degree of correlation between an amp's power rating and its input sensitivity. The GAIN of the amp, though (the relation between output voltage and input voltage), will have a high degree of correlation with the relation between its output power capability and its input sensitivity. As I indicated, and as I'm sure you realize, the gains of the two amps must be closely matched. The sensitivity of the amps (the input voltage that will drive the amps to their maximum power capability) is indirectly relevant, because of its relation to gain.

Also, while I understand that each amp would see a full range signal at it's input, I don't understand why the amp would not still benefit from not having to DRIVE a full range signal. What am I missing?

That is all correct, and you are not missing anything. I was not implying anything to the contrary. In a passive biamp arrangement, each amp will benefit from a significant reduction in the amount of CURRENT and POWER it has to deliver. The point I was addressing, though, is that since the VOLTAGE that will be generated at the output of BOTH of the amps will correspond to the complete full frequency range signal, if there is a large disparity in the maximum power capability of the two amps it is likely that the lower powered amp will be driven into clipping at a volume level at which the higher powered amp is delivering far less power than it is capable of. And of course the volume level cannot be turned up beyond the point at which EITHER amp is clipping, or severe distortion will be heard. Therefore a substantial fraction of the power capability of the higher powered amp will not be able to be utilized.

Best regards,
-- Al