When Bi-amping is there change in sensitivity

No, the sensitivities will not change. You will have to provide some means of compensating for the difference in the gain of the two amps. Otherwise a tonal imbalance will result.

Most likely the 500W amp will have higher gain than the 80W amp, so if the 500W amp does not provide a means of reducing its gain (i.e., a volume control), and assuming that you are referring to passive biamping (i.e., no active crossover ahead of the amplifiers) you would have to place some sort of passive attenuator in series with the input of that amp.

Also, again assuming that you are referring to passive biamping, since the equalized gains will result in both amps having to output essentially the same voltage at any given instant, corresponding to the full frequency range of the signal, you will probably not be able to utilize a lot of the power capability of the 500W amp. How high you will be able to turn up the volume control on your preamp, without distortion, will be limited by the clipping point of the lower powered amp.

Regards,
-- Al

Thanks for your response, Al. The tube amp in question does have level control to try to match the gains in case of bi-amping. You mentioned active crossover, would that be a more preferable approach over the passive bi-amping? In that case I would be able to adjust the gains from the crossover itself. And if I end up doing this, would you suggest removing the crossover from the speakers?

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?

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.