No, You Cannot Bi-Amp

01-21-12: Magfan
I'm sorry, but the power relative power needed IS governed by the crossover frequency.... The amp will only have to produce power for those frequencies for which the speaker has a need....

Hi Magfan,

Somehow my point isn't coming across.

Yes, the amp will only have to produce POWER for those frequencies for which the part of the speaker it is connected to has a need. However, in a passive biamp arrangement, where there is no active crossover ahead of the power amps, both the high frequency amp and the low frequency amp will need to produce the SAME output VOLTAGE, corresponding to ALL of the frequency components of the music.

And therefore if the low frequency amp has a rating of 300W and the high frequency amp has a rating of 30W, corresponding to the maximum power requirements above and below a crossover frequency that is very high, the 300W amp will not be able to produce 300W, or anything close to it (in a passive biamp arrangement), without the 30W amp (which presumably has a far smaller voltage swing capability) being driven into clipping. Therefore how far the volume control can be turned up without severe distortion occurring (and perhaps a blown tweeter as well) will be limited by the output voltage range of the 30W amp, and most of the power capability of the 300W amp will not be usable.

As I said earlier, that is a point that is commonly overlooked. I have often seen questions about passive biamping that refer to the possibility of purchasing amps such that the low frequency amp has a power rating several times greater than the rating of the high frequency amp, which makes no sense.

Best regards,
-- Al

Als right. For me best bi tri amping comes from matching ea amplifier to drivers it will run. This is a pain to pull off but once done worth while. Had a horn system with class d on bass horns, PP on midbass horn,SET on midrange horn,low power class A on horn tweeter worked very well though I had to try many amplifiers ;) Today I mostly biamp using Class D or SS on bass horn and SET on main horns. So 250-500 watts on bass and 12 watts on mains...

It is entirely possible that some speaker manufacturers discourage or outright deny bi-amping because of the warranty problems and damage to their products and their reputations that result from misunderstanding of the process. Our hobby and our websites are alive with unqualified opinions from self-appointed experts who start rumors and create confusion either mischievously, maliciously or naively. It all works out the same, however, with sometimes irreversible rumors perpetrated to no good effect.

The key to this discussion is the crossover itself. If that isn't right, amp matching remains meaningless. A good pair of properly designed crossovers can cost a couple of thousand dollars. When these are included in a repeatable speaker model and sold in volume the costs are amortized, but in my case the designer spent over 50 hours getting it right. He used the same horn and driver that I have and the same woofer in the same size cabinet. This was all done outdoors to provide anechoic conditions with microphones, instruments and a computer. There is a lot of trial and error involved if you have 30 years experience as he does. What would it take for you to pull it off?
I ask that question because when you try to set up your digital speaker management system in your own little bi-amp arrangement, you will need to create all the alignment and compensation that Bill worked out for me on your own. Not only is it not easy, it will prove to be impossible for most of you.
So, we go back to Elizabeth who indicated that it is a fool's errand, too often taken lightly by duffers and conceited neophytes. Some of them will arrive as I have with something they think sounds pretty good, Some will, as I did become frustrated and some will do real damage. None will get it right. Even if you use the thousand monkeys with typewriters logic, the odds of a happy accident are too extreme to be calculated and would require a much longer life than any of us can reasonably anticipate. It is your money and your gear, though , so have at it.

Have to agree with others here who dont see the need for a rant when someone admits they dont know something. They're asking those of us who do have the knowledge and experience to share that knowledge, which is how they become knowledgeable> Did all of us start off knowing everything there is to know about audio? Come on guys and girls,I admit I dont know everything there is to know and I've been involved in this hobby since 1986. Ok, my rant about ranting is over.

JohnK, thanks for your comment.

To be sure it's clear to everyone, I'll repeat that the issue I cited, involving a large disparity in power capability between the high frequency amp and the low frequency amp, just applies to PASSIVE biamping, in which the only crossover that is present is the one in the speakers.

I'll add that my comment was intended to apply to the situation where a single pair of speakers is being passively biamped, with the single pair of speakers having been designed to provide reasonable results (in particular, some semblance of flat frequency response) when driven by a SINGLE amplifier.

John's comments about combining Class D and SET, etc., apply to a different situation altogether.

Regards,
-- Al