Bi-Amping speakers

[Deleted member 2944]

I am familiar with the discussion. He does not ever say you get twice the power AFAIK, but does explain the potential "effective" increase within the range of the amplifiers, or words to that effect, through frequency division (splitting). IOW, a driver might get the full 100 W in one band (e.g. bass), unencumbered by any signal in the other (e.g. treble) band, but will not see 200 W. That is the thing many fail to grasp; two 100 W amps do not allow you to drive either band to 200 W, it is not the same thing as doubling the amplifier's power. The real-life advantage possible depends greatly upon the speaker design, crossover frequency, and source frequency (spectral) content, natch.

Alas, even that potential is lost with so-called "passive" biamping as implemented by most AVPs/AVRs. In those cases you can argue current headroom is gained, though it may be minor, but essentially no practical increase in voltage headroom, thus essentially no real-world benefit assuming decently low amplifier output impedance and cable resistance.

This is why I used the terms "perfect world," and "conditions," and put "double the power" in quotation marks.

You are correct that using a second identical power amp will not increase the peak voltage capability beyond a single amplifier. However, adding the second power amplifier and then band-limiting both amplifiers by moving the system crossover upstream does yield a real advantage in current usage. Whether that might amount to 3db is indeed related to the real-life possibilities you mention. (Many variables here.)

I don't disagree with you on the potential of "passive biamping." It's a marginal improvement, at best.

Dave.

 

[DonH56]

The high-frequency section of the crossover sees all of the same frequencies as the low frequency section, and vice-versa, but the current is different because the impedance is different across the range of frequencies for each crossover section.

I understand that; I clearly said "voltage" in my post.

 

[DonH56]

This is why I used the terms "perfect world," and "conditions," and put "double the power" in quotation marks.

You are correct that using a second identical power amp will not increase the peak voltage capability beyond a single amplifier. However, adding the second power amplifier and then band-limiting both amplifiers by moving the system crossover upstream does yield a real advantage in current usage. Whether that might amount to 3db is indeed related to the real-life possibilities you mention. (Many variables here.)

I don't disagree with you on the potential of "passive biamping." It's a marginal improvement, at best.

Dave.

Yes, the problem is that passive bi-amping implemented in most AVRs does not band-limit the signal to either amplifier. And again, the problem is most amplifiers clip the voltage; I do not dispute the current is different for each band.

I'm repeating arguments made for decades, no sense in trying to carry on further.

 

[blueone]

Yes, the problem is that passive bi-amping implemented in most AVRs does not band-limit the signal to either amplifier. And again, the problem is most amplifiers clip the voltage; I do not dispute the current is different for each band.

I'm repeating arguments made for decades, no sense in trying to carry on further.

And I understand what you're saying, but I have a question about amplifier clipping that I don't know the answer to. As we all know, reproduced music will have voltage levels that vary by frequency. Deep bass frequencies will tend to have higher levels than frequencies above, say 500Hz. So let's take the example of an organ recording, Bach's Toccata and Fugue in D minor, played by Michael Murray will do. (I'm using this specific example because I heard it in the car on SXM radio on my way home a day ago, and I own the CD.) Played very loudly, as it should be, the recording is going to have a very strong 32Hz component at times, but a spectrum analyzer shows a broad spectrum of frequencies with a rather steeply declining amplitude per octave. Let's say that the difference between the voltages will be more than 10db lower at 1KHz than it is at 32Hz (and probably lower than that). I think this recording is a pathological musical case that makes for a good example.

Perhaps I made a grossly incorrect assumption, but I was originally thinking that while the 32Hz signals were being clipped, the 1KHz signals wouldn't be, being at a lower level. But your comment got me thinking... is this assumption correct? If the amplifier is clipping due to the 32Hz signal, will all frequencies being amplified simultaneously be clipped? Or will the higher frequencies at much lower levels not be clipped?

 

[Deleted member 2944]

Perhaps I made a grossly incorrect assumption, but I was originally thinking that while the 32Hz singles were being clipped, the 1KHz signals wouldn't be, being at a lower level. But your comment got me thinking... is this assumption correct? If the amplifier is clipping due to the 32Hz signal, will all frequencies being amplified simultaneously be clipped? Or will the higher frequencies at much lower levels not be clipped?

The link I posted above addresses your question directly. Look in section 1.5.

Remember that your musical waveform is a composite of all frequencies. All amplifiers have voltage-defined limitation (or window) that can't be exceeded. So, if you have low frequencies with much energy slightly exceeding that amplifier capability, high frequencies of a much lower (relative) level are superimposed on that signal and will be affected/limited as well.

Dave.

 

[DonH56]

And I understand what you're saying, but I have a question about amplifier clipping that I don't know the answer to. As we all know, reproduced music will have voltage levels that vary by frequency. Deep bass frequencies will tend to have higher levels than frequencies above, say 500Hz. So let's take the example of an organ recording, Bach's Toccata and Fugue in D minor, played by Michael Murray will do. (I'm using this specific example because I heard it in the car on SXM radio on my way home a day ago, and I own the CD.) Played very loudly, as it should be, the recording is going to have a very strong 32Hz component at times, but a spectrum analyzer shows a broad spectrum of frequencies with a rather steeply declining amplitude per octave. Let's say that the difference between the voltages will be more than 10db lower at 1KHz than it is at 32Hz (and probably lower than that). I think this recording is a pathological musical case that makes for a good example.

Perhaps I made a grossly incorrect assumption, but I was originally thinking that while the 32Hz singles were being clipped, the 1KHz signals wouldn't be, being at a lower level. But your comment got me thinking... is this assumption correct? If the amplifier is clipping due to the 32Hz signal, will all frequencies being amplified simultaneously be clipped? Or will the higher frequencies at much lower levels not be clipped?

What Dave (@dreite ) said. If you do not split the frequencies before the amplifiers, which the vast majority of AVRs do not, then all signals, and all frequencies, are present at the input, and thus the output, of the amplifier. Typically voltage clips so everything gets clipped. That is my fundamental problem with "passive" bi-amping -- without splitting the frequencies before the amps, you are throwing away 99%+ of the benefit.

And before anybody asks, I just made up the 99%, it could be more...

Conversely, if you do split the frequency bands before the power amps (which is what bi-amping meant before Marketing invented a new definition of it), then your argument is valid. When I have bi-amped, that is what I have done.

I have an explanatory thread on bi-amping showing the signals but cannot find it here. It was probably 10+ years ago on another forum. I have the original document at home and may see if I can refresh and post it here. In my spare (hah!) time.

Edit: Found my old article, but it is indeed from 2011 and I need to do some revisions before posting in public again... And I am not using the simulator I used back then so I need to redraw schematics and such. This is a busy week, maybe this weekend...