Bi-amping question for Gene

[slipperybidness]

I don't know of any modern power amplifiers that flip phase from input to output. But I suppose anything is possible, especially in high end audio

Dunno about consumer designs, but I can tell you that many of the chip amps (TI) that I have been reading up on suggest that there could be advantages to using the inverted topology. The datasheet for the LM4780 had some language to the gist of "inverted amp could have better THD performance in certain situations", though I don't think it ever defined what those situations might be.

 

[TLS Guy]

Sorry if I've upset you.

What I've been told by Hydrogen Audio is that if the passive crossovers were 100% efficient, I would gain several watts in the bass amp, because the mids/highs, assuming a typical 3-5 kHz crossover would account for a 10-15% of the total power at most.

So that power I would gain, but it would be negligible, less than 0.8 dB. BUT, they say that because the crossovers are not 100% efficient I won't even gain the 10-15%.

They tell me that I'll gain nothing. Is that correct? I came here because I wanted to ask for unbiased advice - the people at Hydrogen are trying to beat me over the head that it won't make any difference in any conditions.

Look Rich, its time to drop this.

You require 2 db gain to notice anything discernible. You wont get it.

Now say you had the most optimistic passive bi-amp situation possible. That would be a speaker where the woofer crossed at 400 Hz to a mid and HF section.

You might at first think you would get 3db gain, but you would not because of the power requirement of baffle step compensation. This requires three time more power below 400 Hz so you won't get close to telling the difference, because the gain in output is too small to detect.

That is the bottom line and summarizes the answers you have been given. It is the correct answer to your question and is not debatable, except by someone incapable of understanding. There are various epithets to describe such and individual.

 

[TLS Guy]

I don't know of any modern power amplifiers that flip phase from input to output. But I suppose anything is possible, especially in high end audio

I haven't tested a lot of recent amps, but a lot of older amps are and I would be surprised if there are not some in the mix, although I suppose AV makes phase inverting amps problematic if you don't know it is. Older Quad amps and the vintage Crowns I know are phase inverting.

If you want to press a nice older amp into service in HT, then you definitely need to know if it is phase inverting or not.

 

[markw]

Look Rich, its time to drop this.

You require 2 db gain to notice anything discernible. You wont get it.

Now say you had the most optimistic passive bi-amp situation possible. That would be a speaker where the woofer crossed at 400 Hz to a mid and HF section.

You might at first think you would get 3db gain, but you would not because of the power requirement of baffle step compensation. This requires three time more power below 400 Hz so you won't get close to telling the difference, because the gain in output is too small to detect.

That is the bottom line and summarizes the answers you have been given. It is the correct answer to your question and is not debatable, except by someone incapable of understanding. There are various epithets to describe such and individual.

Strangely enough, they are still playing his games at that link I posted earlier. Apparently, they have a much more lax attitude towards mental masturbation.

 

[TLS Guy]

Strangely enough, they are still playing his games at that link I posted earlier. Apparently, they have a much more lax attitude towards mental masturbation.

Good for them! He has used up his quarter with me.

 

[PENG]

I think purists may have to consider the added electronics inherent with active crossovers that will invariably include more amps that have to handle full range signals anyway (albeit low level signals only) so in the end it may not be for them either. In the end it may actually be better to just focus on better passive crossovers and stick with passive bi-amp or simply more powerful amp, but again probably only purists need to worry about the pros and cons either way.

 

[Big Jake]

1). Is how much power you have in reserve before the clip point on the loudest musical peaks.

2). There is insignificant increase in power, because the HF amp is for most speakers only supplying power above 2.5 KHz or so, where there is minimal demand for power.

The acoustic power split is around 400 Hz. However below 400 Hz is in the region of the transition from half space to full space radiator, for monopole speakers. The precise point is dependent on the width of the cabinet. This is called baffle step compensation. Below that transition power has to be increase 6db. Every 3db requires a doubling of the amp power. So you can see that the power demands below 400 Hz have to be doubled twice for the same acoustic output above 400 Hz or so.

The bottom line is that passive biamping with two 150 watt amps is no way equivalent to powering with one 300 watt amp. The 300 watt amp will gain you 3 db the biamp arrangement will barely register and not be audible.

Biamping is to achieve what can not be done with passive crossovers, and the benefits increase the lower the crossover and offer marked improvement below 500 Hz crossover points.

Bottom line, is that passive biamping will never get you a 3db gain doubling the power available, but doubling the power of single amp will.

That's all some excellent info, TLS, thanks.

Which then does beg the question, why do they push biamping? Why do you get these people in reviews stating that they bought this pair of speakers or that, and that they didn't really "WAKE UP" until they biamped them? Would it be that the cross overs in them are so crappy? I'm thinking this could be the case. But from what I've gathered from your info, biamping could be not much more than a marketing ploy.

So, the only negligible benefit would be possibly a better stereo image from your speakers, not more output.

I came here to chat and learn, and that I am.

 

[PENG]

That's all some excellent info, TLS, thanks.

Which then does beg the question, why do they push biamping?

They don't just push biamping, they push cables too right? One reason is that marketing know it is easier to get people focus on electronics and get satisfaction from Placebo effect because it generally takes less money and time to experiment different amps, dacs etc. It is more difficult to get people to spend much more money and time on their speakers, placements and room acoustics to get real sound quality improvements. I am of course simplifying things here and in reality it is a more complicated matter.

 

[Big Jake]

They don't just push biamping, they push cables too right? One reason is that marketing know it is easier to get people focus on electronics and get satisfaction from Placebo effect because it generally takes less money and time to experiment different amps, dacs etc. It is more difficult to get people to spend much more money and time on their speakers, placements and room acoustics to get real sound quality improvements. I am of course simplifying things here and in reality it is a more complicated matter.

Now I feel a little foolish for building that pair of double 8 gauge speaker cables.

It also makes me stop and think about the purpose of some triamped speakers I've seen, unless the intent is to eliminate entirely the need for a crossover, to circumvent it's inefficiencies.

 

[Swerd]

Which then does beg the question, why do they push biamping? … Would it be that the cross overs in them are so crappy?

If a poorly designed crossover in a speaker is the reason for poor quality sound, the solution would be a different and better crossover design, not a more powerful amp or biamping.

Biamping does not per se eliminate crossovers. Active biamping, bypasses a speaker's passive internal crossover, but substitutes an active external crossover upstream from the amps. Wherever the crossover is located, it still has to be properly designed for speakers to sound good.

TLS Guy referred to power demands below about 400 Hz being a problem because baffle step compensation demands extra power for frequencies with longer wavelength than the width of the speakers cabinet. In addition, passive crossovers in that frequency range (as might be found in 3-way speakers) become expensive because large inductor coils and capacitors are required.

Large inductor coils, in particular, are also a problem because their long lengths of copper wire windings introduce significant resistance, leading to signal loss (also known as insertion loss). In that frequency range and below, there is a clear advantage to active crossovers, such as found in the bass management section of nearly all AVRs.