Why passive bi amplifying exists???

[TLS Guy]

Yeah when I wrote some older "upscale Onkyos" I was referring to their flagships and Integra line.

According to one of the world experts on bi-amping (the legit variety) the main benefit to the use of an active crossover over passive is they effectively provide full amp power with no waste. In a normal single amp scenario the loudspeaker's passive crossover elements are never 100% efficient so they gobble up, let's say, 5% of the incoming amplifier power and wastefully turn it into heat instead of music signal to send to the drivers. But in active biamping instead an amp goes straight to the voicecoil (because there is no speaker crossover) so nearly all of the power amp's signal gets there intact (assuming the speaker cable being used is adequately thick). Still these gains are rather modest. He said he measured it as being around 1dB in real world use or at the very best 2dB, tops. Far better is to simply get a fundamentally doubly powerful single amp and wire it conventionally with one wire, which achieves a solid 3dB greater maximum potential output. [And it may cost less than buying those two lesser power amps.}

The loss of power in a passive crossover is much higher than you think and generally 3db per order. So in most passive speakers at least half the amp power is wasted and usually more. In addition in many commercial speakers the components are undersized, with too narrow a gauge of wire in the inductors. This results in the wire heating and dynamic compression, which also changes the crossover point to an extent depending on the power demands. The lower a crossover point, the larger this problem becomes. It is much less of a problem the higher the crossover point, due to lower power demands as frequency rises.

So, my practice is to use active crossovers in the lower crossover points in my reference systems. I have trouble justifying an amp to drive a tweeter. In my passive designs I use far more expensive and larger inductors than would normally be found in commercial speakers.

 

[Kingnoob]

There is no benefit to passive bi-amping unless the speaker has a crossover around 400 to 500 Hz. However even then one amp of twice the power would do just as well or better.

go figure it’s probably very few models Then.
Yeah yet tons of models include the ability I’m sure 99% are passiveeven my old klipsch icon kf26. And lots of avrs including both ones I have this is one manual. Claiming it increases performance. So these companies all feed into the myth keeping it going . Companies make ultra high end cables special for doing this also and regular usage.

I have them hooked up the normal way. Using Dayton 14awg cables seem discontinued now. I considered getting 12awg but never did , not sure I’d notice anything different?

I’m sure it would be pointless to bother with a majority of speakers. But lots of people probably do it because they have extra cables lying around and amp channels unused. I’ve tried it before and couldn’t notice a difference.

 

[m. zillch]

source: Duckduckgo AI search assitant

 

[Kingnoob]

View attachment 76789
source: Duckduckgo AI search assitant

So could you lose more power bi amplifying then gained? Have you tried it at all ? It’s always tempting costing nothing just extra wire and unused avr channels.

 

[m. zillch]

So could you lose more power bi amplifying then gained? Have you tried it at all ? It’s always tempting costing nothing just extra wire and unused avr channels.

The vast majority of AVRs lose power per channel the more channels you activate/drive (some brands more so than others but almost always by considerable amounts) so to answer your question: YES, you'll likely lose power!
Here for example is the Audioholics review breakdown of a somewhat recent Yamaha showing how its power per channel plummets as you increase the # of CH driven:

 

[highfigh]

So could you lose more power bi amplifying then gained? Have you tried it at all ? It’s always tempting costing nothing just extra wire and unused avr channels.

Using more discreet channels can't lose power.

How would you set the channel levels? The crossover already addresses driver sensitivity, if you adjust the levels of each channel and raise/lower one of them, the frequency response will no longer be teh same as before.

If you don't need the added power and don't use the system near the upper end of the amplifier's power, there's really no benefit. Sure, it adds a bit of headroom, but that's about all.

 

[dlaloum]

Using more discreet channels can't lose power.

That depends, if we are talking about an AVR or multi-channel amp, then power supply voltage and current capabilities are a constraint... if one channel uses up the available current from the shared PSU, then the other channel(s) will be constrained (lose power) due to insufficient "power" from the PSU.

Monoblocks of course, don't suffer from this, and the issue often gets worse as you increase the number of channels within a component - which is why it is most obvious on high channel count AVR's.

Often the benefits of biamping relate to bypassing the limitations of the power supply in one amp, by using a seperate amp with its own power supply...

 

[highfigh]

That depends, if we are talking about an AVR or multi-channel amp, then power supply voltage and current capabilities are a constraint... if one channel uses up the available current from the shared PSU, then the other channel(s) will be constrained (lose power) due to insufficient "power" from the PSU.

Monoblocks of course, don't suffer from this, and the issue often gets worse as you increase the number of channels within a component - which is why it is most obvious on high channel count AVR's.

Often the benefits of biamping relate to bypassing the limitations of the power supply in one amp, by using a seperate amp with its own power supply...

If a power supply can't handle all/more channels driven, it should be excluded in any list of 'good choices'. The manufacturers were required to provide specs with ALL channels driven, but that was before surround became popular and the ~1973 FTC rules ended.

Passive bi-amping came along because reviewers decided that it was a good thing and the manufacturers didn't want to lose market share. I don't remember seeing it before about 1982/1983.

 

[m. zillch]

There's a common misconception that passive bi-amping improves maximum possible output by "3 dB", in the same sense that doubling the power of an amplifier from, say, 50w/ch to 100w/ch does. This notion however is false even when using separate monoblocks (where there is no longer a concern regarding the extra strain placed on a single power supply like with typical AVRs' form of passive bi-amping) if one applies the typical FTC rules where the amp must provide the claimed amount of power for any selected frequency one chooses over its stated bandwidth (typically "20-20kHz").

[In the past this test was run I believe with a continuous sine sweep which slowly excites each frequency on its own, albeit briefly, with a test tone slowly escalating in frequency. In modern times AP analyzers instead use dozens? (hundreds?/thousands?) of spot frequencies tested sequentially to effectively accomplish the same thing.]

I demonstrated this with data in the AVS forum. What I proved is that when using a fixed test tone frequency I selected of 200Hz, into a speaker presenting a 4-ohm load with 0 degrees phase angle at that frequency, there is no change in the maximum possible output of it simply by disconnecting the HF input section of the speaker, i.e. removing the gold jumper bars on the speaker's terminals (the change the amp experiences when switching from normal single amp wiring scenario to passive bi-amping just the speaker's LF input alone).

I show that according to Gene's measurements of a particular Denon amp channel (driving 4-ohms) the maximum output at this frequency into this particular speaker's load of 4-ohm with 0-degrees phase angle, under FTC's rules, is 267 watts when using either one amp or passive bi-amping by buying two of them. [Don't let the fact that the data comes from a multichannel amp, an AVR, fool you. Pretend for the moment that to accomplish your passive bi-amping mode you buy a second one.]

To determine the maximum output of an amp at a given frequency used in isolation, you need to know three things:

- what amp is being tested,
- what incoming frequency is being tested, and
- what is the load the amp "feels" at that frequency (shown w/ curves of a particular KEF under the two scenarios)

It's pretty simple: If these three things stay constant then your maximum possible output can't change!

It felt like pulling teeth but I finally got DonH50 (is he here in this forum too?), an EE, to admit I was right on this point regarding what happens at this frequency, comparing the two scenarios:

"At any single frequency the power delivered should not change."

So I don't know about you guys, but when I'm considering upgrading the power of my system one of the frequencies I am looking to increase is indeed 200Hz (ha ha) and passive bi-amping in my stated example using real world data does not improve the maximum possible output of that isolated frequency (using FTC guidelines) whatsoever!

 

[dlaloum]

If a power supply can't handle all/more channels driven, it should be excluded in any list of 'good choices'. The manufacturers were required to provide specs with ALL channels driven, but that was before surround became popular and the ~1973 FTC rules ended.

Passive bi-amping came along because reviewers decided that it was a good thing and the manufacturers didn't want to lose market share. I don't remember seeing it before about 1982/1983.

Sure - but a power supply rated for 8ohm all channels driven, may well run out of puff driving 2ohm all channels driven.

I would like to see amps rated at 8 /4 / 2 ohm (with 1 ohm being optional)...

And there are valid reasons for saying that "all channels driven" may not be representative of actual use...

After all, in 99% of HT situations the load on channels other than L / C / R is lower than the load on LCR - so a more economical power supply could be fitted on the assumption that power requirements would be lower on the rest of the channels.... (or an asymetric design, with lower power amplifiers mixed with higher power ones, like Anthem do in some of their AVR's)

But yes it would be very desirable to get proper specifications from the manufacturers.