More Bi-amping queries

stainless-steel

Active Member
I noted in an earlier bi-amping thread a question asking whether this implied using one amp or two per speaker, now, rather naively on my part I suggested two amps per speaker. :suicide:

In my mind bi-amping has always meant using two amps per channel i.e. L channel from amp 1 driving the bass drivers on the L speaker, L channel from amp 2 driving the HF drivers on the L channel, with the righthand side being a mirror.

My rationale being that when using passive crossovers each amp is recieving and amplifying a full range signal. And with stereo music being asymmetric you would rarely be asking the power supplies of both amps to deliver the same ammount of power in the lower frequency regions.

Picture this simplistic example; a stereo recording of a rock band with the bass drum miked in mono and the bass guitar player off to one side, lets say the left.
With the bi-amping arangement I've described above you have the LH channel demanding rather more power from the bass drivers due to the fact that they're being asked to amplify more low frequencies than the RH channel in addition to the lower efficiency of the bass drivers. This demand is shared by the power supply of two seperate amps.

With one amp per channel you're demanding the same ammount of power but solely from one power supply.

This arrangement is one of the reasons I thought that dual mono power amps were highly thought of, you've got an entirely independent power supply for each channel.

Is there any truth in this? Looking forward to your thoughts...
 

Member 96948

Distinguished Member
I noted in an earlier bi-amping thread a question asking whether this implied using one amp or two per speaker, now, rather naively on my part I suggested two amps per speaker. :suicide:
Not naive at all. Bi-amping (leaving active configurations alone for the moment) means using a discrete amplifier for each drive unit in a two way loudspeaker. So, where you have a two way stereo pair of speakers, this can be accomplished with four monoblocks, two stereo power-amps, or using a spare pair of rear channels on a receiver in addition to the front channels; it is still bi-amping in each respect.

In my mind bi-amping has always meant using two amps per channel i.e. L channel from amp 1 driving the bass drivers on the L speaker, L channel from amp 2 driving the HF drivers on the L channel, with the righthand side being a mirror.
That's the way most would see it, although using the two channels of the same amp to drive each driver would still be bi-amping, as long as its a two way speaker.

My rationale being that when using passive crossovers each amp is recieving and amplifying a full range signal. And with stereo music being asymmetric you would rarely be asking the power supplies of both amps to deliver the same ammount of power in the lower frequency regions.
Where passive crossovers are used, all amplifier channels are receiving and amplifying a full range signal for all of the drive units. Where the demand differs is that the amplifiers supplying the high frequency drivers will suffer a much lower current demand, plus a less reactive load to control. This is a good reason for using one stereo amp for the HF and another for the LF. The HF stereo amp, as a result of it's reduced demands, will have a much easier ride and thus maintain it's composure at high volumes, leading to a less fatiguing sound, even if the mid/bass stereo amplifier is having a harder time.

If you split the a single stereo amp between the HF & LF drivers of one speaker, then the demands placed on the shared power supply could influence the HF performance thus, it's not normally done this way. On the other hand, you could gain a theoretical improvement in separating the channels from each other using the one stereo amp for each channel, which would probably show up in sound stage width and depth. I suppose only listening to the system in question at the levels normally used would indicate exactly which configuration would be preferable.

Picture this simplistic example; a stereo recording of a rock band with the bass drum miked in mono and the bass guitar player off to one side, lets say the left.
With the bi-amping arangement I've described above you have the LH channel demanding rather more power from the bass drivers due to the fact that they're being asked to amplify more low frequencies than the RH channel in addition to the lower efficiency of the bass drivers. This demand is shared by the power supply of two seperate amps.

With one amp per channel you're demanding the same ammount of power but solely from one power supply.

This arrangement is one of the reasons I thought that dual mono power amps were highly thought of, you've got an entirely independent power supply for each channel.

Is there any truth in this? Looking forward to your thoughts...
Music is asymmetrical, but it seems to me that the benefits of bi-amping are mostly as a result of separating the HF driver from the low frequency, high current, high excursion, distortion inducing demands of controlling a bass driver. As such, the quality of power supply is a fundamental limiting factor, but there is no reason why a well designed stereo amp cant deliver in this respect. After all, some go as far as having separate windings on the same transformer for each channel and where would you stop in the quest for separation? After all, two monoblocks are plugged into the same ring main on your wall.....

Simply having four channels of amplification for a stereo pair does not guarantee superior performance over a pair of monoblocks, or even a stereo poweramp. It's quite possible for a good stereo amp to outperform four monoblocks driving the same speakers as there's a bit more to driving a pair of speakers well than simply playing the numbers game, be that multiples of amplifiers or Watts.

The really BIG jump in performance really comes when you remove the passive crossover between the drivers and amplifiers, to a position before the drivers thus allowing each amplifier to really control a driver with a bandwidth limited signal, without the heavy 'gloves' of inductors and capcitors in the way. This is true active bi-amplification (if we're still only considering a two way speaker) and done right, it will make you wonder why you suffered all the extra boxes in your equipment rack for all of this time. Some will get twitchy at not having separate poweramps to upgrade, but in a true active system each amp will have been designed to suit it's particular driver and it results in a dynamic (macro and micro) quality that a passive system will struggle to get near for anything like the price.

IMHO, of course.:)

Russell
 
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stainless-steel

Active Member
Thanks Russell,

Nice to be presented with someone's point of view rather than confronted with it:)

One of these days I'm going to have to look more seriously at active speakers, I nearly bought a pair of ATC SCM20-2 last year. But you're right, the appeal of chest high floorstanders and a big stack of macho class A power amps is hard to resist - even though the head says it might not be the best solution.

Cheers,

Stainless.
 

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