Bi Amp for power?

[Mmo]

so, i've read all the excellent research re bi amp. appears a moderate increase in fidelity is possible given the amp's one channel having to produce sound within a narrower Hz range. or something like that. but, why doesn't it offer a near doubling of available wattage? in a 5.1 system powering only 2 big speakers, only 2 channels are providing amplification whilst the remaining 3 laze about. by recruiting 2 of those channels for each speaker, shouldn't this allow the amp to give out near twice the power?

i had the shop that installed custom cross overs on my speakers also double up the connectors to allow this very thing. technician also said a minor increase in fidelity, but not an increase of power. doesn't work that way he said, and is most knowledgeable.

in my marantz, which is a silly 9.2, i've bi wired the 2 big front speakers and singly the centre and satellites. so that's 7 channels working (the remaining 2 channels are for a different zone, not to be powered at the same time as the 7.1, which is fine).

thoughts? rude comments?

 

[j_garcia]

Biamping from a receiver is a waste of time. To get the actual benefits of that "narrower band" you have to perform the x-over BEFORE the amplification, otherwise the amp is still doing all the same work and the speaker is filtering it out.

 

[Mmo]

still don't see why recruiting the other 2 channels doesn't equal more power going to the speaker. they weren't putting out before?

i've got an emotiva XP-5 gen 2 on the way. wonder how i should configure the speakers with it and the marantz....

 

[Swerd]

We often get questions about bi-amping from people who have a new multi channel AV receiver but who don't use all the speaker channels in their system. They ask if they should convert those unused channels to bi-amp their front speakers. Apparently, AV receiver makers have built-in the ability to redirect the signal for the front left & right speakers into two unused surround channels, and they prominently tout that as an advantageous feature.

Bi-amping an AV receiver in such a manner is of no value at all. Why?

The limiting factor of any amplifier is the capability of its power supply transformer. In a sense, the power supply transformer acts like a car's engine, and the power output transistors act more like a car's transmission. If you want more power, you need a bigger power supply transformer. There is no way around this fact. With an AV receiver, you have one power supply transformer with its power divided among the various output channels. If you have 5 speakers and a 7 channel AV receiver, and convert 2 unused audio channels into a bi-amped 5 channel system, you haven't added any ability to deliver power. Only by adding external amps, with their additional power supply transformers can you deliver more power to speakers.

It's a real disservice that AV receiver makers tout the benefits of bi-amping in their manuals. It is wrong and causes a lot of confusion.

 

[j_garcia]

still don't see why recruiting the other 2 channels doesn't equal more power going to the speaker. they weren't putting out before?

As Swerd notes, one reason is because all channels are served by one power supply. The second reason is what I already said - if you don't filter before the signal is amplified, the amp is amplifying signal you are getting rid of at the speaker.

i've got an emotiva XP-5 gen 2 on the way. wonder how i should configure the speakers with it and the marantz....[/QUOTE]

You simply use the amp for power and not the receiver.

 

[PENG]

Biamping from a receiver is a waste of time. To get the actual benefits of that "narrower band" you have to perform the x-over BEFORE the amplification, otherwise the amp is still doing all the same work and the speaker is filtering it out.

John, I agree with yo on the "waste of time" part but I wouldn't say the amp would be doing the same work. As you mentioned, "he speaker is filtering it out" so for the tweeter (for simplicity let's assume two way speaker), that means the amp that drives it would be delivering much lower current. You can find out by taking some measurements yourself.

 

[j_garcia]

That's correct, but the end result is that you simply have two amp channels delivering the same thing that would have otherwise been delivered on one channel in an AVR biamp setup. There would be somewhat less load, but the result won't be delivery of the types of power gains people are thinking they're getting.

 

[TLS Guy]

still don't see why recruiting the other 2 channels doesn't equal more power going to the speaker. they weren't putting out before?

i've got an emotiva XP-5 gen 2 on the way. wonder how i should configure the speakers with it and the marantz....

The real reason is that the power divide is 400 Hz, acoustically. When you add baffle step compensation, the power divide to the speaker is lower than that. In a two way speaker system, the HF amp only drives the tweeter, which consumes a watt or two at the most.

So to get any benefit, the speaker crossover would have to be 400 Hz or less. Even in three way speakers, for some perverse reason the upper set of terminals only connect to the tweeter, and not the mid and tweeter.

As stated previously to really benefit from bi-amping, you need an active crossover and the cross from woofer to mid needs to be 400 Hz or lower.

 

[Mmo]

well put TLS guy. with the other amp channel on the tweeter, the first amp channel is still doing 99% of the heavy lifting. with an active cross over at 400 Hz or less, then the division of labour would be more equally split between the 2 amp channels.
the conversations with my speaker guru implied the upper set of terminals powered the mid and tweeter, with the lower set the woofer. i may be hearing what i believed, or perhaps he wired it so. wonder if that set up is possible? i'll have to ask him.
thanks for the expert advice.

 

[Mmo]

We often get questions about bi-amping from people who have a new multi channel AV receiver but who don't use all the speaker channels in their system. They ask if they should convert those unused channels to bi-amp their front speakers. Apparently, AV receiver makers have built-in the ability to redirect the signal for the front left & right speakers into two unused surround channels, and they prominently tout that as an advantageous feature.

Bi-amping an AV receiver in such a manner is of no value at all. Why?

The limiting factor of any amplifier is the capability of its power supply transformer. In a sense, the power supply transformer acts like a car's engine, and the power output transistors act more like a car's transmission. If you want more power, you need a bigger power supply transformer. There is no way around this fact. With an AV receiver, you have one power supply transformer with its power divided among the various output channels. If you have 5 speakers and a 7 channel AV receiver, and convert 2 unused audio channels into a bi-amped 5 channel system, you haven't added any ability to deliver power. Only by adding external amps, with their additional power supply transformers can you deliver more power to speakers.

It's a real disservice that AV receiver makers tout the benefits of bi-amping in their manuals. It is wrong and causes a lot of confusion.

well put, thanks. i was under the impression the power supply was divided such in a 5 channel amp that, say a 500 watt receiver or amplifier with 5 channels would have 100W available per channel, not shareable. so your words of wisdom dictate the same amp used for a 2 speaker 2 channel only would have the 500 watts available divided between the 2 speakers. minus the second law of thermodynamics and a few other math computations doubtless

i thought this the main reason 5 channel receivers never match 2 channel ones of equal wattage, when powering the same 2 speakers. bigger reason is likely the honest watts available in a 2 channel amp, i suppose.

thanks again
Mmo

 

[j_garcia]

If you had an AVR and a stereo receiver that had the same amps and power supplies, you'd effectively get about the same power out of them in 2ch. Separate power supplies for individual channels is extremely rare because you'd just go with monoblocks at that point.

 

[Swerd]

well put, thanks. i was under the impression the power supply was divided such in a 5 channel amp that, say a 500 watt receiver or amplifier with 5 channels would have 100W available per channel, not shareable. so your words of wisdom dictate the same amp used for a 2 speaker 2 channel only would have the 500 watts available divided between the 2 speakers. minus the second law of thermodynamics and a few other math computations doubtless

i thought this the main reason 5 channel receivers never match 2 channel ones of equal wattage, when powering the same 2 speakers. bigger reason is likely the honest watts available in a 2 channel amp, i suppose.

You're welcome.

It is important to understand that the Federal Trade Commission (FTC) regulates how AV receiver makers must state their amplifier power specifications. Look at what one manufacturer says in the owner’s manual for one of its AV receivers:

Front Left & Right
145 W + 145 W (8 ohms, 20 Hz–20 kHz, 0.05%, 2 channels driven, FTC)

Center
145 W (8 ohms, 20 Hz–20 kHz, 0.05%, 2 channels driven, FTC)

Surround Left & Right
145 W + 145 W (8 ohms, 20 Hz–20 kHz, 0.05%, 2 channels driven, FTC)

Surround Back Left & Right
145 W + 145 W (8 ohms, 20 Hz–20 kHz, 0.05%, 2 channels driven, FTC)

Front High/Wide
145 W + 145 W (8 ohms, 20 Hz–20 kHz, 0.05%, 2 channels driven, FTC)

Note that these power ratings apply only when 2 channels are driven. What power is available when all channels are driven is not stated, nor is it required by the FTC. This receiver may still be powerful enough when all channels are driven, but it certainly will not be as high as 145 watts per channel.

So to return to the bi-amp question, when you drive 2 speakers with 4 amplifier channels instead of 2, how much power is available to the speakers? Short of doing your own measurements (if you had the right instruments), you won't know.

 

[Mmo]

thanks fellas, all good info.

So to return to the bi-amp question, when you drive 2 speakers with 4 amplifier channels instead of 2, how much power is available to the speakers? Short of doing your own measurements (if you had the right instruments), you won't know.
and following the logic as previously ordained, the power available would be approximately equal with 2 or 4 channels, as all comes from the same power source, ya?

here's another decision i shall soon be making, as i've your attention:
to avoid hum from different grounds, i run everything into my panamax power conditioner, then onto ONE AC outlet. i've decided to run a dedicated 20 amp line from the main breaker box, as i've the wire, room for more breakers, and my basement ceiling is still open to allow the wire to be run to the main floor. 1200 VA amplifier, 1000 for the receiver (most of the load taken by the amp), 500 for the sub, plus another sub, plus all the other equipment and TV. i got this crazy idea to bridge the wire between 2 20 amp CB's and make it a 230V system: very easy to do. my electrician friend will provide adult supervision. my power conditioner, amps and sub support this.
crazy like a fox? volts are potential energy... this have potential?

20 amps x 115 volts = 2300 watts, which puts the power supply in the danger zone, potentially. i ran a dedicated 20 amp line for my microwave (now code), and it popped the breaker once when operating at same time as toaster oven plugged into same outlet.

do the europeans have an advantage with their double voltage system?

cheers,
Mmo.

 

[KEW]

Generally the same amp when run in Europe will produce more power (not double but, if memory serves, maybe 10-15% more).

Your idea definitely has theoretical merit, but I would wait for others to chime in to make sure there are no concerns putting the idea in practice.

 

[Mmo]

thanks kew. it's as much for the hobby end as for the fidelity at this point! as i'm running the wire anyway....
as volts are potential energy, and I'm running it through my power conditioner that handles 220, 230 volts. i wouldn't attach my SACD player without more insight.

 

[AcuDefTechGuy]

the conversations with my speaker guru implied the upper set of terminals powered the mid and tweeter, with the lower set the woofer... wonder if that set up is possible?

It's possible to ACTIVELY bi-amp the woofers only if the speaker is designed that way, like the RBH SX-6300, SX-8300, SX-T2, T30, and the XTZ Divine tower. In this case, one amp powers just the tweeter and midrange and one amp actively powers just the woofers.

But most towers are designed to be 100% passive, so unless you completely REMOVE the internal crossover, you CANNOT actively bi-amp the woofers; you can only passively bi-amp the woofers, which as everyone says is a total waste of time.

 

[Mmo]

the towers are passive, with custom crossovers. but right you are, bi amping from the amp is clearly pointless.
appreciate all the wisdom.
Mmo

 

[RichB]

Passive crossovers do not remove all the benefit. The crossovers for the mid/tweeter still filter out bass but the power consumption goes down because there are not drivers using it.
The amp driving the upper section will use less power and may not clip when the bass amp may.

The bass section will use power liberally but if that amp clips there crossovers will filter out the objectionable frequencies.
So, there can be a benefit.

The primary reason not to pursue this solution is that there is no guarantee of an even split and your paying a lot for amp channels.
You might as well get a mega-amp and be done with it.

I use a Parasound A21 for the mains and an A31 for the center/surrounds.
A second A21 could be used bi-amp'ed mono-blocks because those amps would look great in the 3-bottom bays of my credenza.

I realize that Emotiva XPR-1`'s have more power and are more cost effective, but the A21s aesthetics are acceptable (WAF, you know).

- Rich

 

[Mmo]

rich
so this benefit applies to bi amping the 5 channel amp? all the same single power source, just 2 channels per speaker. the power consumption would decrease compared to not biamping?! cross overs work more efficiently to their frequency range with bi amping?
thanks

 

[RichB]

rich
so this benefit applies to bi amping the 5 channel amp? all the same single power source, just 2 channels per speaker. the power consumption would decrease compared to not biamping?! cross overs work more efficiently to their frequency range with bi amping?
thanks

That depends on the amp. If it has independent power supplies that should apply.

Here is an Audioholics article on the subject:

http://www.audioholics.com/frequent-questions/the-difference-between-biamping-vs-biwiring

Here are some threads with respected members holding both positions:

http://forums.audioholics.com/forums/threads/should-i-bi-amp.56379/

http://forums.audioholics.com/forums/threads/bi-wiring-from-amplifier-to-loudspeaker.30527/

- Rich