Biamp using Receivers as Amps - AVS Forum
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post #1 of 8 Old 09-01-2012, 09:56 AM - Thread Starter
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This is a general approach question - Is it a "good" idea to use receivers that you have lying around to biamp.

To keep the conversation straight foward some simplifying assumptions.

using vertical bi-amping uses a single amp per speaker.
Working with analog stereo source
In this thread don't want to get into 5.1 inputs and either deficient recievers or enhanced receivers with uncommon capabilities.

In my case using Integra Dtr-6.4, Dtr-7.7, Dtr-7.8 so assume you have preouts available for main and zone2 and common inputs tape, dvd. I am driving zone 2 with my Hafler 240SE amp. I am interested in biamping the two fronts on my main with the two receivers.


So the config would be to use one of the Receivers as the source and then the other two receivers to biamp the main front.
Currently I simply use my Dtr 6-4 using it's preout to Hafler 240Se Amp driving zone 2.

Not so much interested in my situation but rather the utility in general of using receivers as amps. I would typically assume just use the preouts of the source receiver to the input of the biam receivers - this would keep the volume control at the source receiver.

The principle question is quality of amplification not (volume) control. Receivers generally don't have jumper available to bypass circuitry though some do, so would not be assuming that capability is available.
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post #2 of 8 Old 09-01-2012, 07:52 PM - Thread Starter
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and why biamp? especially when the common metric is double the power and you get 3db in loudness, which is barely discernable. There is another argument that says that metric is too simple, that it's not overall loudness but rather the ability to supply power at all frequencies with the low frequency is going to draw down power and actual power needed to reproduce all frequencies is as a result much greater. I am simply using 400 watts 2 channel at 8 ohm as guideline and trying to approach that with 200w each monoblock biamp. Recievers like integra fall short of that delivering 100-145 wpc
depending on the model integra dtr-6/7/8 but for the price maybe worth considering

Again, excluded from this thread are preamp strategies, and other biamp strategies that amp frequencies - the active/passive crossover and speaker crossover issues make that approach out of scope here in order to focus on one simple biamp question and approaches and benefits that apply to that.
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post #3 of 8 Old 09-01-2012, 08:42 PM - Thread Starter
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still wondering if this is the only benefit: (from 2/1/2004 thread)

Where bi-amping comes into play is the ability to both reduce clipping of amps with marginal current capacity, and to keep that premature clipping away from the tweeters which, as we know, are most susceptable to clipping damage. By premature, I'm referring to power-supply voltage sagging due to high current loads.
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post #4 of 8 Old 09-02-2012, 04:22 AM
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^^^

your "most common metric" is incorrect... passively bi-amping (what you are suggesting) does not "double the power" to the speaker...

your "theory" is starting from incorrect assumptions...

- chris

 

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post #5 of 8 Old 09-02-2012, 05:31 AM
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There are thousands of speaker designs out there so can only speak in generalities. I am no expert but this is why passive bi-amping is frowned upon (IMHO) ---

And hopefully if I stated any of this wrong, Chris will step back in as he is one of the resident gurus!!

A normal 2 way speaker demands very little power to feed the high frequency driver. Maybe only 5% of the total demand of the entire speaker. Maybe even less. A 3 way or 4 way speaker gets more complicated depending how the internals are wired but still it is separated into high and low range drivers. This of course is assuming the speaker has dual input connectors. So based upon that, you only add the 5% power increase by bi-amping which would not be noticable to most people. There are always exceptions depending upon the speaker being used, the amplifiers, the listening levels. Lots of people have tried this - myself included. I heard no benefit but others may. Try it for your self. It will be kind of messy to wire up the additional receivers being used as amps but it should work. This hobby is supposed to be fun so I say try it and let us know what results you get. You may get clobbered if you don't come back with testing data so be sure to state it is your opinion! ;-)
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post #6 of 8 Old 09-02-2012, 10:55 AM
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Some good info above.

In absolutes, there is a possible benefit to passive biamping.


However, you're overwhelmingly better off spending the time and effort pursuing this toward learning more about room acoustics and the loudspeaker room interface.


fwiw, a segment of an old post of mine discussing this topic;
Quote:
In the passive bi-amp situation, the load that each amp is presented with is reduced when compared to the total load on the amp in the single amp scenario. Load sharing. The inputs are paralleled, and that voltage is amplified, however it's where the current demands are different, that's where one could attain the small benefit.

The load on the HF amp; it possesses a high impedance at low frequencies, so it is easier to drive. As I understand it, the amp stages are boosting voltage, then the current is determined by the load at the terminals, and in this case the current demands are very low because it's amplifiying the upper portion, or the higher frequencies of the signal. Thus, not depleting the current reserves of the amp. High potentials can exist without current flow, it's the high current flow that saps everything from the output stages, the supply rails, and all the way back to the wall voltage during peak current demands. In this scenario, using a seperate amp for the high pass section, that huge current depletion doesn't occur.


Likewise, the amp supplying the low side of the crossover network, is presented with a high impedance above the pass band, so although the voltage amplification remains (parallel input), the current demands are reduced somewhat. Now obviously the dramatic lowering of current demands aren't the same in the LF amp as they are in the HF amp, but a reduction of the load is benefited by the amp, just a lesser degree.

Is it worth it, most likely not....Regardless, to state that there is no possible benefit associated with passive bi-amping, is in my opinion, incorrect.

Perhaps someone well versed in amplifier design can correct my in-accuracies, I'd like to now more about this as well.




The second benefit is the reduction of potential inter-modulation distortion, created in the LF section, and surfacing as distortion artifacts in the HF section. Very briefly, when transient drive voltage ceases at the LF driver, however the driver continues to move prior to settling, this generates a voltage. It is possible that this can contaminate the HF drive signal, if a low impedance path is present to ground (amp terminals), the corruption may be minimized.

Would I reccomend passive bi-amping? No, not if one has to buy gear to do it, it's hardly worth the trouble, even if you have the extra (identical) amps. Gain matching would be important.

There are many things of far greater importance, such as the speaker room interface, whereby one's attention should be focused for much more significant gains. That being said, I do welcome any input, or corrections.

Thank you

Good luck to you

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post #7 of 8 Old 09-02-2012, 11:13 AM - Thread Starter
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Right, the 2/1/2004 thread was by member: ABEX - benefit of biamp was to prevent clipped low frequency from making it two the tweeter. Chris as you say he also says power isn't doubled available current is.

I guess I was relying on the benefit of two amps to two speakers, affectionately also known as "fools bi-amping", as providing the benefit of what Michael Price states as "more headroom to bi-amp than to simply use an amplifier of twice the power rating... the sum of the wave amplitudes with momentary peaks can be double what it was before, that's in theory up to 3db more headroom than a double-power amp with 40% higher voltage rails"

Nonetheless, I accept PeterK assessment.

I might have more succinctly and less technically identified my objective to be something like - "these folks with 500 wpc Carver don't seem to be concerned about clipping so much, maybe I could increase my confidence that I have enough power by using some 25lb 100+wpc receiver gear I have laying around, what do you think?" After all these passive setups are built to bleed off and waste power so make sure you have enough power and used AVR receiver power is amazingly cheap.

However, there are some interesting possibilities in future - The Design of Active Crossovers, Taylor & Francis Aug 2012- The intro of this book says:
"The use of active crossovers is increasing. They are used by almost every sound reinforcement system, by almost every recording studio monitoring set-up, and to a small but growing extent in domestic hifi. There is a growing acceptance in the hifi industry that multi-amplification using active crossovers is the obvious next step (and possibly the last big one) to getting the best possible sound."

thanks for the input.
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post #8 of 8 Old 09-02-2012, 11:58 AM
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Hey sawyerthecat--
I probably should have worded my post better. You have obviously been doing your homework and have read-up on the topic. Sorry if I came across sounding like I was talking to a total newbie with audio.

I say your idea will work fine and is worth the time and effort to do as a science experiment! You may hear very noticable benefits.
Good luck.
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