bi-amping

Discussion in 'AV Receivers' started by Ben Jamin, May 7, 2004.

  1. Ben Jamin

    Ben Jamin Auditioning

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    I have a yamaha rxv3300, onkyo m-504 stereo power amp, and def tech bp2000tl main speakers. Right now the onkyo powers the def techs. Would it be a good idea to use the main channels of the yamaha, and the onkyo to separately power the mids and highs?
    3300 130WPC
    m-504 165WPC

    thanks
     
  2. Paul Clarke

    Paul Clarke Supporting Actor

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    I am a fan of bi-amping and bi-wiring where applicable but in your case I would leave things as they are.

    You do not specify whether you are running a complete surround system or only stereo but either way bi-amping as you are contemplating will likely only add cost to your system and yield questionable (read difficult to measure) results.

    Before engaging in this setup I would do a simple switch out for your Mains of the Onkyo to the Yammy to test for changes in sonic characteristics.

    Good luck.
     
  3. Chu Gai

    Chu Gai Lead Actor

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    The effectiveness or benefit of your approach is really going to depend on a number of factors Ben. For example...

    1) The size of the room and where you sit in relation to your speakers.
    2) The SPL's that you typically listen to which should take into account the short term peaks that require your amp to deliver additional power briefly.
    3) Where the crossovers for your speakers lie.

    Let's consider a few things in general though regarding your setup, the nature of music, and power distribution within a speaker.

    You've got fairly efficient speakers (92 dB) and if you sit one meter away from one speaker and pump a single watt into them your SPL will be 92 dB. That's loud. Now you've got multiple speakers so that single solitary watt is going to result in even greater SPL's as you drive additional speakers. The only point I'm making here is that with additional speakers being played, the sound gets louder and an average SPL level of 92 dB is damned loud to the point where sustaining it for long periods of time will cause irreversible damage to your hearing.

    Music contains a variety of frequencies. For argument's sake, let's say 20Hz to 20kHz. However, the spectral distribution of musical information is not distributed evenly among those frequencies. There is substantially more information at the lower frequencies and consequently more power is needed down there to reproduce those frequencies. I generalize the amount of musical information as being very roughly proportional to the reciprocal of frequency or 1/f. More complete studies were performed by H. Mayr, "Signal Power Spectrum Aspects in Loudspeaker Design," J. Audio Eng. Soc., vol 32, no.9 1984, Sept. To summarize from the paper, at a 3000 kHz crossover, approximately 99% of the power goes to the woofer while only 1% goes to the tweeter. This proportioning or weighting is based upon a large number of studies that examined the medium and long term average spectral distribution of music. As an example, the spectral distribution is attenuated about 12 dB per octave above 250 Hz. While one can always find short term situations that run contrary to this (maybe you like listening to music that only has triangles), it appears to be a rough and valid statement.

    The point of this Ben, is that the tweeter handles only a very small fraction of the total power that you pump into a system. If you've got a 3 way system that's crossed over at say 500 & 5000Hz, then the woofer handles around 3/4 of the power, the midrange close to a 1/4, and the tweeter only does a couple of percent.

    Now if you're thinking that combining the two amp portions gives you an effective 295 watt system, you're mistaken. If your tweeter crossovers are anywhere near the values I tossed out above, you'd only be using a few watts of the 135 that you're providing. IOW, while providing a benefit, it's an enormously dubious and speculative audible benefit.

    If you're running multichannel as in an HT situation, then given that the vast majority of receivers have problems with sustained high power output with all channels driven, I'd use the Onkyo to drive my front speakers and let the Yamaha take over the amplification chores for the remaining speakers. In lieu of that, you could always investigate a far more powerful amplifier for the fronts but again I have serious doubts, given the efficiency of your mains that you'd realize a tangible benefit commensurate with the money you'd have to spend.
     
  4. Marc H

    Marc H Second Unit

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    I think your current set up would sound better. Distributing the amperage of the Yamaha's power supply over more channels may decrease the clarity and dynamics that you have been used to in the effects channels.
    Adding another power amp with the Onkyo for bi-amping the DefTechs would be a better idea in terms of increasing the enjoyment.
     
  5. Ben Jamin

    Ben Jamin Auditioning

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    Thanks, everyone. Lots of good info here. I think I'll just leave things as they are.
     

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