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The high-end when bi-amping

Discussion in 'Amps and Cabs [BG]' started by matt.larson@excite.com, Jan 10, 2001.

  1. What kind of power do I need on the high end when bi-amping? I'm guessing it's significantly lower than the bottom end but maybe I'm wrong. Is there any rule of thumb that would apply here (I.E. "I'm using a 600 watt output from an amp from company X to drive my full range sound and that's sufficient. Therefore if I get two company X amps what should the rated output be for the bottom and the top end?). Thanks all,
  2. MikeyD


    Sep 9, 2000
    There are a lot of variables involved, so it is difficult to give a single, generic answer. Some of these are:

    * What is the crossover frequency?
    * What are the respective sensitivity ratings of the high and low cabinets?
    * What is the lowest note (frequency) you are likely to play?
    * What kind of sound do you want - a dull thumping or a bright slapping sound?
    * Do you tend to like huge amounts of fundamental frequency content?

    Without knowing any of these things, probably the average rig would sound good with a 3:1 power ratio between low and high. This means, for example, 300 watts for the lows and 100 for the highs. Of course, this would depend quite a bit on the above factors. The higher the crossover frequency, the less power the high cabinet would likely need. If your low cabinet is relegated to "subwoofer duty" via a 50 Hz. crossover, then your high cabinet will actually need quite a bit of power - perhaps 80%+ of the power that the low cabinet receives. That is, unless you have a bass with a low F# string and your low cabinet is inefficient. Then you'll need a few megawatts on the bottom! ;) I hope this shows that there is no single answer for all situations. Perhaps the factors I've mentioned will help guide you.

    - Mike
  3. This may be a bit controversial, but I'd suggest equal power for both low and high. This makes for comparable gain structure (ie less signal-noise problems, phase problems, etc). The best PA systems in the world are run like this (Meyer, EV x-array, etc) If the highs are too loud you can just turn down the input gain on the amplifier channel running the highs. In my experience there's not as big of a difference in the power consumption of lows, mids and highs as people think... I've seen many a PA where the high end amps were clipping just as much as the low end amps using the same model amp. In any case you're better off with an stereo amp from one manufacturer than with a mish-mash of stuff. Of course all of the factors that Mike mentioned play in as well. Get an amp with enough power to run your lows, if it's too much for the highs turn the channel running the highs down!
  4. MikeyD


    Sep 9, 2000
    Hi, Spacegoat,
    Yeah, I think I agree with your point relative to PA applications; however, this is a bass amp, and the frequency content is skewed toward the bass end, which is why I advocated more power to the bottom. In a PA, you have vocalists, horns, strings, synths, drums, cymbals, or what have you - which usually require more power in the mids and highs than an electric bass would. Anyway - it's my opinion only, and Matt's actual set-up and sound preferences will probably be even a more significant factor than my guessing at the power balance. I'm sure your suggestion will work, too.
    - Mike

  5. Thanks guys, your suggestions are appreciated. I'd probably be crossing over somewhere between 1500 to 2000 hz. I do some slapping but not very often in a performance situation and prefer a punchy tone. That's why I think the low end amp would get the brunt of the work.
  6. Hey guys,
    you're both right that in a bass guitar situation the low end amp would work harder, especially if you cross at 1.5-2k. Most of the time. That being said, the best sounding rigs that I've heard have used the same power for low and high. I think having the headroom in the top end allows for accurate reproduction of slaps, snaps and pops. I've seen many rigs where when the player started slapping the lows were fine but the highs were clipping. These rigs were crossed over lower than that though...Part of the reason why many rigs use the same power is the fact that most power amps are stereo and therefore the matter of convenience. The most common ratio I've seen is 2-1 or 3-1, in rigs without matched power. MikeyD: Until a few years ago, I was of the more power on subs and less on mids and highs school of thought. Then I read Meyer Sound's handbook about gain structure, acoustic crossover point, phase response and such. When the company I worked for upgraded so that the big Meyer rig had equal power on all bandpasses we couldn't believe the difference! When we put the SIM machine on it (Meyer's AMAZING measurement system), and A-B'd, the phase response of the system was remarkably better, something like +\-50 degrees from 27Hz to 18kHz( which is very good for a PA), versus +\-70 degrees. I can't remember the exact numbers, but you get the picture. I'm a believer now. Oops, I've gone on and on again...sorry, Cheers,
  7. Brad Johnson

    Brad Johnson Supporting Member

    Mar 8, 2000
    Gaithersburg, Md
    DR Strings
    That's pretty high for a bass rig. What are you planning on using for the lows and the highs? Also, I guess the more obvious question would be, why do you want to biamp? The more popular cabs out today have internal crossovers and low and high frequency drivers.

    I'm a reformed tri-amper;)but I'm not trying to talk you out of anything.
  8. MikeyD


    Sep 9, 2000
    Interesting comment. I think there's a lot of credibility to needing serious power reserves to ensure high fidelity in producing transients, such as slaps. I think we're dealing more with "slew rate" issues and peak power reserves here, rather than steady-state power output. I guess I can see how one winds up wanting equal power to the different frequency bands - the lows getting big steady-state power capability, and the highs getting more of the "1,000,000 watts for a microsecond" (BTW, that's only one joule of energy!). Hmmm. Really interesting. I can personally identify with your last statement. It's quite easy to make my clipping LED's blink on momentarily when I'm slapping - even with the compressor on (lightly). I'm starting to come around a bit (in my sleepy state at the moment): I'll stick by my previous position about more power to the lows than highs, but add that this is relative to steady signals. The transient problem is one that I didn't consider fully, and you have made a good point!

    I'm not sure how power reserves affect the phase response, unless it speaks to the transient response. I suppose with more power reserves, it gives those obstinate speaker coils a major butt-kick when a transient comes along, so that the phase of the emitted sound is more accurate (not lagging as much). That's all I can think of right now. I need to take a nap! :)

    Thanks for your comments. I want to ponder them some more!

    - Mike


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