Stereo power amp q. Will I damage the amp, running a speaker out of only 1 side?

Discussion in 'Recording/Live Sound' started by Gandalf5150, Nov 6, 2010.

  1. Gandalf5150

    Gandalf5150 Member

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    I was told many years ago by a sound engineer that a stereo power amp, (P.A, or home hifi) must have speakers running from both sides at all times, otherwise they amp could blow.

    How true is this?

    I run a 2k Peavey P.A, consisting of a 2k stereo power amp, Hysis 2 tops and 15" bins.
    I did a very small gig last week.
    The Landlord told me artists often set up only 1 speaker.

    I politely declined and insisted I had to use 2, or risk damage to my gear.
    The issue has troubled me since. Was I wrongly informed all those years ago, since apparently, other artists at this same venue have used only 1 speaker?

    Clarification on this would not only satisfy my mind, but would also make checking my presets on my HD500 considerably easier, as I have been hauling my full P.A into my living room to check my patches. :bonk
     
  2. GCDEF

    GCDEF Supporting Member

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    Solid state amps are fine, tube amps need a speaker. I assume your PA is solid state, therefore it would be no problem with only one speaker.
     
  3. Gandalf5150

    Gandalf5150 Member

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    Yeah it's a Peavey PV 2000 Never even considered tube power amps for P.A?
    You learn somethin new every day.

    Anyhoo, thanks for clearing up my original question as well.

    Edited...just remembered. There are 3 speakon outputs on the rear (not jacks and binding post outs like on older models)

    middle one is BRIDGE. Do I remember correctly that the bridge out doubles the power from the 2 stereo channels?

    If so, is it safe to use that as my output, as long as I keep the volume low?
    or am I better just using a single channel?

    Thanks again:bow
     
    Last edited: Nov 6, 2010
  4. modulusman

    modulusman Member

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  5. Gandalf5150

    Gandalf5150 Member

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    No can't seem to find my exact model online anywhere. This is the older model. Same power I think...http://www.iclassifieds.com/forsale/electronics/995971835/peavey-pv-2000-power-amplifier.html

    My tops are 500, bins are 700 I think. long time since I looked, but I bought it as a balanced full rig many moons ago.:)
     
    Last edited: Nov 6, 2010
  6. GCDEF

    GCDEF Supporting Member

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    I don't run into tube amps for PA either. I just put that out there for you or anybody else that comes along, to avoid any confusion or misunderstanding.
     
  7. Nelson89

    Nelson89 Member

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    Yeh....only tube PA i ever came across was from the 70s....so like almost twice my age haha...solid state is much cleaner when it gets cranked....hence the push for mostly ss PAs since then...
     
  8. Gandalf5150

    Gandalf5150 Member

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    Bang on the money mate, just the sort of thing peeps need to know.
    Unguarded advice is a dangerous thing, so it's always best to, wherever possible, avoid any ambiguity :)
     
  9. BradS71

    BradS71 Supporting Member

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    You're totally fine not loading both channels of a traditional (i.e. non-valve) amplifier. I would NOT run the Peavey amp bridged. As for power matching, not sure of your speakers' exact ratings, but a good rule of thumb is to size amplifiers at 2x continuous (some manufacturers call RMS) power handling of the speakers. You want your amps to have the capacity to deliver more power than your speakers require. This way, they are always idling (relatively at least) and your power stays clean. A common misconception is that you blow up speakers with too much power. While this can, of course, occur, you will blow up speakers MUCH sooner with amps that are too small. Amp clipping (square waves) burn up voice coils a lot faster than heat from clean power.
    Be sure to match up what the loads are when you calculate your required amp sizes. For example, if you parallel two 8-Ohm speakers (run them on the same amp channel) the load to that amp channel is 4-Ohms.
    Anyway, hope this helps....
     
  10. GCDEF

    GCDEF Supporting Member

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    Gawd, not again. Please stop spreading that nonsense.
     
  11. BradS71

    BradS71 Supporting Member

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    What nonsense is that?
     
  12. GCDEF

    GCDEF Supporting Member

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    The underpowering nonsense. You, as does everybody who doesn't understand matching amps to speakers, for reasons absolutely nobody can explain assumes that the higher the power handling of your speakers is, the more likely you are to clip your amp. Let's think about it.

    You say use double the amp power. Okay. If that's the case, a 200 watt speakers would require a 400 watt amp. According to what you posted, that's correct.

    Now take that same amp and connect it to 800 watt speakers. According to you, you're seriously underpowering those speakers and putting the speakers at risk.

    I'll ask you, why would you be more likely to clip the amp with the 800 watt speakers than the 200 watt speakers? If you do clip the amp, which speakers are more likely to survive?
     
  13. BradS71

    BradS71 Supporting Member

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    There are many reasons that explain it, but from reading your post I can see it would be a waste of time as your mind is made up.

    I'll say this: I've worked in concert/touring sound for the last 20 years and have worked for 2 prominent professional loudspeaker manufactures and have many friends and contacts at most of the others, and I can safely say that they are a lot of people who've done this for a living their whole lives that would disagree with you.

    But, I'm honestly not on here to argue, so each to his own. Do what you like.
     
  14. duanemassey

    duanemassey Member

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    Talk to Bob Lee at QSC.

    You can NOT damage speakers by under-powering them, period. You can damage them by driving an amp into serious clipping. You can damage them by over-powering them, even if you do not clip the amp. You can damage them by attempting to operate them below their designed frequency.

    BUT... you cannot damage a 400w speaker with a 200w amp if you don't drive the amp into clipping.
     
  15. walterw

    walterw Gold Supporting Member

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    the source of the confusion is the idea that the clipped waveform itself damages the speaker. it doesn't (otherwise, rock guitar couldn't exist).

    what happens is the too-small amp gets driven into clipping, at which point it puts out way more power than before. if that power is too much for too long, the speaker overheats and dies. (it's worse because at that point the amp is totally compressed, giving the speaker no time to cool down).

    the bigger amp that's cruising along cleanly is hitting the speaker with big peaks, then letting off in between, giving the voice coil time to cool back down.

    thus, for regular music, you do want the amp rated a bit more than the speaker it's pushing.

    (the bigger amp can still blow the speaker too, but for the same reason, too much power for too long, as well as the other reason, hitting it with too low a pitch for the speaker to handle and pushing it out of its basket.)
     
  16. GCDEF

    GCDEF Supporting Member

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    You could try just answering my questions. If underpowering was dangerous, surely you could explain how in my little scenario. I suspect the reason nobody ever does is that if you really stop to think about it, you can't.

    I'll ask again. Why would 200 watt speakers be safer with a 400 watt amp than 800 watt speakers? After all, that's what the 2:1 rule implies. Part 2, why would you be more likely to clip your 400 watt amp with the 800 watt speakers than the 200? Part 3, which speakers would have a better chance of surviving if you did clip the amp.

    I know you're not here to argue, but if you put out misinformation, it will be addressed. Perhaps you could actually stop for a second and think about the rule you're posting. You're misunderstanding it in much the same way everybody else that parrots it misunderstands it.

    And if you want to bring professionals into it, here's an article from Peavey's Live Sound product development manager.

    http://www.peavey.com/support/technotes/poweramps/HOW_MUCH_POWER.pdf

    "First … let’s stop the spread of a big myth. You cannot burn out a speaker by
    using too little power. If that were the case, then anybody turning down their
    system would be frying their drivers.
    Speakers are burned for these reasons:
    -By applying too much power and exceeding the thermal (heat) rating of the
    speaker, or
    -By applying too much power at too low a frequency (excursion rating),
    thereby mechanically ripping the driver apart."
     
  17. BradS71

    BradS71 Supporting Member

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    You quote Peavey as your source? Let's just say that their touring sound experience compared to the companies I'm referring to wouldn't quite be in the same hemisphere...

    Anyway... I think my point is misunderstood. You're correct when you say that too little power will not blow up a speaker. Wouldn't argue with you there. The issue has nothing to do with the actual amount of "power" but rather the amplifier's ability to deliver that power. If you put too small of an amplifier on a high-power rig and then drive the piss out of it (which is what ends up happening in the real world), you're going to have dead drivers. When that little amp is driven into clipping and square waves are dive-bombing the voice coil, it is going to burn up. Pure and simple.

    If you properly limit the input signal to the small amplifier so that it can never be driven into clip, then OK, you don't blow up your speaker. But you also severely limit what you can get from that speaker. What I'm talking about is getting full potential from the loudspeaker, maximum output available, without blowing it up. In order to do that, you must have clean power (read: headroom) at all times. There's a thing in audio signals called transients. Those transients can require many times the power that typical program material requires. Remember audio is not linear, its all log10....so those differences can make HUGE differences in the power that is required for those instances. That's when amps that are too small run out of headroom and that's when speakers get blown.

    Its a fact. But of course you are free to believe and do as you like. I really seriously am not trying to argue with you. I debated even responding, but I am doing so not in the interest of bickering, but making my original point clear.

    BTW, the comment on the Peavey article that you quoted about "frying drivers by turning down a system" doesn't even make sense. What does "turning down" even mean? Amplifiers don't have "volume" controls. Those knobs control input sensitivity, in other words: how much input signal applied does it take to drive this amp to full output power. Obviously turning that sensitivity way down could prevent the amp from being driven into clip and would prevent drivers from being burned in that way. I don't follow how that applies to driving the amp into clip.
    Also, the two examples quoted from the Peavey article are certainly two ways you can blow a speaker (there are many ways unfortunately). But they are way down the list from the guys putting crap little amps on today's high powered speakers and driving the amps into oblivion.
     
  18. walterw

    walterw Gold Supporting Member

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    yep, pure, simple, and wrong.

    the speaker doesn't care what shape the waveform is, as long as it doesn't create too much power or too low a frequency.
    i suspect those are actually the only two. (ok, except for an amp blowing up and passing DC, but that may still fall under "too much power at too low a frequency".)
     
  19. Gandalf5150

    Gandalf5150 Member

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    I'm really not sure what to believe any more.
    I always thought speakers needed to be able to handle more power than a power amp can deliver?

    One other thing I'd like to know, if anyone can clarify, is...
    Am I better running my power amp on full, and lower on the desk,
    or at maybe 75% and higher on the desk?
     
  20. GCDEF

    GCDEF Supporting Member

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    I'll ask again, and this is getting boring.

    Given a 400 watt amplifier, why would you be more likely to drive it into clipping if you had 800 watt speakers, than 200, and if you did drive it to clipping, which speakers would be more likely to survive? It's a simple question. Why do you refuse to answer.

    We all agree that clipping is bad. The conclusion to draw there is get enough power to do the job. Those who say you need twice the amp power as speaker power are coming at it backwards. As long as you have enough amp power that you don't clip, speaker power is close to irrelevant, as long as they can safely handle the amp. The higher the power handling ability, the safer you'll be. It's a really simple concept.

    I'll address your conclusion again.
    "But they are way down the list from the guys putting crap little amps on today's high powered speakers and driving the amps into oblivion."

    If somebody gets little amps and drives them into oblivion, are you seriously saying that a speaker with lower power handling abilities will survive better than one with higher power handling abilities? Seriously?? Can you explain how that works?
     

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