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


Gandalf5150
11-06-2010, 03:10 AM
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

GCDEF
11-06-2010, 06:13 AM
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.

Gandalf5150
11-06-2010, 08:12 AM
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.

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

modulusman
11-06-2010, 09:21 AM
I would not use bridge mode. Is this the amp you are using? http://pro-audio.musiciansfriend.com/product/Peavey-CS-2000-Power-Amplifier?sku=481438 What are the wattage and ohm ratings on your cabinets?

Gandalf5150
11-06-2010, 09:48 AM
I would not use bridge mode. Is this the amp you are using? http://pro-audio.musiciansfriend.com/product/Peavey-CS-2000-Power-Amplifier?sku=481438 What are the wattage and ohm ratings on your cabinets?

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.:)

GCDEF
11-06-2010, 10:12 AM
Yeah it's a Peavey PV 2000 Never even considered tube power amps for P.A?
You learn somethin new every day.



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.

Nelson89
11-06-2010, 10:16 AM
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...

Gandalf5150
11-06-2010, 10:17 AM
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.

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 :)

BradS71
11-08-2010, 07:21 PM
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....

GCDEF
11-09-2010, 06:37 AM
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....

Gawd, not again. Please stop spreading that nonsense.

BradS71
11-09-2010, 09:19 AM
What nonsense is that?

GCDEF
11-09-2010, 09:56 AM
What nonsense is that?

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?

BradS71
11-09-2010, 04:46 PM
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.

duanemassey
11-09-2010, 10:24 PM
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.

walterw
11-09-2010, 11:33 PM
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.)

GCDEF
11-10-2010, 06:21 AM
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.

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."

BradS71
11-10-2010, 10:40 PM
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.

walterw
11-10-2010, 10:49 PM
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.
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.
Also, the two examples quoted from the Peavey article are certainly two ways you can blow a speaker (there are many ways unfortunately).
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".)

Gandalf5150
11-11-2010, 03:11 AM
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?

GCDEF
11-11-2010, 04:54 AM
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.

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?

BradS71
11-11-2010, 07:42 AM
GCDEF,
If you can read my previous post and not deduce the answer to your 200w vs. 800w speaker question, then you are missing the point.

Lets dig in a little on your statement about my saying you need "twice the amp power as speaker power". What I said was twice the RMS power (its not truly what RMS means, but RMS has come to be accepted to mean something like "continuous average" power handling). According to the way that most manufacturers rate their speakers, 2x RMS (or continuous power) = program power handling. So by recommending 2x RMS power, I am saying an amplifier that will cleanly deliver the max rated program power of the speaker.

You say "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". Brother, we're practically speaking the same language there. Don't you see? If you have "enough" power that assumes you want to drive the speaker to full potential, and if you "have enough amp that you don't clip it"....that translates to what I am saying! To meet those two requirements you need an amp that will cleanly deliver the max program power of the speaker...or 2x RMS.

On the last statement "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?" Absolutely not. That was never my point in any way. They will both likely blow up! I never suggested any speaker would be better at surviving clipping amplifiers. I suggested sizing your amps to drive your speakers to full output capacity without clipping, and that applies to 100w drivers or 1200w drivers just the same.

Anyway, I really don't think our beliefs are as out of line with each other as you think they are. Reread my email above and think about what I am actually saying.



Walterw- I'm sorry, your statement about speakers not caring what shape the waveform is is just patently wrong. I don't even know how to respond to that.

BradS71
11-11-2010, 09:58 AM
Walterw- I've thought about this some more, and in fairness to you I can understand how my generalized statement could be misconstrued. Allow me to clarify my point.

The issue is not the squarewaves themselves per se. It is the state that the amplifier is in when its to the point of delivering them. An amplifier's rated output power is based on the amount of power it is capable of delivering cleanly. When an amplifier is driven into heavy clipping it can and will deliver up to many times that amount (remember this stuff is log10, not linear). This is especially true of the peak transients.

Let's use GCDEF's example of the 200w on the 800w driver. When that 200w amp is driven so hard into clipping that the peak transients exceed 800w, that driver is toast. It happens all the time.

So, could you properly limit the input signal to that 200w and never blow up that 800w speaker? Of course you could. But why would you want to waste your money on high-powered speakers and leave all that SPL on the table?

On that note, one more example... If the 800w speaker is rated at 100dB efficiency (1w,1m of course) and you apply 200w to it, it is going to give you (using rough/rounded audio math) about 123dB SPL. If you put the full rated 800w cleanly into it, you're going to get something more like 129dB SPL. That's a full 6dB of critical headroom. This, of course, has a massive effect on how much you can get out of your rig.

Guys- This wasn't supposed to turn into a huge debate. Most musicians are not audio system designers or R&D engineers. I was just trying to give the OP a good rule of thumb to get the most out of his speakers while having a good shot at not blowing them up. That is all.

GCDEF
11-11-2010, 10:25 AM
Walterw- I've thought about this some more, and in fairness to you I can understand how my generalized statement could be misconstrued. Allow me to clarify my point.



Let's use GCDEF's example of the 200w on the 800w driver. When that 200w amp is driven so hard into clipping that the peak transients exceed 800w, that driver is toast. It happens all the time.

So, could you properly limit the input signal to that 200w and never blow up that 800w speaker? Of course you could. But why would you want to waste your money on high-powered speakers and leave all that SPL on the table?



All that's true, but it has nothing to do with underpowering a speaker causing damage to it. The fact of the matter is, and you appear to understand this, there's nothing inherently dangerous about running a 200 watt amp with an 800 watt speaker. Nothing. The danger comes when you use any piece of equipment beyond it's capabilities, and that includes clipping a small amp and putting too much power into speakers that can't handle it.

I've being so stubborn on this because there's a lot of confusion, misunderstanding and misinformation on the topic floating around out there.

BradS71
11-11-2010, 10:35 AM
GCDEF-
Fair enough. I completely agree with you that so many people just throw out "rules" with no basis in fact and no way to back them up. I hear you.
I hope that we have found some common ground on this. I feel like we have.
take care,
Brad

walterw
11-11-2010, 07:01 PM
and we reach harmonious convergence.

to repeat, the speaker doesn't care what the shape of the wave is, it cares if it's getting too hot (too much power for too long) or being pushed right out of the basket (too low a frequency for too long).

it's just that a clipping amp can cause the first one to happen.

i think that an amp can only go to double its clean rating at full square wave clip, so this 200 watt amp can run full clip into an 800 watt speaker all day long, because it will be producing at most 400 watts of miserable hate.

it's when you've got the 300 watt amp into the 400 watt speaker and you drive the amp to hell that you have a problem. it will be creating a 600 watt square wave that's compressed hard, so the speaker will never get a break and gets cooked.

a 600 watt amp into that same 400 watt speaker, run clean, will create the occasional transient above 600 watts, but will spend most of the time between kick drum hits or bass plucks or whatever doing way less than that, so the speaker coil doesn't get so hot.

the transients are louder (so the music sounds louder), but the speaker overall is hit with less power over time.

walterw
11-11-2010, 07:04 PM
oh, um, one side of a stereo solid state power amp doesn't care what the other side is doing, so yeah, you can run one side by itself (the original question :rotflmao).

BradS71
11-11-2010, 09:56 PM
oh, um, one side of a stereo solid state power amp doesn't care what the other side is doing, so yeah, you can run one side by itself (the original question :rotflmao).

Ha! Perfect...

Gandalf5150
11-12-2010, 02:22 AM
oh, um, one side of a stereo solid state power amp doesn't care what the other side is doing, so yeah, you can run one side by itself (the original question :rotflmao).

Thank you.:D
Whilst you guys were debatin all the other stuff, another question came to me. I'd be grateful if anyone could tell me.

Am I better running my power amp on full, and lower on the desk,
or running power amp at maybe 75% and higher on the desk?

Thanks in advance:bow

Cirrus
11-12-2010, 04:30 AM
Thank you.:D
Whilst you guys were debatin all the other stuff, another question came to me. I'd be grateful if anyone could tell me.

Am I better running my power amp on full, and lower on the desk,
or running power amp at maybe 75% and higher on the desk?

Thanks in advance:bow

Personally, I'd run the desk so that the master volume is showing around 0db. That way the desk is running at the signal level it was designed for - a good compromise between keeping the signal above the noise and leaving headroom for transients. Then I'd turn the power amp up until it was at the volume I needed for the venue/occasion. That way the desk has headroom if you need to turn up a little during the gig, and the power amp hopefully also has headroom to produce the signal cleanly.

Gandalf5150
11-12-2010, 04:45 AM
Personally, I'd run the desk so that the master volume is showing around 0db. That way the desk is running at the signal level it was designed for - a good compromise between keeping the signal above the noise and leaving headroom for transients. Then I'd turn the power amp up until it was at the volume I needed for the venue/occasion. That way the desk has headroom if you need to turn up a little during the gig, and the power amp hopefully also has headroom to produce the signal cleanly.

Thanks for your response. Looks like I'm not a million miles away.

I've been running my amp at full, desk masters at 0db and using the individual channel sliders to accommodate venue.
Just wasn't sure whether or not to run the amp at 9.00 o' clock and increase the individual channel volumes?

Fwiw, I've had conflicting advice over the years.

One engineer told, always run power amps at 75%,
a second one told me to always run them at full, using the desk channels as described above.

Seems to me the word always is the key here.
In an ideal world, perhaps always can be used, but in the real world I would think more importantly, amps should be run to accommodate the relative speaker power being used?

GCDEF
11-12-2010, 11:51 AM
I would tend to run the amps wide open just because it's easier to control. If you get to 0 dB on the mixer and you still need to go louder, you'd have to run to the amp racks and crank the volume on the amps, and that would not only be inconvenient, but would probably require adjustments at your crossover too. Better to just control as much as you can from the mixer IMHO.

Keep in mind the volume knobs on amps are really just input attenuators. Essentially they run on full all the time anyway. If you turn the mixer up and the amp down, all you're doing is supplying a hot signal from the mixer, then attenuating it back down again at the input stage of the amp, which is really kind of pointless.

Gandalf5150
11-12-2010, 12:05 PM
I would tend to run the amps wide open just because it's easier to control. If you get to 0 dB on the mixer and you still need to go louder, you'd have to run to the amp racks and crank the volume on the amps, and that would not only be inconvenient, but would probably require adjustments at your crossover too. Better to just control as much as you can from the mixer IMHO.

Keep in mind the volume knobs on amps are really just input attenuators. Essentially they run on full all the time anyway. If you turn the mixer up and the amp down, all you're doing is supplying a hot signal from the mixer, then attenuating it back down again at the input stage of the amp, which is really kind of pointless.

Makes sense to me. Cheers dude.:bow

walterw
11-12-2010, 05:26 PM
as long as nothing has to get cranked so hard it clips, or gets turned up so loud you start hearing the background hiss, it doesn't really matter these days.

i recommend diming the amps (so you don't have to do it in the middle of the show), setting your channel faders around "0", then adjusting the board's master outs along with whatever EQ andor/crossover is in line so that the actual volume is where you want it.