power to cab ratio?

[bassplayer48]

Thanks guys i think this gives me a pretty good idea of my options either add a 210 cab and run the amp at the full 300 watts to create more headroom or stick with the stand alone 212 and get a more powerfull head so i am running say 300-500 watts into it.

One other question is there an optimum level to run an amp? 1/4 power 1/2 power 1/3 power?

 

[deebee]

dave's opinion = bass rigs

webervst = guitar player notions which have nothing to do w/ bass rigs.

And the laws of physics and acoustics are the same, no matter what instrument/rig is under discussion!

 

[jokerjkny]

Oh God in the garden, not this again.....


Speakers get damaged in 2 ways:

1)Overexcursion (mechanical/physical damage).
2)Too much power (thermal damage). Full stop. Period.

No speaker was ever blown with too little power.

Can you blow a speaker rated for more power than the amp driving it? Yes, but only to a point.

When an amp clips, it puts out more than its rated power. How much more is a function of how far the amp is into clipping. The ultimate maximum is twice rated power. It's usually much less than that in the real world (power supply sag, etc). So, the upshot is that you can blow up a 500W rated speaker with a 400W amp driven to clipping. But it's because the amp can put more than 500W into the speaker if overdriven enough, not because of the distorted waveform itself. Connect a 10W amp to that speaker and you can clip it until it self destructs without damaging the speaker.

In simple terms: Clipping, in and of itself, doesn't blow up speakers. They honestly don't care about the waveform. The danger is that, in some situations, an amp rated for less power than the speaker it's driving can actually put more power into it.

Clear as mud, right?

Sorry, for any of you non-technical cats, I don't think I can put it any simpler than this.

thx mark,

totally cleared up for me.

 

[jokerjkny]

And the laws of physics and acoustics are the same, no matter what instrument/rig is under discussion!

was referring to the overall general guitarcentric attitude of the website. but understood.

 

[vicenzajay]

No, he's right. Clipping and distortion do not, in and of themselves, blow speakers. How do you think guitarists survive? Excessive power and overexcursion blow speakers. You can sometimes get these when you overdrive smaller amps, but it doesn't necessarily happen. By that logic, you could kill an 800 W sub with a 50 W amp overdriven. Ain't likely. let us know if you ever see that happen.

Much too much information about this in way too many places, Richard. I know you don't agree with me, so I'll stay out of the thread...but the plain physics of it have been outlined by too many people much smarter than I. So I'll let them either chime in or not.

The bottom line is that clean power will not hurt the speaker unless it is grossly overpowered. Clipping a 50 watt amp will not immediately kill an 800 watt sub. Of course, I agree with you on this...but it might begin to damage it over time if it's allowed to clip indefinitely. "Popping" your PA system is never a good thing - regardless of the volume or amount of power output you've set on your power amps. Hitting that 800 watt sub with a 700 watt clean signal and peaks to 1000 watts will not only NOT hurt that sub, but will be handled easily and present a MUCH nicer tone.

By contrast, and I will not budge on this...most speakers blown have been blown "as a result of" (whatever the technical reason, overexcursion or overpowering) either clipping or distorting the output of a power amp. Period. Just the simple facts. So (square wave vice even order) hard clipping of that 300 watt amp that's feeding the 500 watt cabinet very well might buy the farm on that cabinet the first time it happens.

The idea here, or so I thought, was to give good advice to the original poster....he needs to understand that having a power amp reasonably powered above his cab's rating is not only not going to result in his immediate blowing of the speaker, it will result in more headroom, better tone, and actually a smaller chance of his blowing the speakers in his cab should he go crazy (or more likely, try to continually turn "up" his amp during a show where he thinks he's getting lost in the mix). That's good advice.

Speaking of the original poster...I believe he was planning on powering his Eden with as many as 180 watts of power? Like another poster mentioned...is he going to have the headroom for his band or group application. If he parks that power at maximum trying to be heard...it has the potential of not being ideal for his cabinet...whether or not it will "blow" it outright.

Jay

 

[throw_this_away]

I'm not sure about the speaker blooming thing either... but my rig (tube) sounds it's best when I make it sweat. Partly due to the tube design... maybe partly due to speaker bloom... maybe due to hearing loss over time

 

[Mark Reccord]

By contrast, and I will not budge on this...most speakers blown have been blown "as a result of" (whatever the technical reason, overexcursion or overpowering) either clipping or distorting the output of a power amp. Period.

Nonsense. For one, about 90% of all speaker failures are excursion related and that can happen with perfectly clean power well below the driver's thermal rating depending on EQ settings and cabinet design. Has nothing to do with clipping, per se.

Thermal damage to voice coils is much less common and is a result of too much power. I'm sure that sometimes this is related to clipping, but it's just as often related to using too much clean power, especially when there's compression involved.

The reason you can get away with using an amp more powerful than your speaker's rating is because of the dynamic nature of music. Dynamics (including rests etc.) means that even when you're driving your amp rated for 2x the speakers power so that it clips every once in a while, the average power being dissipated in the speaker is only a fraction of the maximum power. Adding compression limits dynamic range and decreases that peak-average ratio. In a thermal sense, speakers only care about average power. They don't care about waveform.

There is a lot of information around on this topic. Most of it is wrong.

 

[GreyBeard]

No offense, but this note is kinda misleading, and there have been probably at least 30 threads on TalkBass in the last year that explain things better than this.

The issue here is; are hard clipped (square wave) signals from the power section of a 50 watt SS amp in and of themselves damaging to say a 200 watt speaker? I've read conflicting reports from SWR, Rane, JBL, etc, etc. I do know that one drunken night I fried a PV 15" heavy duty with a PV Centurion. That in and of it's self proves nothing. I've seen EV voice coils literally blown through the cone paper when an amp dies and passes DC. The Rane article makes perfect sense that a 50 watt hard clipped SS amp will blow the tweeter out of a speaker rated at 400 watts cause the whole speaker is rated for 400 watts and not the tweeter which is probably only 75w. A normal 400w bass signal won't have more than 75w in the freq region that the tweater operates. However, a 50 watt SS amp can putout 100w of hard clipping in the freq region of the tweater and thus explains how the un protected tweeter will fail. One would think that any speaker developer would have done extensive tests to determine just what does cause a speaker to fail. The "clipped signal" damaging speakers is still up in the air.
http://www.doctorproaudio.com/doctor/temas/powerhandling.htm
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http://groups.google.com/group/rec....13aa07700eb/c5ff7f883b723f5b#c5ff7f883b723f5b
Anyway, the best advice I can give anyone from all this is that the issue of clipped signals in and of themselves damaging speakers is unresolved. There have been some pretty impressive arguments written on both sides of the issue. In my 30+ years of playing electric and upright bass I've only blown one speaker (mentioned above) but I known about guys blowing everything and anything with all types of amps both tube and SS. I once saw a JBL D140 get blown by a 50w tube Lesley cab. Never will understand that one.

 

[Richard Lindsey]

Much too much information about this in way too many places, Richard.

Yes, I know, but the point is that much of this "information" is wrong. Or, rather, that it isn't information but speculation or supposition. And as for the plain physics of it, the physics have been blatantly misstated in many many places (as when the statement is made that hard clipping is tantamount to DC--this is not a matter of opinion, it is factually wrong). An error doesn't become a true statement merely by being repeated often enough.

 

[Cristo]

Isn't the point that power amp clipping causes MORE than the amps rated power to be produced, thus damaging the speaker?

So, it is not just a distorted waveform that damages speakers (thus how we can have distorted tones) but rather, one that is distorted by a power amp operating at its maximum level and thus produces highly overpowered transients?

 

[Richard Lindsey]

Anyway, the best advice I can give anyone from all this is that the issue of clipped signals in and of themselves damaging speakers is unresolved.

I dunno, I think it has been resolved, really. Every time you hear Eddie Van Halen or Allan Holdsworth or George Lynch, you're hearing a clipped signal, yet the speakers don't immediately blow up.

Basically, the theory that clipping in and of itself damages speakers lacks explanatory power. It fails to explain all the cases where the rule should operate but doesn't. On the other hand, the analysis Mark Reccord gave does have explanatory power: it explains the cases where you damage a speaker with a clipping amp, the cases where you don't damage a speaker with a clipping amp, and the cases where you damage a speaker with a nonclipping amp.

 

[Richard Lindsey]

Isn't the point that power amp clipping causes MORE than the amps rated power to be produced, thus damaging the speaker?

So, it is not just a distorted waveform that damages speakers (thus how we can have distorted tones) but rather, one that is distorted by a power amp operating at its maximum level and thus produces highly overpowered transients?

Yes. Coupled with this is the second mechanism Mark mentioned, which is forcing the speaker into overexcursion.

 

[Richard Lindsey]

Speaking of the original poster...I believe he was planning on powering his Eden with as many as 180 watts of power? Like another poster mentioned...is he going to have the headroom for his band or group application. If he parks that power at maximum trying to be heard...it has the potential of not being ideal for his cabinet...whether or not it will "blow" it outright.

Agreed, to a point. It's good to remember what the original question was. As I and others said earlier, what he needs to worry about is whether his 180 W is enough for his gig. Not whether it's enough for his cab; that's just not really a meaningful concept IMO and IME. If it's not enough for his gig, he does need to get a bigger amp, more speakers, or both. But if it is enough, with room to spare (meaning headroom), there's absolutely no problem with the way his rig is set up. Not that there's no room for improvement, but there's nothing inherently wrong with it. I do think that speaks to his original question.

 

[rockstarbassist]

Just get a PLX 3402 or CA-9 and be covered for all gigs! It's a gimme!

I've spoke with a certain cab manufacturer and I think his point is valid-
Ask a bass amp guy, they'll tell you to match the cabs to the amp's output.

Ask a sound engineer, and he'll tell you to double it.

Just had a thread about this, like 2 days ago, if I remember correctly...

Basically, buy what you can afford. You can never have too much, but can have too little.

 

[vicenzajay]

Isn't the point that power amp clipping causes MORE than the amps rated power to be produced, thus damaging the speaker?

So, it is not just a distorted waveform that damages speakers (thus how we can have distorted tones) but rather, one that is distorted by a power amp operating at its maximum level and thus produces highly overpowered transients?

What I'm trying to say - too much evidence supports this - which equates to the fact that it is not only possible, but factual that amps rated at lower power setting can (and often do) damage speakers rated for more watts that the amp theoretically is rated for.

Certain people obviously have decided that they are God's gift to the science on this subject and cannot be wrong. Or more correctly, that they are the only ones who can use the correct semantics to explain it.

The whole point about speakers caring for the average power from the amp is obviously correct - Yep - completely agree - still lends credence to my argument to have an amp with more power, not less.

Whatever...I never said that ONLY clipping destroys or damages speakers. I never said that I was going to give the 100% technically correct explanation of why. I did say that an amp with less power than a rated speaker has the potential of frying that speaker.

And that's a true statement - no matter what "beef" these guys have with what I'm saying. Two people here saying it is not true does not disprove it.

Unbelievable the goal of proving a "correctly scientifically stated" point instead of giving people practical, useful information that might actually help them protect their equipment

 

[Richard Lindsey]

What I'm trying to say - too much evidence supports this - which equates to the fact that it is not only possible, but factual that amps rated at lower power setting can (and often do) damage speakers rated for more watts that the amp theoretically is rated for.

Certain people obviously have decided that they are God's gift to the science on this subject and cannot be wrong. Or more correctly, that they are the only ones who can use the correct semantics to explain it.

The whole point about speakers caring for the average power from the amp is obviously correct - Yep - completely agree - still lends credence to my argument to have an amp with more power, not less.

Whatever...I never said that ONLY clipping destroys or damages speakers. I never said that I was going to give the 100% technically correct explanation of why. I did say that an amp with less power than a rated speaker has the potential of frying that speaker.

And that's a true statement - no matter what "beef" these guys have with what I'm saying. Two people here saying it is not true does not disprove it.

Unbelievable the goal of proving a "correctly scientifically stated" point instead of giving people practical, useful information that might actually help them protect their equipment

Getting personal is usually a sign of a flimsy argument.

if you're going to disagree with a post, please have the elementary courtesy to actually read, understand, and correctly represent the post you're disagreeing with. If you do this, you will find that neither Mark nor I, nor anyone else on this thread, disagreed with the idea that under some circumstances, you can blow a speaker rated at X watts power handling with an amp rated at less-than-X watts. If you think you saw that statement, tell me where. I'll wait. The source of the disagreement was why this happens, when it does happen (and it doesn't always), and why it doesn't, when it doesn't. In other words, the correct explanation.

Now, why does having the right explanation matter (aside from the obvious argument that on principle, being right beats being wrong)? Well, in some circumstances, maybe it doesn't. For instance, on a practical level, probably everybody in this thread would agree that a 600 W amp into 400 W cab, used with some intelligence and restraint, would work perfectly fine for many gigs. That recommendation would be good advice for many people, whether you arrived at it through good reasoning or faulty reasoning.

But it does matter when believing the wrong explanation for things leads you to do stuff you don't need to do or shouldn't do, or makes you think you have a problem when you don't, or makes you think you can't have a problem when you actually might.

For example, the original poster didn't start by asking how big an amp he should get. He asked if he had a problem simply because his amp put out less power than his cab was rated for. He seemed to have gotten the idea that this was an inherently bad thing, regardless of what his power needs actually were. I think it is doing him a favor to let him know what the real issues are.

If somebody should become convinced, solely on the basis of some ratio, that there had to be a problem with his rig even if it were in fact perfectly adequate for his needs, that would be a potential problem, right?

As another example, I saw a poster once who had a supposedly underpowered rig--something like a 300 W amp into a 500 W cab. He had become convinced that this automatically made him underpowered and liable to speaker damage, again without any reference to his actual playing situation or his actual power needs. He'd gotten hung up on the 2:1 amp:cab thing, so he thought his best bet, to avoid clipping and save his speakers, would be to swap his cab for a 150 W cab. He wouldn't be underpowered any more if he did that, was the reasoning. In his situation, this was unlikely to help. Again, if he'd had a clearer understanding of the issues, he could have avoided that misconception.

If somebody should become convinced that a 2:1 amp:cab ratio was more important than having an amp big enough for the job he was trying to do, that would be a potential problem too.

As yet another example, I had a conversation with Andy Lewis of Acme speakers once, and he complained about getting back speakers that had been messed up by people using them with ginormous amps. Apparently, some folks, believing that you could almost never damage speakers with "clean" power, had been using his cabs with amps rated way over the cabs rating, and frying some drivers as a result.

If somebody should become convinced that you could use any huge amount of power with any cab, as long as you couldn't hear clipping, that would also be a potential problem.

That's why we try to get things as right as we can. It's not personal, and it's not a pissing context. It's because we all benefit from better information. Personally, I appreciate it when some one sets me straight or helps me refine my understanding of something. I benefit from that, and if it's posted publicly, other people benefit as well.

 

[vicenzajay]

I agree with Richard's last post - in that usually people that go personal with something have a flimsy argument. For that I apologize. I never claimed to have either of your technical knowledge...and never claimed to be able to give anyone the scientific equation of why something happened.

However, my words were called "nonsense", a ridiculous allegory between a 50 watt amp and an 800 watt sub was used. And the words of too many other people quite expert in this field were called "wrong" out of hand. So to be honest - I felt as if this had gone personal on me first. To add to that - the last post just alluded to the fact that I lack "elementary courtesy". Lot's of personal things going on here.

I'm sorry that we don't agree...but Marc, the 4 people I know who have blown speakers here in town have ALL done it with underpowered amps pushed too hard. That's why I'm not budging on my advice to the poster or my claim that most speakers damaged are not damaged simply as a result of having an amp that is rated at a higher wattage than the speaker. Of course his amp does not "intrinsically" possess the danger of blowing his speaker cabinet "because" it is underpowered. That's not what I said - or meant. What I said was meant to warn the poster that it is very possible (and has happened often) to damage a speaker with an amp that is powered at a wattage below the rated wattage of the speaker. Your point about the volume he needs being the determining factor is very salient - however, my intent was to inform him of what he might face in the future.

My original post in this thread was to disagree with the statement that "clipping and square waves" don't affect speakers. That's like saying that air doesn't affect humans. It was a post that did not enlighten or (in my opinion) properly warn or address what can (and does) happen in the poster's situation if he/she is not careful.

My basic problem with the seeming need to drive all the technical points home, Richard, is that (although I know you don't mean it) the actual practical, safe advice that I (and several others besides me) are trying to communicate to the poster is lost in the seeming need to make "speaker experts" out of everyone.

I don't want to be a speaker expert...I just want some basic rules of thumb that I can use either as the sound guy or the bass guy for safely acquiring, operating, and protecting expensive gear.

So with that aim, I'll reiterate what I'm trying to say:

1. For me, and perhaps only me, the safest way to run a power amp to cab power ratio is to have a 1.5:1 or 2:1 power ratio of amp to cab

2. Gain structure should be set smartly (as I described in a post far, far above) for both the best signal to noise ratio and efficiency for the power amp. This will provide the best tone as well as allow the most headroom while operating the amp.

3. Average power through your amp to speakers is the important metric - keep the average within the the speaker's optimum range, and transient peaks shouldn't damage or "blow" the speaker.

4. If you are using an amp close to or slightly under the rated speaker's wattage, please be careful if you have to run everything (preamp/amp/signal chain) at max in order to be heard or to achieve your desired volume. Not only will it not sound the best, the amount of available headroom will be very limited, and the potential DOES exist to damage your speakers if you insist on heavy, hard playing (especially in the bass frequency spectrum) under these conditions.

Out here,
Jay

 

[permagrin]

Does it make any difference so the sound when running in less power than the cab is rated at? for instance i have an Eden 212XLT which i am running with a GK backline 600 (300 watts at 4 oms and 180 watts at 8 ohms) its an 8 ohm cab so im running 180 watts into it is this too little watts to get the best from it? or doesnt it make any difference?

Keep in mind - no mention of blowing out drivers, or trying to get more volume... the original post simply asks about how input power relates to the resulting sound, specifically as it applies to his particular rig.

Thanks guys i think this gives me a pretty good idea of my options either add a 210 cab and run the amp at the full 300 watts to create more headroom or stick with the stand alone 212 and get a more powerfull head so i am running say 300-500 watts into it.

One other question is there an optimum level to run an amp? 1/4 power 1/2 power 1/3 power?

Note that if you get another (assume 8 ohm) cab, the power that the amp produces, now 300W, will be split between the two cabs - 150W to each.

As far as where to run an amp, I doubt there is an 'optimum' level, but it is reasonable to assume that things will sound best within a nominal operating range, and the tone can go south when you push the limits. Let your ears be the judge. Also, the level on your 'master volume' level doesn't tell the whole story, it's frequency dependent. That is, if you EQ a good amount of bass into the signal you ask the power amp to amplify, it may start breaking up with the master at noon, whereas a far less bass-heavy EQ might sound clean up to 4 o'clock.

 

[Bassman62]

I wasn't very long ago the the rule of thumb was the the speakers need to be rated at twice the wattage of the amplifier, this applied into the eighties.
Nowadys it is the other way round with new voice coil materials speakers will handle power levels that could only be dreamt of 20 years ago, in the early 60s the blue Celestions (Vox AC30) were only rated at 15 watts, Jensens were similar.
A few replies have said that some speakers need more driving than others, what it really means is that some are less efficient.
A modern loudspeaker is far happier receiving a good high quality signal from a high wattage amplifier than a clipping signal from low wattage amplifier.
When considering suitable speakers the two main issues are frequency response and sound pressure level (not the useless 1K @ 1 watt @ 1 metre) over the whole of the audio specrum.

 

[Richard Lindsey]

My basic problem with the seeming need to drive all the technical points home, Richard, is that (although I know you don't mean it) the actual practical, safe advice that I (and several others besides me) are trying to communicate to the poster is lost in the seeming need to make "speaker experts" out of everyone.

I don't want to be a speaker expert...I just want some basic rules of thumb that I can use either as the sound guy or the bass guy for safely acquiring, operating, and protecting expensive gear.

Jay, I understand what you're trying to say, and you're right in that it is important to give practical advice. Do understand, though, that what Mark and I said was meant as, and was, practical advice. For example, when I say in an early point that the important thing is not the amp:cab ratio but the issue of whether the OP has enough power for his needs, that's an eminently practical consideration. When Mark says that clipping per se is not the problem, that's practical advice too, because it encourages you to think about the real issues, and hekps you to understand how rigs work and how you can avoid future problems.

Regardless, let's leave things here, if you're agreeable. Peace.
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