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Title: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 12, 2009, 04:10:44 PM
I have a conundrum: I am stuck with a Behringer EP2500 amp and a 6925 Tapco Dual 15" speaker. The Tapco is rated 600W RMS/1200W Program and is 8 Ohms. The EP2500 gives 450-500W at 8ohms per channel and 1300-1500W at 8 ohms bridged. So depending on how I can set it up, it seems like I am underpowering the speaker or overpowering it. I've read the FAQ posts here about power, and it seems like clipping is basically the reason speakers die. I plan to put a compressor/limiter before the amp, and make sure my mixer doesn't clip at all. I'm basically using this for a live band, vocals, a keyboard/synth, and a sample pad.

So, my question is: being a total noob, will I be safer underpowering the speaker at 500W or overpowering it bridged with a potential 1500W?

Also, what's the safest way to find the loudest volume, using either setup?

Thanks a lot for reading such a basic question!!
Title: Re: Better to overpower or underpower speakers?
Post by: Silas Pradetto on June 12, 2009, 04:12:13 PM
500W never clipped is safer.
Title: Re: Better to overpower or underpower speakers?
Post by: Duncan McLennan on June 12, 2009, 04:13:46 PM
Answer seems simple enough to me.  You asked if you will be safer underpowering the speaker, and you say you will not clip anything.  So in either case nothing will get clipped, therefore the lower power is 'safer'.

However you'll have more headroom and likely more volume bridged.

If you're sure you'll be able to hear if and when the speakers are reaching their limits, bridge the amp.  If you're not sure, and/or you can't afford to foot the repair bill, don't bridge.
Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 12, 2009, 04:50:16 PM
Silas Pradetto

500W never clipped is safer.


Duncan McLennan wrote on Fri, 12 June 2009 15:13

Answer seems simple enough to me.  You asked if you will be safer underpowering the speaker, and you say you will not clip anything.  So in either case nothing will get clipped, therefore the lower power is 'safer'.


Thanks so much for your help! I have a question though: I don't intend to send the amp anything clipped; but will turning the amp all the way up somehow clip the signal because the speakers are expecting more power than they are being given? Or would it be safe to crank the amp if it is being sent a low volume signal?

Working with speakers seems so dangerous...
Title: Re: Better to overpower or underpower speakers?
Post by: Adam Schaible on June 12, 2009, 05:05:37 PM
Overpowering speakers is always more dangerous.  The term underpowering is almost always misunderstood.

Your speaker will be fine with 1w all year long.  What "underpowered" means is that you're running a hotter signal into the amp so you can get more voltage from the amp, thus more volume.  That reduces your headroom and makes the amp more likely to clip.

There's no real "underpowering" of speakers.  You just want to avoid clipping the amp.

Due to gain structure, you might be able to clip the amp without clippin the mixer.  It just depends.  You want the components to clip at the same time.
Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 12, 2009, 05:15:15 PM
I just noticed the amp has a clip light on it. I guess I just have to make sure not to set that off? Thanks everyone for your help!
Title: Re: Better to overpower or underpower speakers?
Post by: Justice C. Bigler on June 12, 2009, 05:17:58 PM
Stephen Dranger wrote on Fri, 12 June 2009 16:15

I just noticed the amp has a clip light on it. I guess I just have to make sure not to set that off? Thanks everyone for your help!

And to be sure that you know that the clip light is actually functional, i.e it's not burned out, thus giving you no visual indication that something is wrong.
Title: Re: Better to overpower or underpower speakers?
Post by: Rob Timmerman on June 12, 2009, 06:17:30 PM
Speakers die either from mechanical or thermal stress, usually thermal.  An undersized amplifier run into clip can cause more heating than an oversized amplifier being run well below its limits.  But a sufficiently oversized amplifier can cause just as much heating of the voice coil without approaching clip.  And a sufficiently large amplifier may also be able to cause the speaker to exceed mechanical limits.  For thermal limits, area under the curve matters.  For mechanical limits, peak amplitude matters.

Basically, don't feed your loudspeakers more power than they can dissipate, and don't exceed the mechanical limits.  If you plan on having a high peak to average ratio, go with a larger amplifer; if you plan on compressing the life out of everything (or letting you amplifier do that for you), use a smaller amplifier.
Title: Re: Better to overpower or underpower speakers?
Post by: Duane Massey on June 12, 2009, 11:05:12 PM
Yep, the safest method is to either under-power or match the ratings of the speaker and do not clip the amp. Personally I prefer running the input gain on the amp full and setting the levels upstream to avoid clipping the amp. You'll get differing viewpoints on this, but the key is little or no clip light.

As long as it gets loud enough for your needs (and you don't have to compress it really heavily) you're good.
Title: Re: Better to overpower or underpower speakers?
Post by: Bennett Prescott on June 13, 2009, 12:45:11 AM
Stephen Dranger wrote on Fri, 12 June 2009 17:15

I just noticed the amp has a clip light on it. I guess I just have to make sure not to set that off? Thanks everyone for your help!

The amplifier clip light is meaningless. If your amplifier has built in limiters and a limit indication light that is also meaningless.

Clipping does not hurt the amplifier, and it does not hurt the speaker. It tells you that you are entering a realm of soon-to-be-audible distortion, but all that means is that you're at the limits of what your amplifier can do. The waveform that is triggering that clip and/or limit light could be a sine wave (in which case you probably are about to burn up your loudspeakers) or it could be dynamic live music (in which case you're hitting clip/limit on peaks that are likely 18dB above the actual RMS value of your signal).

HEAT is what damages loudspeakers. When you see that clip light blink, with a 500w rated amplifier into the load of a 500w AES rated loudspeaker, you're probably really providing it with 10 watts of heating (RMS) power, which is really no problem. With abusive (heavily compressed, sine waves, etc) music you might be feeding it 50w. But you're probably nowhere near what the loudspeaker can do, i.e. your amp is the limiting factor. Double the amp power is 3dB more signal, so even if you had a 1,000 watt amplifier (which seems big when we use numbers like that) we're really talking about tiny differences here.

That said, less expensive loudspeakers have less expensive crossovers and drivers with smaller, less expensive heat sinks. So it's probably wise to play it a little safe, but I would play it safe by using your ears and that master volume control on your mixer. You should be able to hear when you're starting to push your PA. If you really want to play it safe with amplifier selection, you should be using a 125 watt amplifier on a speaker rated for 500 watts AES. Anything else and you can overheat the loudspeaker.

Since that's totally impractical, I suggest a more reasonably sized amp (at least the AES or "continuous" rating of the loudspeaker) and a little caution. With properly set limiters it is possible to use really big amps and wring another 6+ dB out of a loudspeaker. Otherwise, while the "out of gas" lights on your amplifier may serve as a warning they really tell you very little... you might have 12dB more to go (although it will sound bad as you really push the amp) or you might already be damaging the loudspeaker. It all depends on the signal at hand!
Title: Re: Better to overpower or underpower speakers?
Post by: Bob Lee (QSC) on June 15, 2009, 02:46:13 PM
Most amps don't have separate controls for input gain (as a mixer typically does), just overall gain.
Title: Re: Better to overpower or underpower speakers?
Post by: Chris Strack on June 15, 2009, 03:42:03 PM
Ok I have to say that most of the responses to the original posted question here have me confused.

I have always read and understood that it is always recommended that your amplifier provide 1.5 to 2X the Continous/RMS rating of the speaker.

So if his speakers are rated ay 600W RMS/1200W Program, most of the recommendation here are run them underpowered (which in his case is 450-500W with his amp) which is the opposite of what I have ever read before. WHAT GIVES ?????
Title: Re: Better to overpower or underpower speakers?
Post by: Adam Schaible on June 15, 2009, 04:24:10 PM
It's all about headroom.  Lots of people don't have compression/limiting.  If you're running your amp at -6db rms and then you have a 12db peak, your amp might be clipping.  12db peaks are not irregular.

If you have an amp with 6db of headroom (4x rms) you can run at half power RMS and have room for 12db peaks.

Bottom line, "underpowering your speakers" should be rephrased to "continuously operating your amp too close to it's limit".
Title: Re: Better to overpower or underpower speakers?
Post by: Donnie Evans on June 15, 2009, 04:30:59 PM
Chris Strack wrote on Mon, 15 June 2009 15:42

Ok I have to say that most of the responses to the original posted question here have me confused.

I have always read and understood that it is always recommended that your amplifier provide 1.5 to 2X the Continous/RMS rating of the speaker.

So if his speakers are rated ay 600W RMS/1200W Program, most of the recommendation here are run them underpowered (which in his case is 450-500W with his amp) which is the opposite of what I have ever read before. WHAT GIVES ?????


Because he asked which would be safer for him to run without damaging his speakers.  And if he's not going to clip the signal, the lower wattage is always safer, especially for a noob.
Title: Re: Better to overpower or underpower speakers?
Post by: Bob Leonard on June 15, 2009, 05:11:00 PM
OP,

I've been following this post and I have to say that some of the advice you've been given is as bad as I've read in a long time.

Be aware that although heat is the real danger here that heat has to come from somewhere and it's not the sun in this case. The temperature of the voice coil is a result of the voltages and current put through the voice coil by the amplifier. Just like a light bulb, too much voltage and the voice coil will burn itself out.

Many manufacturers address the issue of heat using voice coil materials and venting schemes which dissipate the heat or are impervious to the heat. Kapton is one of these materials which holds up to heat very well and is often used as a material for forming voice coils. The problem will be that although the Kapton can withstand extremely high temperatures, the voice coil wire coating and adhesives used to hold the wire to the Kapton usually fail first.

Operating your speakers using the proper voltages, amplifier output results in less heat. That's a no brainer. The problem is that many people don't understand that even a very small amplifier is capable of generating enough voltage to destroy a voice coil. Voice coils that are very susceptible to this type damage are the voice coils of your compression drivers.

Ever wonder why the person who shuts down his board before his amplifiers and then brings the system back up has all of a sudden lost output from the cabinet horns? It's because that "snap" he heard destroyed the voice coils in his drivers.

My take in the past 40 or so years has been to never under power a cabinet unless there is no other way. 1.5 - 2x the drivers long term rating is the way to go. And NEVER an amplifier that delivers less than the long term rating of the speaker. And let's be honest here. I don't know of any NUG who hasn't wanted more output at some time or another. The odds are stacked against you. Small amp, larger than normal crowd, I'll just push it into clip for a little while. And then you wake up the next morning to drivers that are useless. Limiters, compressors, etc. are a crutch. Power the speakers properly set the gain properly, balance the board and you won't need them.

Here's an old paper from JBL that's every bit as good today as it was the day it was written;

 http://www.jblpro.com/catalog/support/getfile.aspx?docid=290 &doctype=3

 http://www.jblpro.com/catalog/support/getfile.aspx?docid=246 &doctype=3

Edit: When I re-read Bennett's response I see that we are almost aligned with one exception. The clip light is not meaningless. It should be used as a guide, a reference point, and it should never be ignored.
Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 15, 2009, 05:24:48 PM
I guess it's not surprising that I wasn't able to find easy information from anywhere! I keep getting mixed signals; in fact two different Tapco tech support guys gave me two different answers! Sending power to speakers seems to be pretty contentious.

I guess what I don't understand is that if underpowering speakers is bad, should you never ever lower the volume on your amplifier if it's running at ideal voltages? What if you are sending a quiet signal? What's the difference between sending a quiet signal to a sufficiently powered amp and sending a loud (but not clipped) signal to a slightly underpowered amp? A Tapco guy said to me that the reason underpowering is bad is because you want to get a louder signal out of it, and therefore you end up sending a clipped signal to the amp -- clipped = direct current = broken speaker, no matter what the wattage is.

Things are not easy for a newbie...
Title: Re: Better to overpower or underpower speakers?
Post by: Patrick Tracy on June 15, 2009, 05:28:17 PM
Chris Strack wrote on Mon, 15 June 2009 13:42

Ok I have to say that most of the responses to the original posted question here have me confused.

I have always read and understood that it is always recommended that your amplifier provide 1.5 to 2X the Continous/RMS rating of the speaker.

So if his speakers are rated ay 600W RMS/1200W Program, most of the recommendation here are run them underpowered (which in his case is 450-500W with his amp) which is the opposite of what I have ever read before. WHAT GIVES ?????

Chris, I've been trying to get a handle on this since joining PSW a few years ago. Here's some of what I've gathered so far, subject to correction by Those Who Know.

Start by choosing speakers that can comfortably reach the desired SPL with a bit of extra capacity. Then feed them enough watts to get them to that level, also with a bit of extra capacity. This should help prevent clipping because you won't be tempted to push the system beyond its capacity, clipping the board or amps in the process.

Clipping shifts energy up in frequency (harmonics) which greatly increases the amount of power the tweeters see, easily overheating them, so clipping is bad mainly for that reason.

If the speakers can get way louder than you need then it might not be useful to power them to full capacity, but if they can get just loud enough then you do need to give them all they can take and no more. In that second case something like 1.5 to 2 times the continuous power rating of the speaker allows for peaks to be amplified cleanly (not clipping the amp) without risking mechanical failure of a driver by presenting it with too much peak voltage. The amp simply cannot produce the voltage necessary to harm the drivers mechanically, and if the limiter is set it won't produce the harmonics that may harm a tweeter (though it will reproduce any clipping harmonics made by something upstream).

An amp sized that way can still cause thermal damage to a driver depending on how it's driven. A 500W amp is only a 500W amp when referred to a stated THD (total harmonic distortion) level, usually a fraction of 1%, like 0.1% or 0.05%. It can be driven beyond that (into clip/limit) to produce much higher levels of power at higher levels of distortion. If your system is too small for the application you may be tempted to push it hard enough that the amps begin to clip or limit, and then they may be producing more than their rating (depending on program material) and you may be risking thermal failure. Program material is critical here because a very peaky mix will have much less power in it than a heavily compressed mix with the same peak voltage. Most live mixes are pretty peaky so you are pretty safe at 1.5 to 2 times continuous as the actual long term power sent to the speakers will be much less than the amp's rating. If less power gets you the volume you need then that's okay too, but be sure to avoid clipping by careful operation and setting amp (or processor) limiters. Less power can help prevent thermal and mechanical overload of the speakers except that you may be tempted to push something into clip, creating harmonics that send excess power to tweeters. For heavily compressed sources use more speaker capacity but power at 1 times continuous ratings.
Title: Re: Better to overpower or underpower speakers?
Post by: TJ (Tom) Cornish on June 15, 2009, 05:45:25 PM
Patrick - I think you have added the most important nuggests of this discussion:

The harmonics generated by sawing off the peaks of a wave cause the tweeters to get potentially much more power than in a normal situation, and often turning up the bass too much is what causes clipping, which blows the tweeter even if the woofer is OK.  This is non-intuitive, to say the least.

As long as you don't exceed the power rating of a driver, whether you have a 1W amp or a 1 million watt amp you will be fine.  The trouble comes when you try to squeeze the last couple of dB out of the box and push the thermal limits.  A bigger amp can give you some headroom, but potentially can burn up a driver even if it the signal isn't clipped.  A smaller amp may be quieter and thus more tempting for a hungry operator to try to turn up, which may increase the chances of clipping, and therefore put you box - especially the HF driver at risk.  

I believe this is the wrong place to put your mental focus, however.  If you're in a situation where you need to run the boxes to tip top capacity, you've simply not brought enough rig for the gig.  Any attempt at being on the edge comes with the risk of falling over the edge.  Even if you don't instantaneously blow up a driver with a square wave or DC or whatever, a driver that has been run "pedal to the metal" will wear out much more quickly than one run a little easier.  You're far better bringing more boxes and keeping things within a safe margin - your gear will last a lot longer.
Title: Re: Better to overpower or underpower speakers?
Post by: Adam Schaible on June 15, 2009, 05:53:16 PM
Bob Leonard wrote on Mon, 15 June 2009 16:11

OP,

I've been following this post and I have to say that some of the advice you've been given is as bad as I've read in a long time.

Be aware that although heat is the real danger here that heat has to come from somewhere and it's not the sun in this case. The temperature of the voice coil is a result of the voltages and current put through the voice coil by the amplifier. Just like a light bulb, too much voltage and the voice coil will burn itself out.

Many manufacturers address the issue of heat using voice coil materials and venting schemes which dissipate the heat or are impervious to the heat. Kapton is one of these materials which holds up to heat very well and is often used as a material for forming voice coils. The problem will be that although the Kapton can withstand extremely high temperatures, the voice coil wire coating and adhesives used to hold the wire to the Kapton usually fail first.

Operating your speakers using the proper voltages, amplifier output results in less heat. That's a no brainer. The problem is that many people don't understand that even a very small amplifier is capable of generating enough voltage to destroy a voice coil. Voice coils that are very susceptible to this type damage are the voice coils of your compression drivers.

Ever wonder why the person who shuts down his board before his amplifiers and then brings the system back up has all of a sudden lost output from the cabinet horns? It's because that "snap" he heard destroyed the voice coils in his drivers.

My take in the past 40 or so years has been to never under power a cabinet unless there is no other way. 1.5 - 2x the drivers long term rating is the way to go. And NEVER an amplifier that delivers less than the long term rating of the speaker. And let's be honest here. I don't know of any NUG who hasn't wanted more output at some time or another. The odds are stacked against you. Small amp, larger than normal crowd, I'll just push it into clip for a little while. And then you wake up the next morning to drivers that are useless. Limiters, compressors, etc. are a crutch. Power the speakers properly set the gain properly, balance the board and you won't need them.

Here's an old paper from JBL that's every bit as good today as it was the day it was written;

  http://www.jblpro.com/catalog/support/getfile.aspx?docid=290 &doctype=3

  http://www.jblpro.com/catalog/support/getfile.aspx?docid=246 &doctype=3

Edit: When I re-read Bennett's response I see that we are almost aligned with one exception. The clip light is not meaningless. It should be used as a guide, a reference point, and it should never be ignored.


If your amp is not clipping, and THD is say below 1%, then you aren't damaging your loudspeaker 500w rms loudspeaker.

If your amp is generating a lot of high frequency distortion because you're asking too much of it, then yeah you can fry a compression driver voice coil.

Can you explain what parts of this are not accurate?  Not trying to stir you up, honestly curious.  I don't see any posts that are too far off from that simple logic.
Title: Re: Better to overpower or underpower speakers?
Post by: Patrick Tracy on June 15, 2009, 06:10:34 PM
Stephen Dranger wrote on Fri, 12 June 2009 14:10

I have a conundrum: I am stuck with a Behringer EP2500 amp and a 6925 Tapco Dual 15" speaker. The Tapco is rated 600W RMS/1200W Program and is 8 Ohms. The EP2500 gives 450-500W at 8ohms per channel and 1300-1500W at 8 ohms bridged.


The Behringer's power rating for 8 ohm, bridged, 20Hz-20kHz is 1300W which is probably close enough to be safe as long as you aren't running super hard. The 1500W rating is for a 1k sine wave which seems to me less representative of what your use is than the 20Hz-20kHz spec. But you can try it first on one channel with the limiter on and if it gets loud enough without the limit light going on constantly you're set. If not then bridge the amp with the limiter on and turn down a bit if the light blinks. Avoid clipping anything upstream, especially with the amp bridged.
Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 15, 2009, 06:12:12 PM
There's another question which would clear up a lot of things for me: does the wattage of the speaker alter how the amp works?

Because if I'm not sending the amp a clipped signal, what I'm reading says that I can still clip the amp by cranking the volume. But why wouldn't an amp that's rated higher (and 1.5x RMS wattage rating) also start clipping if you cranked the volume on the same signal? Because what I'm hearing is that even if you gave the amp a signal that wasn't clipped, that volume knob is going to push the amp past its distortion level at some point no matter what amp you have.
Title: Re: Better to overpower or underpower speakers?
Post by: Greg Cameron on June 15, 2009, 06:12:18 PM
Stephen Dranger wrote on Mon, 15 June 2009 14:24

 A Tapco guy said to me that the reason underpowering is bad is because you want to get a louder signal out of it, and therefore you end up sending a clipped signal to the amp -- clipped = direct current = broken speaker, no matter what the wattage is.


The statement by the Tapco guys is absolutely false. Power (wattage) is power, period. For reference, an amp that's fully clipped can produce 2x the power of the same amp running at full power just before clip. So if you have a 1 watt amp and you drive it to 100% clipping, it will put out a maximum of 2 watts. This brings the next point: that same amp producing 2 watts fully clips will never blow a 100 watt rms rated driver. It will blow a driver rated at 1 watt rms though. And lastly, clipped amps do not generate ac current. They merely raise the dc heating equivalent which is what is described by the rms rating of a given driver. And speaking of dc, if you connect up a 1.5 volt battery to a speaker, you are feeding it dc. I can guarantee that you will not blow a 100 watt speaker because you hooked up a dc source. The source has to be capable of delivering enough current to damage the voice coil. Hope that clears things up.

Greg.
Title: Re: Better to overpower or under power speakers?
Post by: John Roberts {JR} on June 15, 2009, 06:18:52 PM
Arghhh

The reason simple advice about mating speakers and amps is sometimes contradictory, is because it isn't a simple problem so simple answers gloss over or ignore important exceptions to the rules of thumb.

Then you will get a full house of posts that say, " no, just worry about this one thing" ... bzzzt  wrong. Worry about everything

The fundamental problem on the speaker end is that loudspeakers have multiple failure modes (heat and mechanical travel are two most dominant ones). On the power amp end of the problem we have amplifiers that are designed and specified for rated power output using pure tones. I won't even start to discuss the many and complex differences between music and test tones, with even multiple failure vectors associated with simple clipping. When we say X watts of power, it may have specific meaning wrt to heating a voice coil resistance, but getting there from amplifier power ratings is not a straight line when music and clipping is involved.

Rules of thumb are good starting points but no combination of speaker and amp can be completely operator proof while delivering anywhere near it's capability. Sometimes life is just too complex for simple answers so we need to buck up and learn to deal with it... just like I must accept differing POV.

I have problems with several of the answers given but have had some of the same arguments with some of the same posters before so I will only say, read them all, and if interested in my "opinions" do a search. This has been discussed at great length and depth before.

JR
Title: Re: Better to overpower or underpower speakers?
Post by: Greg Cameron on June 15, 2009, 06:25:01 PM
Bob Leonard wrote on Mon, 15 June 2009 14:11

Limiters, compressors, etc. are a crutch. Power the speakers properly set the gain properly, balance the board and you won't need them.


I have to disagree with you here Bob. Compressors are a valuable tool for a variety of reasons. Speaker limiters are too. Compressors in the context of inserts are very useful for keeping dynamics under control for a variety of inputs from vocals , drums, percussion, etc. They can help bring things out in the mix as well as increase the overall apparent output of the entire system. Granted, they can be overused, but I'm not talking about those situations. And IMO limiters are essential protection even on the biggest, most powerful/high headroom, & expensive systems. Limter protection is for everything from dropped mics & feedback to being able to push the system all the way to it's limits without fear of failure - so long as the limiters are set properly. Not having proper limiting in place would be foolish. You might have a top of the line, biggest/baddest L'Acoustic rig where in one venue you might not come close to using up the headroom, but the next night you might be in an open field with 100,000 punters an you might need to push the rig all the way up until you're tickling the limiters. I don't see anything wrong with that. Big system or small even when you bring enough rig for the gig, limiters are never a bad idea.

Greg
Title: Re: Better to overpower or underpower speakers?
Post by: Patrick Tracy on June 15, 2009, 06:40:24 PM
Stephen Dranger wrote on Mon, 15 June 2009 16:12

There's another question which would clear up a lot of things for me: does the wattage of the speaker alter how the amp works?

Because if I'm not sending the amp a clipped signal, what I'm reading says that I can still clip the amp by cranking the volume. But why wouldn't an amp that's rated higher (and 1.5x RMS wattage rating) also start clipping if you cranked the volume on the same signal? Because what I'm hearing is that even if you gave the amp a signal that wasn't clipped, that volume knob is going to push the amp past its distortion level at some point no matter what amp you have.

Decent pro amps are typically designed to handle at their inputs any signal level they are normally likely to be presented, and then some. If the piece of gear driving the amp can produce a clean signal at a very high level and the amp's attenuators are set wide open then something in the amp, perhaps the output stage, may clip. In this case lower the level of the upstream gear or back the amp's attenuators down from wide open.

A bigger amp can also be pushed into distortion but the volume will be higher. The goal is to make sure that the speakers can get loud enough and to use an amp big enough to get them that loud without clipping. A bit of excess capacity in both the amps and speakers helps.
Title: Re: Better to overpower or underpower speakers?
Post by: Art Welter on June 15, 2009, 07:15:54 PM
Stephen,

The position of a “volume knob” does not determine if a signal will be clipped.

Any electronic device can be overdriven, and when it is, it “clips” the waveform of the audio, unless it has a limiter in the circuit, in which case the waveform won’t be clipped but the average power will be increased when it is “turned up”.

There is no difference between sending an unclipped signal to a large amp or a small amp, other than the amount of voltage gain.

An “Underpowered”  speaker simply is not using the full potential of the speaker, but whether a speaker is “underpowered” or “overpowered” is program dependent.

An amp driven into full clip can put out up to double it’s rated power.
Once a 500 watt amp is driven above the clip light coming on, you can’t tell by looking whether it is putting out 501 or 1000 watts.

If you mash (clip) a 500 watt amp to the point where it is putting out 1000 watts, the speakers are seeing much more average power than they would if a they were hitting 1000 watt peaks using a 1000 watt amp.

Speakers are not very efficient, so much of the power used turns into heat.

The speaker voice coil is heated by the average power.

If the music you play through your speakers is highly compressed, or heavily clipped, or contains a lot of droning sine wave like tones, it could have average power approaching the full rated output of an amp when the amp is at clipping.

With that type of music, an unclipped amp rated at the continuous rating of the speaker would be appropriate.

With ordinary music, at clip the average amount of heat would be a small fraction of the peak power, so multiples of the continuous rating of the speaker can be used, as long as the amp is not clipped and the speakers are not driven to the point where they rip.

A 500 watt continuous speaker should be fine with 1500 watt peaks of “normal” music.
It will go up in smoke with just a bit more than 500 watts of sine wave tones.

So both the “underpowered” school of thought and the “overpowered” are correct, it’s up to you to decide which is appropriate for the way your system is used, and the type of music played through it.



Title: Re: Better to overpower or underpower speakers?
Post by: Andy Peters on June 15, 2009, 07:59:56 PM
Stephen Dranger wrote on Mon, 15 June 2009 15:12

There's another question which would clear up a lot of things for me: does the wattage of the speaker alter how the amp works?


No.

Quote:

Because if I'm not sending the amp a clipped signal, what I'm reading says that I can still clip the amp by cranking the volume.


Yes, you can clip the amp output.  Let me try to explain this in a simple way.

Your amplifier has a specification called "input sensitivity." This is the voltage that you must feed the amp at its input that will drive the amp to Full Tilt Boogie (c). This voltage is spec'ed with the amp's gain control set full. A common value for an amp's sensitivity is 1 Vrms.

That's right -- one little volt will drive your amp to its full output.

So this is why many users will dial back their amps' gain controls so that it requires more signal -- out of your mixer, out of your crossover, out of whatever actually drives the amps -- to drive the amp to full output.

Quote:

But why wouldn't an amp that's rated higher (and 1.5x RMS wattage rating) also start clipping if you cranked the volume on the same signal? Because what I'm hearing is that even if you gave the amp a signal that wasn't clipped, that volume knob is going to push the amp past its distortion level at some point no matter what amp you have.


I suppose I should ask: "Crank the volume WHERE?" Do you mean crank the level going TO the amp, or crank the amp's gain control?

Actually, it doesn't matter.

If the input signal times the amp gain (which is what you set with that big knob) exceeds what the amp can deal with, then you will clip the amp. So that clean input signal at 1.23 Vrms (which is what your mixer outputs when its meter reads 0 dB) will clip an amp with a 1 Vrms input sensitivity when the gain control is all the way up. If you turn that gain control down 6 dB, then you need 2 Vrms to clip the amp and your 1.23 Vrms signal is fine.

The whole point here is that you NEVER want to clip your amp. Why? Because when in clipping, the amp's output can easily be double that of its unclipped state.  So your clean 500 W amp can put out 1000 W when clipped, and if your speakers are rated only for 750 W, you are in trouble.

Does this help, even just a little bit?

-a
Title: Re: Better to overpower or underpower speakers?
Post by: Greg Cameron on June 15, 2009, 08:20:17 PM
Andy Peters wrote on Mon, 15 June 2009 16:59


If the input signal times the amp gain (which is what you set with that big knob) exceeds what the amp can deal with, then you will clip the amp. So that clean input signal at 1.23 Vrms (which is what your mixer outputs when its meter reads 0 dB) will clip an amp with a 1 Vrms input sensitivity when the gain control is all the way up.


One exception to that 1.23Vrms (+4dBu) figure would be Mackie mixers. They use a 1:1 relationship for VU meter to dBu unlike most. I think the only mixer besides their digital one that doesn't conform to their standard is the older 8 Bus "studio" mixer where 0 VU = +4dBu. I figured it was worth mentioning since there are many Mackie mixers in use out there by newcomers.

Greg
Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 15, 2009, 08:26:09 PM
Andy Peters wrote on Mon, 15 June 2009 18:59


I suppose I should ask: "Crank the volume WHERE?" Do you mean crank the level going TO the amp, or crank the amp's gain control?

Actually, it doesn't matter.

If the input signal times the amp gain (which is what you set with that big knob) exceeds what the amp can deal with, then you will clip the amp. So that clean input signal at 1.23 Vrms (which is what your mixer outputs when its meter reads 0 dB) will clip an amp with a 1 Vrms input sensitivity when the gain control is all the way up. If you turn that gain control down 6 dB, then you need 2 Vrms to clip the amp and your 1.23 Vrms signal is fine.

The whole point here is that you NEVER want to clip your amp. Why? Because when in clipping, the amp's output can easily be double that of its unclipped state.  So your clean 500 W amp can put out 1000 W when clipped, and if your speakers are rated only for 750 W, you are in trouble.

Does this help, even just a little bit?

-a


This helps fabulously -- I was not aware of the relationship between the dBs my mixer is putting out compared to the voltage my amp is taking in. It definitely answers my question of why you can still "clip" an amp despite sending it an "unclipped" signal.

My mixer is a Carvin, and I will definitely take the time to look up its specs.
Title: Re: Better to overpower or underpower speakers?
Post by: Greg Cameron on June 15, 2009, 09:02:04 PM
Stephen Dranger wrote on Mon, 15 June 2009 17:26

My mixer is a Carvin, and I will definitely take the time to look up its specs.



You might look up a different mixer while  you're at it, from a different catalogue of course Wink
Title: Re: Better to overpower or underpower speakers?
Post by: Bennett Prescott on June 15, 2009, 09:02:56 PM
Bob Leonard wrote on Mon, 15 June 2009 17:11

Limiters, compressors, etc. are a crutch.

This is where we disagree.

Ideally a system will never be pushed into limit, but properly set RMS limiters can allow a system to achieve its maximum performance nearly regardless of input signal by keeping the heat generating RMS level of the waveform below what the loudspeaker can handle, while maintaining most of the integrity of the dynamics. It's like insurance for your car... no crutch, but a prudent safety margin for that unexpectedly loud show or when you hand the keys to your nephew so he can do a supermarket run.

Now fast, "peak" limiters... those cause more harm than good.
Title: Re: Better to overpower or underpower speakers?
Post by: Greg Cameron on June 15, 2009, 09:15:06 PM
Bennett Prescott wrote on Mon, 15 June 2009 18:02



Now fast, "peak" limiters... those cause more harm than good.


It really depends on the quality of the limiter. There are some really cruddy sounding peak limiters for sure. But there are peak limiters that sound pretty good. Of course, that quality of limiter comes at a premium. Only the most expensive DSPs seem to have ones that are relatively transparent and don't get crunchy. There are some good sounding analog ones as well, though they're not very common these days. The peak limiters that KT used in their older analog DN800 crossover worked very well and let the system get really loud and clean when they were engaging. I have yet to find a low to mid cost DSP that I can say the same about. For subs, I'm using an old Symetrix 501 peak limiter on subs that can hit up to 45dB of gain reduction before it starts sounding ugly. I usually don't hit it that hard but when it's active it actually sounds pretty good.

Greg
Title: Re: Better to overpower or underpower speakers?
Post by: Bob Leonard on June 15, 2009, 09:56:39 PM
Bennett Prescott wrote on Mon, 15 June 2009 21:02

Bob Leonard wrote on Mon, 15 June 2009 17:11

Limiters, compressors, etc. are a crutch.

This is where we disagree.

Ideally a system will never be pushed into limit, but properly set RMS limiters can allow a system to achieve its maximum performance nearly regardless of input signal by keeping the heat generating RMS level of the waveform below what the loudspeaker can handle, while maintaining most of the integrity of the dynamics. It's like insurance for your car... no crutch, but a prudent safety margin for that unexpectedly loud show or when you hand the keys to your nephew so he can do a supermarket run.

Now fast, "peak" limiters... those cause more harm than good.


In the context of the OP's question the use of limiters wasn't really relevent. Maybe what best fits the reply is that the use of limiters or gain controls will often lead to a feeling of false security. Setting the gain structure from board through amp is still the best method of controlling output IMO. Compressing vocals, instruments and the use of Aphex Dominators and such is a seperate subject.
Title: Re: Better to overpower or underpower speakers?
Post by: Bob Leonard on June 15, 2009, 10:24:12 PM
Stephen Dranger wrote on Mon, 15 June 2009 17:24

I guess it's not surprising that I wasn't able to find easy information from anywhere! I keep getting mixed signals; in fact two different Tapco tech support guys gave me two different answers! Sending power to speakers seems to be pretty contentious.

I guess what I don't understand is that if underpowering speakers is bad, should you never ever lower the volume on your amplifier if it's running at ideal voltages? What if you are sending a quiet signal? What's the difference between sending a quiet signal to a sufficiently powered amp and sending a loud (but not clipped) signal to a slightly underpowered amp? A Tapco guy said to me that the reason underpowering is bad is because you want to get a louder signal out of it, and therefore you end up sending a clipped signal to the amp -- clipped = direct current = broken speaker, no matter what the wattage is.

Things are not easy for a newbie...


Steve,
The key point here is that quiet or loud the amplifier doesn't clip. Setting the gain structure for your system properly should allow allow full output at 0db. Full output would be ideal if the speaker handled 500 watts and the amplifier was putting out no more than 500 watts - EVER. Less power would be fine because once again the amplifier is not clipping.

That also answers the reason for the x2 recommendations. It's not only possible, but depending on the type music being played, probable that your amplifier will be called on to produce output levels that actually exceed the long term rating of the speaker. This figure is usually referred to as the "program power rating" and it is a figure that reliable manufacturers use to let you know the speaker is capable of handling those short term peaks.

Having the additional power available to handle those short term peaks almost eliminates the possibility that your amplifier will clip and damage the speaker. That power is held in reserve until needed by the system, so once again, the overall system gain will determine the final output from the amplifier which in almost every case should not be more than the LONG TERM power rating of the speaker.

Here's a thought. Draw a straight line across a piece of paper. On the left side write the number 100. Call that the power output of a 200 watt amplifier producing a steady 100 watt sine wave. Your speakers are rated for 200 watts "program power" 100 watts long term. Push that sine wave to the speaker for 4 hours and you're still OK.

Draw a vertical spike on the line anywhere you want and call it +3db. That equals 200 watts output from the amplifier. Did the amp clip? No, because it didn't exceed it's power output rating.

If you clip the amp you can easily double the output. How long will your 100 watt speakers last??
Title: Re: Better to overpower or underpower speakers?
Post by: John Roberts {JR} on June 15, 2009, 10:27:38 PM
Greg Cameron wrote on Mon, 15 June 2009 20:15



It really depends on the quality of the limiter. There are some really cruddy sounding peak limiters for sure. But there are peak limiters that sound pretty good. Of course, that quality of limiter comes at a premium. Only the most expensive DSPs seem to have ones that are relatively transparent and don't get crunchy. There are some good sounding analog ones as well, though they're not very common these days. The peak limiters that KT used in their older analog DN800 crossover worked very well and let the system get really loud and clean when they were engaging. I have yet to find a low to mid cost DSP that I can say the same about. For subs, I'm using an old Symetrix 501 peak limiter on subs that can hit up to 45dB of gain reduction before it starts sounding ugly. I usually don't hit it that hard but when it's active it actually sounds pretty good.

Greg



At the risk of stating the obvious, clip limiters built in most power amps are in fact very fast attack/release peak limiters.  These are pretty transparent (IMO). The only criticism they usually get is that the amp doesn't get as loud as when defeated.

JR

Title: Re: Better to overpower or underpower speakers?
Post by: TJ (Tom) Cornish on June 15, 2009, 11:01:13 PM
John Roberts  {JR} wrote on Mon, 15 June 2009 21:27



At the risk of stating the obvious, clip limiters built in most power amps are in fact very fast attack/release peak limiters.  These are pretty transparent (IMO). The only criticism they usually get is that the amp doesn't get as loud as when defeated.

JR




Which is pretty much the point, no?

Title: Re: Better to overpower or underpower speakers?
Post by: Bennett Prescott on June 16, 2009, 12:25:08 AM
I don't care how good they sound... a loudspeaker is not a recording, where there is a set level beyond which catastrophic failure occurs. Clipping does not hurt loudspeakers, amplifiers, mixing consoles, or anything. A peak limiter sounds somewhat better than clipping sometimes, and that's great, but a peak limiter cannot control voice coil heating without drastic sonic consequences and loss of performance. The two concepts are opposite. Peak limiters can be used to control overexcursion, sometimes, but everyone is setting their limiter thresholds and seemingly ignoring attack and release.

Greg Cameron wrote on Mon, 15 June 2009 21:15

Bennett Prescott wrote on Mon, 15 June 2009 18:02



Now fast, "peak" limiters... those cause more harm than good.


It really depends on the quality of the limiter. There are some really cruddy sounding peak limiters for sure. But there are peak limiters that sound pretty good. Of course, that quality of limiter comes at a premium. Only the most expensive DSPs seem to have ones that are relatively transparent and don't get crunchy. There are some good sounding analog ones as well, though they're not very common these days. The peak limiters that KT used in their older analog DN800 crossover worked very well and let the system get really loud and clean when they were engaging. I have yet to find a low to mid cost DSP that I can say the same about. For subs, I'm using an old Symetrix 501 peak limiter on subs that can hit up to 45dB of gain reduction before it starts sounding ugly. I usually don't hit it that hard but when it's active it actually sounds pretty good.

Greg


Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 16, 2009, 12:25:15 AM
Bob Leonard wrote on Mon, 15 June 2009 21:24


Steve,
The key point here is that quiet or loud the amplifier doesn't clip. Setting the gain structure for your system properly should allow allow full output at 0db. Full output would be ideal if the speaker handled 500 watts and the amplifier was putting out no more than 500 watts - EVER. Less power would be fine because once again the amplifier is not clipping.

That also answers the reason for the x2 recommendations. It's not only possible, but depending on the type music being played, probable that your amplifier will be called on to produce output levels that actually exceed the long term rating of the speaker. This figure is usually referred to as the "program power rating" and it is a figure that reliable manufacturers use to let you know the speaker is capable of handling those short term peaks.

Having the additional power available to handle those short term peaks almost eliminates the possibility that your amplifier will clip and damage the speaker. That power is held in reserve until needed by the system, so once again, the overall system gain will determine the final output from the amplifier which in almost every case should not be more than the LONG TERM power rating of the speaker.

Here's a thought. Draw a straight line across a piece of paper. On the left side write the number 100. Call that the power output of a 200 watt amplifier producing a steady 100 watt sine wave. Your speakers are rated for 200 watts "program power" 100 watts long term. Push that sine wave to the speaker for 4 hours and you're still OK.

Draw a vertical spike on the line anywhere you want and call it +3db. That equals 200 watts output from the amplifier. Did the amp clip? No, because it didn't exceed it's power output rating.

If you clip the amp you can easily double the output. How long will your 100 watt speakers last??


I'm starting to understand here but here is another piece of the puzzle I'm missing:

If I have my 600W RMS/1200W program rated speaker hooked up to a 1300W amplifier, the idea is I can send a big fat synth sine wave at 600W to those speakers all day, and if there are any sudden peaks, my speakers can handle them, and that'll be the safest way to run my speakers. Whereas if I have a 500W amp, and it is running that same sine wave at its max, 500W, the speakers will still be fine -- but, if any peaks happen, that means the amp will send a clipped signal at say, 1000W, but my speakers can't handle that kind of clipped signal like they could an unclipped signal from the 1300W channel, and they'll overheat or pop or something. That's because the clipped signal from the 500W amp is at 1000W but is more like a sine wave; whereas the speaker is designed to handle the peak signal from a 1300W amp running at 600W RMS.

I think all that is correct.

Here's what I don't get: let's say I go with the "safer" 1300W amp setup. How the heck do I make sure I'm only sending 600W RMS to my speakers? It seems like if I had a 0db sine wave signal and I just cranked up the amp all the way, I'd overheat the speakers because eventually I'd be sending 1300W of RMS to the speakers. It feels like I have to know exactly how far I can push the big volume knob on my amp to get the 46% amount of power to the amp.

I guess my question is: is part of the safety of the 2x RMS setting contingent on the fact that I don't turn up the amp too much?

I should point out that I will in fact be sending sine waves along with peak-y music: I'm going to use it for a synth, vocals, AND sampled recordings.
Title: Re: Better to overpower or underpower speakers?
Post by: Bennett Prescott on June 16, 2009, 12:46:33 AM
Whether or not the signal is clipped has no bearing whatsoever on whether your loudspeaker can handle it or not.

The issue with overdriving an amplifier is, an amplifier that can cleanly supply 500 watts can be severely overdriven and provide 1,000 watts. It will sound horrible, there will be no dynamic range, it will be severely distorted, but the amplifier will do it. That dense, high-RMS-value signal can then destroy a loudspeaker that can only handle 500 watts.

However, if your loudspeaker can handle 1,000 watts (and it's really not this simple, but let's pretend it is to keep the discussion on one path) then that severely distorted signal from the 500 watt amp is probably fine. It will just sound terrible, because you've run out of amplifier long before you've run out of loudspeaker.

You'd be much better off using a 1,000 or even 2,000 watt amplifier and not clipping it. The loudspeaker will see basically the same heat from the signal but, assuming you haven't reached the excursion limits of any drivers, it will obviously sound a lot better.

Side note: That severely clipped signal actually has more RMS heat value than the same signal cleanly reproduced by an amplifier 2 or 4x the size, because all of that clipping generates significant energy in the higher frequencies (clipping = higher order harmonics). In a biamped system this is of little concern, but in a passive solution all that extra high frequency energy is going right into your tweeters. It's basically wasted power that you're throwing away from the low frequencies and dumping into the highs.

The moral of the story is: Use an amplifier that has enough power to drive your loudspeaker to its peak capabilities (which are almost never listed, unfortunately) and then use an RMS limiter to keep the signal from overheating the drivers (one limiter per passband). This will result in maximum performance and fidelity, and is the reason why we (ADRaudio) feed 500+ watts into compression drivers rated for 100.
Title: Re: Better to overpower or underpower speakers?
Post by: Greg Cameron on June 16, 2009, 08:22:27 AM
Bennett Prescott wrote on Mon, 15 June 2009 21:25

A peak limiter sounds somewhat better than clipping sometimes, and that's great, but a peak limiter cannot control voice coil heating without drastic sonic consequences and loss of performance. The two concepts are opposite. Peak limiters can be used to control overexcursion, sometimes, but everyone is setting their limiter thresholds and seemingly ignoring attack and release.



I guess the thing is how the amps are sized for the speakers. I agree that peak limiters aren't the proper tool for controlling voice coil temps. In my case, the amps are sized such that if you are hitting the peak limiters even fairly hard, you are also just under the rms limit of the drivers. So having separate rms limiting is not necessary. If you are using 'oversized' amps, then separate rms limiting would be a requirement with secondary peak limiting for extra protection. As far as self powered boxes go, I believe both type are usually present. I'm sure you as a manufacture's rep are more in the know on that one. But as far as external processing goes or 'smart' amps, it seems that dual functionality limiters are only incorporated in the top end models if at all. That being the case, having an amplifier that can supply 4-5x the continuous power rating of a speaker can be a dangerous thing since peak limiting is the most common tool at one's disposal sans companies with a lot of money. So while your method works for you, it may not be an option for many and sizing amps to speakers is the way to go - IMHO.

Greg
Title: Re: Better to overpower or underpower speakers?
Post by: John Roberts {JR} on June 16, 2009, 09:53:17 AM
Bennett Prescott wrote on Mon, 15 June 2009 23:25

I don't care how good they sound... a loudspeaker is not a recording, where there is a set level beyond which catastrophic failure occurs. Clipping does not hurt loudspeakers, amplifiers, mixing consoles, or anything. A peak limiter sounds somewhat better than clipping sometimes, and that's great, but a peak limiter cannot control voice coil heating without drastic sonic consequences and loss of performance. The two concepts are opposite. Peak limiters can be used to control overexcursion, sometimes, but everyone is setting their limiter thresholds and seemingly ignoring attack and release.




This may not be immediately obvious. Yes the immediate function of a peak limiter is to clamp down gain in response to peaks, this gain clamping down also lowers the average level and total voice coil heating that would occur without the limiter.

I have experienced a related phenomenon in power amp modules. During sharp pencil design, the power transformer is sized just big enough to survive (copper and iron cost money). Using a clip (peak) limiter like DDT makes the difference between life or death for marginal power transformers. This is a direct parallel to the mechanism that destroys voice coils from overheating. Modest sized power models get abused more by customers than larger amps.

So obvious or not, peak limiting reduces average power too. For sound reinforcement silence is the most drastic sonic consequence, so it's somewhat academic to debate performance of a loudspeaker when operated at unsustainable power levels.

Sophisticated protection can apply slow smooth gain reduction in response to measured or calculated VC temp rise, but these are not widely available (yet).  

JR

PS:I know you know this but for the group, excursion limiting is not a simple peak amplitude function, but perhaps within a narrow passband of a multi-way system it could be close enough to be useful.
Title: Re: Better to overpower or underpower speakers?
Post by: Chris Tate on June 16, 2009, 10:34:13 AM
Man....this thread is three pages long.....I can't even be arsed reading through every reply.....

Has anyone pointed out Bennett's article on the main page of PSW?

He is 100% correct....if you don't understand it, read it again....and then again....it well and truly nails the lid on this thread in my humble opinion...



chur


Chris









Title: Re: Better to overpower or underpower speakers?
Post by: Bob Witte on June 16, 2009, 12:45:17 PM
Bennett has hit the head right on the nail - RMS power generates heat, RMS limiter limits RMS signal = limits heat = protects speaker from that failure mode (meltdown).

Peak limiter only can limit excursions IF set up correctly. The reduction of heating power (RMS content) of a fast peak is basically "nil" compared to everything else.

You need to also use your ears - again Bennett stated this - as you can hear (or should be able too) when you are pushing the system to a limit!
Title: Re: Better to overpower or underpower speakers?
Post by: Bob Lee (QSC) on June 16, 2009, 01:00:14 PM
Bennett Prescott wrote on Mon, 15 June 2009 21:25

Peak limiters can be used to control overexcursion, sometimes,



Voltage applied to a loudspeaker is an accelerative force. Therefore, if a peak limiter can be frequency weighted it could control overexcursion.
Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 16, 2009, 01:09:14 PM
Chris Tate wrote on Tue, 16 June 2009 09:34

Man....this thread is three pages long.....I can't even be arsed reading through every reply.....

Has anyone pointed out Bennett's article on the main page of PSW?

He is 100% correct....if you don't understand it, read it again....and then again....it well and truly nails the lid on this thread in my humble opinion..


Thanks so much for the article! It was pretty informative, though I had pretty much gathered most of what it said from this thread.

For posterity, I'll include the link so anyone reading this thread later can find it:
http://www.prosoundweb.com/article/managing_power_to_properl y_use_and_not_abuse_professional_loudspeakers/

I'm still confused about running speakers with 2xRMS powered amps: if I turn the volume knob on the amp up all the way, wouldn't I surely break the speaker if I sent a 0dB organ sound into the amp?

I'm right in thinking that it's just a matter of figuring out how far to turn the big knob on your amp, right? That is, assuming you are keeping your signal under control.

How does one figure out how far they can push their speakers if you're giving them 2x their RMS rating?
Title: Re: Better to overpower or underpower speakers?
Post by: Greg Cameron on June 16, 2009, 01:43:21 PM
Good article indeed. Bennett, you should have mentioned it earlier on, didn't even know it was there. It seems to pretty much cover what I said in an earlier post in this thread: correct amp sizing is important in lieu of true rms limiters. I would add though to that section of the article that peak limiters are important for protection still and that not all peak limiters are created equal. I would also add that if they're the only protection you have, they need to be treated as a traffic light. When you start hitting red, it's time stop pushing. I'd rather have limiter LED's letting me know what's up rather than clip indicators when possible- so long as the peak limiters are of decent quality.

I'll also mention amp sizing when you plan on pushing the limits of your system without rms limiting is no arbitrary thing either. Not all amps of the same power rating work the same way on a given speaker load. Some can produce peaks higher then their average ratings without clipping better than others and some work better with reactive loads at low frequencies. I know the particular setup I run can be pushed all the way into fairly heavy peak limiting without blowing things up by exceeding rms limits and still sound decent as it has been tested over many years by a company that has the resources to do so. Most people don't have the luxury of testing several different amps and blowing up drivers to find the limits of their system and what amp works best for their speakers with peak only limiting. So they need to be particularly careful since it's really a guessing game and only destroying drivers will tell them when they've gone too far.

Also as I mentioned before, rms limiting is not a readily available function on most processors and amps. Even if it was, it's not something that the average Joe would know how to setup correctly. So I guess this could make a stronger argument for self powered boxes where rms and peak limiting are both implemented. Now that's a marketing tool that might deserve a little more attention. That said, systems have been run for many decades that have survived well without rms limiting, though having it would have certainly allowed more output and less headaches I'm sure.

Greg
Title: Re: Better to overpower or underpower speakers?
Post by: Chris Strack on June 16, 2009, 01:46:52 PM
First Thank You Bob Leonard and Bennett Prescott for your posts here. I attached a post from each of you that I think are well written and makes this entire subject a lot easier to understand. I didn't think I was crazy !!

Quote:

Bob Leonard Wrote:

The key point here is that quiet or loud the amplifier doesn't clip. Setting the gain structure for your system properly should allow allow full output at 0db. Full output would be ideal if the speaker handled 500 watts and the amplifier was putting out no more than 500 watts - EVER. Less power would be fine because once again the amplifier is not clipping.

That also answers the reason for the x2 recommendations. It's not only possible, but depending on the type music being played, probable that your amplifier will be called on to produce output levels that actually exceed the long term rating of the speaker. This figure is usually referred to as the "program power rating" and it is a figure that reliable manufacturers use to let you know the speaker is capable of handling those short term peaks.

Having the additional power available to handle those short term peaks almost eliminates the possibility that your amplifier will clip and damage the speaker. That power is held in reserve until needed by the system, so once again, the overall system gain will determine the final output from the amplifier which in almost every case should not be more than the LONG TERM power rating of the speaker.


Quote:

Bennett Prescott Wrote:

The issue with overdriving an amplifier is, an amplifier that can cleanly supply 500 watts can be severely overdriven and provide 1,000 watts. It will sound horrible, there will be no dynamic range, it will be severely distorted, but the amplifier will do it. That dense, high-RMS-value signal can then destroy a loudspeaker that can only handle 500 watts.

However, if your loudspeaker can handle 1,000 watts (and it's really not this simple, but let's pretend it is to keep the discussion on one path) then that severely distorted signal from the 500 watt amp is probably fine. It will just sound terrible, because you've run out of amplifier long before you've run out of loudspeaker.

You'd be much better off using a 1,000 or even 2,000 watt amplifier and not clipping it. The loudspeaker will see basically the same heat from the signal but, assuming you haven't reached the excursion limits of any drivers, it will obviously sound a lot better.

Side note: That severely clipped signal actually has more RMS heat value than the same signal cleanly reproduced by an amplifier 2 or 4x the size, because all of that clipping generates significant energy in the higher frequencies (clipping = higher order harmonics). In a biamped system this is of little concern, but in a passive solution all that extra high frequency energy is going right into your tweeters. It's basically wasted power that you're throwing away from the low frequencies and dumping into the highs.

The moral of the story is: Use an amplifier that has enough power to drive your loudspeaker to its peak capabilities (which are almost never listed, unfortunately) and then use an RMS limiter to keep the signal from overheating the drivers (one limiter per passband). This will result in maximum performance and fidelity, and is the reason why we (ADRaudio) feed 500+ watts into compression drivers rated for 100.


My only additional advise to Stephen Dranger who started this thread is "Gain Structure". It took me some time to understand this concept but it is really important that you read all you can on setting up the proper gain structure for your mixer/amps/speakers. By doing this you will be able to get the most headroom out of your PA system and run it the safest way possible. Turning up the gain control as high as it can go on your amp does not give you the most head room, having a proper gain structure set up between you mixer and amps does. Proper Gain structure also helps you protect your amps from clipping. So if you haven't read about this concept, you need to before you just use your amp bridged and then turn the amp all the way up.

Title: Re: Better to overpower or underpower speakers?
Post by: Art Welter on June 16, 2009, 02:12:52 PM
Stephen,

Power takes a while to burn a speaker.
Too much excursion can instantly kill a speaker.
Excursion is dependent on many factors in the design of speaker and enclosure, and will increase rapidly below the box tuning, which is why it is important to Hi pass woofers.

When speakers are pushed beyond Xmax, they distort.
Some speakers distort quite a bit, some not so much.
Beyond Xmax is Xlim, or Xmech.
Reputable raw speaker manufacturers provide those parameters.
They vary from less than 2mm to over 30mm.
How much power a speaker's voice coil can absorb before burning up is a separate issue than how far it can move.

When pushed beyond Xlim, a speaker may be  mechanically damaged, either by tearing up or deforming the voice coil when it hammers on the back plate.

You can measure the excursion of the cone with a ruler and see how far the cone is moving.
Putting a white dot on the cone makes it easy to see if the grille is removed.
Xmax and Xlim are one way measurements, when you measure a speaker excursion it is easier to see the peak to peak movement, then divide that by two.

Power that pushes a speaker past Xmax is mostly wasted, and just makes for more heating and thermal compression.

Art Welter
Title: Re: Better to overpower or underpower speakers?
Post by: Bennett Prescott on June 16, 2009, 02:48:37 PM
Chris Tate wrote on Tue, 16 June 2009 10:34

Has anyone pointed out Bennett's article on the main page of PSW?

Hey, I didn't know that was out yet! Thanks for pointing it out, I wonder if it'll be in the issue that's available at InfoComm. That would be cool.

Here's a link for those of you who don't, or haven't yet, get the magazine:

http://tinyurl.com/speakerpower

Thanks again to everyone that sent in photos, months ago, for that article.
Title: Re: Better to overpower or underpower speakers?
Post by: Phil Lewandowski on June 16, 2009, 02:51:05 PM
Bennett Prescott wrote on Tue, 16 June 2009 00:46

... and then use an RMS limiter to keep the signal from overheating the drivers (one limiter per passband).


Bennet,

Any suggestions on a limiter or device to do just this?  

I have been searching for a long time and all I have found is finding a limiter that has a long enough attack and release times to achieve this.

Thanks, Phil
Title: Re: Better to overpower or underpower speakers?
Post by: Adam Schaible on June 16, 2009, 03:00:35 PM
My amps have this built in - not sure what your budget is, but they are I-Tech HD's
Title: Re: Better to overpower or underpower speakers?
Post by: Phil Lewandowski on June 16, 2009, 03:04:06 PM
Adam Schaible wrote on Tue, 16 June 2009 15:00

My amps have this built in - not sure what your budget is, but they are I-Tech HD's


Haha, yes I have read and heard much about the Itech's amazing built in limiters, unfortunately, besides the budget problem, it would be going in a rack with all QSC's so that wouldn't be the best for cooling.


So I am hoping Bennett will be able to suggest me something.

Thanks!
Phil
Title: Re: Better to overpower or underpower speakers?
Post by: Greg Cameron on June 16, 2009, 03:06:17 PM
That was my point previously, you can't get rms limiters in all but the most expensive amps and/or processors. It pretty much rules out that type of setup with budget conscious purchasing unless you go with self-powered and processed boxes. Even the lower cost ones seem to provide rms limiting. In lieu of self powered boxes, the other choice is to try and size amps correctly to match the speakers, use peak limiting, and don't push too hard.

Greg]
Title: Re: Better to overpower or underpower speakers?
Post by: Bennett Prescott on June 16, 2009, 03:07:08 PM
Phil Lewandowski wrote on Tue, 16 June 2009 14:51

Any suggestions on a limiter or device to do just this?  

I have been searching for a long time and all I have found is finding a limiter that has a long enough attack and release times to achieve this.

Try using a compressor instead of a "limiter". Any of the quality units should do it, or any DSP that lets you really slow down the limiter. Getting that time constant correct can be the difference of a few dB in output capability.
Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 16, 2009, 03:18:46 PM
Chris Strack wrote on Tue, 16 June 2009 12:46


My only additional advise to Stephen Dranger who started this thread is "Gain Structure". It took me some time to understand this concept but it is really important that you read all you can on setting up the proper gain structure for your mixer/amps/speakers. By doing this you will be able to get the most headroom out of your PA system and run it the safest way possible. Turning up the gain control as high as it can go on your amp does not give you the most head room, having a proper gain structure set up between you mixer and amps does. Proper Gain structure also helps you protect your amps from clipping. So if you haven't read about this concept, you need to before you just use your amp bridged and then turn the amp all the way up.




I come from Recording Land so I am at the very least familiar with the idea of gain structure. What I'm not getting is that even with proper gain structure, how can I make sure I don't overheat the speakers if I'm pumping 1300W into 600W RMS speakers, especially since some of my inputs are going to be sine-wave-like? Is there something I can listen for? Do I just need to make sure not to turn it up all the way?
Title: Re: Better to overpower or underpower speakers?
Post by: Art Welter on June 16, 2009, 03:26:50 PM
Stephen,

If your hearing ability is like your reading comprehension, then no, there is nothing you can listen for.

Smoke 'em if you got 'em.
Title: Re: Better to overpower or underpower speakers?
Post by: Phil Lewandowski on June 16, 2009, 03:28:51 PM
Bennett Prescott wrote on Tue, 16 June 2009 15:07

Phil Lewandowski wrote on Tue, 16 June 2009 14:51

Any suggestions on a limiter or device to do just this?  

I have been searching for a long time and all I have found is finding a limiter that has a long enough attack and release times to achieve this.

Try using a compressor instead of a "limiter". Any of the quality units should do it, or any DSP that lets you really slow down the limiter. Getting that time constant correct can be the difference of a few dB in output capability.


What slow attack and release times do you think are good points to start with?  

I believe I remember seeing the Itech average limiter with an attack time of several seconds.
Title: Re: Better to overpower or underpower speakers?
Post by: Adam Schaible on June 16, 2009, 03:30:05 PM
If you've got a 1300w amp, you'd have to be riding -3db to be pushing 650w continuous.  That's very very high.


What's the sensitivity of your cabs?  Do the math to figure out what 1300w continuous would do compared to say, 130w continuous.  It's a 10db difference, which is significant - but chances are 130w will be plenty of power for you RMS.

On that note, most of the time I try to run the amps at -20db on average.  In your case, that would be 65w (18ishdb gain over stated loudspeaker sensitivity).  Lets say your loudspeaker is rated at 100db 1w/1m - 118db is pretty darn loud.

It sounds like you're small potatoe's, as am I.  Run the amp at -20db and you should be solid.


Side note - is there a way to calculate at what voltage the loudspeaker reaches xlim/xmax?  I believe it's an exponential formula right?  My gut feeling is that this cannot be calculated by T/S specs and has more to do with construction materials.
Title: Re: Better to overpower or underpower speakers?
Post by: Greg Cameron on June 16, 2009, 03:37:10 PM
Stephen Dranger wrote on Tue, 16 June 2009 12:18

What I'm not getting is that even with proper gain structure, how can I make sure I don't overheat the speakers if I'm pumping 1300W into 600W RMS speakers, especially since some of my inputs are going to be sine-wave-like?


Stephen, if you know for a fact that you're going to be running true sine wave signals through your amp for extended periods, get an amp that has a continuous output rating that is equal to or less than the rms rating of the speakers rather than one that is 2x the rms rating and never hit the clip lights on the amps. This is the only way without an rms limiter that you can ensure you won't cook your speakers. Also be aware that a lot of amps don't like running full power sine waves for extended periods of time and will ramp the output down if you're running full tilt. This is especially true with the newer class D style amps and low impedance loads. Older designs will tend to just overheat or pop their internal breaker if you're running low impedance loads with full power sine waves.

Greg

edit: fixed quote
Title: Re: Better to overpower or underpower speakers?
Post by: Art Welter on June 16, 2009, 03:43:25 PM

The voltage that is required to reach Xlim/Xmax varies with frequency.

The voltage ratio between Xlim/Xmax varies with suspension and motor design.
Title: Re: Better to overpower or underpower speakers?
Post by: Adam Schaible on June 16, 2009, 03:49:31 PM
Ok, I should have specified.  We're only interested in the lowest frequencies we're asking the speaker to play right?

So if we're high passing our subs at 40Hz - we could calculate this for 40Hz and set our peak limiters to limit voltage below the calculated value.

Is this possible to do?
Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 16, 2009, 03:50:16 PM
Art Welter wrote on Tue, 16 June 2009 14:26

Stephen,

If your hearing ability is like your reading comprehension, then no, there is nothing you can listen for.

Smoke 'em if you got 'em.

Please, point me to the post in this thread where this answer was given to me. I know I didn't see it.
Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 16, 2009, 04:01:21 PM
Greg Cameron wrote on Tue, 16 June 2009 14:37


Stephen, if you know for a fact that you're going to be running true sine wave signals through your amp for extended periods, get an amp that has a continuous output rating that is equal to or less than the rms rating of the speakers rather than one that is 2x the rms rating and never hit the clip lights on the amps. This is the only way without an rms limiter that you can ensure you won't cook your speakers. Also be aware that a lot of amps don't like running full power sine waves for extended periods of time and will ramp the output down if you're running full tilt. This is especially true with the newer class D style amps and low impedance loads. Older designs will tend to just overheat or pop their internal breaker if you're running low impedance loads with full power sine waves.

Greg


Well, as I said in the OP, I am poor and I'm stuck with what I have Sad

From what one of the other posters wrote, if I don't ever go above 0dBu on my mixer, the amp is not going to distort that signal because its input sensitivity is 1.23V. That means I'm safe running it at 500W. This was echoed by a poster who told me exactly what you just did: run it low and just make sure you never overdrive the amp.

Some people, though, have said that I shouldn't trust that my mixer will never peak above that level, and that running my amp at 1300W would be safer because if I did have any accidental peaks, the amp wouldn't clip and therefore the speakers could handle it. My next question was: how to make sure I wasn't sending too much continuous power to the speakers if I was operating at that high a wattage.

I really appreciate everyone's help and I appreciate most of you being patient with me...hopefully you can see how confusing this is to someone doing it for the first time!
Title: Re: Better to overpower or underpower speakers?
Post by: John Roberts {JR} on June 16, 2009, 04:32:26 PM
Stephen Dranger wrote on Tue, 16 June 2009 14:50


Please, point me to the post in this thread where this answer was given to me. I know I didn't see it.


Regrettably these threads degenerate into a this kind of dueling experts often.

Regarding audible "tells" from loudspeakers in distress, for overheating there is a mechanism before complete melt down called "power compression", where you have to turn  the amps up more than when the speakers were cold to get the same output. This is subtle and hard to hear unless you are pretty familiar with your system and the room.

For over excursion, there is no graceful audible warning. When woofers bottom there will often be a loud snap. This may be terminal on the first event, or give you a second chance if driver is robustly engineered.

For setting level, most amps will have front panel clip or limit LEDs. These will be more accurate to detect (amp) clipping than console meters or calculated gain structure.

If you amp has clip limiters make sure they are engaged.

Good luck.

JR
Title: Re: Better to overpower or underpower speakers?
Post by: Art Welter on June 16, 2009, 05:33:48 PM
Stephen,

Messages #444077, #444087, #444251, #444275, #444286 and the linked article all point out that that when driven too hard, a speaker’s sound will change.

The changes should be apparent  before the speakers are damaged, other than exceeding Xlim.

However, some music is so distorted to start with that it is hard to tell the difference when speakers distort.
Oh well.

If you have a decent set of headphones, you can compare the sound of your speakers to them, using the phones as a reference.

As you start pushing your speakers too hard, there will be a level where they no longer sound the same.
The speakers will be out of their linear operating range.
The point where you need more rig for the gig.
As speakers  exceed Xmax, the woofers will distort.
Distortion sounds different than clean. A pure sine wave will start to sound like a sawtooth wave.
Clean vocals will start to sound like Joe Cocker, etc.
If the woofers or tweeters hit Xlim, they may make clacking, or popping noises.

The voice coils will have heated up, which causes their impedance to rise, and the speakers will now not be as loud, thermal compression has set in.
Compression sounds different than uncompressed, less dynamic. A three dB increase in drive level may only result in a one dB increase in SPL.

As the voice coils change impedance from heating, the passive crossover points and slopes will change.
This sounds different, like an EQ change, usually a “thinner”, “harsher” sound will result.

Get yourself some cheap disposable speaker from Goodwill or laying unused in some closet.
Put your amp in bridge mono mode, play music through the speaker and listen.
Continue to turn the level up a dB at a time every 3 minutes. Use earplugs so your ears don’t distort, and listen for the effects listed above. If you hear clacking noises, raise the high pass filter.

I have moderately clipped a 400 watt amp into eight  4” speakers rated 5 watts RMS apiece, 40 watts RMS total, with no problem. The musical peaks were 10 times the speaker RMS level. Same ratio as 5000 watts into a 500 watt RMS speaker.

I have also (by accident) burned up a 100 watt RMS speaker in approximately one second with a 400 watt 200 HZ sine wave. If I would have turned that speaker up slowly, (and had not been doing tests while drunk) I would have noticed the distortion well before I had exceeded the power level by six dB.
I was reading a dB meter set on “A” instead of “C”, so it read about 6 dB SPL low, using my eyes instead of my ears...

You will probably be quite surprised how much peak power a  speaker will take before it finally burns up if the music has reasonable dynamics.

Art Welter
Title: Re: Better to overpower or underpower speakers?
Post by: Bennett Prescott on June 16, 2009, 05:38:12 PM
Phil Lewandowski wrote on Tue, 16 June 2009 15:28

What slow attack and release times do you think are good points to start with?

This is not a simple issue, and it is difficult to give an accurate answer without knowing a lot about the box, its application, and the drivers. The frequency range being worked with, driver loading, driver capabilities, and excursion can all be an issue. For instance, it is perfectly possible to have a loudspeaker that is excursion, rather than thermally, limited... i.e. (usually at lower frequencies) the driver runs out of excursion before it will ever overheat.

That said, and please be aware that to really get this right takes a lot of almost certainly destructive testing, the best guess for attack and release times for a low frequency driver that I have are on the order of 5-10 dB per second attack, and .5-1 dB per second release. That should be a good starting point, adjust more or less within that range until it is inaudible. Driver overheating generally occurs on the order of 30+ seconds, so these times can be very slow because of that... but too slow and it's too audible, and too fast and it's too audible. We're talking about really very small reductions in SPL here, compared to what we normally nail compressors with. Maybe 3-6 dB, maybe as high as 9 for a really big amp and really abusive source material, but the amp's rail voltage will become the limiting factor again very quickly.

Good luck!
Title: Re: Better to overpower or underpower speakers?
Post by: Bennett Prescott on June 16, 2009, 05:39:50 PM
Art Welter wrote on Tue, 16 June 2009 17:33

If I would have turned that speaker up slowly, (and had not been doing tests while drunk) I would have noticed the distortion well before I had exceeded the power level by six dB.

Don't give away the loudspeaker tuning secrets of the pros, Art!

Art Welter wrote on Tue, 16 June 2009 17:33

You will probably be quite surprised how much peak power a  speaker will take before it finally burns up if the music has reasonable dynamics.

Indeed!
Title: Re: Better to overpower or underpower speakers?
Post by: Phil Lewandowski on June 16, 2009, 06:33:23 PM
Bennett Prescott wrote on Tue, 16 June 2009 17:38

Phil Lewandowski wrote on Tue, 16 June 2009 15:28

What slow attack and release times do you think are good points to start with?

This is not a simple issue, and it is difficult to give an accurate answer without knowing a lot about the box, its application, and the drivers. The frequency range being worked with, driver loading, driver capabilities, and excursion can all be an issue. For instance, it is perfectly possible to have a loudspeaker that is excursion, rather than thermally, limited... i.e. (usually at lower frequencies) the driver runs out of excursion before it will ever overheat.

That said, and please be aware that to really get this right takes a lot of almost certainly destructive testing, the best guess for attack and release times for a low frequency driver that I have are on the order of 5-10 dB per second attack, and .5-1 dB per second release. That should be a good starting point, adjust more or less within that range until it is inaudible. Driver overheating generally occurs on the order of 30+ seconds, so these times can be very slow because of that... but too slow and it's too audible, and too fast and it's too audible. We're talking about really very small reductions in SPL here, compared to what we normally nail compressors with. Maybe 3-6 dB, maybe as high as 9 for a really big amp and really abusive source material, but the amp's rail voltage will become the limiting factor again very quickly.

Good luck!


Thanks Bennett for the info,

And I do understand from other times I've asked this question that there is no one size fits all and you just have to play with it.  Which is what I would love to do!


Now I just have to find an appropriate compressor to use for a job like this...
Title: Re: Better to overpower or underpower speakers?
Post by: Stephen Dranger on June 16, 2009, 10:01:28 PM
Art Welter wrote on Tue, 16 June 2009 16:33


I have moderately clipped a 400 watt amp into eight  4” speakers rated 5 watts RMS apiece, 40 watts RMS total, with no problem. The musical peaks were 10 times the speaker RMS level. Same ratio as 5000 watts into a 500 watt RMS speaker.

I have also (by accident) burned up a 100 watt RMS speaker in approximately one second with a 400 watt 200 HZ sine wave. If I would have turned that speaker up slowly, (and had not been doing tests while drunk) I would have noticed the distortion well before I had exceeded the power level by six dB.
I was reading a dB meter set on “A” instead of “C”, so it read about 6 dB SPL low, using my eyes instead of my ears...

You will probably be quite surprised how much peak power a  speaker will take before it finally burns up if the music has reasonable dynamics.

Art Welter


This was really helpful. I appreciate the advice, even if I don't seem to be quite understanding the plethora of information out there.
Title: Re: Better to overpower or underpower speakers?
Post by: Art Welter on June 16, 2009, 10:54:53 PM
Stephen,

I have mixed thousands of shows on thousands of speakers.
I have burnt a total of four speakers, all on the one night I mentioned when I was testing rather than mixing.

The plethora of information boils down to:

1) Set up your system gain structure so nothing clips before the amps
2) Don’t hard clip your amps, lest they put out lots of squashed power.
3) Properly high pass your LF speakers.
4) When a speaker starts to sound different, don’t turn it up any more.
5) Have ample headroom to reproduce musical peaks.
6) If the music you are playing is really compressed or full of droning sine wave like tones, be conservative with the power ratings, as the average, not peak power is what burns coils.

I have mixed thousands of shows on thousands of speakers.
In that time I personally have destroyed a total of four speakers, all on the one night I mentioned when I was testing rather than mixing.
Make that 6, two tweeters went on another test with a mini line array that had the center tweeters getting 10 dB more power than the outside tweeters, you can view that and many other basket cases in Bennett’s request for speaker failure pictures a while back.

Art Welter
Title: Re: Better to overpower or underpower speakers?
Post by: Jeff Hague on June 16, 2009, 10:56:58 PM
Stephen Dranger wrote on Tue, 16 June 2009 13:09



How does one figure out how far they can push their speakers if you're giving them 2x their RMS rating?


That is determined by properly setting the gain structure through the system as a whole. There are many posts here and elsewhere on how to do that so I wont go into it but the idea is to set everything up such that, if you clip the output of the console, you also clip the input of whatever devices follow that and you clip your amps at the same time - every device clips at the same level. When the system is set that way you wont send an organ sound to the amp that will cause a problem unless you clip the output of the console. Keep in mind that just because the amp can send 1.5 to 2X the RMS rating of the speaker , generally its really nowhere near that (unless you just don't have enough "rig for the gig" to begin with). In fact, it probably isn't sending even 1/8 of that most of the time. Even with an organ / synth patch, its still music after all and it is generally very dynamic. Thats 1 of the reasons that you want all that extra power to begin with - the dynamics. It needs to get really friggin loud for a split second every now and then but most of the time it wont be "sending" anywhere near that amount of power to the speakers. The term "RMS" is the key here and it can be a difficult concept to grasp in these terms. It is roughly equivalent to "average" and amps have an RMS rating and so do speakers but they don't necessarily mean the same thing. An amp that can produce 500 watts RMS typically wont do that. It can, but typically (when the band is playing) it may only really produce 100 watts. A speaker may be rated at 500 watts RMS and that means that you could send a 500 watt sine wave to it all day long and the voice coil wont heat up to the point that it melts. Again, typically that wont happen. The reason you want an amp that can do 2X the RMS rating of the speaker is so that the music can have the dynamics that make it sound good - if you do actually send 1000 watts to the 500 watt speaker, it is only for a split second - not enough time to overheat and melt the voice coil but enough time for the peak to make the music sound natural. Clipping an amplifier generally makes it output behave more like a sine wave (in simple terms) such that you will be sending far more "average" power to the speaker and will heat the voice coil up much faster - not good. Unfortunately, compressing your mix can be similar - it increases the average power sent to the speakers (and limits the dynamic range) so it can also lead to voice coil failure. That is why most folks here suggest that you never compress the overall mix, use limiters if you can and if you have the capability, use RMS limiters whenever possible but always use amps that can deliver 1.5X to 2X the RMS rating of your loudspeakers. The problem is that far too often, even when these suggestions are observed, there just simply aren't enough speakers to handle the gig - that causes clipping and speaker failure...

Edit:
Quote:

that causes clipping and speaker failure...



Thats not really what I menat to say... What I meant to say is that not enough rig for the gig causes the Operator to run the system to its limits in an effort to get "enough" sound and that causes voice coils to heat up and fail...