Help me understand the usefulness of peak power ratings.

[yepimonfire]

Let's assume an 8 ohm speaker is rated for 75w continuous, that's 24v RMS. Since power handling is generally derived using pink noise with a 6dB crest factor, that gives a peak power handling of 300w, or 48v. For the sake of simplicity, let's just assume this rating is 100% accurate.

What I'm confused on, is whether this means a speaker can handle a 300w burst of a couple of seconds (for example, let's say a gunshot sound or a heavy hitting bass drum) without being destroyed, or if it simply means at 24v RMS, the speaker can safely handle +-6dB dynamics, for example, listening to a rock album with a compressed dynamic range of 6dB at 75w continuous, vs an orchestra with 12dB of dynamic range at the same average power.

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[Irvrobinson]

Speaker power handling ratings are almost always meaningless. I recommend ignoring them completely. There are no standards for what they mean or how they are determined. This is perhaps the silliest and most unreliable specification in the entire audio industry.

 

[shadyJ]

Speaker power handling ratings are almost always meaningless. I recommend ignoring them completely. There are no standards for what they mean or how they are determined. This is perhaps the silliest and most unreliable specification in the entire audio industry.

Yup, all you have to do it use common sense. How much current can that coil take before it falls apart? It can't really be stated, since different conditions will have differing effects. The higher frequencies will burn the coil, while lower frequencies will overdrive the moving assembly. There are ways to kill a speaker well under its rated power handling, and there are ways to safely drive it with more current than it is normally rated for.

 

[ski2xblack]

@Yep, it's not just the raw power that damages speakers, but that plus the length of time over which the power is applied.

The leading edges of notes, hard drum strikes, or gunshots typically have a duration of a tiny, tiny fraction of a second, with the body of the note or sound at much lower levels. Even though high power is necessary for these leading edge transients (and the coils will indeed heat up when the power is applied), because it's so brief, the coils then immediately begin to cool back down, and no speaker damage ensues.

 

[Pogre]

Speaker power handling ratings are almost always meaningless. I recommend ignoring them completely. There are no standards for what they mean or how they are determined. This is perhaps the silliest and most unreliable specification in the entire audio industry.

That's one of the things I learned here and it makes sense. You can tell when a speaker starts to struggle and that's when you dial it down a notch or 2. I haven't paid attention to power ratings on speakers in a while now.

 

[yepimonfire]

So how do you determine what's safe and what isn't? Obviously, distortion is a warning sign, but I'm willing to bet there are circumstances where no audible distortion would be heard in cases of thermal overload at mid and high frequencies. For example, a 5.25" driver could easily output 127dB at 1500hz @1m with only 2mm of total travel, although this would require about 10kW assuming an 87dB sensitivity. The major source of distortion in well damped woofers (>10% thd) is caused by the nonlinear behavior of the driver and motor assembly when large amounts of excursion cause the voice coil to travel to the outer limits of the magnetic gap (exceed xmax). If a driver has a total of 5mm of xmax, and can easily reproduce a 100hz sine wave at 100dB using 25w with little distortion, would a high frequency sine wave well below xmax present distortion, or would there be no real warning assuming unlimited amplifier power?

How can one determine a safe level of peak power? Again, back to the gunshot sound. Recognizing that the majority of the frequency content of a gunshot is in the mid and lower high frequencies, its unlikely we will exceed xmax, let's assume a driver can handle 100w continuous with full range pink noise. At 87dB 1w1m, this is 106dB. If someone were to be seated 10' from the speaker, watching an action movie with the volume turned to 0dBfs, and a gunshot's peak sound utilized the entire dynamic range of the soundtrack (105dB), it would send (assuming a capable amplifier) 600w to the speaker at the crest of the soundwave, would this spell instant death for the speaker considering that would be 6x the rated continuous power or would it likely be fine due to the extremely short duration?

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[shadyJ]

So how do you determine what's safe and what isn't? Obviously, distortion is a warning sign, but I'm willing to bet there are circumstances where no audible distortion would be heard in cases of thermal overload at mid and high frequencies. For example, a 5.25" driver could easily output 127dB at 1500hz @1m with only 2mm of total travel, although this would require about 10kW assuming an 87dB sensitivity. The major source of distortion in well damped woofers (>10% thd) is caused by the nonlinear behavior of the driver and motor assembly when large amounts of excursion cause the voice coil to travel to the outer limits of the magnetic gap (exceed xmax). If a driver has a total of 5mm of xmax, and can easily reproduce a 100hz sine wave at 100dB using 25w with little distortion, would a high frequency sine wave well below xmax present distortion, or would there be no real warning assuming unlimited amplifier power?

How can one determine a safe level of peak power? Again, back to the gunshot sound. Recognizing that the majority of the frequency content of a gunshot is in the mid and lower high frequencies, its unlikely we will exceed xmax, let's assume a driver can handle 100w continuous with full range pink noise. At 87dB 1w1m, this is 106dB. If someone were to be seated 10' from the speaker, watching an action movie with the volume turned to 0dBfs, and a gunshot's peak sound utilized the entire dynamic range of the soundtrack (105dB), it would send (assuming a capable amplifier) 600w to the speaker at the crest of the soundwave, would this spell instant death for the speaker considering that would be 6x the rated continuous power or would it likely be fine due to the extremely short duration?

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That depends on certain factors, like how hot is the coil already, how well can it dissipate heat, etc. Pro-audio drivers for live sound applications go to great lengths to both reduce heat buildup and also withstand heat buildup. My guess is that a very brief power surge to a typical driver like you describe might not destroy the driver.

 

[Irvrobinson]

ShadyJ's response was a good start, but there are so many factors that you basically can't know what a speaker will handle and give it a figure of merit in watts. Spectral balance, for example. If try to blast some heavy metal music to 100db at your listening seat 15 feet from the speakers, which might have a lot of power in the lower range of the tweeter, you might blow your tweeters with less than 20W of power. Organ music might do something similar to smallish woofers +/- an octave centered at 60Hz. Use common sense - for conventional speakers you need a lot of voice coils to dissipate a lot of power. Those RBH things that ADTG and Gene use are good examples, as are the higher-end speakers from Legacy Audio.

 

[Irvrobinson]

For example, a 5.25" driver could easily output 127dB at 1500hz @1m with only 2mm of total travel, although this would require about 10kW assuming an 87dB sensitivity.

I'm sorry, I just read this response. What makes you think a 5.25" driver's voice coil could handle 10KW, even for a short duration? My guess is that the crossover is likely to get fried too.

 

[TLS Guy]

Numbers don't mean much. Drivers are easier fired than you think especially tweeters.

There are just so many factors, of which probably the most dominant is program.

Voice coils are not made of toaster wire! They are made of fine copper or aluminum wire with a low melt point and the insulation is easily cooked. In fact the insulation is often the first thing to go. You then have a lower impedance driver of lower sensitivity and a recipe for amp failure. In my experience this form of failure is more common then open circuit failure. I think it can go unnoticed for extended periods.

Speaker factors are robustness of the suspension, whether or not the VC wire is flatenned and edge wound, cooling of the cap, keeping the gap space small. For tweeters ferro fluid really helps reduce tweeter failure.

It is always important to remember the out of band power. A spec may correctly say a crossover is fourth order. However the acoustic roll off may be second order and then the electrical crossover is second order. So there is much more out of band power than you think.

Compressed rock music can be death to drivers, especially tweeters.

Classical music often has tremendous mid and high frequency energy, from huge brass and percussion sections.

Baroque pipe organs in particular can have continuous energy in the HF tweeter range that is continuous. It is very easy to blow tweeters with this program.

As far as avoidance, I like to keep tweeter crossovers as high as possible with careful driver selection. I like to have two VC on the midrange if at all possible. If I can use two 10" woofers rather than a single 15" I will. Actually it is in the 80 Hz to 2.5 KHz range that most speakers are woefully short on power and output. That is why I don't listen to bookshelf speakers out of preference. To say bookshelves and a sub is equivalent to a larger more capable speakers is not true.

As far as telling if you are about to blow a driver, that is difficult. Speaker distortion apart from hard motion limitation of a woofer is hard to spot. The best bet is to listen for thermal compression and note if the crescendos are getting blunted and lacking detail.

And last always remember pretty much any driver is destroyed by a lot less power than the manufacturer says it will be.

 

[yepimonfire]

Does horn loading help at all? I've noticed klipsch tends to use xover points that would normally destroy tweeters that were direct radiating.

Basically, is it safe to assume if the sound sounds clear, open, and dynamic, you're likely safe?

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[shadyJ]

Horn-loading helps in the sense that it boasts efficiency and sensitivity so that you need less current to achieve higher SPLs. It doesn't do anything to cool the drivers as far as I know, unless the horn itself were made from a material that could possibly help as a heatsink. The lower crossovers are due to the higher acoustic impedance on the diaphragm of a horn-loaded driver, ie. since its contact with the air is more 'effective' and it does not need as large excursions to generate the same SPL.

I don't think it is safe to assume that if the speaker sounds fine, it is not near its limits. It can sound fine and then just die instantly as the adhesive that binds the coil is cooked off.

 

[TLS Guy]

Does horn loading help at all? I've noticed klipsch tends to use xover points that would normally destroy tweeters that were direct radiating.

Basically, is it safe to assume if the sound sounds clear, open, and dynamic, you're likely safe?

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As horn loading may increase sensitivity, it will reduce VC heating somewhat. However if you do an Internet search you will see that Klipsch very likely does have an excess incidence of tweeter burn out on some models.

You can never assume a driver is safe from burnout, especially tweeters, by how the speaker sounds. If you are playing at low or moderate volume in all probability you will be safe. At higher power all bets are off.

 

[TheWarrior]

Harman's Northridge CA facility has their loudspeaker torture room. A double bulkhead room where they torture test individual drivers for 24+ hours. You could smell the death that had occurred in there!

Point is, loudspeaker specs are one of many areas this industry could really stand to see some standardization. Think of the usefulness of the sidewall of a tire. Weight rating, speed rating, weather rating, size, width, recommended pressure stamped right on the side. Almost no speaker/component manufacturer comes even close to offering that amount of comprehensive data, and worse, many of them lie, especially in regards to frequency response.

 

[yepimonfire]

As horn loading may increase sensitivity, it will reduce VC heating somewhat. However if you do an Internet search you will see that Klipsch very likely does have an excess incidence of tweeter burn out on some models.

You can never assume a driver is safe from burnout, especially tweeters, by how the speaker sounds. If you are playing at low or moderate volume in all probability you will be safe. At higher power all bets are off.

I see you're of the opinion modern klipsch speakers (post audiovox takeover) are junk, why is that?

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[everettT]

I see you're of the opinion modern klipsch speakers (post audiovox takeover) are junk, why is that?

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Pretty sure he said "some" models. But if you push him I'd bet he will trash the entire line

 

[yepimonfire]

Harman's Northridge CA facility has their loudspeaker torture room. A double bulkhead room where they torture test individual drivers for 24+ hours. You could smell the death that had occurred in there!

Point is, loudspeaker specs are one of many areas this industry could really stand to see some standardization. Think of the usefulness of the sidewall of a tire. Weight rating, speed rating, weather rating, size, width, recommended pressure stamped right on the side. Almost no speaker/component manufacturer comes even close to offering that amount of comprehensive data, and worse, many of them lie, especially in regards to frequency response.

I 100% agree. I'd like to see the same data sheets used for pro cinema speakers or even pro audio speakers applied to HT speakers. It would at least be nice if manufacturers would explain how they derived their numbers, for example, it's a little known fact klipsch derives their sensitivity ratings in a reverberant field similar to a typical living room, nobody else does this, it's usually anechoic, which is why reviews will find their speakers are about 3dB lower than claimed.

Low frequency response can be derived either full space, half space, 1/4 space, or even 1/8 space, Polk audio comes to mind as an offender here, for example, their massive rti a9 is spec'ed at 30hz -3dB, yet sound and vision measured 49hz -3dB. I have no doubt they can achieve 30hz in room, but it'd be nice to know how the measurement was obtained.

Nearly every speaker manufacturer rates their response as being +-3dB, yet most consumer HiFi/HT speakers, including many high end flagship models, fail to achieve this degree of linearity.

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[Irvrobinson]

I see you're of the opinion modern klipsch speakers (post audiovox takeover) are junk, why is that?

They stopped using compression drivers and started using dome tweeters, and there has been a thread or two on this forum about blown tweeters. And Mark is a perfectionist who designs and builds his own speakers (not that there's anything wrong with that). FWIW, he also thinks the Revel Salon2s I use are poorly designed. ;-)

 

[TLS Guy]

Pretty sure he said "some" models. But if you push him I'd bet he will trash the entire line

It is principally the speakers using this diaphragm.

One clue is that "every man and his boy" is selling them.

 

[TLS Guy]

I 100% agree. I'd like to see the same data sheets used for pro cinema speakers or even pro audio speakers applied to HT speakers. It would at least be nice if manufacturers would explain how they derived their numbers, for example, it's a little known fact klipsch derives their sensitivity ratings in a reverberant field similar to a typical living room, nobody else does this, it's usually anechoic, which is why reviews will find their speakers are about 3dB lower than claimed.

Low frequency response can be derived either full space, half space, 1/4 space, or even 1/8 space, Polk audio comes to mind as an offender here, for example, their massive rti a9 is spec'ed at 30hz -3dB, yet sound and vision measured 49hz -3dB. I have no doubt they can achieve 30hz in room, but it'd be nice to know how the measurement was obtained.

Nearly every speaker manufacturer rates their response as being +-3dB, yet most consumer HiFi/HT speakers, including many high end flagship models, fail to achieve this degree of linearity.

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A speaker that can really perform well at high power is a formidable affair. As I have pointed out the power demands in the 80 to 1.5 KHz range are huge, especially from 80 to 600 Hz. To be realistic you really can't do that at above all a size and secondarily the expense that most will tolerate.


However that does not excuse dishonesty.

Getting the power required in the power band to reproduce large forces cleanly at concert level is the reason for my unique design approaches. This includes TL loading to really control driver excursion, and support output. Sharing the power band among sufficient drivers with robust motor systems supported by adequate amp power. Doing this does require a solution that can not be done entirely with passive crossovers. I wish their were short cuts, but if there are I don't know of them.