Power rating question

[Mrcloc]

Hi. What do speakers quote as their power rating? I mean, when they state 100Wrms, does it mean you can push an average of 100W constantly, say a 100W sine wave (or, say, use a 250W amplifier at maximum for music)? And when they state amplifier power of 100W, does it mean they can only handle something like 40W average, since music has a fairly low average? And where does the power rating come from? Voice coil of one of the drivers, crossover, excursion limits?

I'm making the assumption that music will carry a peak (rms) to average power of 40%.

I've read some articles, and I also understand power capability also takes enclosure into account. But how do manufacturers determine the power rating?

 

[GDO]

If your program is a pure sine wave the rms power to the speaker is 50% of the peak power.

Your 40% assumption is hence very pessimistic, or maybe you play synths...

AES standard assumes rms is 25% of peak power, that is the dynamic range of the program is only 6db. Very pessimistic too, but... for heavily compressed music, pa use, might be a prudent one...

For home use, in my case i would assume my rms to peak power ratio might be in the 1-10% range.

Even for tweeters, loudspeakers power ratings for hifi use are not really a matter for concern. No stress, no heat, no problem. At least in my case...

 

[JonSnell Electronic]

This is a good question but a bit of a grey area.
Manufacturers like JBL, Gaus or Black Widow, that are a quality product and have certification like ISO9001 etc, will show on their specification sheet that is available for a particular loudspeaker that 100W RMS means continuous power at 100Watts.
Cheap fleabay and unknown manufacturers that just badge the loudspeaker may state that but not likely to be the case.
Check the spec sheet. Some manufacturers state a power level in RMS but for a given length of time as the speech coils do heat up. A lot list a 1000Watt speaker but when you read into it it actually is rated at less than 1/4 of that.

 

[eriksquires]

Hi. What do speakers quote as their power rating? I mean, when they state 100Wrms, does it mean you can push an average of 100W constantly, say a 100W sine wave (or, say, use a 250W amplifier at maximum for music)?

No consumer speaker I know of is rated for continuous duty. If brand X said "Maximum 100W amp" I would assume it meant:

"Playing music with an amp rated for 100W that is never driven into clipping"

Of course, you can use a bigger amp, so long as you stay below the power envelope.

And when they state amplifier power of 100W, does it mean they can only handle something like 40W average, since music has a fairly low average?

There is no legal requirement, but speaker makers may specify more explicitly the use of certain test signals.

And where does the power rating come from? Voice coil of one of the drivers, crossover, excursion limits?

Maximum excursion is of course the most dramatic. A speaker cone can become ballistic in a single cycle!

Then there's the voice coil which over time can heat up, (causing thermal compression) and then melt. You'll read professional speaker drivers discuss thermal management a lot in their literature.

There are also components in the crossovers which may be over-burdened, especially resistors. This is actually pretty common among speaker failure modes. Modern simulation tools make this less likely than in the past.

Best,


E

 

[Mrcloc]

Ok, thanks! That helps a lot. GDO, I mean music average power vs peak rms power (or pure sine wave), so the 40% is 20% of peak power. Sorry, it's difficult to describe power.

So let's follow the AES standard. Would a 100W rated speaker then be capable (theoretically) of handling 400W peaks? In other words, the ideal amplifier for such a speaker would be 400W?

 

[eriksquires]

In addition to those "absolute" limits, a great manufacturer takes distortion and compression into account as well.

All drivers begin to become non-linear as they reach the limits of their travel. GREAT speakers are operated in a range that this never becomes noticeable. A big plus for a lot of high-efficiency, horn loaded speakers.

 

[GDO]

So let's follow the AES standard. Would a 100W rated speaker then be capable (theoretically) of handling 400W peaks? In other words, the ideal amplifier for such a speaker would be 400W?

Here the question is that power specs for amps are based on pure sines ( peak power is 2XRMS), and AES specs for speakers are based on 6db peak factor ( peak power is 4XRMS).

So forget about RMS, the real thing is not the average but the PEAK, and to match and amp and a speaker they simply should be specified with equal peak powers.

But...this is only valid in the AES attempt to figure out what a musical program is made of. No big science nor truth in all that jazz, just a scenario for a non destructive thermal stress test...

 

[eriksquires]

Mrcloc,

For a "SPEAKER" and not a driver no.

The rating is "100W" represents the peak output, with an average far below.

You CAN use a 400W amp, so long as you don't turn up the volume so the max signal exceeds the rating.

Best,

E

 

[eriksquires]

Peak is important, but as noted in my writing about thermal effects, you can melt a coil over time. That comes from the average power.

 

[eriksquires]

There are a couple of famous proponents of the Uber-amp out there. Bob Carver, Roger Sanders (ESL maker) who feel anything under 250 watts distorts. I've never seen evidence to back up their claims that transient peaks are actually much higher than we think they are.

Personally I'm with Nelson Pass. I prefer the first watt to be the cleanest, not the last 25. ESPECIALLY when it comes to noise measurements. Measuring the relative noise at peak output for an amp makes little sense to me. I want the distortion and noice in the first 50 watts to be absolutely pristine because that is where the music usually lives.

Best,

E

 

[Mrcloc]

Thank you! eriksquires, lots of good info, and pretty much what I would think would simply make sense.

It's a complicated thing, because then a power rating of a speaker tells one nothing about its peak power, unless they quote a standard which can give you the numbers. In addition, the average power tells you nothing about the excursion limits.

If I take the question further, Visaton, for example, quotes a peak power, and generally half that for the nominal power. I would guess the nominal power would be the rated amplifier power then?

And I'm also a firm believer that the 1st watt is the important one, and an amplifier needs to be powerful simply for headroom.

 

[GDO]

Peak is important, but as noted in my writing about thermal effects, you can melt a coil over time. That comes from the average power.

One thing is the rootmeansquare affair, a purely intellectual one mainly used to justify fake power specs regardless of the rms and the peak, and another one is that things get old and used over time and die... as life.

 

[GDO]

If I take the question further, Visaton, for example, quotes a peak power, and generally half that for the nominal power. I would guess the nominal power would be the rated amplifier power then?

Sadly enough, Audio is a country without laws: you cannot trust anybody.

If power really matters to you ( to 99% of human beings it does not at all!) do like the pros: only trust your own experience, based on things you burnt and thing that have resisted.

 

[Lojzek]

My motto regarding power is don't worry about it. Worry about keeping your hearing capabilities so you can enjoy the hobby in your retirement days too. You can't replace your ears as you can speaker units.

I don't think many manufacturers is interested in specifying exactly what power levels the speaker is capable of and for how long. That would be a bad policy. What do you think, for how long can a Ferrari hold its max speed before it breaks down and goes to pieces?

 

[GDO]

how long can a Ferrari hold its max speed before it breaks down and goes to pieces?

How many JBL/RCF/18Sound/etc... super hi-specs hf drivers Lady Gaga might blow in less than one hour?

 

[Mrcloc]

Power isn't what matters to me - it's headroom. More headroom gives better dynamic range. But regardless, I listen at fairly low levels on average. I like the odd song loud. But movies can really test the excursion of your speakers!

 

[Lojzek]

Headroom, well that's an easy one, increase the ceilling height.

 

[charlie2]

my opinion rightly or wrongly......................sesitivity/efficiency...requires....watts =DB

choose your poison

 

[GDO]

Sure, mechanical stress due to cone excursion is a real issue, but power specs only deal with thermal stress, heating, not movement.

Power specs are strictly based on thermal stress tests, nothing else.

 

[basreflex]

part of the AES spec is the temperature of the chassis after 1 hour. the manufacturers should state what temperature of the chassis and magnet structure have been reached at the 1 hour power test. the speaker is hung in free air during the test. a nice padded cabinet insulates more so the AES rating may result a bit too optimistic for cabinets with litte ventilation like horn drivers with closed back chamber. very few manufactrures give the temperature numbers. I called up beyma for the 12nd1000. 95 degrC for the chassis and 106degrC for the magnet structure as far as I remember ..