too many watts into a speaker?

[black_labb]

Not that this is particularly relevant to the discussion, but an important back-pocket item to have, is that is for a tube amp. For a solid state amp, you want the opposite, the amp to be 2x the power of the speaker. This is because you do not want the amp to clip and send square waves to the speaker. At high power levels, that will shred it. This is how the pro audio guys setup their racks for live sound.

http://www.prosoundweb.com/article/danger_low_power/
BTW, that's a very good site to dig through. Those guys know their stuff.

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To simplify the measurement process, I'd run a signal generator through the amp with a dummy load and measure power at a couple of different frequencies, like 60 hz, 1 khz, and maybe at 5k. From there do the RMS calculations and get an idea of where your volume knob range is.

i didnt read the article, but if its saying that suqare waves are very harmful to speakers, its not really true. the square wave isnt any more harmful than a sin wave. its just alot of harmonics. the only real danger is all the harmonics blowing a tweeter, but usually there are protection circuits to protect them. only other consideration is the square wave having a higher watts rms rating.

keep in mind that synths use square waves as an effect, and they are played through speakers all the time.

thanks for the help re the power calculating MWJB. will have to try that to see what i am getting out of my amps.

[Bruce / Mission Amps]

You are forgetting the time constant

Wait a sec... I think square waves are very harmful to speakers driven to their max power because the speaker cone is thrown out to it's excursion limit and held there for a longer moment in time, drawing max current.... then it is slammed backwards to the inner stop and does the same thing but in the other phase.
It's like connecting a + DC voltage and then slamming it negative..

9vac across a perfect 8 ohm speaker is about 10 watts.
But it is not 9v very long because it starts at zero and ramps up to 9v and then back down to 0v and then ramps further negative to -9v... any 15 watt speaker should be able to handle that... now connect a tiny 9v transistor battery to the speaker leads and watch what the speaker does with respect to where it physically goes.
Same 10 watts if it was an unlimited current source but it stays there drawing max current until you reverse the battery and then it stays there forever!

If you have an amp that can put out a lot of power in square waves, the average time the speaker is handling max current (in max speaker excursion) will be quite a bit more then a clean sine wave at the same max output voltage.
The voice coil will overheat, distort and eventually fail or at the very least,
cause a severe voice coil rub and buzz.

Unless you can guarantee never exceeding speaker power limits, anyone who runs a 100 watt speaker from a 200 watt SS amp is using the speaker as fuse to protect the PA finals.

[tubeswell]

On the square wave versus sine waves...

If I dredge through my memory, I dimly seem to remember learning about functions at high school. The area under the sine wave (on a wave function plot) indicates something useful (if I remember correctly). And if you compare the area of the graph under a sine wave function to the area of the graph under a square wave function where the 'tops' and 'bottoms' of the square wave are at the same y axis measurements as the peaks of the sine wave, and the frequency of both waves is the same, then the area under the sine wave is about half the area of the area under a square wave IIRC. (Danged if I can remember the function formulas tho' - But I have been known to blow out a speaker or two). Now I would say that has something to do with comparing power of sine wave AC versus square wave AC.

[defaced]

Yea, you're talking about integrating. RMS for sine waves is different than RMS for square waves. And you're about right on the amplitude (way down the page): http://www.allaboutcircuits.com/vol_2/chpt_1/3.html

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The thing to think about is that music is not a lab created wave. It's very dynamic with regard to frequency and aplitude. A solid state amp is limited by max power, a tube amp can saturate and give more power with compromized fidelity, and a speaker has a program and a max power. I can run 100w continuous into a speaker with a hit of 200w every once in a a while (kick drum for examples) and it'll sit there all day long and smile - if the 200w is a nice clean wave. If it's clipped you'll get what Bruce is talking about. So you need an amp with the head room.

When people talk the two, amps and speakers, they're usually mixing the two kinds of power which is comparing apples and oranges.

And which is worse, speaker distortion from over power by a clean source, or square wave amp distortion into an under powered speaker? That's really what we're weighing.