i'm trying to prove something to my friend. i'm trying to tell him that if the RMS of a woofer is 250W, and his amp can give out 150W max to that channel..... assuming that everything is flat and the source isn't clipping, he can put the gain to max without worrying about the speaker blowing or clipping.

well, thats my understanding at least. either i get schooled or i get confirmation...

thanks

Speakers blow because of distortion (bad signal, clipping, wrong frequencies) not overpowering (except in extreme cases).

You can give a 5-10W speaker well over that and it will work fine... but the minute you give it too much bass or the signal gets distorted it's gone.

The speakers may not clip, but the amp may well...

Say the HU outputs a 4V lowlevel signal. Say his amp has a gain range of 0.25 to 8V
Setting the gain to 0.25V (max) would mean that the HU could only reach 1/16 of max if he's playing a full amplitude test tone (normal music is rarely at full amplitude, though normally at some point in a song it is (normalization)) before overdriving the amp.

/Michael

The problem is you need to match the HU output(volts) with the amp gain input.If the HU puts out 2volts max, then you set your amp to accept 2volts. Any less(which means turning the setting towards max) would result in possible clipping of the amp and signal.While the wattage would be the same the signal would be clipped. well, thats my understanding at least. either i get schooled or i get confirmation...

Speakers blow because of distortion (bad signal, clipping, wrong frequencies)

but the minute ... the signal gets distorted it's gone

Sorry, can't agree on that - how can we reproduce a distorted electrical guitar?

IMO/E, two things kill speakers - going beyond their mechanical limits or going beyond their thermal limits.

Mechanical limits - running a way to large signal to the speaker (even short term) can make the coil move beyond its limits damaging the coil and/or cone.

Thermal limits - running to much power to the speaker may burn up the coil leading to shorts between turns of the wire or broken wire. Could also lead to failures of glues...

Take a 100W speaker and feed it a 100% distorted signal (square wave) of 10W and it won't complain one bit. The thing is that if you have an amp and speakers matched (say 300W each) and you drive the amp into serious distorsion it will put out more than 300W. If you compare a 300W sinus signal with a square wave of the same amplitude as the sinus signal, the square wave will be 600W.

It's not the distorsion that kills speakers, it's the associated increase in power - if you go beyond the power handling capability of the speaker.

/Michael

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Speakers blow because of distortion (bad signal, clipping, wrong frequencies) not overpowering (except in extreme cases).

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hehe, thats so not true. a few months ago, i decided to start playing w/ test tones. my front stock components are rated 15w. i played a 1khz test tone @ 0db... gain on my amp was about halfway, and it outputs 50w/channel. i had the empeg at -10db , and i start smelling something burning...

well, on a happier note, i finally replaced my fronts w/ 2 CDT-HD62 speakers. i'm loving the mid-bass of these things.

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It's not the distorsion that kills speakers, it's the associated increase in power - if you go beyond the power handling capability of the speaker.

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What's particularly relevant to mechanical failure is the amount of power to the speaker as a frequency distribution. Speakers can handle a certain amount of power at 1kHz, and a different amount at 2kHz, for example. Distortion causes the power distribution curve to change even though the total power may be constant, and this is what can blow the speaker.

Thermal effects of the supplied current (which is all that matters to the amp) are not frequency-dependent (or not to any significant extent, at audio frequencies).

ok, say that the gain is 0.25v-4v. since my empeg gives off roughly 4v, does that mean setting the gain to anything past min (4v) will overdrive the amp?

also, how would you know that the amp is at full power already, and its overdriving? theres no real indication, unless your amp has those diagnostic LEDS.

The potential will be there - if you play a full amplitude sound (generally test tones)

Only way to know is to have perfect ears (I definately don't) or to hook up an oscilloscope to the speaker outputs and play a steady 0 dB note - if the tops are flattened you have clipping.

/Michael

Most music looks more like noise rather that a single tone. While single and 2-tone tests are important ways to measure systems, probably a Noise-Power-Ratio (NPR) test will give you your max gain setting. It's somewhat complicated to run, but it will give you the truest setting.

Definitely agree with the previous posts though: impedance will vary as a function of frequency, so speakers react differently at different freqs. I've been meaning to download some test tones into my RIO for this very purpose. Better yet, how about a test tone routine embedded in hijack???

-ted

This really is a technical area. Defining a speaker as 250W RMS is misleading at best. You could define it as 250W RMS @64-120Hz +-0.5THD with a duty cycle of .5sec, for example. Manufacturers rarely give the full specs out.

These are the important parts of the test. The total power output at a specific frequency range falls inside a tolerance of distorsion for a set period of time.

Physical excusion of the speaker will kill it; that is, too high a voltage going in. Sending a high signal for too long is the same thing. The higher the voltage, the shorter the burnout time.
Reproducing distorsion can be done quite well by most speakers, usually the distorsion is caused by an under powered (or overdriven) amplifier. In this case the amp usually burns before the speaker does. If there aren't obvious signs it was the amp, the speakers are thrown out in error.

Some speakers can handle a high RMS for a short duty cycle but can't win any competitions because they can't deliver over the required time.

Improtantly, having high powered speakers and amps doesn't mean you have to have a stereo only playing loud, it may mean that you play things softly but with less probability of distorsion. But this then brings in a different array of arguments