Chris, you're right on the math. I realize my earlier mistake (I'm surprised modifry didn't catch me on it, like he usually does)...I multiplied the rms POWER by 2^0.5 rather than the voltage. That's a no no, so I was off by an extra factor of 0.5. A 2000Wrms amp would therefore spit out 4000Wpeak, rather than the 3000Wpeak I originally calculated. So, in that particular case the speaker would probably blow. Thanks for keeping me honest.

 

i should have caught that as well... sorry Mac.


still, throw in a small FOS on the speaker (25% or so), and you're at 3750. it would probably be close and would depend on the QA/QC and FOS for the manufacturer.

 

Gee...............thats what I was saying all along...........Hmmm

 

You're definition of distortion seems OK to me, given the context of your ststement. I just think you don't yet have a clear understanding of how distortion and power are related. It may be easier if you draw out several waveforms, one a clean music signal (make it easy on yourself and raw a sine wave) and the other nasty disortion (a square wave is the worst). Now calculate for yourself the power involved in each waveform and you'll see how distortion essentially means "Increasing the average power".

You're right in what you say, but only up to a point, and this is where the engineer in many of us come out to play. The cause is simply too much power, but the reason FOR that extra power is distortion. As Chris just cleared up my math above (oh vey, can't believe I did that...need to stop doing all of that stuff in my head and write it down for once), a 20Wrms deck will output only 40Wpeak power (in the case of heavy distortion, the "peak" now becomes the average power). If the speaker is rated to handle an AVERAGE of 70W, there's no reason it cannot handle the deck's new "average" of 40W.

I would have to look at exactly what you wrote again in the beginning, but I believe my contention with your remark was one of "Why do that", whereas you were making the point in terms of "Just in case". I think we're trying to solve the same problem from different angles, mainly prevention of speaker destruction.

Assuming I understand you correctly, you're telling the guy not to buy an amp that's much more than the speaker is rated for because the distortion at high levels will destroy the speaker, so you should heavily underrate the amp. I agree that you will destroy the speaker (for reasons of high power approaching the spec limits of the speaker, as mentioned above) IF the amplifier is pushed into the distortion range.

However, I'm approaching the problem from another standpoint. I say purchase an amp that is rated 10-20% beyond the capabilities/specs of the speakers. My method, though, requires self-control on the users parts NOT to set the gain too high. By setting the gain correctly, the amplifier should never reach the point of distortion (bad stuff) and still be able to pump out the speaker's rated power. Obviously if you set the gain higher, distortion results, too much power is spent in the coil and POOF. So, you get as much power out of the speaker as it's rated for, no distortion results with the gain set properly, and everyone goes home happy with a properly tuned system that's getting every last ounce of power out of it.

Your point of changing output powers versus car voltage is valid, but up to what point? Set the gain as before to give the power spec'ed on the speaker while the car is running, since this is your typical listening environment. If the car is off, voltage is lower, so you MAY not get the same level of amplification (I say "may" because it depends on the design of the gain stages), but do you really listen to the amp at full tilt while sitting in a parking lot? I see another possibility of where you would be heading with this argument, but distortion from slightly lower voltages is only a real concern as you approach the limits of the amp's design (long sotry short, it took me several hours to figure out why one design of mine started clipping so heavily at max gain when it worked significantly better the day before when running the exact same tests...turns out, someone bumped my bench power supply and knocked it down about 2.5V...que sera).

 

ya know though...

it was never clear -- we are talking about a 2000 watt amp and a 3000 watt speaker. but assumed the 2000 watt amp was RMS and the 3000 watt speaker was peak??

i know i'm splitting hairs, but in reality - this would matter quite a bit, as the 2000 Wrms amp would produce a peak of 4000 W, and the 3000 Wrms sub would be rated for peaks of 6000 W.

it's another case of where being specific really matters.


edit:

 

Sorry, you little weasel, that's NOT what you were saying all along. You don't get out of this whole mess that easy. To quote you from your very first post in this thread, second line...

"I hope I can shed some light on some of the myths and misinformation that has been written in this post regarding car amplifiers. First, any amp can blow any speaker........regardless of its manufacturer or power rating."

This statement is absolutely false. Go take a 500W speaker and hook it up to a Walkman....now tell me if you ever blow that speaker.

 

[QUOTE]Originally posted by PJK3


i should have caught that as well...

 

[QUOTE]Originally posted by PJK3
it was never clear -- we are talking about a 2000 watt amp and a 3000 watt speaker.

 

Oh, and before anyone gets their pantyhose in a bunch, I'm negelecting the cooling power of the cone movement and just assuming the coil has enough cool air flowing around it. In the real world and particularly in closed boxes, you definitely have to take this into account when determining the power handling capability of the speaker coil, but I'm trying to keep this discussion as first-order-problem as possible.

Edit: Evidently I typed in the word "account" as acocu*nt (remove the '*'), so the spellchecker flagged the work as dirty and put instead...now fixed.

 

[QUOTE]Originally posted by MacGyver