how much power is enough?

ilikesound

how much power? that's a big question most of the time, what with amps being under-rated, not accurate, so one, so forth. if you go buy a "500" watt amp, how do you know what it's actually pushing? well, it would be nice if someone in the know would key us all in!

example
my alpine mrp-m450 says that it produces 220watts x 1 under a 4 ohm load. i would really like to know HOW exactly to calculate this, and if this rating is BS or a real-world number.

300m

That is a loaded question. In particular when listening to music. Just because an amp has the ability to produce 5oow doesn't mean you will actually use that much power. Maybe when playing pink noise at full tilt boogy. The answer I always fall back on when trying to decide how much power to use is this "As much as I can afford" The speakers I am currently using are ratted 40w continuous and 60w max. The amps I am running on them can produce almost 300w per channel. This is safe when listening to music and NO CLIPPING. Head room is the key here. That means having power in reserve for dynamic peaks in the music. The power going to the speakers will always be CLEAN. If you are always running your amps at near the max power they can produce, when you come across a very demanding passage in the music there will be no extra power to deliver to the speaker. The amp will start clipping and intern increase the heat in the voice coil of the speakers. If your speakers cannot dissipate the added heat, you will destroy your speakers. Plus a clipped signal sounds terrible anyway. As long as you stay with a quality brand of amplifier you shouldn't have any worries about the power they say it can do. Believe it or not price is an excellent predictor for amplifiers performance. Brand x amp at $300 will probably perform similar to brand y amp that costs $300 regardless of how much power they say it can produce. Just my thoughts.

neomagus00

300m - i think you're on the right track, but i don't think all of what you said is universally applicable

first, ignore peak power specs - duh. second, every company has their own methods of testing RMS power output, but they all basically boil down to running a sine wave through and cranking it up till it clips. this is why the new cea-2006 power specs are important, because any company that posts a spec of this form is using the same testing procedure as any other company posting a cea-2006 spec.

the bit about running more than the RMS of the speaker (thiele-small spec 'Pe')... yes, it's true that an amp with a higher power capability than the speakers it's driving will never clip, even with a surge in the music, any decent amp will be able to do this anyways. for low-quality amps, it may be relevant, however.

it is also true that clipping will heat up the speakers much more quickly than a smooth wave, and that heat is the primary cause of speaker death; it is therefore in your best interest to always have at least the Pe of the speaker available.

price vs. performance - not necessarily true. my $500 polk amp will match a true-tech one costing twice that in every audible way. same caveat applies, though - for low-end amps, you do get better sound as you spend more money, but there comes a point where it simply doesn't matter any more. this is a personal opinion and is one of the biggest points of contention in the audio world, so i'll just leave it at that.

rskarvan

6.9 giga-watts is enough.

300m

neomagus00 wrote: »

300m - i think you're on the right track, but i don't think all of what you said is universally applicable

first, ignore peak power specs - duh. second, every company has their own methods of testing RMS power output, but they all basically boil down to running a sine wave through and cranking it up till it clips. this is why the new cea-2006 power specs are important, because any company that posts a spec of this form is using the same testing procedure as any other company posting a cea-2006 spec.

the bit about running more than the RMS of the speaker (thiele-small spec 'Pe')... yes, it's true that an amp with a higher power capability than the speakers it's driving will never clip, even with a surge in the music, any decent amp will be able to do this anyways. for low-quality amps, it may be relevant, however.

it is also true that clipping will heat up the speakers much more quickly than a smooth wave, and that heat is the primary cause of speaker death; it is therefore in your best interest to always have at least the Pe of the speaker available.

price vs. performance - not necessarily true. my $500 polk amp will match a true-tech one costing twice that in every audible way. same caveat applies, though - for low-end amps, you do get better sound as you spend more money, but there comes a point where it simply doesn't matter any more. this is a personal opinion and is one of the biggest points of contention in the audio world, so i'll just leave it at that.

.
Correct, not "universally" the case, there will always be exceptions. But it is a good predictor in "most" cases.

ilikesound

rskarvan wrote: »

6.9 giga-watts is enough.

yes. plenty of headroom to play with there. is that the car from the movie, or did someone mod that?

exalted512

Ill have the capability of running 4450w rms...and thats just if you count what theyre rated at...Closer to 5450w if i had everything turned up. Unfortunately, my speakers wouldnt survive the experience.

All my gains aside from my sub amp will most likely be a 0.
-Cody

MacLeod

Overpowering is the only way to kill a speaker. Either by pushing the suspension beyond its limits or by building up more heat in the voice coil than it can dissipate. And it doesnt matter if that overpowering signal is "smooth" or clipped. A speaker doesnt care what shape the wave is. If its beyond its thermal handling limits, it wont matter.

You should listen to 300M. After all - he builds speakers for a living.

He's not saying hook a 500 watt amp up to a 50 watt speaker, crank the gains and the volume and take off. Think of it like a car. You may only drive around at the speed limit so you think who would want more horspower. But the first time you want to pass somebody in a hurry or merge onto freeway traffic, for those instances the more horsepower you have the better. Its the same here.

You hook that 500 watt amp up to a 50 watt speaker and dont overdrive the speaker (youll know when you are by the tell tale BANGING) and only listen to music that amp wont produce enough power or heat to fry that speaker but when a really dynamic part comes into the music, the amp will have plenty of reserve power to reproduce that part with authority. And a decent 50 watt speaker can handle a 400 watt slam so long as its just a couple seconds.

killerb

i agree. well said.

ilikesound

in some demented way, this was kind of a trick question. i don't know how it got on the topic of heat dissapation, but the questions on the forum always end up somewhere else...
at any rate, the real question was simply this: how can you determine if an amp is truly outputting the amount that it claims? what instrument would one use, and how do you do it? with all the hubbub about "oh, look i have a 1000 watt amp in my trunk" i would love to see the expressions on some people's faces to learn that it isn't true at all.

neomagus00

off the top of my head, ohm says P=V^2/R, so put a sine wave on, measure the RMS voltage across the terminals of the speaker (that's V), divide by the Re of the sub (just measure the resistance across the terminals with the system off - that's R), and compute

does that sound right?

300m

This might help. http://www.audiogroupforum.com/csforum/showthread.php?t=65656

MacLeod

Yeah, the original question was just too easy to answer so we just couldnt resist the urge to derail!