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Maximum Amplifier Power

4528 Views 109 Replies 23 Participants Last post by ChrisDixon, Mar 24, 2005

BNW

Discussion Starter · Feb 23, 2005

I run B&W 605 lefts & right fronts, LCR600 center, & 602 rears. I auditioned & loved the Bryston 6B SSB 300W/CH amp much more than the 4B SSB 200W/CH amp. My question is can i run that kind of power fornt & rear or even just the front three?

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ijd

· #2 · Feb 23, 2005

Speakers draw the power (current) they need to reach the volume (voltage) you operate them at ... the amp doesn't force-feed the power onto an unwilling speaker!

Average 'loud' (~90dB SPL) listening volumes only draw an average of about 1 watt from the amp ... but millisecond peaks may require 10 or 100 times that power, hence the more "open" sound from having higher-powered amps drive the speakers to the same average volume. This extra reserve is referred to as "headroom".

So the short answer is: Take the one that meets your sound quality and budget requirements ... both would be good choices (though I haven't heard either of them). (FWIW ... and as a sweeping generalisation

... I reckon one needs 200W/ch from a high-current amp for clean analogue sound at 90-100dB SPLs with full-range speakers. YMMV.).

BNW

Discussion Starter · #3 · Feb 23, 2005

Thanks for the explanation from down under. I never understood that. The 300W unit did sound so much more open & dynamic & all those words i've never understood here, having always used only a 120W x 5 receiver. In audio, just as in life, power is addicting.

ChrisDixon

· #4 · Feb 23, 2005

I still don't undertand the mixed messages that are sent on these forums regarding amp power. On one hand, you often hear the reality that ijd said above: at very loud levels, your amp is only using 1-3 watts. On the other hand, you hear people saying that more power = better sound quality and imaging (especially with music). Break out your SPL and listen to music at 90db. I don't know about you, but I don't usually listen much louder than that, and I am generally more comforatable in the 80s for "loud" listening. So, what is it about headroom (that is almost never used) that makes a system sound better?

It's probably similar to the "all amps sound the same" argument, but if you compare apples to apples, the difference between a true 100watt amp and a true 200watt amp is probably only noticable at ear-bleeding levels, or in a cavernous room. If you are in a typical room with typical listening habits, my guess is that there may be a few seconds per week that might actually sound different - especially given the fact that your sub amp takes the most demanding job of low bass during movie passages!

The key here is "apples to apples" (amp to amp with adequate power supplies and the same pre/pro for example). I totally agree that a 200 watt separate amp sounds better than a 100 watt receiver, but the reasons for that are many. Just read any receiver vs. separates thread to see why. Am I completely off base here, or is extra "headroom" one of the more overrated priorities?

Chris

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BNW

Discussion Starter · #5 · Feb 24, 2005

Chris, I'm not very educated regarding any of this. I listened to a 200W two channel Bryston stereo amp through the Bryston pre-amp out of paradign studio 20's as I remember. Then muted the sound, which was Bela Fleck's flight of the cosmic hippo which is my audition test piece. Unplugged the 200W & plugged in the 300W 6B SST which is a 3 channel, but obviously didnt use the third channel. The difference was very distinctive. Huge really. All the positive adjectives that people use here became clear to me. I listen to movies 5:1 over music. My second thought was that if I got this amp i would change that to maybe 2:1. It was that good! I've worked in indyCar and other racing series my whole life as well as shops & now on military aircraft. I never thought i'd be able to really discern the subleties people talk about here, but here I am singing there praises. This is gonna cost me a forture!

DMF

· #6 · Feb 24, 2005

Chris, a 90 dB average listening level may well have 120 dB peaks. Assuming you have 90 dB/[email protected] efficient speakers, you're probably using 4W for 90 dB at the listening position.

Here's your assignment. Knowing that power doubles every 3 dB, starting with 4W at 90 dB, how many watts does it take to feed the 120 dB peaks?

Grond

· #7 · Feb 24, 2005

If they are 90db anechoic efficiency then it's probably close to 1 watt at the listening postion for 90db unless it's a very heavily damped room. In my opinion it is also a noticeable difference listening to music with 110 db peaks which would only take 100 watts which would suggest the max power used is not the only factor. If I were to try to describe it I would say it sounds like the amp has a more iron fisted control of the speaker drivers and prodcues a clearer, cleaner sound. In audio techno jargon I believe it would be called better transient response.

DMF

· #8 · Feb 24, 2005

Grond, is your name Chris? Or don't you think he can do the math?

Grond

· #9 · Feb 24, 2005

I didn't answer the question you gave him.

You shoud have made it simpler for him though and explained +10 db = 10x power. The point is though even when your not using the extra power the more powerful amps tend to sound different.

DMF

· #10 · Feb 24, 2005

That makes it sound additive, as if +20 dB is 20x the power. It isn't. +20 dB is 100x. And my method give him a better feel for how quickly the power requirements can change.

ChrisDixon

· #11 · Feb 24, 2005

I do know the math. My argument was not the requirments for 120db peaks or highly inefficient speakers. My question was around opinions that I often hear that music sounds a lot better with more overhead like BNW's anecdote above, and Grond's statement that "more powerful amps tend to sound different". These statements may be true. I just want to know why.

Just for fun, I listened to some loud progressive metal last night (Dream Theater) with an SPL meter at levels that made me uncofmfortable. Even at this level, I did not peak higher than 92-93db. I also tried some stuff that has "sub-human" bass (Peter Gabriel's Sky Blue for example), and again... not even close to 100db, which is what, 10wpc? If I did an a/b comparison with a 100wpc amp and a 200wpc amp, what would be different when I am using 10% vs 5% of the available power? This is pure speculation (that's why I posted the question - I'm curious to hear opinions). My guess is that if I heard a difference at all, it would be due to some other piece of the construction that was better in the 200wpc amp, not the overhead itself.

It seems to me that the average consumer buys more powerful amps with the same thought process as a more powerful car engine: better performance from 0 to 60. This is not the case with amps as we know. Using that same analogy, I wouldn't buy a V6 if it only meant better acceleration between 100 and 120 mph for the two times per year that I may do that.

Chris

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DMF

· #12 · Feb 24, 2005

Your SPL meter gives you a weighted average - either A weighted, or C weighted. It does not track peaks. (It is also rather insensitive in the bass range where most current draw occurs). I rather suspect that is the source of your confusion.

The car analogy is inapt for amp power since the source signal defines the motor acceleration and the amp either provides the power or doesn't. (The buyer may indeed be thinking that!

)

To tell you the truth, I'm not convinced that increased overhead makes *that* much of a difference. But it does make a difference. And clipping certainly does.

Another facet to this issue is that receiver ratings don't seem to be real. From what I understand "100W" from a receiver and "100W" from a decent power amp (separate) is not the same 100W. Lots of games being played with the ratings. While 100W from the amp might be enough, the receiver might not be. And here I thought we got this all settled in the 80s!

dsmith901

· #13 · Feb 24, 2005

Chris,

The SPL meter you used in all likelehood was much too slow to measure dynamic peaks, which could easily hit 110-120 DBs for a very short duration - the meter will never show that. And it is those very brief peaks, usually the onset of a note, that usually allows a high current amp to keep up without clipping, and hence sound much better than a lesser amp. A typical speaker may demand 500-1000 watts during those brief dynamic peaks, and all but the most powerful amp will clip noticeably. And if that clipping continues long enough your tweeters will be damaged. Even though most amps are capable of exceeding their max rating for brief periods, 1000 watts is way beyond the capability of all but the most powerful amps. And not just tweeters are at risk. For example, get the Telarc CD of the 1812 Overture and play it at reference volume with your 100 watt amp on full range speakers, and when the cannons go off watch the smoke come out of those woofers. Time to buy new speakers.

ChrisDixon

· #14 · Feb 24, 2005

Good point about the slow SPL meter. I didn't realize that the actual peaks are THAT much higher than the weighted average. See, I'm willing to admit defeat if I hear a good explanation! I'm curious to know how often these peaks hit, and how audible they are if the clipping is a small fraction of a second.

This is a good resource, by the way:

http://www.myhometheater.homestead.c...alculator.html

It gives a pretty good indication of max SPL (taking into consideration room, sensitivity, distance, number of speakers, etc.). 100 watts gets my system to 110db according to the chart.

For the record, I have a 125wpc Anthem PVA7, which is supposed to be conservatively rated. I totaly agree (and said so earlier in this thread) that receivers are a whole different ballgame, and amp ratings in general are a mystery as DMF implied.

DMF

· #15 · Feb 24, 2005

Cool calculator. Grond, plug in the numbers I used in the example. Assume 3 speakers away from walls and 12' to the listening position. How many watts amp power does it take to get 90 dB at the listening position? That number look familiar?

Vergiliusm

· #16 · Feb 24, 2005

I'm with Chris on this one. Who in the hell is going to listen at an average of 90 dB and even if they do(very unlikely, especially if they want to keep their hearing),who isn't going to have a sub and its amps for those 120 dB peaks?

gwsat

· #17 · Feb 24, 2005

I listen at an average level of about 65-70dB with almost all peaks less than 95dB using C weighting. That's loud enough for most people. My subs, two old Hsu HRSW10s, take almost everything my 375w per channel Carver M1.5t amp can give them at those levels. Thus, I am convinced that there is no such thing as too much power. I agree that all amps OF APPROXIMATELY EQUAL POWER are pretty much alike. But I disagree that 50w per channel is going to provide sound at reasonably loud listening levels, which is as good as that of a 200w per channel amp.

dsmith901

· #18 · Feb 24, 2005

Here is a good read on amp power requirements:

http://forum.ecoustics.com/bbs/messa...79/109459.html

ChrisDixon

· #19 · Feb 25, 2005

I would be curious to know how much power those dynamic peaks require from the amp when the sub takes the lower frequencies. dsmith's article also points out that speakers may suffer dynamic compression when given spikes of power from a clean beefy amp anyway. At any rate, it's been an interesting exercise.

Chris

Grond

· #20 · Feb 25, 2005

Quote:

Originally posted by DMF
Cool calculator. Grond, plug in the numbers I used in the example. Assume 3 speakers away from walls and 12' to the listening position. How many watts amp power does it take to get 90 dB at the listening position? That number look familiar?

Now try near a wall and then try in the corner. See the difference?

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