Axiom Home Page Forums General Discussion Technical Questions More on Amp power

New book idea:

Electronics From Dummies; All the wrong answers you won't get anywhere else.

I'm gonna start writing tonight...

Make sure it has lots of pictures in it Fred, with illustrations..."never cross the positive and negative terminals, like this... BSHHHZZZTT!!! "

Thanks guys for the input on the amps(mostly to John ).

I've read user reviews(with a grain of sodium) about comparisons of some 2 channel amps where users have claimed such things for instance, as, 2 channel Amp "A" rated at 75 watts per c. is as powerfull as 2 channel Amp "B" rated at 200 watts per c. Wishfull thinking? trying to justify a new purchase? insider?

So to simplify for us noobs,

-- In a medium sized room, say about 14x22x7

-- Using a pair of M80's

-- Attached to good receiver (AVR-3311ci - 125 watts/channel)

-- Playing at a comfortable listening level

Would the M80's sound better, worse or the same if one added a 2-Channel 200 watt/channel amp?

You're still going to get about 15 different answers to that question. Different people think different things about that question. I can just about guarantee that it wouldn't sound worse...

Physics. It works Bitches!

If I'm reading that right, you are saying that to pump out volume 'x' a speaker will require 'Y' Amps.

If it gets more than 'Y' amps it won't use them at volume 'x'.

Just like if I plug a 60watt light bulb into a 11,000 watt plug (110volt*100amp) It still only draws 60watts.

Am I on the right course here?

That's correct, but it's actually a bit more nuanced than certain people like to portray it as. Sound reproduction doesn't use a constant amount of power--it's peaking and dropping all the time. So the theory goes (not sure if I subscribe to it or not) that the more you have in reserve, the easier it is to achieve those peaks.

Yes, program material has dynamic peaks. That is why you add in some headroom when you are calculating the amount of power needed.
This Crown page talks about power requirements, dynamics in different program material and a few other things.

Is is worth while noting that good 'ol rock 'n roll requires very little head room, maybe 6 db.

To complicate things more, you have a little power 'in reserve' in your receiver in the form of charged capacitors that can handle very brief peaks in power demand. I have seen some pro amps described as 'more ballsy' because they have larger caps capable of sustaining peaks for longer periods of time.

The short answer is that if you give yourself 12 db of headroom and subtract 5 for room gain and then calculate the power you need in average sized rooms when listeneing at around 10-12 feet, you need a lot less power than you would think

So the theory is that a 1" garden hose would fill a 10 Gallon bucket faster from a 1,000 gallon tank than from a 100 gallon tank? Ok I guess you could make a case for higher water pressure generated from the 1,000 gallon tank. But thinking way back to basic physics, flow in an electrical circuit is governed by resistance not wattage.

Really? Let's try it!

I took my SPL meter to a National Symphony Orchestra concert last week. During the crescendos of "Also Sprach Zarathrustra" (aka the 2001 theme) the meter peaked around 90dB (we were in the cheap seats). So we'll use that.

So 90dB + 12dB for headroom

At home, the primary seating is ~3-Meters from the speakers.
The M22's have 93bd Sensitivity. Plugging all that into the calculator:

Listener Distance: 3m
Desired Level at Distance: 90db
Sensitivity: 93
Headroom: 7db (12db -5bd? for room gain and I'll have to google what that is)

I need, wait for it.... 23 Watts.
Umm, err, 23? Wait, why in the hell were we talking about amps in the first place?