Amplifer Wattage Question

Russb - try this formula L = P^(1/3.5) where P is a ratio of power and L is a ratio of loudness. In your case L=(250/10)^(1/3.5)=2.508

Russb - 100W is 2x louder than 10W. 200W is 1.23x louder than 100W and 250W is practically the same as 200W. So in total 250W is about 2.5x louder than 10W.

Thanks everyone for your responces.

I was woundering if a amp. is rated for 10 watts of class-A operation 250 watts totel A/B. At what volume level is the amp coming out of class-A ?

How loud is 10 watts ?

How maney watts is a amp. putting out at normal listening levels ?
Just curious how this works.
Thanks Russ

Here are a couple a simple-to-built LED audio output meter schematics. Easily fast enough to register peaks. They're limited to 10 power levels, and won't give you fine measurements though. (http://freecircuitdiagram.com/2008/09/13/audio-power-meter-show-audio-amplifier-actual-output-power/) (http://www.circuit-projects.com/audio-circuits/10-led-vu-meter-project-by-lm3915-and-lm324.html)

Magfan - I don't listen to sinewaves either, I find it a little boring.
If the goal is to measure RMS power delivered than standard RMS meters will be probably useless. They don't measure well at high frequencies and they have limited crest factor. Since RMS is defined as DC that produce equivalent heat perhaps measuring temperature will be more accurate (resistor in series?). I wonder myself if there are any professional power meters that measure music power accurately. I'm not sure how important it is.

As for Zobel in D-class - many people complain about it. Yes it will be damaged with prolonged exposure above certain frequency but it will never happen in real live.
I would say that average power that amp can deliver is not of use. I want to know how much peak power (or peak current) amp can deliver. 80V supplied 1kW Icepower (1000ASP) can deliver about 40A on 2 ohm load for about a second and that is very impressive (3.2kW). At 10kHz its output power is limited to 200W but this would make person deaf and I don't know of any tweeter that can take continuous 200W (more like 20W max). In real life average music power that tweeter receives is a fraction of a Watt. The most important is match, that you mentioned. My experience is limited, but from what I'm reading certain amps just "like" certain speakers more than others.

Kij,
Let's say you kept away from 'max power'.
could you at least get a number that made sense using the technique I describe?

Also, My ICE amps (max) power spec is time limited. I suspect you'll fry the Zoebel network at that output.

Agreed, however. Even if you could do it, why bother? Properly matched stuff and even a minimal ear should provide ample warning of impending doom.

Also, now that i re-read, the OP specified 'normal listening session'..... I haven't listened to sine waves since the 60s.....
Can you figure out power output during regular music sessions? How much bench equipment would it take..... Scope? Multiple DVMs?

Magfan - It cannot be done since woofer midrange and tweeter have completely different power ratings. Applying full power at midrange frequency will most likely damage midrange speaker and doing the same at high frequency will definitely take out the tweeter. It is difficult to estimate proportions between lows, mids and highs since it is recording dependent. Music power delivered to speakers is only a few percent of peak power so measuring speakers' max RMS power is not the answer.

Russ - You have to remember that listening is logarithmic so power has to increase/decrease ex-potentially. Half as loud means 1/10 of the output power. If you add to it silence in the music it will become obvious why average music power delivered is only few percent of peaks. Measuring amp with sine waves (test tones) on a dummy load won't tell the story either since speaker impedance is complex. In addition 100W rated amp might put much higher momentary peak power - design dependant. IMHO measuring doesn't make much sense. I would be the most afraid of under-sizing amp since it will lead to clipping = high frequency energy delivered to tweeter = overheating. If your amp is strong you should be able to hear when your speakers distort.

How about electrically?
Use a DVM and if speaker impedance is known at frequency, use test tones measure the voltage and using ohms law and the impedance, calculate the actual wattage?
Will this work? It actually doesn't sound like THAT much trouble, if you really care enough to know.

Will this work?

LEDs give the best reading, meters are too slow to capture peaks. To get a general idea get a Radio Shack sound meter and check the sound level in DBs at one meter. Take the sensitivity of the speakers and see how many watts would be required to drive them to that level. For example. if your speakers are rated at 86 DB for one watt and you are playing at 92 DB then you are using 4 watts. The sensitivity of the speakers will always be given as a single number ranging from the low 80s to over 100. This is the output level of the speaker at one meter with one watt input. To raise the level 3 DB requires twice the power so in this case you get 1 x2 x2 =4. In most cases you will be using a surprisingly small amount of power but peaks will call for much greater output. There is absolutely no agreement about how much power is optimum, there are 3 watt SETs and mini power stations that really need wheels. Enough to drive the speakers you are using is about the only standard.