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Amplifer Wattage Question

I was just woundering if there is a way to measure the wattage during a normal listning session that your amp. is putting out. I know that a 250 watt amp. is not at full output at normal listning levels, or low volumes ?
How can you determine output at different volume levels?

I am just curious.

Thanks
Russ
russb
stanwal's avatar
stanwal
3,147 posts
 
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.
magfan
1,583 posts
 
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?
kijanki's avatar
kijanki
4,433 posts
 
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.
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