Re: How many watts am I actually using?? - AlK - Tweakers' Asylum

Tweakers' Asylum

Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

Re: How many watts am I actually using??

64.86.32.4

In Reply to: How many watts am I actually using?? posted by Chr3is on March 1, 2002 at 08:12:12:

From Ohm's Law: power = (voltage * voltage)/resistance. At first glance it should simply be a matter of measuring the AC voltage at your speaker terminals, squaring it, then dividing it by the impedance of your speakers (most are rated at 8 ohms). This would give you the power in watts.
As you acknowledged, however, there are some complications such as meter response time and actual speaker impedance (which varies with frequency). In addition your meter probably doesn't read the true RMS voltage which is needed to calculate the RMS power output of your amp (amps are rated in terms of RMS power). Without getting in to a long discussion, RMS is a means of comparing the power capability of an AC signal to a DC signal of the same voltage. As a gross approximation you can take the AC voltage you read from your meter and multiply it by .707 before squaring it.
The answer you get will probably be a small fraction of a watt. Does that mean you only need a one watt amp? No. Remember that your measurement technique can't possibly capture the *peak* power your amp must deliver which can be 10dB - 30dB higher that the average power. A 10dB-higher peak requires 10 times the power of the average level. A 30dB peak requires *1000* times the power. In general, rock music tends to have a fairly low ratio of peak/average power while orchestral music a higher peak/average power ratio.
If you don't have enough amplifier power to satisfy the demands of your speaker, the amp will "clip," a kind of distortion that is particularly dangerous to tweeters. More tweeters have been killed by 35 watt amps than by 350 watt amps.
Sorry for the long-winded response. Hope it helps.
Al Kirchner

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Follow Ups Full Thread

Topic - How many watts am I actually using?? - Chr3is 08:12:12 03/01/02 (0)

Thanks to all for the help !! (nt) - Chr3is 13:00:58 03/02/02 (0)

Re: How many watts am I actually using?? - john curl 15:46:48 03/01/02 (0)

Haven't been to CES, but I've seen the police many times! (nt) - Joe Murphy Jr 15:51:37 03/01/02 (0)

Re: Haven't been to CES, but I've seen the police many times! (nt) - rcrump 18:44:12 03/01/02 (0)

The wily audio terrorist..... - Thorsten 09:53:30 03/02/02 (0)

mood music in a small college town - wdc 12:22:15 03/02/02 (0)

Re: What Al said plus a web site link - Russ57 10:39:36 03/01/02 (0)

Re: How many watts am I actually using?? - AlK 09:49:12 03/01/02 (0)

Re: How many watts am I actually using?? - sam9 08:41:02 03/01/02 (0)

Re: How many watts am I actually using?? - jteg98 10:42:42 03/01/02 (0)

Re: How many watts am I actually using?? - sam9 17:31:50 03/04/02 (0)

Follow Ups

Re: How many watts am I actually using?? - AlK 09:49:12 03/01/02 (0)

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