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Hi - I want a ball-park estimate of how many watts my speakers are using in my listening room with my equipment and favourite music playing. It seems to me that I should be able to estimate this using a multimeter and simple math, but I do not know how. Can someone tell me?I did a search of the archives, but haven't found an explanation yet - maybe I am using the wrong key words.
I know that my multimeter probably won't be fast enough and that the impedence changes, but again, I just want an estimate.
I am doing this because I am starting to think about buying a new amp. But I do not want to spend my money on, say, a pretty good 250 watt amp if all I really need and what I should be buying is an excellent 35 watts.
Thanks, Chr3is
Follow Ups:
d
There are several easy ways to approach this problem. First, you can just look for a short time at the AC output of the amp playing something (loud) and get an average reading. For example, 2.8V average means that you are using 1W / 8ohms average. On my WATT 1's, this would be over 90dB in my room. This is very loud for my taste. Usually I am at 70-80dB. Of course, then 20 dB headroom would be good. This would mean 100W minimum for my power amp.
This approach can use a sound level meter (Radio Shack) and/or the spec sheet of the speaker that you are using, to get a better understanding of what you need.
Don't worry too much about impedance differences. The amp will usually cover them with enough current. It is the voltage that usually clips.
Some loudspeakers and realistic levels make almost any power amp too small. For example, at the CES, we used 3000W with a ribbon arrayed speaker system and I could clip the amps, but then the police came in, and stopped us. ;-)
.
It actually was a SWAT team and when asked what he was doing by the kind officer Mr. Curl told him "just testing".....
Hi,When I thought the neighbours party was getting too late and too wild I connected 200W RMS Solid State per channel up to my 95db/W (measured and real and they do that down to around 35Hz) Tannoys, put Dr Dre "Keep their motherf...ing head ringing" and let it rip near clipping level for around a minute. They all call me "Sir" now....
Ciao T
PS, a 300B SE Amp on those is enough for as much reaism as I can take, real high power was juct scary.... ;-)
a housemate back in my college days had a pair of voice of the theatre behemoths (97db/W ?) running off of a 40 watt denon amp though extra long wire so that he could roll them out onto the covered porch of the big victorian houseOne rainy day I walked out of a building 4 or 5 blocks away and heard the beginning of the door's riders on the storm - clear as a bell and sounding not so faint in the distance - rather surreal with the recorded thunder from the speakers followed by the echo off the buildings and the sound of the natural thunder in the distance.
I made my way to the porch and sat on the railing directly in front of one - not a bit of strain to the ears. When the song was over - I looked to the owner and said "you know, these things image amazingly well" to which he smiled, then I continued "when you're standing across the street" ;)
inside - one was never aware of how loud they were playing until one tried to be heard over the music - amazingly clean
Al pretty much answered your question. Let me point you to the following site. At the bottom is a calculator that will do the math for you.http://www.listenhear.co.uk/ohms_law.htm
For example, I was curious about proper fuse size for speakers. I played mine about as load as I thought I might ever be likely to. I measured around 6 VAC steady with peaks a few volts higher. Entering that data into the calculator tells me that 6 volts into 4 ohms equals 9 watts and 1.5 amps. Get the picture. But as Al said that doesn't begin to tell you what you need in an amp. Your speakers really dictate that. Speakers vary widely in their power requirements. The type of music, room size, and listening level all have a bearing. Last but not least is how accurate the amp rating really is. Home theatre products are often quoted only driving one channel at a certain Hz! This will give you are radically different idea as to how much power you need. An amp that can double it's wattage each time the load is halfed will let you get by with a much smaller wattage. A high quality 50 watt per channel amp will easily outperfrom a lower quality 100 watt per channel amp. Bottom line, think of it like a car engine, watts are like horsepower, but it's torque that matters and that' amps.
Russ
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
Everthing I've heard says that if you are listening at reasonable level and the program is limited to mid range frequencies (this is pehaps 75% of typical content) the speakers are using olny a couple of watts. Only when you get in to louder passages and heavy duty bass does the amplifier get put to work.Except for wasting heat anf electicity, it doesn't hurt to have more power available that you will use, but it would obviouslt be silly to connect a pair of itsy-bitsy satellites to a 500Wrms / channel monster.
As a rule of thumb I like to have amlifiers rated at least 2/3 the distance between the min-max power specified by the speaker. But that is only my personal rule of thumb and I generally exceed it if I can do so without spending a fortune.
You can closely estimate power that you are using, by calculating as the previous poster mentioned ( volts * volts ) / impedance. Problem is in holding the multimeter to the speaker and seeing the read out i.e.. 17v you have really no idea what impedance the speaker is currently at, unless there was a review done on your speaks and they printed a impedance chart for your speak, and given you are listing to a test tone of a given frequency. Sooooooo like another poster said unless you are using very inefficient speaks or listening very loud you are only using a couple of watts at most. How ever the thing that I, and most of us like about the music we listen to is there is dynamic range, and peaks to it. Those peaks take significant power to reproduce accordingly, i.e.. the swell of a orchestra.No for my personal opinion I like headroom, I dont like getting to a loud passage just to hear clipping. It seems to me the better the recording, the more dynamic range is represented, the more I need amp headroom.
I dont drive a geo because its too slow, I dont drive a ferrari(sp) because its too expensive, I do drive a honda becase it is affordable and when a big rig is bearing down on me it has more than enough pick up.Hope that makes $ents, I'm trying to work.
Just so. It has been said you that you can't have too much power. Probably it should have been said you can't have too much headroom.Still, I'm sometimes surprised at how little you can "get away with".
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