measure watts out

kappclark

Is there an easy way to measure watts produced by my amp ?? I am trying to simulate 4-5 watt output (nothing wrong with the parasound amp, just want to get an idea how loud 4-5 watts is with a pair of Monitor 40's at approx 3 meters

THX

Speedskater

Into load resistors with test tones or into loudspeakers with music?

mhardy6647

Yup, pure resistive loads (i.e., the dummy load reistors need to be noninductive) will let you use an AC (true RMS) voltmeter to measure output voltage into a known, fixed load and use Ohm's law to calculate watts.

ambiophonics

I would guess if you have a digital multimeter that will display an average over a period of time you could hook the multimeter up to the positive and negative speaker terminals of one speaker and then measure the AC voltage with music playing. If you square that voltage then divide it by the load (most likely 8 ohms) you will come up with watts. You wouldn't really have to do an average over time but since music is so dynamic that might make it easier to figure out. I do this in my repair shop but with a sine wave into a dummy load to check power output on amps. Since you want to know what 4-5 watts of music sounds like I would guess you would not be interested in hearing a 5 watt sine wave or seeing what 5 watts looks like on the scope!

kappclark

Thanks all .. I have re-arranged my speakers, so now I am actually seated closer ... speakers playing at very low level but more than satisfying ... I think 4-5 watts will be fine ...

- now I need advice on a good *basic* multi-meter (under $ 40 if possible) .. I used to have a decent one, but damaged in the move up here to VT

Thanks again

mhardy6647

You're in southern VT?! Practically a neighbor! Well... maybe :-) Anywhere near the CT River Valley?

Back on topic - Should be plenty of cost-effective DMMs that'll be adequate for your needs.

kappclark

yes - Windham, VT .. 25 mins from Manchester, 45 from Brattleboro ..


bought the place right after 9-11 ...

Pleased to meet you, neighbor

mhardy6647

We're just a hoot 'n' a holler from White River Jct here... but on the other ("Live Free or Die") side of the river ;-)


DSC_8109 by mhardy6647, on Flickr

If you need a loaner DMM at some point, let me know...

John K.

Bill, you can measure the output as mentioned above, but your basic question can be answered with good accuracy without going through that procedure. Polk specs the Monitor 40 at 89dB for 1 watt at 1 meter. In typical home listening rooms the sound level beyond 1 meter drops about 3dB per doubling of distance(taking into account both direct sound and room reflections). At 3 meters the level would be about 4dB lower, i.e., 85dB for 1 watt. This level would be increased 3dB with each doubling of power, so with 4 watts it would be 6dB higher, i.e., 91dB. This is a quite loud level, which you can measure with an SPL meter if you care to.

mhardy6647

.. and it will probably get the OP closer to the question he really wants to answer! ;-)

When it is all said and done, IMO it is hard to beat empiricism in this hobby... which is why I, for years, had a pair of Acoustic Research AR-3 speakers driven by an old Maggotbox (Magnavox) push-pull 6BQ5 stereo console amp in my basement. No one who played by the rules would ever do that...

lanchile

I have seen some Fluke multimeters like Fluke 27FM for around $50 on ebay. These Fluke 27FM multimeters were used in the Army, they are very good multimeters, just make sure you get the "grey" ones....the ones that have the 27FM on the front, they are true RMS meters. I have a few Fluke multimeters including the 27FM and I love it.

tonyb

kappclark wrote: »

Is there an easy way to measure watts produced by my amp ?? I am trying to simulate 4-5 watt output (nothing wrong with the parasound amp, just want to get an idea how loud 4-5 watts is with a pair of Monitor 40's at approx 3 meters

THX

4-5 watts on M40'S is going to be pretty darn loud. The difference you want is in current capacity to handle fast transients and fast low end. That's what sucks up power.

kappclark

Looks like Nelson Pass himself uses a Fluke 114 in his very detailed instructions of his Amp Camp (which is what I am hoping to build this winter )

http://www.diyaudio.com/forums/diyaudio-store/221212-amp-camp-amp-1-pictorial-build-guide.html