Measuring rms watts.

[I like FI 10+ year member]

Ive done it before with with dmm and clamp.

How do i measure amps at 35-40hz. most clamps pick up 50-60.

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[CadillacMatt 10+ year member]

Ive done it before with with dmm and clamp.How do i measure amps at 35-40hz. most clamps pick up 50-60.

Clamps? What the hell are you talking about?

Play 50Hz test tone (or whatever tone is in the range you intend to amplify) @ 0db with speakers unhooked, set DMM to AC volts, measure across speaker terminals.

 

[99grandprixGT 5,000+ posts]

Clamps? What the hell are you talking about?
Play 50Hz test tone (or whatever tone is in the range you intend to amplify) @ 0db with speakers unhooked, set DMM to AC volts, measure across speaker terminals.

 

[CadillacMatt 10+ year member]

Thanks for that I lol'd //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif

 

[99grandprixGT 5,000+ posts]

Thanks for that I lol'd //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif

no problem.

 

[I like FI 10+ year member]

Ac volts is gona give me anything.

ac amps and volts i need. Clamp meter is a device that measures ac amps, sound new to you?

People are able to measure at 40 hz and i wanted to find out how.

at 50hz i berely get bass, means that my re curve is high probably and measurement of amplifier output will be wrong.

 

[scoob8000 10+ year member]

I'm sure he probably means a clamp on ammeter.

volts * amps = watts

But I'm not sure this is the best way to get the measurements your looking for..

Play 50Hz test tone (or whatever tone is in the range you intend to amplify) @ 0db with speakers unhooked, set DMM to AC volts, measure across speaker terminals.

Excuse my ignorance, but won't the load of the sub (2, 4, 8, etc) have an effect on the voltage?

FWIW, I've used a few different clamp on meters at work and some are better than others. Some don't care about the frequency, and I even have one that measures DC amperage.

 

[jrwalte 10+ year member]

If you want *actual* watts going to your speaker then you need to place an AC clamp over either the pos or neg of the speaker and measure the AC voltage of that connection with a DMM and play a test tone of your choice (speaker must be connected to cause a load). Amperage * voltage will equal the real watts output from your amp that your speaker is drawing at that volume.

Be sure not to place the clamp over the pos and neg of the speaker wire, as they'll cancel each other out. You won't need more than a standard 70 amp AC clamp unless you're running in the range of 3500+ watts.

 

[I like FI 10+ year member]

which clamp on meter will work on 40hz? Doesnt a true rms dmm also measure ac amps?

 

[mokedaddy 5,000+ posts]

Its not hard at all to do and you are on the right track. Dmms can read ac amps but only to usually 10 or so. Any rms clamp meter rated at high enough amperage should do the trick.

But remember that is only a ballpark figure and once a load is hooked up and music is played your 'rms' is completely invalid in the real world.

 

[I like FI 10+ year member]

it is valid! resistence will be off ofcource, Which can measure 40 hz.?

 

[scoob8000 10+ year member]

FWIW try this too: Play whatever tone at whatever volume you want with subs hooked up.

Measure AC voltage at speaker terminals on amp. Multiply that reading by itself and divide by impedance of the subs.

If I'm thinking about this right, that should get you pretty close..

ie:

33 volts bridged 4 ohm load

33 * 33 = 1089

1089 / 4 = 272.25 watts

 

[Ed Lester 10+ year member]

FWIW try this too: Play whatever tone at whatever volume you want with subs hooked up.
Measure AC voltage at speaker terminals on amp. Multiply that reading by itself and divide by impedance of the subs.

If I'm thinking about this right, that should get you pretty close..

ie:

33 volts bridged 4 ohm load

33 * 33 = 1089

1089 / 4 = 272.25 watts

That wont be close at all.

Speakers are a reactive load and the impedance will change while the woofer is moving. so using the nominal impedance rating of the coil is useless.

There is also box rise which can sometimes add another 1 or 2 ohms depending on frequency and volume.

 

[jrwalte 10+ year member]

it is valid! resistence will be off ofcource, Which can measure 40 hz.?

I think you're a little confused. Based off your OP, you want to determine wattage output. You don't do that by measuring hertz (which will obviously be 40 if you play a 40Hz tone). You do that by determining voltage [DMM] and amperage [AC clamp that can read at least 70 amps] going through the speaker wire with a [40Hz] tone playing.

 

[CadillacMatt 10+ year member]

Excuse my ignorance, but won't the load of the sub (2, 4, 8, etc) have an effect on the voltage?

This is something I've been confused about because most of the tutorials out there say to disconnect the speakes, but then the eD tutorial uses a load resistor, I'm so confused. If someone could please clarify this. Sorry //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif