Measuring 2.83v

[NyxOne]

Hi,

I've been searching for a while on how people like Zaph and John do take their measurement at 2.83 (2v VRMS ?).

Do I take my measurement directly on the amp ouput with my DMM ?

Must I add a resistance (4/8 ohm) in parallel and then measure with my DMM ?

Or should I take measurement with my speaker connected ?

Any input would be helpful

Thanks,
Chuck

[eb15]

Most solid state power amplifiers should maintain the same output voltage for a test tone set at 2.83V with zero load, 8ohms, or 4ohms. Make sure your DMM is rated for the audio frequencies you're measuring, not just 50/60Hz line power. You shouldn't see a big drop from any decent speaker cabling.

[Amphiprion]

Most measurement gear corrects for amplitude. But if you want a true 2.83V drive level, any decent solid state amp should give you a fairly constant 2.83Vrms with a reasonable load connected(4ohm to no load).

For example, an amp with a damping factor of only 100 into 8 ohms would only give you a variation of 55mVrms between a 2.83Vrms no load measurement and the actual voltage delivered when hooked up to a 4ohm load. And that's a pretty mediocre damping factor for a SS amp.

[NyxOne]

Most solid state power amplifiers should maintain the same output voltage for a test tone set at 2.83V with zero load, 8ohms, or 4ohms. Make sure your DMM is rated for the audio frequencies you're measuring, not just 50/60Hz line power. You shouldn't see a big drop from any decent speaker cabling.

Ahh !? That's new! I did some testing today, I've connected a 4ohm speaker, then an 8ohm speaker and finally no speaker at all and my Voltage reading were the same all along so I guess your right!

I did some test with 100Hz and 400Hz and result were the same. I then tried with 1kHz and 5kHz value and result weren't as reliable so I guess my DMM is not so good with HF values!

Most measurement gear corrects for amplitude.

Do you mean measurement software like justMLS ? I'm not sure how I can get absolute values that way ?

Thanks guys,
Chuck

[Amphiprion]

Do you mean measurement software like justMLS ? I'm not sure how I can get absolute values that way ?

I'm not sure about justLMS, but my let's say I'm using Praxis to take a sensitivity measurement of a driver. It has a probe right across the driver to measure the voltage, and then corrects the response if the result is not 2.83V (or 1Vrms, depending on how you have Praxis setup). So if I'm actually sending 2.4Vrms instead of 2.83Vrms, Praxis will scale the data to make up for that fact.

[5th element]

I will also add, just so it's clear.

2.83 volts is an rms figure and is what your digital multimeter should output. Do send a few sine waves at different frequencies, but at the same amplitude to the multimeter just to check.

The peak to peak (the top of the sine wave to the bottom of the sine wave)voltage however is 8 volts. This being the result of 2*2.83*1.41.

Power doesn't really have an rms figure but it somehow acquired one for audio.

Prms = (Vrms*Vrms)/Loudspeaker impedance.

Ergo (2.83*2.83)/8 = 1 watt.

Which is why, I assume, 2.83Vrms was arrived at as the standard.

[Dennis H]

Most meters have crummy frequency response at both the high and low ends. I think ARTA settled on 400Hz for calibrating your signal with a meter as a frequency where most meters are least bad.

[Amphiprion]

Meters are fantastic at 60Hz because even the cheapest ones can be expected to be used for power line applications. I know 400Hz is also a power transmission frequency, usually in airplanes b/c it shrinks the size required for transformers (and thus saves weight). Most "True RMS" multimeters have 1kHz bandwidth or so, so 400Hz would be well within their limits. Also not too far from good old 440Hz

[NyxOne]

I'm not sure about justLMS, but my let's say I'm using Praxis to take a sensitivity measurement of a driver. It has a probe right across the driver to measure the voltage, and then corrects the response if the result is not 2.83V (or 1Vrms, depending on how you have Praxis setup). So if I'm actually sending 2.4Vrms instead of 2.83Vrms, Praxis will scale the data to make up for that fact.

Ahhh that's smart! Now that I think about it, I might have read something in TrueRTA's manual explaining something similar (or maybe not?)...

In anycase, I don't think justMLS can do that... It's as simple/dumb as it can get!

I will also add, just so it's clear.

2.83 volts is an rms figure and is what your digital multimeter should output. Do send a few sine waves at different frequencies, but at the same amplitude to the multimeter just to check.

Thanks for the details! Looks like I misunderstood what I've read on the net! I must admit that I just don't get it when there is Maths implied! Shame on me!

Most meters have crummy frequency response at both the high and low ends. I think ARTA settled on 400Hz for calibrating your signal with a meter as a frequency where most meters are least bad.

Indeed! I did some testing yesterday and my Mastercraft DMM wasn't precise over 800hz! At least when compared to the Fluke 175 I borrowed from work!

So, 400hz will now be my reference test tone! Thanks Dennis.


I love to see a thread have a clean conclusion so here it is :

1. 2.83v is much louder than I would ever thought it would be! 400hz is ok but try a 5khz and you'll see what I mean!

2. The voltage doesn't change whether I have no speaker connected, a 4 or 8 ohm speaker connected.

3. I took my measurement directly from the Amp output. I've also tried in parallel with the speaker connected. Both method works fine.

4. Remember to verify your connections before testing ... you wouldn't want to make this test on your tweeters ... which would happen to be a Seas H212! Sending a 400hz test tone at 2.83v with to your tweeter with no xover will almost kill it! Yes, I did it by mistake!!! LOL!

Thanks,
Chuck