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# Vrms

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## Vrms

(OP)
How can Vrms be defined as relating to acoustics.
thanks

### RE: Vrms

It's often used with SEA to mean the rms velocity of the radiating panel, tho it would usually have an overhead bar to indicate that it was an average across the panel as well.

Is that what you meant?

Cheers

Greg Locock

### RE: Vrms

Sorry, just thought of another use, when you calibrate an FFT analyser one setting for the units is often volts, rms.

Cheers

Greg Locock

### RE: Vrms

In the acoustics world you can convert the voltage to a decibel (dB) level.  This is done by first calculating the voltage ratio.  I am not sure of your context but lets say that you have a reference signal of 94 dB and it produces a 1 Volt rms signal.  Then you take a sound level measurement of a machine and it produces a 0.5012 Volts rms.

Then:  Voltage ratio = 0.5012/1=0.5012

and     dB difference = 20 log(base 10) x 0.5012 = 6 dB

The measured sound level is 94 - 6 = 88 dB

The formula is dB = 20 log V/Vref where

V = measured voltage
Vref = reference voltage (this can be changed on the analyzer and is usually set to 1 volt).

If you need in depth details, see the book "Acoustics" by Leo L. Beranek.

C. Hugh (www.Hatch.ca)

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