# Vas measurement using REW

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Hello everyone!

I'm working with a Peerless M16KI 6.5" midbass driver and trying to find its T/S parameters using REW (Mac). REW has an option to "Compensate for leakage losses" and "Compensate for Air Load" when calculating the T/S parameters. If I uncheck both, the measured Vas is about 63 litres. Whereas, with both the options checked the resultant Vas is 45 litres. I'm not sure which of the two values for Vas is the correct one. I'm using sealed box method to measure Vas. The sealed box is of 7.64 litres.

To solve the dilemma I tried going backwards (I may be completely wrong with this). I started working with a sealed box calculator and kept changing the Qtc (with all other parameters remaining constant) with Vas set to 45 litres. At Qtc of .89 I was able to achieve an Fb of approx 85 Hz and a box volume of about 7.6 litres. These numbers closely matched the sealed box I was using for Vas measurement. The Fb from the sealed box calculator closely matched the Fs on the impedance curve for the driver in the sealed box in REW. Next, I repeated the steps with Vas of 63 litres. However, I wasn't able to achieve a match as with Vas of 45 litres above. This makes me believe Vas of 45 litres is the correct one.

Am I correct with my assumptions? What does "Compensate for leakage losses" and "Compensate for Air Load" do and when are they necessary?

#### Ron E

Without any actual data I am just guessing below:

Compensate for air load may use something similar to thiele's formula for Vas - the air load on a diaphragm changes between free air and mounted on a baffle or box.

Compensate for leakage losses - leakage will reduce the peak at resonance.

On second thought, probably the program is using an impedance model and "fitting" the impedance to it.

#### LewinskiH01

Vinny,

You are probably better off asking this at the REW forum at hometheatershack. Iam kearning how to measure driver T/S with REW and the times I've asked there I received good and fast feedback.