| # Speaker Project # Added Mass Testing

> > > Sealed Box and Added Mass are both ways to let Speaker Workshop approximate your driver's VAS value. There is no doubt that Added Mass is easier and in some ways even more precise - the main issue with Added Mass is that it is more sensitive to temperature and humidity than Sealed Box.

> > > To use the Added Mass method of testing a driver, just use a mass equal to about 1/2 to 1x of the specified mass of the driver.

> > > I attach the mass to the center of the dust cap with a tiny bit of FunTak (a blue non-marking putty-like adhesive available at hobby stores and some drugstores and Home Depot stores). Weigh the mass and adhesive together for best accuracy. Since midrange/woofers can have mass in the 1 ounce area it is important to have this mass accurate to the nearest gram, if not 1/10 gram.

> > > I added 1 ounce to the Vifa woofer to get added mass results (the Vifa is speced at a mass of about 17 grams, but I had a 1 ounce weight lying around) and then went to the Driver properties dialog and selected "Use Added Mass" and entered 1 oz for the mass.

> > > Unlike sealed box, which raises the resonant frequency, adding mass lowers the resonant frequency - with a woofer that's an issue because the accuracy of the sound card is suspect at very low frequencies (and the jitter increases). Anyway, the following chart resulted:

> > > Take a look at the subwoofer test for some more discussion of added mass testing. Once the added mass test is finished it's time to have Speaker Workshop estimate the T/S (thiele/small) parameters, including VAS.

> > > That process is the same for both sealed and added mass techniques, so go here.

> > > last updated March 12, 2001