| # Speaker Project # Testing the Subwoofer ## Things to consider

> > > I spent a number of days testing my subwoofer, as it turned out, and learned a number of things.

> > > First, I was unhappy with the Sealed Box approximation and took a look at the data and the program. As a result of this I changed the way the program calculates sealed box data and the way it calculates driver parameters. These changes are in place as of version 0.76.

> > > Second, after doing a large number of tests on the woofer I found that a number of factors are important in the test.

> > > 1) Make sure you clamp the woofer frame - this reduces the shakiness in the data read in by Speaker Workshop and improves the results.

> > > 2) I placed some heavy books on the driver magnet to test the sealed box (see the picture later). These seemed to add a low frequency resonance and cause other issues so I removed the books and retested and that is the data I actually used.

> > > 3) The woofer had markedly different results right side up and upside down. Since the sealed box test is upside down I did both tests upside down. This lowered the resonant frequency in free air, but otherwise the two charts are much more similar now. The final box will have the driver vertically oriented. If you're using the added mass test do your testing right side up for both.

> > > 4) After testing in the sealed box (or with added mass) check the impedance charts at the high end. The two should agree closely - that portion of the curve is mainly the inductance of the voice coil, and that should not change between the two tests (free air and sealed/added mass).

> > > On to the next page.

> > > last updated July 13, 2000