| # Speaker Project # Prototyping

> > > Now that the prototype is built we start by testing the woofer in the prototype with the port hole sealed (and no port). This is mainly for confirmation. When we do that we get the following impedance chart.

> > > The red line is the impedance built by the enclosure resource with a box slightly larger than the one I've tested. It is very comparable to the tested chart - a good sign. Also note that the chart is smooth. If there were an air leak we would tend to see a hump near the free air resonance point of the driver. There is no hump and so the box is well sealed.

> > > Note one anomaly way over by 600 Hz. There is a spike there. Zoomed in that area looks like this:

> > > The box the woofer sits in is about 11" deep and if you do the math it becomes clear that the spike is caused by back wall reflection. This will also produce a glitch in the frequency response - not a good thing. We can fix this simply by adding some stuffing to the empty box. I stuffed the box 40% with polyester fibers (sold as Christmas decoration snow by Ace Hardware) and retested the impedance. Here's a comparison chart.

> > > Notice how the glitch got almost completely smoothed by stuffing the box appropriately (the red line is the stuffed impedance curve).

> > > On to the next page.

> > > last updated March 12, 2001