| # Speaker Project # Prototyping

> > > The next step is to start working with a prototype enclosure. I have built a prototype enclosure that is the exact same size as the final is expected to be with just a few differences.

> > > [1] The back only covers the portion for the woofer. This reduces the weight of the enclosure, gets built easier and lets me get into various pieces of the enclosure.

> > > [2] It's made entirely out of MDF, rather than real wood. This should not affect the sound particularly and is way easier to build.

> > > [3] It only holds one woofer, although the final is expected to be a dual-woofer system. The differences between one and two woofers are minimal for most things. The second woofer will affect the crossover and dispersion patterns.

> > > Here are a couple of pictures of the prototype

> > > In the first view you see the stuffing in the top part of the prototype. Note the tweeter doesn't need an enclosure so that's just a hole. The second view shows the enclosure with the woofer in it (with a hand holding it in place). Both views show the port sticking out of the enclosure - that's just for you to see the port - not how the port actually ends up. Here I've put the port on the side of the enclosure. After building the box that was the only place I could drill a hole large enough for the port with my drillpress. In fact the port can go pretty much anywhere for tuning and testing purposes since the low frequencies a port produces are primarily omnidirectional.

> > > In my experience you don't want the port on the front of the box because it has a number of ill effects. First, it can transmit midrange frequencies bounced off the back wall. Second, the port hole causes interference with the sound waves from the woofer and tweeter. Putting the port on the side or back are preferable if you won't place the speaker against a wall.

> > > The steps we will follow are

> > > (a) Test the woofer impedance in the box with the port hole sealed (before a port is installed, so it doesn't take up volume). This lets us verify the box is completely sealed and also lets us check our compliance and T/S parameters for the woofer.

> > > (b) Test the woofer impedance with a port installed. Tune the port to get the right response. This impedance will confirm our tuning and be used as input to the crossover module - it is the final impedance.

> > > (c) Get the frequency response of the woofer installed with port. This is the frequency response used to synthesize the crossover. Don't install the tweeter yet because you can get spurious tweeter output caused by magnetic coupling of the two drivers.

> > > (d) Install the tweeter and measure its impedance and frequency response in the box. It won't generate enough magnetism to cause the woofer to generate spurious output. These measurements are used to synthesize the crossover.

> > > (e) Synthesize the crossover.

> > > (f) Test the built crossover.

> > > On to the next page.

> > > last updated March 12, 2001