Here s a really cool housing application. As you shop the charity outlets for circuits to bend, you re bound to run into the small voice-changing megaphones meant to make kids sound like robots or parrots, or be just plain louder (what were they thinking ). These are often bendable and in need of a larger housing for added controls. Just waiting for the transformation are any number of two-part water carafes. Some, like the Mr. Coffee carafe shown, are designed to filter water from the top half to the bottom. Building a megaphone circuit into these is usually easy. Mount the electronics in the top with the speaker firing out the bottom of the filter chamber (just cut out the bottom of the actual carafe with a hole saw). Hold the pouring handle instead as you would the handle of a megaphone, and charm the karaoke crowd (see Figure 11-21).

If you ve chosen an unusual housing, you ll probably need to create a port of some kind for your speaker to sound through. Let s look at a few possibilities. If the speaker is really small (up to 1.5 inches), you can enlarge a hole using your hand bore set. Bring the hole up to an inch or so across. Next, glue a grill cloth or fine metal screen to the speaker and trim off any excess (see Figure 11-22).

Finally, glue the speaker to the backside of the hole behind which it is to reside. Bolting is also an option if you want to drill mounting holes around the speaker s edge. If the speaker is larger, the best bet is to use a hole saw mounted in either a hand drill or, better, a drill press. Hole saws are sold in sets as well as individually. Steer away from the sets that rely upon a central spindle upon which the varied blades fit. The blades in these sets are flexible as well as ill fitting, both problem points. Obtain instead one of the more expensive, nonflexing hole saws the kind that mounts on a hole saw drill bit, or mandril. After the hole is drilled, you ll be at the grill cloth stage again, unless you want to find a cover that mounts to the outside of the case like an automotive speaker grill. Drill mounting holes and use bolts instead of glue for larger speakers.

Easier still is using a box with a speaker already built in. If you shop surplus, you ll undoubtedly run into various speaker enclosures from intercoms, computer sound systems, and the like. Many of these will serve as really great housings for circuit projects and save you the hassle of using a hole saw to mount a speaker in a standard project box. Additionally, many older extension speakers and intercom speakers have great design lines and look so much better than the bland plastic and aluminum project boxes you might be tempted to use otherwise. Here s another photon clarinet, this time built into a 1940s intercom salvaged from an old garage (see Figure 11-23).

Getting a good control layout can take a while, especially if you need to position your added components precisely to maintain important clearances. If you intend to reproduce the instrument for yourself, friends, or for sales, making a template for marking component locations is a very, very good idea. All you ll need for this is transparent film sheets (such as the 3M overhead transparency film, part # 5470296) and your ultra-fine felt tipped Sharpie brand, permanent ink marker. Here s how: 1. After you have the instrument marked for the new control locations, and before you drill even the pilot holes, lay a sheet of film over the instrument. 2. Either position the film so that its edges line up with edges on the instrument (see Figure 11-24) or position the film at key detail points of the instrument s design (see Figure 11-25). These will be used to align the film with the same features on the next instrument.