Using two scraps of walnut, he carved out a slot for the horn, a dock for his iPhone and a channel to carry sound between the two. Lo-fi, but pretty effective.
Side note: Magnavox invented the loudspeaker in 1915 in Napa, CA. The company eventually moved to San Francisco, then Oakland, which means someone in the Bay Area probably has a garage filled with these horns. I'm on a hunt. Write me if you have any leads:
steven AT boingboing DOT net