Digitalmedia Blog Images Dangling-Boom2A
David writes –

The AirPort Express receives the Wi-Fi music signal from iTunes, converts it to analog, and then injects it into the old boombox through a car cassette adapter. The belt raises the tweeters to brighten the sound.

All components were items I salvaged from closets, including the boombox-with-no-line-input, the Old Belt, and the cassette adapter, which I hadn’t used since I’d replaced my factory car stereos.

Stupid Wi-Fi Speaker Tricks – O’Reilly Digital Media Blog – Link.