Hard-drive speakers (Hackaday)

A Hackaday writeup of Niv Singer’s build that turns hard disk drives into loudspeakers by driving their head actuators with audio. It is the spoke’s first unconventional-transducer source — and a vivid demonstration that the moving-coil motor is the whole trick: an HDD’s voice coil, built to position the read/write head, becomes a speaker driver the moment you feed it an audio signal instead of a seek command.

How it works

• The actuator is a voice coil in a magnet gap. A hard drive positions its head with a voice-coil actuator — the same coil-in-a-magnetic-field motor as a loudspeaker‘s. Feed it the audio waveform and the arm vibrates, radiating sound directly. No cone, no enclosure — the bare arm is the radiator, so (in the builder’s words) “you get limited volume with a terrible frequency response.”
• A real crossover, across drives. The build uses four Western Digital Caviar 500 GB drives, two per stereo channel, with a crossover splitting the band: one drive handles low frequencies, the other high — the same woofer/tweeter division a normal two-way speaker makes, here spread across two whole disks. This is the spoke’s first concrete instance of the crossover idea named on loudspeaker-driver.
• Spinning platters as a second instrument. The platters are spun synchronized to the music via PWM, adding a percussive layer on top of the actuator’s tone.

The demo

It plays “Second Reality”, Future Crew’s landmark 1993 demoscene production (Assembly 1993 winner) — the “classic demo” of the title, chosen to suit the lo-fi, hacker spirit of the output.

Why it matters here

It isolates the spoke’s core physics to one component. A loudspeaker-driver is, at bottom, a voice coil moving in a magnetic field; strip away the cone, surround, and box and you still get sound, just badly. So this is the transduction principle without the engineering — the opposite end from the T/S predictive design loop, and the first step toward the synthesis’s flagged broadening into general electroacoustics. Same publisher as the spoke’s fundamentals primer (loudspeaker-primer-hackaday).

Related

loudspeaker-driver · loudspeaker-enclosure · loudspeaker-primer-hackaday · synthesis