Stephen W. Moore
Hard Drive Loudspeaker
A good audiophile should be able to make anything play music! Time to recycle that old 20MB Maxtor paperweight!
Does that look like a voice coil to you?
I was reading a hard drive spec sheet, and I noticed that the read mechanism was referred to as a “voice coil.” If you are a good audiophile, that should cause you to lie awake at night. Alas, a voice coil.
I wanted the hard drive to operate (spin) and play music at the same time. No problem! A little circuit tracing led me right to the amplifier for the drive’s seek mechanism. The voice coil measured a very audio amplifier compatible 17.6W.
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Now for a little additional amplification. The amplifier pictured is of the home-brew variety, using 60 Watt amplifier modules:
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second image here
Voila! A hard drive duet!
Reading the literature, this hard drive had seek times in the millisecond range, which would suggest usable frequencies up into the kHz range. High frequency signals (over 5000Hz) created unusable output. On the other end of the scale, low frequency signals caused excessive motion of the drive heads and a buzzing noise. I finally settled on using pre-processed program material, using Cool Edit (trial version) to implement a digital 400Hz – 5000Hz bandpass filter. The first tracks successfully played on my new speakers were AC/DC Hell’s Bells and Clint Black Killin’ Time. The track selection was based on easily recognizable vocals.
How does it work? The signal from the external amplifier excites the voice coil contained in the magnetic gap. The voice coil’s motion causes the read heads to vibrate in sync with the signal. This vibration is what you hear. The system did not work as well when the hard drive was operating (disks spinning) because the heads “float” over the disks in actual operation (the spinning disk causes air motion, which lifts the heads from the surface once the RPMs build up). With the heads floating, the platters could not serve as a sounding board.
Contact
stephenwmoore@insightbb.com