Electroacoustic musings

I took apart a big old laser printer yesterday and found some nice electromagnets. Here’s what I did with them, and an old autoharp I found at a tag sale this summer.


The strings on the autoharp are steel, and thus are somewhat ferrous. I placed the magnets close to the strings with a bracket repurposed from the printer. Then I ran an oscillating current through the magnets to vibrate the strings. I think a saw tooth wave works the best. The strings resonated at different frequencies, producing a dynamic harmonic mash that I think sounds great. I accomplished this by hooking the electromagnets to the speaker outputs of a stereo amplifier, and driving a signal into the amp from my computer running Pure Data. The other thing you can do is play music through it. Jimmy Hendrix works well, but as of late I have been running the local country station through it; the undulating resonations please the ear far better than “boot scoot and boogie.” The electromagnets are about 150 ohms at DC, so this is totally safe. In fact I had trouble getting too much power into them because of their high impedance. The volume knob is turned all the way up on the amp to get a medium volume level out of the electrozither.

electrozither coils

Next, I taped a piezoelectric transducer to the body of the autoharp and fed it’s output into my computer. I set up a feedback loop this way, producing some even more interesting sounds. The only problem with this setup is that I’m getting a lot of 60hz hum from the wires going to the piezo transducer, so there’s always a foreign signal exciting the loop. I’d like total quiet to be a possible state of the feedback loop. To get around this, and also to effect the timbre of the instrument, I’ve been experimenting with putting filters in the feedback loop. A resonant lowpass filter works pretty well when the Q is high. This also cuts out the 60 hz hum, which sadly is jagged and can be heard in virtually every area of the sound spectrum, not just the low end.


Here is a recording of the electrozither feeding back on itself with a three band EQ on the feedback loop for one channel, and a resonant low pass filter on the other channel. The rattling you hear is one of the strings, lose, vibrating up and down in the varying electromagnetic field. It looks quite supernatural.

I hope to get more of these electromagnets. With only two, a great deal of of sonic possibilities have yet to be realized.



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