Zach Poff

Inductive Pickup Experiments

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The contemporary world produces a sea of electromagnetic (radio) noise. Most electronic devices emit radio byproducts as they operate – especially motors and microprocessors. A small fraction of these emissions occur at frequencies that we could hear if we could sense electromagnetism… but luckily we can’t.

A coil of wire wrapped around an iron bar can detect these fields – and allow us to hear them. It will produce a voltage proportional to the fluctuating electromagnetic fields that cross it, via electromagnetic induction. This is nothing new (it’s the foundation behind transformers, motors, electric guitars and tons of other common devices) but nonetheless it’s fascinating to experience this hidden world with your ears.

Telephone Pickup

Back in the days of Ma Bell, the inductive “telephone pickup” was a common way to record a phone conversation. It picked up the electromagnetic field produced by the handset’s speaker, without making any electrical connection to the phone system. (Thus undetectable to the other party.) Theoretically, Radio Shack still sells them, but I’ve had trouble finding them on the shelves.

New Life For Old Relays

Recently I almost threw out some un-needed 120V relays, but decided to use them as inductive pickups instead. I extracted their coils and soldered them onto an 1/8″ stereo cable. The fragile coil wires are anchored with hot-glue, and large heat-shrink tubing protects against “fall-apart”.

Some short examples:

Laptop:

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Minidisc Recorder (spinning up the disc a few times):

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Two mobile phones:

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The inductive pickup only works when held close to the source, so it’s able to pick out individual fields in the crowded electromagnetic atmosphere. If you’re looking for longer range and less selectivity, you may be interested in VLF “natural radio”.

Further Research

• Read chapter 3 of the excellent book Handmade Electronic Music by Nic Collins. It explains more about inductive listening, and there are some great tracks on the included DVD.
• Jean-Edouard Miclot’s sound design blog has some great sounds, obtained with guitar pickups.
• Read about the Electrical Walks of veteran sound-artist Kristina Kubisch.