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.) Radio Shack used to sell them, but good luck finding one these days. I have made several stereo sets by wiring two of these cheap telephone pickups together on one 1/8″ TRS plug. Or you could spring for the super duper stereo boutique option, the LOM Elektrosluch! (Hint, it doesn’t sound any better than the $4 option above, assuming you already have a recorder.)
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:
Minidisc Recorder (spinning up the disc a few times):
Two mobile phones:
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.
- Read about the Electrical Walks of veteran sound-artist Kristina Kubisch.
