Audio Fun with Inductor Coils


As Ethan and I await the arrival of components necessary to embark on our spring reverberation tests, we pass the time by winding inductor coils and playing with magnetic fields. With Vangelis’s Albedo 0.39 playing in the background and Björk (fat, white cat) to encourage us, we set about the task of winding the 10.5 mm insulated copper wire around two large, steel bolts.  Accidentally, we arrived at almost precisely 8 ohms of resistance by making four passes up and down the 2.25 inch bolt with layers of tape in between. wpid-wp-1426875743536.jpeg I started with a coil wound layer of tape to make the winding easier.  It’s still not easy because of the unevenness of the surface, but it’s better than nothing.wpid-wp-1426875759580.jpeg wpid-wp-1426875766913.jpeg wpid-wp-1426875774408.jpeg Here’s the finished product with the tape on the surface just to hold everything in place.wpid-wp-1426875779591.jpeg Doing the math, (2.25/0.0105)*4 tells us we came pretty close to 8ohms of resistance completely by accident.  Nice work, us!

Below is a video of the coils in action.  I apologize for any ads Gewgle puts on the video.  Their all-knowing Corpo-Bot 5000 detected the Amon Düül track playing over my phone, identified it, and informed me I wasn’t the copyright owner and that ads were going to play over the video if I didn’t “remove the soundtrack.”  Well, it’s not a sound track, it’s not the complete song, and ITS PLAYING THROUGH MAGNETIC COILS, but copyright is such a disaster in this country that this is the result.


As Ethan plays with the polarity of the “receiving” coil, you can hear the magnetic fields repelling each other and the audio getting quieter.

This is a nice little experiment you can do at home with nothing more than some wire, steel bolts, and a couple of amplifiers / desktop speakers.

  • Steel Bolt x 2 10.5mm insulated copper wire
  • Paper tape
  • LM386 amplifier circuit
  • Banana clips x 6 (2 from cable below to the amp circuit, 2 from the circuit to the first coil, and 2 from the 2nd coil to the desktop speaker 1/8” cable.)
  • 1/8” stereo headphone cable (from phone to amp circuit)

To hook up the banana clips to / from the coil / circuit, connect one clip to the tip of the jack, and the other to the base/sleeve (GND) of the jack.