So here are some notes from my presentation at Frequency Freaks.

The origin of the idea came from a thinking about Aeolian harps which I’ve had interest in since I was young.

Aeolian harp

An Aeolian harp (also wind harp) is a musical instrument that is played by the wind. Named for Aeolus, the ancient Greek god of the wind, the traditional Aeolian harp is essentially a wooden box including a sounding board, with strings stretched lengthwise across two bridges. It is often placed in a slightly opened window where the wind can blow across the strings to produce sounds. The strings can be made of different materials (or thicknesses) and all be tuned to the same pitch, or identical st…
The idea of a sound machine that plays in non-deterministic ways has been something I’ve wanted to make for a long time.
I was toying with the idea of wind chimes without any percussive sound and was doing stuff with ribbons outside.

Those ribbons would play once in a while in strong wind, but left me wondering, is there some other “frictionless” way to vibrate a string? I knew that electromagnets need a lot of power, but a strong permanent magnet might not need much mechanical energy to excite a string, so my friend, JP Timmerman, modelled and print me an 8 slot wheel that I could arrange 8x3mm magnets.
(https://www.amazon.ca/dp/B01MZ6EJE2/ref=cm_sw_r_tw_dp_U_x_bRcqEbWM614GC )
Here’s one of those early test…
There was a lot of EM noise from the motor coming through the bass pickup so I had JP do a 16 slot tapered wheel so I could move the motor away from the strings.
https://photos.app.goo.gl/fnWxjGxRPJ7PDidp9 1
That’s puredata talking firmata to an arduino to control PWM on a MOSFET to do variable speed control on a little DC motor.

So at this point, everything seems to work but I’m not finding what I like in terms of sound. I’m hearing the bass and the effects. This is all just a couple days before Toronto Sound Festival. At the festival I lurked around but didn’t see anything that was in my groove. While at the festival, I went on Craigslist, found a humbucker pickup, went back to my workshop and made this…


I was going to Winnipeg and staying at rental house that had a grand piano, so I built a rig that I could clamp into the piano and use the wheel to drive a set of strings. Here’s the rig being tested on a metal spring…


I used that through effects pedals to create Test Flight…
http://stefanpowell.ca/sound/TestFlight/ 1

In Winnipeg, the guitar pickup did not work very well. The soundboard of the piano was like hundreds of antennae making a horrible racket. I wasn’t expecting much at that point, but I decided to place my handheld recorder on a little tripod directly on the soundboard, which of course picks up every footstep in the house… anyway, I was super thrilled with one of those recordings.
That recording is November Crows

Here is video of that rig in the piano:

href=”http://stefanpowell.ca/sound/NovemberCrows/” target=”_blank”>http://stefanpowell.ca/sound/NovemberCrows/
Here video of that rig in the piano…

Here is a recording that my daughter called “The String’s Song” made using that duochord.
http://stefanpowell.ca/sound/TheStringsSong/ 1
and that is roughly what I performed for my first set at FF. That’s the duochord tuned to G#1 and C2. On my second set I changed to G1 C2.

Here’s a link to the wire that I used…
High Carbon Steel Wire

High Carbon Steel Wire, 2B (Smooth) Finish, Full Hard Temper, ASTM A228, 0.045″…

Packaged wire is shrink wrapped, bar coded, and packaged in an easy to use pull-type dispenser box.

CDN$ 11.58
I also ordered the tuning pegs from Amazon, but I wouldn’t recommend them, as they are a bit flimsy for the task.

I’ll post a link here shortly to the wheel plans once posted on Thingaverse.

The motor speed controller I used was a DC speed controller that I got a Creatron that uses PWM.


This works sooo much better that the arduino control I was using. If there is a more simple, affordable, plentiful, easy to access solution for motor speed control, I’d like to try it. I have not had ANY success with just adjusting voltage with various types of potentiometers.

Yesterday I found a fella online who has built a similar magnetic wheel about 4 years ago. https://vimeo.com/160780036 His appears to use a brushless DC motor salvaged from a harddrive and speed controlled using a hobby brushless speed controller and an arduino. I think he’s using just one magnet. I like his term “Rotary Magnetic Bow”. That kinda nails it.

Those who are into the mathy stuff might find this interesting…
Matt Baker’s Math Blog – 25 Jun 18

The Balanced Centrifuge Problem

Next week I start a new position as Associate Dean for Faculty Development in the Georgia Tech College of Sciences.  One of the things I’m looking forward to is getting to know more faculty o…

Here is my favourite arrangement of magnets…


I really don’t fully understand why this arrangement works so well compared to everything else I’ve tried. It lets me shift into different harmonics in interesting ways without a lot of high pitched ringing. I’m sure someone could figure out a good explanation of the interaction of the pattern and the vibration of the strings. The RPM of the motor for those FF performances was around 1000-2000 RPM.

Here’s a nice 5 magnet arrangement on a 24 slot wheel although the orientation of the magnets on my 24 slot wheel are not ideal so I haven’t spent much time working with it.


Like I said at the FF workshop, I don’t really know where I’m going with all this, but I’m going to keep scratching the itch.

What I would like to see …

  • an amplified electromagnet unit to feed a signal into strings
  • dual pickups for stereo separation
  • workshops to build and experiment with these types of devices
  • a CV controlled motor speed controller
  • this technique used for site based installations
  • a nicely crafted completely mechanical acoustic version

I’ve given my friend JP a little poke about posting the wheel file. I just sent him the little blurb about it and I’ll post the link here as soon as I get it.

I just got back from Costa Rica and while I was there I recorded this…

JP just posted the wheel here: https://www.thingiverse.com/thing:4228053

For the recording in Costa Rica, I mounted the wheel on an articulating arm (https://www.amazon.ca/SmallRig-Adjustable-Articulating-Monitor-Lights-2066/dp/B076KDDBW5) which was tied to the tree separately.

Here’s what my setup was like for that Costa Rica recording…


Do you have a humbucker pickup? Just solder up a jack to the humbucker. I added a volume pot to my first one but never dialed it down, so I skipped that part for the recent pair I made.