The original design of the métallique resonator features a gong driven by a voice coil to resonate creating a haunting sound rich with harmonics. Compared to the previous experiment creating a métallique speaker, where a sound exciter was used, the use of a voice coil should increase the drive capability, reduce the weight on the gong (or cymbal in this case) and more reliably attach the driver.
What is a voice coil?
A voice coil is a tightly wound wire that, when current is passed through, creates a magnetic field. The polarity of this magnetic field reverses by changing the direction of the current traveling through the wire. When a voice coil receiving electrical current is suspended inside a permanent magnet, it will either attract or repel depending on its polarity. Because this polarity can be accurately controlled electronically, the voice coil can move back and forth inside the magnet thousands of times per second – perfect for recreating audio. In speakers, the voice coil is glued to a cone which pushes the air, creating sound waves.
A demonstration, placing a voice coil inside of a magnet while audio is being played through the wires.
Acquiring a Voice Coil
The size and construction of the voice coil (number of turns, materials, etc.) requires specific measurements and needs to be properly matched to the magnet to ensure the correct impedance and wattage. Creating a custom voice coil and matching it to a magnet is outside of the scope of this experiment, so a working model needs to be sourced. Unfortunately, for as simple and pervasive as voice coils are, few places (other than bulk wholesalers) have them available online. The best solution available is to purchase a cheap speaker and dissect it to get to the voice coil and magnet.
- Small, cheap speaker: Goldwood Sound 70 Watts 4ohm Shielded 4″ Speaker Woofer Black.
- X-ACTO blade.
- Power drill with titanium bit.
- Soldering Iron.
- Remove the dust cover (small circle in the center of the speaker) by using a sharp X-ACTO blade exposing the voice coil. The dust cover will not be necessary, so do not worry about damaging it.
- Carefully cut the down the sides of the voice coil to separate it from the speaker cone. Be careful not to damage the voice coil – it is better to have glue and pieces of the cone remaining than to cut into the coil.
- Unsolder the wires from the connection plate.
- Detach the wires from the speaker cone. This can be difficult as they are adhered using epoxy. I did this with some force and careful cutting, but have read that acetone could be used to dissolve the epoxy.
- Remove the rest of the cone and spider (thin membrane above the magnet).
- Remove the metal casing. This requires drilling out the rivets from the magnet. If possible, put tape over the hole in the magnet to reduce debris that gets inside.
- Use a piece of card stock to clean out magnet hole so there is no friction when the voice coil is inserted.
Unfortunately, I did not take pictures or video of this process, but there are videos of people re-coning speakers on YouTube demonstrating much of the process.
Inspiration from Plate Reverbs
Information about the métallique resonator is limited, at least in English, but its design is similar to that of a plate reverb. There are active communities of people discussing the creation and maintenance of plate reverbs and resources are plentiful:
Assembling the Voice Coil Métallique Resonator.
- Isolated voice coil and magnet (from above).
- Cymbal or gong.
- Device to suspend the cymbal/gong. I chose to use a mic stand and shoe string.
- Device to hold the magnet in place. A camera tripod with an iPhone adaptor is a good solution.
- Hot glue gun.
- Aligator clip wires.
- Power amp and speaker cable.
- Adhere the voice coil to a cymbal using the hot glue gun.
- Suspend cymbal from the mic stand so that it can resonate, but it’s movement is restricted.
- Attach magnet to tripod iPhone adaptor, adding tape for additional support.
- Position and secure the magnet so the voice coil fits inside and can move back and forth without friction. A camera tripod was used in this experiment with an iPhone adaptor, which worked well because it is designed to move and lock in all directions.
- Use alligator clips to attach voice coil wires to speaker wires. Ideally, the braided wires that were removed from the speaker would be used to attach to a connection plate. The voice coil moves so often and quickly, that it will cause other wires to break. I did not follow this for this demonstration.
- Attach speaker cable to power amp and play audio. Start quietly and slowly increase the volume.
The métallique resonator driven by a voice coil had a more powerful, fuller sound compared to the audio exciter driver. This design resonated a much larger and darker cymbal. Unfortunately, the experiment was short-lived, as the voice coil overheated and began to smoke when low frequencies were played. 100 watt signal was sent from the amplifier to the 70 watt voice coil / magnet, burning it out.
- Find a better source for voice coils so I don’t have to keep buying speakers and taking them apart. I think speaker repair shops might be a good resource.
- Design an enclosure to secure cymbal and magnet.
- Learn more about the science of voice coils – impedance, ohms, turns, etc.
- Research plate reverb drivers.
Please reach out if you have any ideas or questions. I plan on continuing these experimentations with the end goal of creating my own métallique in the most musical form possible and experimenting with plate reverbs.