For a couple of years, I made Electrostatic (ES) headphone drivers (the part of the headphones which produce noise) for my personal use. This was inspired in large part by the incredible post and documentation found here about a similar project undertaken by a user on the “head-fi” forum about headphones. This project presented a great opportunity for me to improve my skills in CAD modeling, build a CNC Router, and end up with a great-sounding pair of headphones to boot!
Briefly, ES transducers use electrostatic attraction & repulsion, rather than magnetic attraction & repulsion, to move a diaphragm, thus creating sound. They rely on the same force which allows a rubber balloon to stick to the ceiling after you’ve rubbed it on your hair or a fuzzy blanket. In both cases, a static electric charge on an object (either the balloon or the diaphragm of a speaker driver) causes it to be attracted to a less negatively charged object. In the case of audio transducers, this allows for large diaphragms with a proportionately tiny mass (one which doesn’t require an electromagnetic coil to be attached) and a more accurate reproduction of the audio signal. For a more thorough explanation of how this results in a great sounding headphone or speaker, I’d refer you to this explanation on Ken Rockwell’s site.
In addition to the fact that ES drivers sound great, the technology presents an exciting project for DIYers in audio because…
unlike magnetic drivers, ES drivers are quite mechanically simple and can be built at a home shop,
they can be built using copper-clad FR-4 board (commonly used for making printed circuit boards), and there is a wealth of information about routing techniques as well as tooling available online for their construction,
the designs are quite modular, and there is plenty of opportunity to change the size and shape of the diaphragm, even going so far as to build quite large electrostatic speakers.
So, given these facts, and the additional satisfaction of making headphones which would normally retail for many hundreds and sometimes thousands of dollars at home, why aren’t they a more common project for DIYers? Two reasons:
they require an external power supply which means they are not portable (notable commercial exceptions exist, but I haven’t seen DIY equivalents),
these power supplies provide dangerously high voltages (up to 800+ Volt peak-to-peak swings) and must be duly respected / feared.
Below are photos of my ES drivers at various stages of their design and construction:
Various versions of the cut headphones:
I designed and built this rig for stretching the mylar diaphragms in a repeatable way:
Once construction of the drivers was complete, I used a laser cutter to make cases: