I analyzed the impedance as a function of frequency (using the handy Analog Discover 2 USB oscilloscope), shown below. We can see the fundamental resonance a bit above 100 Hz (note: next prototype should make this lower).
The pattern for this speaker stressed my coil laying tool in ways that my previous prototypes hadn't, and the the applicator tip became a point of failure. I'm working on two improvements to this. First, the software correction for tool offset from rotational axis has been a pain to keep calibrated and is a source of error when pushing the limits of radius of curvature. To get around this, I designed a mechanical correction in two axes for the tool center point using 3/16-100 microadjustment screws. By using these adjustments and measuring the output with my zund microscope tool, I can dial in the alignment to about 10 microns.
Second, the winding paths of this speaker membrane put torque and axial load on the single 3mm OD ball bearing (with 1mm balls inside!) that I had been using to apply the wire. After a few jobs, this roller would have the characteristic "crunch" of an overloaded bearing. I owe an offering to St. Venant. To fix this, I made a small roller applicator, held by two 3mm OD bearings. This effectively limits the torque seen by the bearings and doubles the effective radial load (because there are two instead of one). It also allows me to experiment with different applicator profile shapes. Two are shown below, on a penny for scale.
