It could be better because it seems hard to make low-pass solids at audio range and beyond: for example, while you can easily make a spring which has low pass b

It could be better because it seems hard to make low-pass solids at audio range and beyond: for example, while you can easily make a spring which has low pass behavior in the few Hz range, the spring itself is made of metal and conducts sound normally. I guess you have felt pads and foam (which have thin strands and large number of interfaces for sound to reflect). The magnetic force however should retain its springy behavior up to arbitrarily high frequencies.