Freq. down-translation at speaker?

[Bill Knight]

This question follows on from the one about telephone line bandwidths.

Is there anyway the standard speaker coil in a home telephone headset
can be made to emit a frequency lower than the apparent applied audio
signal?

IOW by additive or destructive combinations of waveforms, phase
modulation, etc. Or utilizing some electrical property of the coil
itself.

Thank you,

Tim