This shows the relationship between the voltage applied to the terminals of a loudspeaker drivers (shown on the oscilloscope) and the excursion of the driver.

The frequency of the sine wave driving the system ranges from 1 Hz to 6 Hz, so we stay below the resonance frequency of the driver.

The jump in level as the frequency is increased is caused by the low frequency roll-off of the DAC that I’m using to send the signal to the amplifier. Its manufacturer wasn’t expecting anyone to use it at 1 Hz…