Control of an electrostatic acoustic device

A control circuit operable for an electrostatic acoustic device including a membrane, a first electrode and a second electrode, wherein the first electrode is disposed parallel to the membrane, wherein the membrane is configured to respond mechanically to a varying first electric field in accordance with an electric potential applied between the first electrode and the membrane, wherein the second electrode is disposed parallel to the membrane opposite from the first electrode;

• wherein the membrane is configured to respond mechanically to a varying second electric field in accordance with an electric potential applied between the second electrode and the membrane, wherein the first and second electrodes have through holes configured for acoustic transmission to and from the membrane, the control circuit comprising:
• an audio signal input;
• a detector configured to detect a current or charge signal from the electrostatic acoustic device responsive to motion of the membrane, the current or charge signal including an audio signal varying at audio frequencies, wherein the detector is configured to produce an audio output signal varying at audio frequencies;
• a transform circuit configured to transform the audio output signal to produce a feedback signal;
• a comparator configured to compare an input audio signal at the audio signal input to the feedback signal to produce an error signal;
• and
• a controller configured to input a control signal to the electrostatic acoustic device, the control signal responsive to the error signal;
• wherein the control signal is configured to control acoustic transparency of the electrostatic acoustic device, from outside space through the through-holes of the first electrode, across the membrane and through the through-holes of the second electrode.