A signal converter includes a magnetic circuit, a diaphragm, a first coil, a second coil, and a variable resistor. The magnetic circuit has a magnetic gap. The diaphragm is disposed over an opening of the magnetic circuit. The first coil is disposed in the magnetic gap and configured to output an electrical signal based on vibration of the diaphragm. The second coil is disposed in the magnetic gap and configured to brake the diaphragm. The variable resistor is connected to a first end and a second end of the second coil and configured to form a closed loop circuit together with the second coil.