They work with prepolarized microphones. Common applications are automotive, aerospace, and appliance testing, where it is important to find out how the human ear perceives sound pressure levels at different frequencies. Filters attach directly to a preamplifier's BNC connector, or between the preamplifier and a 4 to 20-mA constant-current supply, via coaxial cables. Filters operate from the same power used for accelerometers so microphones and accelerometers can use the same signal-conditioning equipment, minimizing setup time.