Linearization of condenser microphones under non-ideal laboratory conditions using a two-speaker setup

This paper demonstrates that the nonlinear distortion of capacitive microphones, including the vast majority of micro-electromechanical systems, studio condenser designs, and laboratory measurement microphones, can be characterized and linearized in a simple laboratory environment. The proposed setup requires only two off-the-shelf loudspeakers, a low-cost amplifier, and a sound card to generate and analyze the signals. By driving each loudspeaker with a harmonic signal at a different frequency, the microphone's internal quadratic nonlinearity is isolated through second-order intermodulation products. This allows the characteristic parameter required for post-processing linearization to be calculated directly from the recorded signal without requiring proprietary manufacturer data, high-end laboratory speakers, or a specialized method for source linearization with a reference measurement microphone. The paper provides the mathematical derivation for this source-independent estimation, demonstrates its scale invariance for both analog and digital-output microphones, and validates the approach against high-precision laboratory standards. Results show that the identified parameter remains stable across a wide dynamic range, providing an accurate and robust solution for real-time microphone linearization in practical and field-testing environments.