Acoustic Characterization of loudspeaker and microphones

P. Cobo & C. de la Colina

A microphone positioned in front of
a loudspeaker in the Anechoic Room of the CSIC

The characterization of sound transducers is carried out at the Anechoic Room of the CSIC using the self-design Virtual Instrument IMSA-EPE. The IMSA-EPE manages a digital board NI DAQ PCI-MIO-16E, of maximum sampling frequency 250 kHz, with 2 outputs and 8 inputs, controlled with MATLAB. It allows to measure the impulse response of acoustic systems using four types of signals:

  • Maximum Length Sequences (MLS).
  • Inverse Repeated Sequences (IRS).
  • Time- Stretched Pulse (TSP).
  • Logarithmic Sine-Sweep (LSS).

This setup allows obtaining two characteristics of the microphone:

  • Its frequency response curve.
  • Its directivity pattern.

The frequency response curve of the microphone in its acoustical axis is measured by comparison with that of a reference microphone. The directivity pattern of the microphone is obtained by measuring the impulse response of the loudspeaker-microphone pair as a function of the turn angle with respect to their acoustic axis, θ. Therefore, the 2D directivity pattern in the horizontal plane containing both the loudspeaker and the microphone, depends on the frequency and the turn angle, D(f,θ).

Polar directivity pattern of a microphone at 125 and 8000 Hz