Acoustic equipment and sound field calibration

High-quality microphones make it possible to select loudspeakers with appropriate specifications and to test the sound field. Shortcomings in the loudspeakers' frequency responses may be overcome by using digital signal processing techniques. Only under free-field conditions do sounds reach the experimental subject from the loudspeaker alone. Free-field conditions rarely exist even in anechoic rooms, since echoes from the setup create an inhomogenous sound field, but sound reflecting objects can be located by measuring the acoustic impulse response of the setup, and their disturbance of the field can be minimized by reducing their dimensions or covering them with sound absorbing material. Outside the sonic range special problems prevail, especially at very low frequencies.