Without echo. Said of an acoustic which is free field (i. e. without boundary or reflecting surfaces), and specifically of a room which is designed to produce no reverb or other echo effects. This is achieved by making the walls with very irregular surfaces of considerable and varying depths, in such a manner as to ensure that (in theory) all sound pressure waves which strike the walls are completely absorbed. Rooms of this type are used to test audio equipment such as loudspeakers and microphones and for other types of research.
microphone
