Acoustic Testing of High Fidelity Receivers

The broadcast listener desires the illusion of being present in the auditorium or studio where the sound is being produced. Therefore the sound heard by the listener in a living room should have essentially the same qualities. In broadcasting, the studio reverberation, the microphone technique, the loud speaker characteristics and the living-room reverberation are among the more important factors which must coöperate in obtaining the desired illusion. The latter two factors are evaluated by testing the loud speaker in representative living rooms. The test microphone is located respectively at each of three stations selected to be representative of listening points. Acoustic fidelity curves for these stations are superimposed on a single record. An acoustic recorder is described which has been developed for automatically tracing each curve in about three minutes. Curves are reproduced which show the effect of frequency wobbling in integrating the reverberation.