Acoustic Considerations Involved in Steady State Loud Speaker Measurements

Certain difficulties encountered in acoustic measurements of the performance of loud speakers are described. Because of the nature of these difficulties it has not yet been possible to specify a complete and simple set of measurements or conditions which will completely express the performance of a loud speaker. Data are given showing the performance of two representative types of loud speakers both when measured in outdoor space free from reflections and when measured under varying conditions in a specially treated acoustic laboratory. The differences serve to emphasize the importance of certain precautions in the making of indoor acoustic measurements. SCOPE N view of the general misconception of the meaning of many claims which are made regarding the operation of loud speakers, it appears desirable to discuss in some detail the requirements which should be taken into account in making measurements for setting up ratings of loud speaker performance. For example, claims to "uniform response at all frequencies in the audible range" or " f l a t characteristic" can not be accurately applied to loud speakers which have thus far been made available. In many cases the claims for a loud speaker are based upon carefully made electrical measurements but these are often obtained in such a manner and under such conditions that they do not represent the performance of the loud speaker as it would be normally observed, and therefore are misleading. The main consideration in making loud speaker measurements is not the electrical circuit arrangement or apparatus of the measuring system but rather the acoustic conditions under which the magnitude of the sound output of the loud speaker is determined.