Alternative metrics for the directivity of acoustic sources

While the directivity of an acoustic source at a given frequency is thoroughly characterized by a directivity function over the angular coordinates, it may also be characterized to a lesser degree by a single-number directivity factor. The directivity index (i.e., the logarithmic version of the directivity factor) is a related figure of merit. Recent efforts to quantify the directivity of sources for architectural acoustics measurements have led to several alternatives to these values. One example is the area-weighted spatial standard deviation of radiated levels over a free-field measurement sphere. This paper presents and compares this and other directivity metrics for several types of sources, and discusses their benefits.