Setting speech privacy criteria for closed rooms in terms of speech privacy class values.
John S. Bradley, Bradford N. Gover · The Journal of the Acoustical Society of America · 2010
The new ASTM E2638 standard defines speech privacy class (SPC) as the sum of the measured average noise level at the position of a potential eavesdropper outside the room and the measured level difference between a source room average and the transmitted levels at the same potential eavesdropper location. For a given situation, the likelihood of transmitted speech being audible or intelligible can be related to the probability of higher-speech levels occurring in the meeting room. Increasing speech privacy criteria can be defined in terms of increasing SPC values. For a particular meeting room speech level, there is an SPC value for which transmitted speech would be below the threshold of intelligibility or even below the threshold of audibility. One can therefore create a set of increasing SPC values corresponding to increasing speech privacy and for each SPC value, one can give the probability of transmitted speech being either audible or intelligible. This paper describes a new procedure that makes it possible to specify degrees of speech privacy for meeting rooms and offices in terms of the expected risk of a privacy lapse and varying from quite minimal to extremely high-speech privacy.