Correlation Coefficients as Criteria for Randomness of Reverberant Sound Fields
Richard K. Cook, Seymour Edelman · The Journal of the Acoustical Society of America · 1950
A reverberation room which is used to measure sound absorption coefficients should have a completely random sound field. This we define to be a field such that at every point within the room, plane waves of a particular frequency having the same average intensity for all directions and phases will have passed by after a sufficiently long time (short, however, in comparison with the reverberation time) has elapsed. For such a sound field, we find the correlation coefficient to be R = sin kr/kr, where k = wave number and r = distance between two microphones whose pressures are being correlated. The correlation coefficient is R = 〈p1p2〉Av/(〈p12〉Av〈p22〉Av)12, where p1 is the sound pressure at one microphone, p2 that at the other, and the averages are for long times. Results of measurements of R as a function of k and r for steady sound sources in our 15,000 cu. ft. reverberation room will be presented. Results for bands of frequencies will also be presented.