The acoustical properties of the large anechoic chamber at the National Bureau of Standards were investigated by two methods over the frequency range 40–63 000 Hz. In the first method described, deviations of mean‐square sound pressure from an assumed inverse square law were measured as a sound source and microphone were moved apart. Over most of the frequency range, the deviations were found from a least‐squares curve‐fitting procedure by means of digital‐computer processing of the data. The effective acoustic centers of the sources were obtained as a by‐product of the procedure. In the second method, the source and microphone were kept at a fixed separation as they were moved together across the chamber, and deviations from the mean value of the sound pressure level were estimated from recordings. The significances of the two methods are discussed with a view towards their application.