Performance of the Anechoic Room in the Parmly Laboratory

The anechoic room of the Parmly Laboratory is being used by the Armour Research Foundation in its acoustic research. Performance of the room has been evaluated by the following means: 1. inverse-square-law measurements from 60 to 17,000 cycles per second; 2. measurements of the effect of nearness of the walls on the response curves and the acoustic impedance of loudspeakers; 3. ability to obtain consistent data with different geometrical arrangements. Results of these experiments will be presented and some of the techniques of measurement will be discussed. A method of measuring the wall attenuation will be described. It is estimated that it would be necessary to have a distant sound source produce an average intensity of 10−7 watts per square centimeter at the walls to be heard within the room.