The surfaces of a room partly reflect and partly absorb sound falling upon them and the proportion either reflected or absorbed varies according to the nature of the surface of the material and the form of the construction. In every case the proportion varies from one frequency or pitch of sound to another.

This digest covers the insulating properties of various materials and reverberation times in halls and auditoria.

Corrections: page 3, third paragraph, second sentence, should read: "Absorbers that are solely cavity resonators are of less interest to the average designer than others, as their use is limited. They can be "tuned"....etc....."

Table 1 Column heading for High Frequency, should read 2000 c/s, not 200 c/s.

Table 1 Item No. 21, absorption coefficient at Low frequency should read .3, not .03.

A revised edition was published in 1962.