Audio teleconference rooms—general guidelines
C. D. Stockbridge, T. H. Curtis · The Journal of the Acoustical Society of America · 1977
General guidelines for the installation of audio teleconference equipment have been written and distributed to Bell System Operating Companies. The guidelines cover conference-room acoustics, teleconference equipment, suggested equipment arrangements, and transmission considerations. The guidelines recommend that microphones be installed in a conference situation so as to provide (1) a 20-dB (speech) signal-to-(ambient room)-noise ratio and (2) a 6-dB (direct speech) signal-to-(reverberent speech)-signal ratio. As a rule of thumb, microphones placed on a table within two to three feet of a talker give good results, microphones mounted in ceilings do not. Charts, tables, and worksheets are included which enable an installation engineer to determine the appropriate microphone-to-talker distance.