A Study of Talking Distance and Related Parameters in Hands-Free Telephony

The hands-free telephone, which provides a convenient way of carrying on associated activities such as turning the pages of reference material, referring to drawings, etc., while the user is talking into a microphone and hearing from a loudspeaker located on his desk, has become an attractive supplement to the handset. This type of operation was first provided as a customer service in the mid-1950's in the form of the 595 telephone set, and soon thereafter in supplementary form as the No. 1A Speakerphone system, 1 neither of which employed voice switching. The fact that under certain operating conditions hands-free operation can result in singing, in the transmission of reverberation or a barrellike quality and in excessive noise for the handset listener at the other end of the line has been recognized. The effects of reverberation or liveness of the room and of talking distance have been appreciated. There 1529 1530 T H E BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER I960 lias been some speculation concerning the acceptability of reduced talking distance as a remedy for such operational characteristics. 2 More recently, switched gain, in which loss is introduced into the receiving path when the user is talking and into the transmitting path when the user is listening, has been explored as a remedy for some of t hese effects.3 This paper reviews the operational problems of hands-free telephony and gives the results of some experiments in which user reaction to, and acceptance of, various ways of achieving hands-free operation were studied.