System of audioconference by telephone link up

Claim 1

An audioconference system for conference connecting a plurality of groups of remotely located conferees, said system comprising at each conferee group location: a loudspeaker assembly; a plurality of microphones, each microphone of said plurality being assigned to a conferee; each of said plurality of microphones being spaced apart from said loudspeaker assembly by an equal radial distance to provide a circumferential array of opposed pairs of microphones and each being spaced apart from an adjacent microphone by an equal circumferential distance; said plurality of microphones being divided into microphone groups, each group having n microphones producing voice signals in the audiofrequency range; phase shifters connected to the microphones of a microphone group, said phase shifters providing phase angles of the audiofrequency signals transmitted by opposing pairs of microphones equal to 2π/n; means for mixing the output audiofrequency signals of said opposed microphones which have been phase shifted by said phase shifters; a detection unit for each microphone which includes a pass band filter tuning onto a characteristic audiofrequency independent of acoustic coupling and the acoustic level of the loudspeaker assembly, whereby the acoustic level of the microphone only provides transmission of audiofrequency by the conferee at a microphone; a transmit stop band filter connected to said mixing means for cutting out the audiofrequency signals lying in the stop band width of said transmit stop band filter; address coder means identifying the location of a conferee relative to a specific microphone generating digital signals to identify a conferee who has begun speaking adapted to actuate an indicator for visual verification of the conferee and microphone; said address coder means being controlled by said pass band filter and said transmit stop band filter generating a carrier output whose frequency lies in said stop band filter band width modulated by said address digital signals; means for transmitting said audiofrequency signals filtered by said transmit stop band filter and said address digital signal modulated carrier to one or more remote conferee group locations; means for receiving from one or more remote conferee group locations said audiofrequency signals filtered by said transmit stop band filter and said address digital signal modulated carrier; a receive stop band filter substantially identical to said transmit stop band filter which is connected to said receiving means; filtering and demodulating means connected to said receiving means for filtering and demodulating said address digital signal modulated carrier; and address decoder means controlled by said filtering and demodulating means.