Improvements in teleconferencing sound quality and gain before feedback through the use of DML technology
Peter A. Mapp, Henry Azima · The Journal of the Acoustical Society of America · 1999
One of the primary limitations of teleconferencing systems is the premature onset of acoustic feedback. The current trend toward the use of desktop personal computers as the teleconferencing platform, rather than dedicated and acoustically treated video conferencing rooms, further exacerbates the problem. Local, sound reflecting surfaces including the desktop, conference table, or computer screen, etc., can cause undesirable specular reflections from the loudspeakers to occur. These are then picked up by the system microphone(s), causing the formation of strong comb filtering and resultant sound coloration, reduced speech clarity, and reduced gain before feedback. Historically, a number of approaches have been adopted to help overcome such effects, including echo cancelling, phase shifting and ‘‘smart’’ microphone techniques. The paper illustrates the effects of such reflections and shows that distributed mode loudspeakers can produce less boundary interactions and comb-filtering effects. Experimental data are presented to show that DML technology can passively offer a 4–7-dB improved gain before feedback advantage over conventional cone devices in typical teleconferencing applications. The fact that significant gains in feedback margin and reductions in potential coloration are achieved without the need for additional DSP or active techniques implies a radically different and advantageous acoustical radiation mechanism.