Integrator's Reference Manual for Polycom HDX ... - 1 PC Network Inc

Integrator’s Reference Manual for Polycom HDX Systemsambient noise level). A room built to the description found elsewhere in thissection will usually fall between NC-30 and NC-35. The actual NC value is notcritical; what is important is that the room be built with the intent and carerequired to achieve the low noise rating. Typically in architectural design, asite evaluation and analysis are required to certify the noise performance of agiven space. The quieter the room, the easier it is to hear others in the sameroom as well as be heard by others who are participating via conferenceconnection to a far-end location (or locations).Almost every conference room of medium to large size (larger than 12’x15’)requires some level of acoustic treatment to provide good speech-rendering toother conference sites. The quality differences lie in the areas of intelligibilityand consistency of loudness as presented to the far-end. While the people atthe far-end may hear the sounds coming to them, it may be hard for themclearly to distinguish all of the vowels, consonants, inflections and nuances ofactual human speech communication. (We all know that it is not simply whatyou say but how you say it—i.e., the inflections and intonations—that makesthe difference in perceived meaning in human communications.)Good audio practice dictates that the treated surfaces be composed of at leasttwo nonparallel walls. And, as the VCS hardware is a potential source ofdistracting fan noises, the walls to be treated should include the wallimmediately behind the VCS hardware, whenever this hardware is within theconference room proper. To help prevent meeting audio from leaking intoadjoining hallways or offices, the walls along those areas also should betreated.Approximately 50 percent of the wall area needs be covered with acousticpanels. The type recommended is 1” thick compressed, dense-core fiberglass,fabric-covered, or equivalent, with a SABIN (sound absorption index) value of0.9 average. This specification is sometimes referred to as NRC (noisereduction coefficient). If reduction of sound passing through is required, thenan additional barrier layer is laminated to the dense-core material, usually3/8” thick fiber compression board. The barrier layer is placed against theexisting wall material, then the acoustic absorption panels are placed on theinterior-room side of that. The barrier panels will have a SABIN of 0.9, but willhave an additional specification of an STC (sound transmission coefficient) of20. STC is a measure of the amount of reduction in loudness of sound passingthrough the material. Having an STC rating of 20 means there is a factor of 10reduction in the amount of sound passing through that material. Ahigh-quality conference room wall usually has an STC of 60 or more—that is,less than 1/1,000 of the sound in the room leaks through the wall.Room LightingThe brightness of the lighting in a videoconference room plays an importantrole in determining the far-end view of the meeting. When there are low tomoderate amounts of light—20fc to 35fc (footcandles), typical officelighting—the distance range of “in focus” objects (depth-of-field) usually isA - 6