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

Room Design and Layoutdelays)—will be recognized by the echo canceller as “new audio information,”and it will send those distortions to the far-end, perhaps wreaking havoc onthe system audio quality. In short, speaker power should be matched tooverall audio subsystem power. The speakers should provide adequatecoverage and be able to present approximately 80 to 85dBA-SPL (continuous)at the local site with the system operating at nominal power utilization, andhave a peak reserve of 15 to 20dB before distortion.Range/Frequency ResponseThe human ear is able to hear sounds in a very wide range of frequencies (aslow as 70Hz and as high as 12,000Hz). The human voice is able to producesounds in a narrower range (100Hz to 8,000Hz). Most spoken communicationoccurs, however, in a range that is only 150Hz to about 6,000Hz. This meansthat we need to select speakers that operate with ideal performance in a fairlynarrow range for human voice (as opposed to speakers used for music, thatmay have ranges of 20Hz to 20,000Hz). We must also be alert to the crossovercharacteristics of the speakers we select. Many coaxial and paraxial speakershave their crossover within the middle audio frequencies, thereby inducingpotential distortion within the spoken frequency range and creating anomalieswithin the system that hinder voice communication.Video ElementsAs a general rule, any display used in a videoconferencing environmentshould be sized for the number of attendees, the physical distances involvedand the type of material presented onscreen. The screen size should allow forclear and easy viewing at the various distances experienced within the room.A measure of required screen size that often is applied to projectiontechnology is: no closer than 1.5 times the diagonal measure and no fartherthan 7 times that measure. Nobody should have to sit closer than 2 times thescreen diagonal measure, nor farther than 8 times that measure.Direct viewed tube-type displays (monitors) almost always are sharpest andbrightest in a videoconferencing environment. “Retro-projector cabinet”displays (which look like largescreen TVs) are next in sharpness andbrightness, and “front-screen” projectors come in last. Glare and uncontrolledambient room lighting adversely affect the quality of the image most withfront-screen projectors and least with direct view tubes. A very limitednumber of frontscreen projection systems have sufficient brightness andcontrast to be useful in a properly lit videoconference room.A - 11