Polycom vsx7000 Manual De Referencia

Integrator’s Reference Manual for the VSX Series

A - 10

For conference communication we do not really care about producing the 

thundering roar of jet aircraft engines, or other sounds reproduced on TV or in 

the movies. We are interested in reproducing the human voice. The tone, 

intonation, pitch and level of people speaking from the far-end should sound 

as much as possible like the sound they would make if they were speaking in 

the room. Given what has been covered in other sections of this book [Basics of 

Audio and Visual Systems Design], we will touch base here on a couple of simple, 

basic elements of the speaker technology we deploy in the conference room. 

These basics fall into three subcategories: direction, power and 

range/frequency response.

As human beings, we feel most comfortable when the voice we hear appears 

to come from the same direction as the image of the person speaking. This 

means that reliance on ceiling speakers alone is not an ideal practice when the 

system is used for videoconferencing. In many small and medium-sized 

systems, front-firing speakers alone can provide proper direction and 

adequate coverage. Larger rooms (greater than 12’x15’) probably need both 

front-firing and side or top-fill speakers in order to maintain proper coverage 

at nominal power levels.
In planning systems for larger rooms, we need to take advantage of the HAAS 

effect. Basically stated, this is the human brain’s interpretation of sound 

direction when the same sound arrives at the ear from two or more directions 

within a certain time period. We attribute the direction of the sound to the 

direction from which the sound is first perceived, even if it is mixed with that 

same sound arriving from a completely different direction, as long as the two 

(or more) instances of the sound are within about 30ms of one another. Since 

sound travels faster electronically than it travels through the open air we may 

need to add audio delay to the side firing or ceiling speaker arrays in order to 

keep the primary perceived point source as the front of room/front-firing 

speakers.

Power is a function of loudspeaker efficiency and total available system 

power. Most speakers operate in a power range that is broader than the range 

in which they operate without distortion. For the purpose of conference 

communication, we are interested in sound that has little or no distortion. 

Sound that is reproduced accurately (with no distortion) will most accurately 

represent the voice of the people from the far-end (our primary goal). Accurate 

reproduction also will aid the echo-cancellation circuitry in the system, 

minimizing the amount of echo that the system sends back to the people at the 

far-end, and thereby increasing perceived ease of intelligibility and 

understanding. Remember that any distortions present in the playback audio 

system—whether harmonic, amplitude (gain compression) or temporal (time