Specifications

Sources of possible acoustical interference in a room - open window, hard walls, overhead projector, ventilation shaft
Audio Systems Guide for
MEETING FACILITIES
7
CHAPTER TWO
THE SOUND SOURCE
The sound source most often found in meeting facility
applications is the speaking voice. Voices may be male or
female, loud or soft, single or multiple, close or distant.
Pre-recorded audio from video or audio tape is also very
common in a meeting facility.
In addition to these desired sound sources there are
certain undesired sound sources that may be present:
building noise from air conditioning, buzzing light fixtures,
noise from meeting participants, sounds from street or air
traffic, etc. All these undesired sounds can interfere with
the desired sound source. (See figure below.)
In this context, the loudspeakers of the sound system
must also be considered as a sound source. They are a
desired sound source for the meeting participants, but an
undesired source for microphone pickup. Feedback (an
annoying howl or ringing sound) can occur in any sound
system if microphones “hear” too much of the loudspeakers.
Finally, the acoustics of the room are often as
important as the sound source itself. Room acoustics are
a function of the size and shape of the room, the materials
covering the interior surfaces, and even the presence of
the human bodies which absorb sound. The acoustic
nature of an area may have a positive or a negative effect
on the sound produced by talkers and loudspeakers before
the sound is picked up by microphones or heard by
listeners. Room acoustics can absorb and diminish some
sounds while reflecting or reinforcing other sounds. The
latter can contribute to undesired sound in the form of
echo or excessive reverberation. In general, intelligibility
problems caused by room acoustics must be solved by
acoustic means, not electronic means.
In review, sound sources may be categorized as
desired or undesired, and the sound produced may be
further classified as direct or ambient. In practice, the
“soundfield” or total sound in a space will always consist of
both direct and ambient sound except in scientific
“anechoic” chambers or, to some extent, outdoors, when
there are no nearby reflective surfaces.