Audio and Audio-Visual Design

An audio system provides reinforcement of the original spoken word or music source so that it can be heard better at distance, and can cover a larger audience.  Sound reinforcement system design includes choosing the system components, the speaker locations and aiming, and then commissioning the finished system.

Sound system performance is highly interrelated with the natural acoustical properties of the room. Good equipment, good design and good acoustics all work together to produce a good result.  The design goal for most rooms is not necessarily to create an audiophile quality listening room, but rather to provide a reasonable audio and acoustical environment that supports speech clarity and intelligibility.

Many sound systems use one cluster, or just a pair of speakers, to serve an entire room.  When the volume is turned up loud enough to reach the farthest seating, the energy reflects strongly from major surfaces in the room.  The listeners then hear a jumble of live and reflected signals, all at similar loudness but arriving at slightly different times.  (An analogy is an analog TV picture with "ghost" images, or multiple images arriving out of phase).  This confusion of signals quickly destroys speech intelligibility.

It is better to have several loudspeakers, each generating lower sound levels, all located as close as possible to the listeners.  This maximizes the ratio of direct versus reflected sound.  When the direct signals are much louder than reflections from walls and other surfaces, speech intelligibility is preserved. 

Distributed speaker layouts minimize this problem, by placing the loudspeaker much closer to the listener.  Because less volume is needed for adequate listening levels, less energy is then available to reflect around the room.  This is particularly important for teleconferencing systems, where open microphones will pick up the amplified sound plus the room reverberation.  We recommend a distributed speaker array for most rooms, especially “live” rooms.  A central cluster can work, but it must be carefully designed and commissioned to achieve decent results.

Loudspeakers can cover only a certain amount of floor space.  Just as an entire room cannot be adequately illuminated with one of two spotlights, audio coverage is best achieved by an array of sources located throughout the room.  Ideally, loudspeakers should be placed so that no listener is more than a few feet from the nearest source.  Otherwise, some speakers will have to be turned up so loud that strong reflections will be excited, and speech clarity will suffer rapidly.

Sounds from all sources also need to arrive at the listener at the roughly same time.  This can be accomplished artificially using a digital delay device.  In very large spaces - with dimension more than 100 feet - the signal should be is electronically delayed by a certain number of milliseconds (increasing with greater distance) before it is sent to more distant loudspeakers.  This synchronizes the sound coming from both near and far speakers.  The net result is less confusion for the ear, and improved speech intelligibility.  Delay times will be set for certain "delay zones", depending on distance from the microphone location.

See also:     room acoustics