Public Address in large volumes

Public Address in large volumes

Worship spaces, conference rooms, amphitheaters, railway stations, shopping malls, gymnasiums, industrial workshops…

All these large volume spaces exhibit :

• a large reverberation time (Sabine law),
• and / or a high level of background noise

two factors that tend to impair speech intelligibility and sound clarity of voice and music.

In order to get high speech intelligibility / clarity, you need :

• a strong direct sound: the PA system must send sound energy on the audience but not elsewhere, in order to minimize acoustic energy reverberated to the room. Accurate control of the radiated field (directivity) is therefore essential.
• An adequate signal-to-noise ratio : the level of the PA system must be approx. 15dB above background noise.

For a good acoustic comfort, you need :

• a homogeneous sound coverage : SPL and timbre should be essentially the same everywhere across the audience area.
• An adequate level of diffusion : enough for a correct SNR, but not more. If the background noise level varies, the level of diffusion should be vary accordingly.
• High quality loudspeakers : low harmonic distortion, large frequency bandwidth…

Distributed PA / Centralized PA ?

In order to get a homogeneous coverage and a strong direct sound over the audience area, there are 2 options :

• Distributed PA : a large number of small loudspeakers are spread throughout the volume, so that each listener is close to one of them. But results obtained are often poor, and the visual impact generally quite strong.
• Centralized PA : a single central cluster using a number of small loudspeakers operating in a coherent way ensures coverage of all the audience area. Results obtained may be excellent, and the visual impact may be minimal.