TOA Canada - High Ceiling Open Area Speaker, Reverberant Field
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11-Dec-2009 11:00

High Ceiling Open Area Speaker, Reverberant Field

Application: Industrial warehouse paging, using the SC series of paging horns.

The goal for these types of applications and facilities is to produce a high intelligible voice page. An even sound field throughout the coverage area combined with adequate sound pressure levels (SPL) to overcome ambient noise (typically 10dB above ambient), frequency control within the voice band and a high directivity are requirements to achieve this goal.

Working against the intelligibility issue is the reverberant nature of large spacious areas with hard surface materials. These areas typically have a very short Critical Distance do to the excited reverberant field produced by speakers that do not have controlled directivity. Directivity control is essential to prevent energy interacting with the ceilings and walls. Typically a paging horn is used to achieve this when musicality is not required.

Paging Horn
Paging horn type speakers have tighter pattern control (directivity) and frequency bands suited to the speech band. Critical speech bands are weighted in three groups, 500 Hz (16%), 1000 Hz (25%) and 2000 Hz (34%). The percentages indicating the weight that these frequencies add to the intelligibility of the spoken word. Frequencies below 500 Hz add “body” and may be problematic do to excitation of the reverberant field, poor directivity and those above 2000 Hz add “sizzle”. The critical band is the 2000 Hz band. Speakers should not have crossovers in this region and if the speaker contains a woofer and tweeter often the woofer is required to support this critical 2Khz band.  Full range paging type horns with directivity control have these desirable characteristics.

When possible, paging horns should be installed to allow the audio wave front to travel in one direction. Starting at one end of the area, speakers would be mounted such that they are all facing the same direction down the length of the expected coverage pattern. This helps to prevent phase cancellation which can cause uneven SPL.

Also of importance, but not associated with speech intelligibility, is the sensitivity of the speaker since many speakers are generally used in such situations. High sensitivity speakers (97dB/1W/1M) requires less amplifier power.

TOA provides the free speaker placement program (SPV) that will assist in laying out speakers and also provides direct SPL values to assure adequate sound pressure levels are obtained.