Voice Evacuation Audibility in a Sanctuary with a Balcony

For public-mode notification, the alarm must be at least 15 dBA above the ambient sound level, and it must also meet the code's minimum sound-level criteria. The main-floor ambient is 78 dBA, so the required alarm level is at least 93 dBA. The measured 82 dBA is 11 dBA below that requirement. Under the balcony, the ambient is 74 dBA, so the required level is at least 89 dBA; the measured 76 dBA is 13 dBA short. The balcony underside also creates a partial enclosure, so the reduced level there is not surprising. The existing horns fail both locations. The proposed speaker/strobes cannot be accepted on the basis of the appliance rating alone; the designer must calculate the sound pressure level at the farthest listener and under the balcony, including the effects of the 28 ft ceiling, carpet, and balcony soffit. The design should add speakers under the balcony and increase power or reduce spacing in the main floor, then retest with the organ at full volume. The measured levels should be recorded at representative seating positions, not only at one central point.

The visible design cannot be approved from the 110 cd rating alone. Visible coverage depends on the appliance's listed candela rating, mounting height, ceiling height, and the manufacturer's published coverage table. A 28 ft vaulted ceiling with wall-mounted appliances at 15 ft is not a simple flat-ceiling application, and 35 ft spacing is likely to exceed the listed coverage for 110 cd in this geometry. The balcony underside also blocks direct view of wall-mounted strobes for some seats, so visible notification under the balcony must be evaluated separately. For voice intelligibility, the large volume, hard vaulted ceiling, and amplified speech create reverberation and echo concerns. Speaker spacing at 35 ft may produce uneven coverage and poor intelligibility even if the sound level is high enough. The designer should provide a speaker layout with coverage calculations, a tap-power schedule, and an intelligibility assessment, and should add visible appliances under the balcony or on the balcony face. The owner's preference to avoid appliances on the balcony face cannot override the need for visible notification in occupied seating areas.

The designer should first correct the audible deficiency by adding speakers under the balcony and increasing the main-floor sound level to at least 15 dBA above the measured ambient, while staying within the code's upper sound-level limits. The revised layout should reduce speaker spacing or increase tap power where needed for intelligibility, and it should include speakers aimed into the balcony underside. Visible notification should be redesigned using the manufacturer's coverage tables for the actual mounting height and ceiling geometry, with additional strobes under the balcony or on the balcony face if the coverage analysis shows a gap. After installation, the contractor should perform a witnessed acceptance test with the organ at full volume, measure dBA at multiple seating locations including under the balcony, verify visible coverage from seated eye height, and conduct an intelligibility check. The test results, device locations, tap settings, and any deficiencies should be recorded and provided to the owner. Acceptance should be based on measured performance, not on the appliance's nominal rating.