BuCom recommends WHELAN Voice and Siren Systems

Performance Statement
WHELEN High-Power Voice and Siren Systems are tested and certified in anechoic chambers, where extraneous factors that affect sound measurement are eliminated. Anechoic chamber measurements are extrapolated to 100' free field measurements for each system, which are verified by extensive field testing. The use of "gain" factors attributed to ground reflection are considered questionable and are NOT employed in performance documentation of WHELEN High-Power Voice and Siren Systems. All 100' performance levels listed in our brochures represent repeatable results and can be achieved within + 1 dB to stated levels under free field conditions when warning systems are maintained to factory specifications.

Government Guidelines
For a guide to planning your outdoor warning system, we suggest a document prepared for the Federal Emergency Management Agency (FEMA) titled "Guide to Outdoor Warning Systems, CPG 1-17." This document reviews the many aspects involved in planning a warning system, including community noise levels, sound coverage, equipment and site selections. In the report, guidelines are established for the predictability of siren sound coverage. Also offered is a model that demonstrates how a siren's sound pressure level (SPL) attenuates at the average rate of - 10 db per each doubling of the distance from the initial reference measurement. The report goes on to suggest that the coverage cutoff is the point where the estimated SPL value is 9 to 10 db above the average ambient noise level (approximately 60 dB in rural and residential areas and as great as 80 plus dB in city and urban areas). In most cases, this siren cutoff point is generally taken to be a value of 68 - 70 dB for rural and residential areas and 90 to 95 dB in urban and city areas.

Why Low Frequency Warning Tones Are the Most Effective
The tone frequency of a warning tone used in rating a siren's SPL is critical in evaluating the performance of an outdoor warning siren, where the siren's warning tones are expected to carry over great distances. It is documented that higher frequency tones attenuate (lose power) more over distance than low frequency tones. For that reason WHELEN High-Power Voice and Siren Systems are designed to optimize the production and projection of low frequency warning tones. A warning siren capable of producing 124 dB at 100' with a 700hz warning tone will be more effective than a siren producing 124 dB at 100' using a 1,000hz warning tone. This factor should be considered in planning a warning system.