Siren Standards

• NCJ Number: 69588
• Author(s): R A Little
• Date Published: 1978
• Length: 12 pages
• Corporate Author: California Dept of Highway Patrol
• Sale Source: National Institute of Justice/
• Language: English
• Country: United States of America
• Note: Report prepared for presentation at the Workshop on Optimization of Emergency Vehicle Audible Warning Devices, Boston, Massachusetts, June 22, 1978

Annotation

Discussion of police siren research as conducted by the California Highway Patrol looks at sound cancellation problems from two sirens and other speaker mounting problems.

Abstract

Tests of siiren audibility have been conducted by the California Highway Patrol ever since an authorization to approve sirens was granted in 1923 and were conducted by ear and sound level meters. Tests of siren effectiveness conducted with both electronic and electromechanical sirens mounted on a vehicle in a simulated chase revealed that electronic siren speakers are very directional and should not be mounted under the hood. Other tests were conducted to remove some of the site variables in siren testing. Sound tests conducted with dual speakers exhibited a severe sound cancellation problem, particularly for dual speakers in the manual mode. However, other experiments have shown that stacking dual speakers of the use of two drivers connected to one speaker bell greatly diminish sound cancellation problems. A major experimental finding from testing speaker shapes is that the wide-mouth speaker with the opening mounted vertically produces about 4 decibels more than a good round speaker, and 6 decibels more than when the speaker is mounted in its customary flat mode. Tests of siren sound patterns provided support for U.S. Department of Transportation findings that the hi-lo sound is not as effective as the wail and yelp sounds. Oscillation rate tests suggest that the rapid oscillation rate of the 'yelp' mode is a good attention-getter and does a fair job of moving traffic at an intersection. Analysis of people's occasional inability to hear the siren of an approaching emergency vehicle in time to react supports training for emergency vehicle drivers in defensive driving. Generally, more psychoacoustic studies are needed in order to determine the warning system that is most audible without creating a nuisance in the community. Numerous diagrams illustrate siren sound distribution patterns under varying test conditions.