EMERGENCY VEHICLE SIRENS. SUMMARY REPORT

A test program was conducted using 23 automobiles, four electronic sirens, and nine electromechanical sirens. Measurements were made of the directional radiation pattern and spectral distribution of the sirens, the field insertion loss (FIL) of the cars when closed, masking noise in the cars while being driven over a test route, and the phase cancellation pattern due to reflection for an electronic siren. Directional response measurements were also made for a pair of electronic siren speakers in three arrangements. Directional response and sound power were measured in an anechoic chamber; other measurements were made in the field. Adjusting the measured mean sound pressure levels for spherical spreading, the pressure level for the electronic sirens ranges from 104 to 128 dB. at a loudspeaker-to-subject distance of 16 m., and from 92 to 116 dB. at 64 m. The corresponding values for the nine electromechanical sirens are 93 to 106 dB. at 16 m., and 81 to 94 dB. at 64 m. For a FIL of 30 dB. (maximum loss at 1000 Hz) and a value of effective loudness sufficient for recognition in the presence of masking noise, the sound pressure required from the siren signal at the exterior of a subject vehicle ranges from 100 to 108 dB. The maximum value is within the range of sound levels of electronic sirens at 64 m., but outside the range of electromechanical sirens even at 16 m. On the basis of the siren signal power level required, there is little advantage in shifting the tone of maximum power from 1000 Hz. to 2000 Hz. and none in shifting to 500 Hz. Directional response data favor the 1000 Hz. vs. 2000 Hz. frequency. Siren performance could be improved by optimizing the radiation pattern to concentrate signal power in the preferred directions. The combined effects of sound attenuation properties of cars, the masking noise inside the cars, and the spherical spreading of the siren signal severely limit siren effectiveness as a warning device on emergency vehicles. Subjective psychoacoustic tests as a supplement to this test program are indicated.

• Supplemental Notes:
  • At head of title: Law Enforcement Standards Program. Prepared for National Institute of Law Enforcement and Criminal Justice.
• Corporate Authors:

  National Bureau of Standards

  Law Enforcement Standards Laboratory
  Washington, DC  United States  20234
• Authors:
  • Jones, F E
  • Quindry, T L
  • Rinkinen, W J
• Publication Date: 1974

Media Info

• Features: References;
• Pagination: 55 p.

Subject/Index Terms

• TRT Terms: Design; Emergency vehicles; Performance; Sirens
• Subject Areas: Design; Safety and Human Factors;

Filing Info

• Accession Number: 00394077
• Record Type: Publication
• Source Agency: National Highway Traffic Safety Administration
• Report/Paper Numbers: LESP-RPT-0502.00, HS-026 584U
• Files: HSL, USDOT
• Created Date: May 31 1985 12:00AM