Sound Propagation

The measure of Electronic Siren efficiency is sound pressure level (SPL), expressed in decibel (dB) at 30 m distance from the source. For example in the event of DSE-300S siren the SPL calue is 103 dB at 30 m distance from the siren. With increase in the output of a siren the SPL value is also increased, e.g. for DSE-600S siren SPL value is increased to 109 dB/30m and for DSE-900S to 112 dB/30m.
Above specified SPL values refer to a siren with omnidirectional sound characteristics.
Slotted speakers can be so arranged as to achive desired directional characteristics of sound, thus sound intensity in one direction is much higher than in other directions.

Propagation of Sound Pressure Level (SPL)

Shown below are formulae to be used for the purpose of sound pressure level (SPL) estimation at a distance ‘d’ from the sound source in compliance with recommendations issued by FEMA (Federal Emergency Management Agency, USA):

  • SPL(d < 800 m) = SPL(30) – 20 * log(d/30) where the distance is less than 800 m, and
  • SPL(d > 800 m) = SPL(30) – 33,3 * log(d/30) – 33,3 * log(d/30) where the distance exceeds 800 m

where SPL(30) means sound intensity in dB, measured at a distance of 30 m from the siren; this parameter is specified by siren manufacturers. Average city noise level of 70 dB shoud be assumed for the purpose of estimating the siren’s reach.

Shown below are examples or relationships between the sound intensity and distance from the DSE-600S and DSE-1200S sirens.

Characteristics of directional sound pressure level (SPL) Power of 300 W, 600 W and 1200 W