Sounders and sirens are used to attract attention particularly when an immediate response is required. To alert a person, it is recommended that a sounder or siren reaches between 5 and 15 dB(A) louder than the background noise of the given area.
There are several things to consider before selecting a sounder or a siren:
- The sound pressure level achieved (quoted as decibel or dB(A).
- The distance it must be audible over.
- The frequency quoted in Hz.
- The background noise of the area it will be installed in.
- The duration of each use – duty cycle or prolonged use.
- Ensuring the tone of the sounder or siren does not sound similar to any machinery etc in the same area.
To enable an easy comparison, the dB(A) stated for a sounder or siren is usually measured at a distance of 1m. When the distance is doubled the dB(A) is to drop by 6. This is why it is important to know not only the dB(A) of the sounder or siren is capable of, but also the distance away from the intended area it will be placed.
Using our IAS-E sounder and MDS-2 siren as an example of this:
| Distance | IAS-E Sounder | MDS-2 Siren |
| 1m | 110 dB(A) | 114 dB(A) |
| 2m | 104 dB(A) | 108 dB(A) |
| 4m | 98 dB(A) | 102 dB(A) |
| 16m | 86 dB(A) | 90 dB(A) |
| 128m | 68 dB(A) | 72 dB(A) |
| 256m | 62 dB(A) | 66 dB(A) |
| 512m | 56 dB(A) | 60 dB(A) |
| 1024m | x | 54 dB(A) |
As you can see from the above, when choosing a sounder or siren, louder is always better. It is worth noting however that studies have found that is it possible to distinguish a sound that is up to 10 dB below ambient as long as there is sufficient frequency differential.
