Especially when an old electro-mechanical siren is replaced on site with an electronic siren, it is not uncommon for some people to think that the new system is quieter than before. But this is not the case. Electronic sirens such as the ECN or ECI models are even louder than an E57, for example. The only difference is the sound characteristic.
Comparison of the sound characteristics of electro-mechanical sirens and electronic sirens
With an electro-mechanical siren, the sound first catches in the siren canopy, i.e. under the curved bonnet, and then spreads directly downwards (vertically) towards the ground. This has the effect that the siren is perceived as very loud in the immediate area, e.g. at the fire station on whose roof it is installed.
With the electronic siren, on the other hand, the horns are designed and arranged as sound emitters in such a way that the sound spreads primarily horizontally and only falls exponentially towards the ground from a radius of approx. 30 m. This means that people who are in the immediate vicinity of the siren will perceive it as very loud. People who are in the immediate vicinity of the siren therefore initially perceive the sound as not being as loud compared to the conventional motor siren.
The difference is therefore that the electronic siren achieves a higher sound range. This means that fewer sirens are needed to cover a given area. The positive side effect is also that people who are directly below an electronic siren are no longer exposed to a potential risk of hearing damage.
The following figures can be used to substantiate this:
Maximum sound pressure level at 1 m distance:
E 57 130.50 dB(A)/1 m
ECI 600-DT 138.50 dB(A)/1 m
ECI 1200-DT 144.50 dB(A)/1 m
Average sound pressure level at 30 m distance from siren (in built-up area)
E 57 101 dB(A)/1 m
ECI 600-DT 109 dB(A)/30 m
ECI 1200-DT 115 dB(A)/30 m
Average sound range (in built-up area)
E 57 approx. 450 m
ECI 600-DT approx. 550 m
ECI 1200-DT approx. 650 m
Here, 65-70 dB(A) is generally assumed to be the limit at which the average human ear can just perceive the siren signal, provided it is not drowned out by direct ambient noise, e.g. a passing truck.
Especially when an old electro-mechanical siren is replaced on the spot with an electronic siren, it is not uncommon for some people to feel that the new system is now quieter than before.
Of course, it is also the sound of the electronic siren that differs from that of an electro-mechanical siren. The reason for this is that the wailing sound of an E57 is produced mechanically and that of an electronic siren is digitally modelled on it. However, the points listed clearly show that one must not be misled here.