Using your Siren wisely
Author: Tyrone Date Posted:15 September 2017
It seems nearly every race we go to, when we are talking around the camp fire there is a topic that always comes up. Trying to overtake someone and being held up, maybe they couldn’t see the lights or couldn’t hear the siren. For whatever the reason, a lot of time the car in front can barely hear the siren. There are various reasons for this, basically when you are travelling at speed you are starting to outrun sound.
Sound outdoors falls off in level at 6dB per doubling of distance. The sound at the siren source has a maximum safe level that is largely set by the hearing protection requirements. Let's look at a general example.
Assume the siren level at 10' (3m) in front of the vehicle is 100dBA.
at 20' (6m) it will be 94dBA
at 40' (12m) it will be 88dBA
at 80' (24m) it will be 82dBA
at 160' (48) it will be 76dBA
at 320' (97m) it will be 70dBA
at 640' (195) it will be 64dBA
Most race vehicles are quite loud at revs so that you needed 90dBA of siren level to be audible inside the car, then you only have about 35' (10m) of distance where the siren is loud enough to be heard inside the car. You're relying entirely on the lights through dust to warn the navigator in the lead car, they likely won't even hear the siren. At 30MPH (48KPH) closing speed, that's less than 1 second for the driver to hear the siren and react. At 60MPH (96PKH) closing speed that's less than 1/2 a second of warning time.
So, if the siren can be more directional and it can be louder way out in front of the vehicle without being as loud inside or beside the vehicle, you can "reach out and touch someone" in a car and give them more warning time to react. 6dB more siren level out in front of the vehicle doubles the warning distance. 10dB more siren level out in front of the vehicle is 3.1 times more warning distance.
So in the short of it all, something to consider is being strategic with the siren, knowing when to use it so it’s more effective such as:
When coming up to a corner or a hazard when the lead car comes off the accelerator or a slower section where the cars are not at full noise overall noise is a bit quieter.
Sometimes you don’t have to spend huge dollars on something like a siren when you can keep this in mind, use them more effectively and it will be of more benefit.
Feel free to comment your thoughts, questions or suggestions. What would you like us to write about next?
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