100w vs 200w siren

Steveo17

New Member
Jun 6, 2020
29
Essex uk
Good morning I am looking for some help regarding sirens at the moment I have a haztec siren that is set at 100w 11ohm with a whelen sa315p speaker. The siren has the ability to run 200w is it worth fitting the extra speaker and running 200w or will I not notice any difference Cheers Steve
 

shues

Lifetime VIP Donor
May 21, 2010
10,276
NW Indiana
@NPS Ranger explained the math, and a little of the physics, of 200 watts versus 100 watts in a thread about overdriving your siren some years back:

This comes up over and over again. The speed of sound in air at sea level at 20 degrees C (about 68 degrees F) is 343 m/s or about 767 MPH. If the siren sound is coming towards you at 767 MPH and you're going 80 MPH in the same direction, you can see how "outdriving" the siren is not going to happen.


What happens is that the engine noise, airflow noise, tire noise etc go up the faster you drive, and make it more difficult to hear things around you including sirens, when the sound pressure of the siren sound is the same as or lower than the sound pressure of noise inside the car. Also, sound pressure varies with distance so a siren half a mile back is not going to be very loud in any case. But you're not "outdriving" it.


Since most of this interior vehicle noise is toward the higher frequency range, using something like a Rumbler might help. Also, using something like a Q or Grover horns which are relatively louder might help. But a 200 watt siren is only a moderate improvement over 100 watts. If you double the acoustic power in watts, you get only a 3 dB or 1.41x (41%) increase in sound pressure and 1.23x (23%) increase in perceived loudness.


So, a 200 watt siren will seem about 23% louder than a 100 watt siren, at the same distance. But you're not going to outrun or outdrive the sound unless you're in a jet. Then it's called breaking the sound barrier.


http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm
 

MtnMan

Member
Dec 20, 2012
1,533
Eastern PA
Doubling the power produces a 3 dB increase, which is noticeable, but unimpressive.

It also means the sound will be audible, at the same db level, at twice the distance (in hypothetical, completely unobstructed conditions). On open roads, that might buy a few seconds of advance warning, but in traffic it just means that the driver who ignores your siren when you're 10 ft away can now ignore equally well at 20 ft.

That said, I like having 200 W of power (required on US ambulances). But don't expect miracles.
 
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Steveo17

New Member
Jun 6, 2020
29
Essex uk
I might try and make up some brackets tomorrow in the metal shop then and give it a try. Speaker wise I have 2 sa315p are these any better than the sa314 cheers
 

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