How many decibels is a train whistle at 1150 feet?

Question

How many decibels is a train whistle at 1150 feet?

Answer 1

Though it rarely happens, you have asked a question for which there is not a definite answer, due to the many variables at play.

Not all locomotive whistles are putting out the same amount of sound pressure, measured by the decibel.  So, at the beginning, the results vary.

As sound waves propagate, the are subject to atmospheric conditions, since sound is moving air, creating the sound waves in this medium.  For that reason, propagation is affected by barometric pressure, including altitude, as well as air temperature, humidity, wind, man made obstructions or natural ones.

With obstructions, even in a room, low frequency sound waves tend to go around the obstruction due to "refraction" whereas high frequency wave forms are more directly affected.  Locomotive whistle are of high pitch so buildings, walls, outcrops, trees or even snow filled air all have an impact on the behavior of the sound waves.

There is also the 'inverse square law."  This is an exponential equation, much like exponential notation (where ten to the third power = 1,000) in reverse, as the sound pressure drops off exponentially as the distance from the sound source increases.

So, to make an actual calculation, you would have to know the amount of decibels of a particular whistle then measure the dB at your distance of 1150 feet.

But, even this can be variable as well, depending on whether you are making your measurements either "A" or "C" weighted.