Sound Intensity Level

  1. Not a homework... simple curiosity by trying to know this a bit better in order to learn and understand possible effects of sound to marine mammals auditory systems.
    In sea water, at distance of 1m from a localized sound source, you measure the intensity level as 237 dB.
    How far away from the source must you be for the intensity level to fall to 180/170 dB? I am trying to do this but i come up with distances that don't seem right to me...

    Been using this equation taken from http://www.underwaternoise.org.uk/measuring_noise/source_level.shtml

    SPL = 237 - 25.35 log(R)

    by replacing SPL with 180 dB, R comes up with a ow value for the distance which shouldn't be that low... it should be around 500m, distance that we consider to be safe for marine mammals.

    Am I doing it right?

    Would appreciate some help and some explanations!
     
  2. jcsd
  3. mfb

    Staff: Mentor

    ~180m is not so far away from 500m, especially with a logarithmic scale. With 170dB, it is very close to 500m, and some safety factor is always a good idea.

    In addition, several factors can change the formula:
    - different wavelengths can have different absorption in water
    - if the depth of the sea is not large compared to the horizontal distance, the floor can be relevant.
    - reflections elsewhere can be relevant
    - ...
     
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