Saving Whales and Comparing Sounds

[el director]

Hi guys,

I have a problem. Well my friend does. He is shooting a documentary on the effects of sound basting bedrock (bottom of the ocean) on fish/whales. He wants to convey just how loud this sound blasting is. So...

...if the sound blasting is 240dB and a rock concert is 120bD how much louder is that and how do you figure it out? I came up with a figure of 100 times...but I don't think that is correct.

I also told him that comparing sound in air to sound in water isn't a fair comparision, is there a way to make the comparision more fair.

(I'm up to my eyes in study myself and this has already taken up too much of my time, so I reluctantly open it to the floor...:) ) P.S my first post here...go easy;)

 

[Borek]

240 dB vs 120 dB means 10¹² ratio of powers, this is a logarithmic scale.

However, loudness is a subjective thing, it is not easy to say how many times one thing is louder than the other.

 

[Bobbywhy]

el director, Welcome to Physics Forums!

For an excellent reference with clearly written definitions, see the below site:

“Sound levels extend over many orders of magnitude and, for this reason, it is convenient to use a logarithmic scale when measuring sound. Both Sound Pressure Level (SPL) and Sound Intensity Level (SIL) are measured in decibels (dB) and are usually expressed as ratios of a measured and a reference level:
Sound Pressure Level (dB) = 20 log (p/pref) where pref is the reference pressure
Sound Intensity Level (dB) = 10 log (I/Iref) where Iref is the reference intensity”
http://www.fas.org/man/dod-101/sys/ship/acoustics.htm#intensity

If you have any remaining doubts, do post them here. Members of Physics Forums are always ready to assist any true searcher.

Bobbywhy

 

[el director]

Excellent. Thanks guys. I'll check that out later and let ye know how I do.