Saving Whales and Comparing Sounds

1. Oct 30, 2013

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;)

2. Oct 30, 2013

Staff: Mentor

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.

3. Oct 30, 2013

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

4. Oct 30, 2013

el director

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