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.

 

[PJC01]

As a scientist, it is important to accurately convey information and make fair comparisons in order to understand and address issues such as the effects of sound blasting on marine life. In this case, comparing the loudness of sound in air (such as a rock concert) to sound in water (such as sound blasting) is not a fair comparison. This is because sound travels differently in air and water, and the decibel scale used to measure sound is different for each medium. In order to make a fair comparison, we need to convert the sound levels to a common scale for both air and water.

One way to do this is by using the sound pressure level (SPL) scale, which measures the intensity of sound in both air and water. On this scale, the sound blasting at 240dB would be equivalent to a sound pressure level of 194dB in air. This means that the sound blasting is about 74dB louder than a rock concert (which has a sound pressure level of 120dB).

To put this into perspective, the difference between a rock concert and sound blasting is equivalent to the difference between the sound of a normal conversation (about 60dB) and a jet engine (about 140dB). This shows just how loud and potentially damaging sound blasting can be for marine life.

In terms of conveying the loudness of sound blasting in the documentary, it may be helpful to use visual aids or sound clips to demonstrate the difference in sound levels. This can help viewers better understand the intensity of the sound and its potential impact on marine life.

In summary, it is important to make fair and accurate comparisons when discussing sound levels and their effects on marine life. By using a common scale, such as the sound pressure level scale, we can better understand and address the issue of sound blasting and its potential impacts on whales and other marine animals.