Water in your Ear

My attention was recently brought to this article on BBC website, about a new concept for concert goers, an underwater concert! At first it seems a really bizarre concept, but there are strengths this holds over a standard concert. So without further ado, let’s dive straight in… (sorry I couldn’t resist it)!

Mainly, the listener is in charge of their own concert experience, through moving around and finding positions where it sounds best to them, giving them a sense of control over their experience. The main problem with this though is that as the swimmers move around, so does the water, and as the sound is travelling through the water, this means that the sound waves are getting moved around as well, distorting and altering the shape of the sound. This is most probably the main reason for the strange sound created. A similar effect, although not quite as extreme, could be created on land with extreme and sudden alterations in air temperature where sound is propagating through, causing the sound to bend and move with the air temperature (as sound travels at different speeds in different temperatures).

In the video, the swimmers say that they can mainly hear high frequencies, which is because this is when sound travels best in water. It is also mentioned that the speed of sound in water is different, being at 1,481m/s* for water compared to 343m/s for air, making water 4.3 times faster for sound than air. This is why the high frequencies are heard better, because they have a shorter wavelength. Sonar systems rely on very high frequencies for this reason and the fact that humans cannot hear at frequencies this high.

There is only one way to experience what this concert may sound like and that is to go to one; however, if you don’t fancy this method, then it could be also simulated on a computer. Normally in a concert hall, an Impulse Response** (IR) is recorded then this can be mixed with a ‘dry’ recording of some music (no reverb added) and the output file sounds like the music would if it were played in the space. This technique is called convolution and is common practice in concert hall design and testing. Trevor Cox made a particularly interesting example of this when he recently measured the longest reverb ever. My plan was to try and find an underwater IR and try this to find out what it actually sounds like, however, I could not seem to find one online. Please comment below if you have one or know of where I can get one as I think this would be an interesting test.

The concept of an underwater concept is a very interesting one, one I would be interested to try, although not one that would give the high quality sound given in a state of the art concert hall! Would you ever try an underwater concert and if so who would you like to hear played underwater?

Notes

*m/s stands for metres per second and is the distance that a sound wave can travel in 1 second in the specified medium

**An Impulse response is a recording of a gun shot, balloon bursting or a hand clap (an impulse in a space

References

[1] http://www.bbc.co.uk/news/uk-26445429

[2] http://www.bbc.co.uk/newsround/26445927