Professor Trevor Cox, University of Salford
Part of the show How We Hear, Echolocation and Giant Whoopee Cushions
Chris - Let's get this out of the way to start with: why have you made the world's biggest whoopee cushion?
Trevor - A couple of weeks back I presented a science show at the Royal Albert Hall. Over the two shows we presented to 5000 kids a piece of science to try and make them interested in acoustics in general and science more broadly. The whole thing was call Beautiful Music, Horrible Sounds, and a whoopee cushion actually behaves like a musical instrument, so it was an excuse to make a giant whoopee cushion.
Chris - When you say that it plays like a musical instrument, you'll have to explain that a little bit more. It doesn't sound like a kind of Beethoven definition.
Trevor - No, it probably doesn't, but the mouth pieces of wind instruments such as trumpets and actually your vocal cords, all behave using the same science as a whoopee cushion, which is the Bernoulli effect. We were talking about the Bernoulli effect with the kids and we needed something big and impressive because this show was at the Royal Albert Hall, so every prop had to be massive. We built the world's largest whoopee cushion.
Chris - Now Trevor, your research is in the science of acoustics and you talk about big halls and things. So tell us a bit about big halls and how they can be built better to render sound, and what happens when you play sounds in certain environments.
Trevor - If you think about playing a sound outside, the sound is rather dry. You might have been to a classical concert where you have your picnic and the fireworks going off. You have a dry sound because all that's coming off is from the orchestra. When you go indoors, what you get is all the reflections from the walls and the ceiling and the floor. That enriches the sound and gives you a much richer experience. I suppose the most obvious effect is from reverberance, the thing you can hear in cathedrals as the sound echoes round.
Chris - Now you were kind enough to send me a bit of a sample of that, so I can try and play it. Talk us through what we're expecting to hear with this one with reverberation on it.
Trevor - Well this is actually played in a hall and is a bit of Tchaikovsky's 4th. You should hear quite a rich sound as you would normally expect from a concert [music].
Chris - Sounds good.
Trevor - Now the other piece you've got is actually played outside the hall. Imagine it being played on a snowy day, when there are no reflections at all. It was actually played in a special chamber called an anechoic chamber, and you'll notice that it's very very dry. This is the sort of sound you'd get from outdoor concerts [music].
Chris - Sounds totally different doesn't it. I suppose it goes without saying that it's the environment that makes the concert.
Trevor - Well it's part of it. Of course musicians are probably the most important part, and there are things like trying to get to your seat without getting wet walking from the car park. It's all very important, including the seat being comfortable.
Kat - My sister used to be a tour guide at the Albert Hall. Now they have all these little mushrooms in the ceiling, don't they? She said that they were put in because the echo was so incredible that a review of a concert in the Albert Hall when it was first built said 'this represents the best value for money as you can here two concerts: one three seconds after the other!' What do those sort of mushrooms and baffles do?
Trevor - If you're not familiar with the Albert Hall, what it's got is a great big dome on the ceiling. This focuses sound a bit like a concave mirror that you use for shaving. What you get is very strong reflection off these domes into certain places in the audience. It's so big and the delays are so long that you actually hear multiple sounds. You can hear the trumpets more than once; you can hear people talking more than once. The idea of the mushrooms is that they hang down below the dome, so you can't really see the dome in the Albert Hall very well. They just stop the stop the sound from getting into the dome and shorten reflection paths and reduce the echo problem.
Chris - Now if you go to the station and I try to understand the announcements, it's almost impossible. Why are stations so bad for things like echoes?
Trevor - Well a lot of the big famous stations, such as Paddington, are such vast spaces. So you've got these reflections from the ceilings and the walls taking a long time to reach you. What literally happens is that your ear decodes them as separate sound sources. If these reflections arrive early enough, your ear will just interpret them as all being from the same sound. That's the reason why when we're in a normal room, we don't get confused by all this sound echoing round us. We feel as though it's all coming from one source. But as soon as the sounds are delayed because the room is too large, we then start hearing multiple sources. Once you hear multiple sources and words start running into each other, it's very difficult to hear announcements.
Chris - One of things you made headlines for a few years ago was proving that ducks quacks echo, even though there's an urban legend saying that they don't.
Trevor - Yes, I did try to find the source of this myth because it was bugging me. If there's anyone listening now that knows where it comes from, let me know. But for some reason, you get these phrases that people recount as science fact, even though they're wrong. The phrase was that a duck's quack doesn't echo and no-one knows the reason why. We were contacted by a few media organisations asking whether it was true, and we thought we out to do something to dispel this myth. Any sound echoes, but it might be that in the case of the duck, they're very hard to hear.
Chris - And you actually proved that. What was her name, the duck that featured?
Trevor - The duck who featured originally was called Daisy, but unfortunately poor old Daisy's been eaten by a fox now.
Chris - So her echo certainly doesn't quack any more.
Trevor - No. We filmed it for a channel, and it was the daughter of Daisy who was very temperamental and vicious for a duck, I can tell you!