Can you play the guitar underwater?

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1:06Caroline Steel:Welcome to CrowdScience from the BBC World Service, where we're taking you into an underwater world filled with odd sounds and bizarre inventions. Such a strange experience. We're the show that explores your weird and wonderful science questions and this time we have a question from seven-year-old Cornelius in Berlin, Germany. He wants to know... It's such a good question. Can you remember what made you think of that question? Because guitars vibrate and the hole helps it make louder so if water's in, I wasn't sure if the sound could go into the horn vibrate that well. So you're wondering if without the air, when the guitar hole fills with water, whether it will still make a sound?

2:03Caroline Steel:Or not. Or not. Have you ever tried playing a guitar underwater? No, I don't have my own. What do you think might happen if we get a guitar and put it underwater and try and play it? Maybe also just a small sound, not like on land. I'm not sure. Thank you, Cornelius, for your brilliant question and to your dad, Daniel, for sending it in. Now, as far as we've been able to discover, underwater guitar acoustics is not something scientists are studying. So we can't do our usual thing of finding an expert in the field and asking them to explain what they do. Instead, we've acquired a second-hand guitar, specifically for the purpose of submerging it in water.

2:51Caroline Steel:I feel like I'm serenading myself into the building. To help us on our quest, we've tracked down some underwater acoustics experts. We're at the National Physical Laboratory in London, the UK's Metrology Institute. Metrology being the science of measurement. They have all sorts of spaces to measure sound, including, crucially, a water tank big enough for our guitar. But our first stop was a nice dry room, where we put Cornelius's question to Dr Freya Malcher. I guess guitars aren't really designed to work underwater is probably the main problem. Freya works in the ultrasound and underwater acoustics department.

3:34Caroline Steel:Underwater guitars aren't her regular area of expertise, but like us, she's intrigued. I mean, all the physical things, still the strings would move up and down and there'd be some propagation of sound, so it would do something. Based on your answer, I'm assuming you've not personally played a guitar underwater. I have not. OK, so let's talk about guitars on dry land first then. Here's my lovely guitar. Do you like it? It's lovely. It's quite small. Thank you, yes. It's a mini one. So when you play it in the air, on land, what exactly is going on? How does the guitar make a sound? So you've got the strings, which are tensioned across from the tuning pegs at the top, and then this bridge at the bottom, which is where you've got the main body of the guitar.

4:17Caroline Steel:The bridge is a small block that connects the strings to the guitar's body, just below the hole at the front. So as the strings are tensioned, they create different sounds. They've also got different thicknesses and that varies the note that will be played. What the strings do is they then make this soundboard vibrate. And by soundboard, do you just mean sort of the top of the body of the guitar? The strings are actually very bad at vibrating the air itself because they're so small. They need a bit of help. So as you pluck a string, it will create a note. The wave transmits along the string and then into the body.

4:50Caroline Steel:The body of the guitar acts as what's called a Helmholtz resonator. So the volume of air inside acts as a spring, and then the volume of air that's near the sound hole acts as the mass, and so it's like a mass on a spring. The springy effect on the air inside the guitar amplifies the sound waves created by the soundboard. So we hear richer, louder notes. So you pluck your string and then the mass moves up and down at that frequency. So it's somehow basically amplifying the sound that the string would make on its own. Yes. But crucially, air is playing quite an important role in this process. Yes, it is.

5:29Caroline Steel:Interesting. So that might be a problem when we submerge it underwater. Yes. OK. I believe you've got some water that we can dunk it in. We have indeed. We head upstairs to the development lab. OK, so we're in sort of what looks like a lab and in the middle is a giant fish tank, only there's no fish. And it happens to be the perfect size for my little guitar. Yeah, as if it was meant to be. Do you want to give it a play? Tell me what you think of my guitar. This is Freya's colleague, fellow underwater acoustics expert Ben Ford. who we've recruited for both his scientific and guitar tuning skills.

6:15Caroline Steel:Now, I was very impressed that listener Cornelius knew that the hollow chamber of the guitar is important for amplifying its sound. So our first experiment is to see what it sounds like if you fill that chamber with water. Our plan is to test sounds with and without water. The lowest string, which is made of metal and makes a low E note. the higher string, which is made of nylon, one octave higher, and the chord E major. I'll just kind of strum the E string. So we're going to go to the metallic E string? Yep, yep. OK, and now I'm going to start pouring it, filling the guitar with water. OK. Ben is plucking the low E string as I pour water from a jug into the hole to see how the sound changes as the guitar fills up.

7:00Caroline Steel:It's full! And it doesn't sound that much less bright. No, no, not at all. One thing to note is that it's currently sat on a table and some of that acoustic energy that's getting into the body of the guitar would be transmitting into the table when making the table kind of a speaker. I don't know how easy it is going to be to lift it up without spilling it. Oh, it's quite heavy. I'm lifting it. So we've decoupled the guitar from the table. Let's see how it sounds. Yeah. That sounds more damp, doesn't it? That's a lot less bass right there. What's happened is we've lost a lot of the low frequency acoustic energy.

7:34so the bass, and that's because the Helmholtz resonator, which the body of the guitar is acting as, isn't really working as well. It's got less space within the body, and so it kind of stops amplifying the acoustic energy as much.

7:50Caroline Steel:It does sound different. To me, it just sounds muted. It's easier to hear the difference when you play them back to back. So here's our dry guitar from earlier, followed by the water-filled guitar.

8:07Caroline Steel:The sound waves created by a guitar aren't just a simple wave with a single frequency. They're made up of lots of complex frequencies or harmonics. In our water-filled guitar body, the lower end of those frequencies seem to be the most affected. That's probably because they have longer wavelengths, so they need more space to bounce around in. And on top of that, the water is pushing against the soundboard from the inside, which stops it from vibrating as freely. And that means everything comes out a bit quieter overall. So our listener Cornelius thought that if you filled a guitar with water it would change how it sounds.

8:45Caroline Steel:And he was right? He was right, I'd say so. It just might sound a bit sort of less bassy. OK, I think we should try submerging it. Ready? Time for the more radical approach of fully dunking our little guitar into a fish tank. It takes a bit of force to submerge the guitar because it's filled with air. Okay, so Ben has our guitar submerged underwater. It's trying to pop itself back up again, but you're sort of holding it down. Yeah, that seems okay. Okay. I'm excited. So here we have the low E string. Oh. Nothing. We're standing next to the fish tank, craning to pick up any sound. So hearing a little bit there.

9:29Caroline Steel:Yeah, it doesn't sound like a note. To me, it just sort of sounds like a tap. If we turn up the volume on our recording, you can hear it better. How about the high E string?

9:43Caroline Steel:Even less. So obviously it sounds a lot quieter. Yeah. And there's a few mechanisms that might be doing that, including the fact that we're listening outside of the water. Sound doesn't travel well between water and air, which you might have noticed yourself, because when you dunk your head in a bath, you stop being able to hear what's going on outside. This is the same thing, but in reverse. It's related to how closely packed the molecules are. Those are the tiny particles that make up air and water. Here's Freya again. Sound propagates through a fluid, air and water here, by the particles moving further away and closer together.

10:23Caroline Steel:That creates your sort of wave. And so in air, the molecules are quite far apart, and then in water, they're closer together. So in water, sound travels much faster, so it's 1 ,480 metres per second approximately. In air, it's 343. Water is a great medium for transmitting sound. The problem comes when water and air meet. Sound waves travel much faster in water, 4.3 times faster in fact, and water is 800 times denser than air. If you multiply the speed of sound by the density of a material, you get something called the materials acoustic impedance. And when you have a mismatch in that acoustic impedance, which you do between air and water, the acoustic waves tend to be reflected back into the water.

11:13Caroline Steel:Not so many of them go out into the air, and that's why you won't hear as much. So how about we avoid the waves having to travel through air entirely by lowering my ear into the water? So we've dumped the guitar, now we're dunking the carol. It's my own little underwater concert. Whoa, whoa, it's pretty cold. OK, it's a little bit louder. But that's it. Not an underwater concert. So does that mean we kind of have an answer? You can't play a guitar well underwater. I would say a human would have trouble perceiving the guitar that's played underwater. Yet another problem to overcome. Our ears are designed to hear in air, not in water.

11:56Caroline Steel:Ah, OK. So if you're adding a fluid into your ear canal, you're loading one side of your eardrum. So it's going to be more difficult for sound to travel through your ear in the traditional sense. If we were fish, would it be better? Do fish have good underwater ears? Yeah, so fish, marine mammals and things, are designed to hear underwater. Marine mammals have a fatty bit at the bottom of their jaw that helps the sound waves go into their head and they kind of hear through that path. Lots of sea creatures are excellent at both producing and hearing sounds underwater and their anatomy is specially adapted to allow them to do so.

12:35Caroline Steel:So maybe our underwater guitar only sounds rubbish to our air-evolved ears. Time to throw technology at the problem. A special underwater microphone called a hydrophone connected via various contraptions to a laptop. This particular hydrophone, it's like black rubber at the end, is where the sensor is located. It's a small ceramic sphere. The ceramic is piezoelectric, so it can translate sound waves into electrical signals. An important safety note here. Using electricity around water is potentially very dangerous. This lab is meticulously set up to make it safe. We're going to be playing the guitar in the water with the hydrophone.

13:19Caroline Steel:This is what our mics heard outside the tank. And this is what the hydrophone picked up from the inside. Much better. And if we compare it to the low E string played in air, you can also hear the pitch goes down a bit in water. Ben thinks that's because the water slows down the string's vibration, therefore lowering the frequency of the sound waves and pitch of the note. Experiment over, we drain the guitar. It's held together remarkably well. Sounds normal. Nothing even happens. Our long-suffering guitar lives to play another day. And that's lucky because we're not giving up. We have an inkling of what an aquatic guitar might sound like.

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15:08Caroline Steel:Apple Vacations, where your story starts.

15:15Caroline Steel:at next You're listening to CrowdScience from the BBC World Service the show that searches for answers to your science questions in this case one from seven-year-old listener and avant-garde music legend Cornelius Is it possible to play a guitar underwater? We've just tried it out in a lab in London and learnt lots about underwater acoustics but the musical results were a little underwhelming. Now we're taking our guitar on tour to an unusual music studio near Aarhus in Denmark. If we can find it. I don't suppose you know where Acrosonic are? So an underwater band? A underwater band, yeah. Yes, an underwater band.

16:01Caroline Steel:Nice to meet you. Hi, hi. We're entering an underground studio. This is so cool. It looks a bit like a big sports hall filled with lots of intriguing objects. Instruments, speakers and, importantly, a large tank of water. Aquasonic is basically an exploration of how to play music live underwater. This is Robert Carlson, a musician and innovative director of the group Between Music, with the lowdown on their underwater project Aquasonic. It started as an experiment and it ended up with a full-blown concert with five aquariums on stage. Five musicians are totally submerged and singing and playing on custom-made instruments underwater.

16:47Caroline Steel:Okay, I want to ask you more about that, but first I have to ask you for your sort of initial reaction to our listeners' question. Is it possible to play a guitar underwater? Well, the short answer is no. The long answer is we, I think maybe we tried it in the very, very beginning. Water creates so much resistance. So it kills the vibration of the string immediately. As soon as you pluck the string, you only hear like... Yeah, so earlier I went to the National Physical Laboratory in the UK. We strummed a guitar underwater. And it just sort of sounds like a tapping sound. Very dead, yeah. So dead.

17:26Caroline Steel:But you've managed to do entire underwater concerts. So sort of how did you get to that point? Did it start with a question like Cornelius's of can I play an instrument underwater? Yes, but it started with a voice. So our artistic leader and composer Lila Skowman, she thought, what about if I sing in the surface of the water? Then, OK, what happens when I'm totally submerged, when I actually sing underwater? And she had this vision of what if we put a whole band underwater? What could that be like? So we tried a lot of things underwater. Some percussion, and some percussion were really good, some were really dead.

18:06We wanted to try a violin, so we found a really cheap and really bad violin to try in a swimming pool, and it actually worked. Of course it collapsed after a few days, but it worked sound-wise. And we had one built in carbon fibre.

18:22Caroline Steel:The violin is a string instrument, like the guitar. but unlike plucking a guitar string, the bow of the violin creates constant friction as it scrapes along the strings, enough to sustain a note underwater.

18:39Caroline Steel:Discovering and adapting instruments that worked was an epic process of research, trial and error, with the earliest experiments starting way back in 2004. The experiments even led to the invention of entirely new instruments. My name is Nana Beck. I'm an underwater musician. So I started playing in this band as a singer, but then the rotacorda came in and then I had to learn to play that. The rotacorda is a specialist aquatic instrument built for the band by inventor Andy Cavatorta. It's tuned like a guitar, so it is sort of a cousin, albeit a very strange one. So this is the rotacorda? This is the rotacorda.

19:22Caroline Steel:It looks sort of almost like a metal caterpillar. A long metal tube, but rather than having a solid body, it's sort of got horizontal slats of metal. And then it's got six strings taut between one end and the other. And at one end, there's also a handle that you turn. And then there's an important thing that we need to put on too. Nana attaches a big old gramophone horn to one end. And this is actually quite important for underwater because this makes the bass sound. The rotocorder is based on a medieval instrument called the hurdy-gurdy, which works by turning a wheel that scrapes against its strings.

20:01Caroline Steel:As with the violin, constant friction is very important. So it has this wheel going, and the wheel will give a constant friction, which will make the tones. And we had to try out lots of different strings for it, and we ended up finding some strings for sweaty guitar players. So designed for people who are making the strings wet anyway, when they're playing. Exactly. Okay, I didn't know there were sweaty guitar player strings. No, you get to know many strange things in this project, yeah. Okay, how does it sound when we play it in the air? Well, it doesn't sound good, but you can hear.

20:43Caroline Steel:Just as our guitar struggled underwater, the rotocorder is struggling in air. I think that sounds quite nice, but you think it sounds better in the water? Oh, much better. Much better than awesome. The acoustics of water are so different that you need to adapt your instrument accordingly. That might mean changing its strings, the shape of its body and the way you play it. So behind us is what looks like a giant fish tank. And I'm guessing that's where you and the rotocorder go. That's true. Yeah. Robert compares the tank to the instrument's body because the movement of sound waves within the tank shapes and amplifies the sound.

21:21So it's really important to work with and understand what makes the difference for the acoustics. Is it the shape? Is it the height of the tank? Because the deeper tank you have, deeper sounds you can get.

21:33Caroline Steel:The water that Nan is about to get into isn't just any old water either. When they were developing the project, the band couldn't understand why the same setup sounded great one day and rubbish the next. We found a professor in underwater acoustics in Texas who could explain a lot of these things to us. And one was how much air is in the water, because when you fill a tank with fresh water, there's a lot of air going into it, which dampens the sound. So you have to have a pump system to de-array it, so all the bubbles and all the air disappears. You just hoiked yourself. You did that so elegantly.

22:12Caroline Steel:Robert's passing you the rotocorder. It takes up most of the tank. And I need to place it quite precisely. The position of the rotocorder in the tank is really crucial. Robert tells me that as little as 15 centimetres can make a difference as to how their instruments sound. So now I'm placing the mics. When they perform, each musician is submerged with their instruments in their own mini aquarium, miked up and amplified for the nice dry audience listening outside, as well as to each other via in-ear headphones. and again water and electricity can be a highly dangerous combination so they did extensive safety testing for this project so you're playing it underwater into a hydrophone which is coming out of a speaker exactly

23:19And it also has all these kind of soundscape, nice sounds, I feel.

23:27Caroline Steel:Just listening to Nana play in the tank was impressive enough. But it gets even better. Music is often processed with extra reverb to give it a sense of space and more interesting sounds. Unfortunately, underwater reverb wasn't available when the band wanted to add it. So they decided to make their own. We went to Arctic Finland and Sweden and Greenland and Faroe Islands and recorded underwater reverbs in deep fjords and lakes. What you basically do is to go out to two boats. One boat is making a strong sound, two hammer strike together underwater. And then the other boat has two underwater microphones on two levels.