A Celebration of Architectural Acoustic Aberrations by Professor Trevor Cox, Head of Acoustics Research, University of Salford. Hosted by IOP West Midlands, Keele Centre.
Acoustic consultants try to make sure rooms do not have problems such as focussed echoes from domes, excessive reverberation and flutter echoes from parallel walls. This talk will celebrate these acoustic ‘defects’ and other extraordinary architectural sounds.
The science behind some historical examples, such as the whispering gallery in St Paul’s in London, was solved around a century ago, but others, like the underneath of Echo Bridge in Massachusetts, which was debated in the scientific literature in the 1940s, have never had the physics fully resolved until recently. Acoustic phenomena play with our perception of sound: in the spherical radome on top of the disused Cold War spy station at Teufelsberg near Berlin, you can whisper into your own ears.
Using prediction models, in this talk we explore what sound effects could be created if designers deliberately set out to maximise acoustic aberrations.
Welcome to those that have just joined us um and we’re going to move on to the subject of acoustic engineering I’m going to introduce this evening main speaker which is Professor Trevor Cox and I apologize TR I’m going to read from a little script here because I have
Got a memory like the proverbial C so um also it tell me how good Google is at um telling me how of your expertise and your background you can even nod or you know um shake your head as we go through so um Trevor is a professor of acoustic
Engineering at University of Soulfood he is a past president of the UK’s Institute of Acoustics and was awarded the Institute of Acoustics tindo medal for his achievements and services in the field of Acoustics This research covers ar ar here we go um architectural Acoustics psycho Acoustics and audio he
Has been the uh principal investigator on 10 plus epsrc projects and built environment Acoustics uh Trevor Co wrote The Definitive text on room acoustic absorbers and diffusers which is published by the CRC press he won an sprc senior media fellow and has presented more than 25 documentaries for
The BBC including the physic Guide to the orchestra he won an ASA science writing award for his Popular Science book Sonic Wonderland uh in which good I got the plugin there we go um BR envelope no joking and the book describes um an oil tank where he broke
According to this the Guinness world record for the longest Echo you shall learn about that at the end of today fabulous I’m hoping the AI worked here and that was mostly right if it’s not I’m sure Trevor will correct me um but as we normally do here ladies and gents
A nice warm kill welcome to Professor Trev [Applause] Cox yeah so my kind of when I’m doing my day job at at University of Salford I’m doing things like working on hearing aids working on making Machin sound better or I’m working on architectural Acoustics so if you take any space like
This lecture theater here you’ll notice there’s some absorbers in the corners there that are there to try and make it sound better or you might work in a grand space so I worked in this this concert hall and the things that look like crispy bacon bits hanging in the
Ceiling are diffusers and that was what my PhD research was about and this is a hall across in America where it was designed but this talk is not going to be about necessarily how to make an acoustic function best for speech or music which is what’s going to hear it’s
Going to be about odd acoustic act things you get within places and my journey actually started in a sewer so I was invited to do an interview for residence FM in the London sewer it was the most peculiar visit because we literally walked into the park he opened
Up a manhole cover and said we’re going down there I thought it was some official visit but we literally on a sort of midday afternoon walked in under a park in London and walked down a storm drain I wouldn’t necessarily recommend it um but the Acoustics were quite
Amazing now there’s an effect that I expected to get which is an echo so so you’re in a big tunnel you shout Echo the sound goes down hits something comes back delayed that’s what I kind of expected to have but there was a weird Sparling effect so as I my voice
Disappeared it seemed to be going round and round and round the inside of this uh this tunnel and I was kind of wondering well what’s what’s going on there and I was middle of a radio interview so I made something up and I’ll tell you what the answer is and
Luckily what I made up was kind of right um but as we come out I came out the SE it kind of way me wonder here’s an acoustic phenomena I had never witnessed before I’ve been in it you know in this field for decades what other weird acoustic aberration have I been
Overlooked so having got into a shower for about an hour and scrubbed off a sewer it’s not very pleasant I would say down there I then came up with this idea of I should go and investigate the most amazing sounds in the world and I expected it would be an easy sort of
Afternoon playing around the internet but it turned out that no one had actually really looked at this so I collected them together and wrote this book which then came out so I’m going to take you on a journey around some of the places I visited with weird Acoustics
It’s going to be a rough Journey around the world these are roughly where we’re going so we’re going to go over to America in a moment quite a lot of them in Britain few bits in Europe um and we’re going to talk about some of these
Places so let’s first of all go across to Salt Lake City because if you have a phrase like this this building has an international reputation as one of the most acoustically perfect buildings in the world you have to go and visit it don’t you so this is the Mormon
Tabernacle in saltt Lake City um and you can see it’s got this kind of strange DED roof at the top and it’s has got some strange Acoustics but it’s not that surprising really when you think that we’ve probably understood this many centuries ago so if you look here this
Is anthus ker sort of scholar from the 17th century describing what you get in the Mormon Tabernacle if you stand at one focal point imagine playing billiards in this this sort of weird shaped curve if you down at one focal point and send the ball off it always
Goes to the other focal point that you get into in the ellipse so all the sound going to the ceiling goes from this person to that person very efficiently and that’s what you get in the Mormon Tabernacle you’ve got an elliptical ceiling which transmits sound very effectively from one point to the other
Now you don’t have to take my word for it here’s a graph of a computer model now don’t worry about what this number is on the right hand side all you need to know is red is poor and blue is good roughly in terms of how loud it is so if
You in the Mormon Tabernacle and you stood right in the middle of the I’m going to call it the stage cuz I know it must be the altar I guess the blue square thing in the middle there um then if you talk there there’s a really distinct focal effect and if you look
Down right near me actually can reach this here there’s a focal point where it’s light blue again so that’s where the focal point happens now if you go and visit it they will actually demonstrate it for you they’ll rip Bits of Paper on stage make sure you go in
The balcony because I don’t actually know where the focal point is and I had to point out I need to go upstairs to experience this so that’s one sort of weird acoustic phenomena that happens because of focusing but actually when you design a room you avoid this why because the
People over here are very happy they can hear everything really clearly the people over here can’t so it doesn’t work cuz it doesn’t work for one to many communication so when we have these sort Dome ceilings we normally do something about it actually Mike you mentioned um
Roll Lait Hall didn’t you when we’re having a meal earlier on so the roll Lait Hall down in London a big domed roof it holds about 8,000 people vast concert venue that Dome focuses sound so if you go in there before the late 1960s um basically you would hear the
Orchestra multiple times you’d hear it’s coming from the stage and these focused Reflections from the ceiling I mean you get you know you get value for money because you hear every bit of music twice but maybe that’s not such a good good expense so I you the BBC did these
They brought what called the mushrooms these thck clouds hanging down and basically blocks theart from sound going from the stage to the Dome and therefore you don’t get these Echoes they’re 95% effective it’s actually a very difficult room to to treat so there are places still Echoes but quite a lot of places
Work much better so that’s the kind of thing we do normally when we design a room is we try to get rid of this effect because it’s not really good news but if you’re like me you go well obviously rooms which have curves are interesting what’s the biggest curve you can go to
Well maybe a sphere would be a good start so I’ve been to a completely sphere room but the one I’m going to show you here I’ve got a recording in there completely spherical Dome you can go to in Boston but they don’t allow you to record in it which is a bit annoying
So I went here instead which is tburg um and someone who German will now correct my pronunciation but anyway it doesn’t matter it’s on the outskirts of Berlin and it was a listening station so this was in American was actually in British territory post second world war and they
Were spying on the east from Berlin so if you don’t know your geometry Berlin was right in the middle of the east Europe it was just a sort isolated island as fact actually and when you’ve got these big things picking up I mean they’re picking up uh radar and
Electromagnetic signals that these big antenna they have to protect the antenna for things like snow and wind so they stick a dome on top and so this is the thing right at the top there you can see it’s called a ray Dome so it’s a almost
Spherical room um and you can go and visit it now if you like visiting it and you’re scared of heights you might want to point out the state of this place is there’s sheer drop actually in that Dome on the other side there’s a hole in the
Wall and you can look down several hundred me I mean it really is not for the faint-hearted or not to take small kids to but I went in there and when I go into this room um I had a little digital recorder with me and so I I was
Right in the middle cuz the focal points in the middle I knew that’s very interesting and I unzipped my bag and then it seems to be the unzipping from above my head this most weird kind of effect goes on um and I’ll give you a sense that I can’t give you that sense
Cuz you need to be really there to experience it but what I do carry with me as well as my digital recorder is a balloon ballon or several balloons and so I burst a balloon in there and what you’ll hear is the effect of the sound
First of all coming from me going up to the Dome and then being Focus straight back to me go to the Dome being Focus straight back to me you can see it there’s direct first second third fourth fifth Reflections so each judder you hear is a focus sound coming back again
I’m going to play it three time you’ll hear it three times in case you miss it the first time so it’s a really really nice effect nice judging effect has all to do with an acoustic Focus but the other things you can do in there is because if you’re
Stood right in the middle you at the focal point if you move slightly to the side the focal point goes to your ear so you can actually whisper into your own ear and you you can go this way and Whisper into your other a it’s kind of
Quite a weird room to play with if you go to YouTube you’ll find lots of musicians playing around with it it’s quite a common sort of place for people to kind of record strange things but you have to go to Berlin for that so let me
Get you something a bit nearer to home um this is up near Sheffield near pedone and it’s part of the national cycle Network so you can even cycle down it or walk down if you want and I I came to this place after I wrote the book um and
I did a channel 5 recording they were walking Britain’s lost Railways and they said this place sounds weird do you want to come down and do an interview there so I went down and again a bit like the S I didn’t actually know what was going
On and I had to make it up but fortunately I seem to have made it up correctly when I analyzed it a bit better later on now the key to this tunnel is can you see how it Curves in it’s like a horseshoe shape now that’s not like most tunnel most tunnels are
Kind of semicircular but it bends in it’s got a bow on the side and that’s what gives it an interesting effect now nowadays if you want to be a Sonic Explorer you can go on YouTube there’s lots of options when I was doing there was less options but here is someone
Making a weird sound in there and you’ll hear obviously a lot of reverberates a lot of echoin but the thing to listen out for it is his voice has got a warble on it it’s not cons w w you’ll hear it warbling almost metallic sound to It now that’s something which is really unusual a war bble now now I’ve identified I can find other places which I’ll show you some other ones that have it as well now here’s actually the measurement now just look at the black line at the bottom forget the other two
There just predictions we don’t have to worry about that and this is me measuring it again I did a bit more sophisticated than this kind but you can imagine I burst a balloon and I’m just looking at the energy over time can you see there’s lots of Peaks and bumps
Peaks and bumps those are the warble sounds that you can have going along um and you can see actually my prediction models predict it well I did a paper on this one so what’s going on there what’s causing the warble well it has to come
Something to do with this shape and if I don’t know if anyone got physics background who’s done billiard tracing before which is kind of a field of mathematics where you see essentially it’s how billiard balls or snooker balls move around the space and there’s all sorts of kind of things about looking at
Ergodicity well I use those kind of techniques and I can show you what goes on here so we’ve got Source in the middle and you can imagine the receiver is the sort of lilet colored or purple colored thing so the sound goes direct to the receiver and then it goes
Wandering back and forth and eventually it keeps and it returns to the receiver it’s got what called a closed path so it keeps repeating and then it comes back again so it keeps going round and round and every sof often will come back to the receiver and that’s the key is this
Closed loop if it went past every time so it was Square walls it would be a bit like being in a stairwell you know when you clap in a stairwell you get a high pitch tone you get that effect the reason it’s a warble is because of the
Delay between the reflections and how your ear processes sound it’s far enough apart that your ear hears them as separate kind of warbling events and it’s because you get reason you get this is it’s because of the bod sounds sides means it doesn’t go up to the ceiling
Very readily it doesn’t go to the floor it just stays in this horizontal but it takes many Pathways before it gets gets back to you so if you want to go and visit one of these places go along natural cycle Network near penstone and go and find the tunnel and you can play
Around with it so there’s another place which I met after I wrote the book um so one of the things when you a book like this is you going to do promotions and I got invited to go and talk at the Oslo contemporary music festival which is
Kind of not something I would normally talk out I’m a physicist but anyway and I was in the bar afterwards having done my talk and someone came up to me and said whatever you do you must go to this place which is the place on the picture
Um uh because it’s got the most amazing acoustic and so I’m going to do you a little piece which I recorded there and and then explain what’s going on so you’re going to hear me talking I’m going to start off at the bot this picture I’m going to walk into the
Middle where you can see the the circle is at Center and walk out again this is a little piece I recorded to explain what is going on I’m in a booking Hall of an Oslo train station and uh you can just hear me chatting here but as I approach the
Middle of this space I think you can hear how my voice is suddenly Amplified and then distorted by the shape it’s a cylinder and actually if you look at the floor there’s a plark saying acoustic sculpture so it’s not an accident it was deliberately designed quite amazing I shall Wonder
Out again and you’ll see you should be able to hear it Disappear it’s like goty talking of course for that but you can hear how the dramatic sound effect suddenly gone it’s like I’m in a normal room again so this is the National Theater railway station the entrance near the American Embassy in Oslo now if you should like me go on a
Trip to Oslo to Listen to Crazy places don’t go to the American embassy it’s moved so don’t don’t follow my my room now in that little bit I was kind of working out trying to work out what was going on there um blur eyed and slightly
Hung over from the night before um and I so I took some recording and came back to try and work it out um and trying see what happens um so the first thing is it looks like a cylinder when you stood in it it’s obviously a cylindrical space so
You think well maybe it’s a focal effect but it doesn’t sound like the twalberg it sounds different and I’m going to burst a balloon in two places so you can actually hear the difference so this is tberg on the left hand side you’ve already heard that kind of
Effect this is still tberg just doing it three times so that’s a kind of circular focal room I was expecting here’s a balloon in the right hand also Lo place got that warble in it so I knew something was going on there so um there’s a pitched home bway
Which comes from this sort of kind of Step ceiling but it’s the warble I’m going to talk about today and I kind of what’s going on what’s creating that effect so I I actually contacted the architect and he was very kind and did me a Skype call um we chat about it I
Learned a couple of things that I didn’t know first of all it was not an acoustic sculpture so what happened was they he built this circular booking Hall so these were old ticket offices and it was a disaster because it had this horrible warble in it and and actually the
Norwegian rail were going to sue him for quite a lot of money for making such a disastrous space and then sound artists found it and started doing recordings there so the the railway people put a sign in the middle to say it was an acoustic sculpture so people would stop
Complaining about it so that’s actually the truth of the story which I obiously didn’t know at the time but the other thing is he sent me a nice diagram of it um so you left hand side is the entrance right hand side’s the escalators you may have heard but what’s interesting
Because it’s a booking hall there’s actually two diameters going on here so there’s a bigger diameter at the bottom than there is at the top which I didn’t radius might be a better way describing it there’s a bigger curve at the bottom than at the top which I didn’t kind of
Realize and this is what’s part of what’s behind the effect so if you think about sound going out going out there’s a short path where it goes to the nearest wall and comes back and there’s a longer path a delay path when it goes to the bottom and comes back but if you
Think of second order Reflections the one which goes in that direction to the short one to the long one and back again is the same lengths as the one which goes in the opposite direction so what you have is you had two quart arrivals and then one bigger arrival two quart
Arrivals and one bigger arrival which is the sum of two Reflections going on and that’s part of what’s behind the warble in that space so you need something a bit odds your pure circle of room doesn’t give it you need something a bit odd going on uh to get those sort of
Effects now um I was interested you you struggle with architectural Acoustics because one of my areas is even hard to pronounce AR olical Acoustics or archa Acoustics which is even even harder one to say um so this is Stonehenge which I’ve done some work on um and it came to
My attention uh there was a paper where people said well in the olden days when all the stones were there there would have been a focal effect and there’s a paper actually in a journal which kind of demonstrates what’s going on so you know you got curved mirror like I’ve
Been talking about showing you rooms left hand side that will give you a focal point in the middle and the picture in the in the in the paper said oh look there’s a circular when it was complete there’s a circular set of stones there’ll be a focal point in the
Middle of Stonehenge and produce some grass which I won’t showed you which were obviously not quite right and my feeling with acoustician was nah so I was kind of wondering well what do I do about it it’s this paper here I could write to the editor I could complain
About it and maybe they’ll withdraw it I don’t know probably wasting my time aren’t I I’ll be much better off to go and prove it so I built a whole model of Stonehenge to prove that this scientist was incorrect um so that’s about 6 months worth of work to make this thing
Just to make my point and if you want to read about it there’s a decent archaeological Journal um publishing it so this is a 1 to 12 scale model of Stonehenge um so uh what you do with scale modeling is you basically shrink everything but when you shrink
Everything you have to think that the wavelength of sound has to be the same size relative to the stone so you have to shrink the wavelength of sound so you work at 12 times the frequency so when you test this thing you’re working ultrasonic frequencies so you might see
There it might be a bit small I’m holding a little loud speaker in my hand but it’s a tiny loud speaker because I’m testing up to 7080 khz in this space I’m not testing at normal frequencies um but actually this is a Technique we were
Talking about old days at sulf I bet you had models like this when at sulfur um they certainly were doing in the 70s this this is a technique in room Acoustics that goes back to the 30s or 40s and so I’ve made a lot of measurements I won’t go into the detail
CU I’m talking about ation today but I wanted to say there aren’t any focused Reflections and I’ll explain why there aren’t any just by showing a picture from within the model so the claim the person was making was the Outer Circle would be a focal Circle you can just
About see the Outer sarson Circle can’t you there peeping between the stones the problem is there’s lots of things in the way between the outer circles and the Inner Circle and they scatter the sound all over the place and that’s what they weren’t explaining correct and that’s
When I looked at the paper and I thought no um um so you don’t get a focal effect because there’s too many other stones that would have been in the way but I can make you I can just play you what it was like and you can hear there isn’t
Really a focal effect so I’m going to play you a little extract we did for Radio 4 of um of a discussion around the voice and you can hear how what actually really happens in the place so I measured and did a normalization process so at the start of this bit you’ll hear
Just a normal Studio voice and then I add the effects of the stones on so you can imagine the first discussion is outdoors we’re just chatting and then the stones appear and you’ll hear the change in the voice and it’s kind of like I don’t know singing in then going
In the bathroom how the tone of your voice changes it’s the same kind of effect okay now we are recording this interview we’re not actually live on on Radio 4 right now and and you’ve now got a ston heny filter which you can add uh onto the Acoustics that we’re recording
Right now so could you just talk us through that process and halfway through your answer I want you to switch to ston hen so what we do when we measure a model is we measure What’s called the impulse response and if you’re doing a a real
Room you could say burst a blue to make an impulse and on a microphone measure uh the sound that you pick up and it’s similar in the scale model but you use different signals and stuff like that so this gives you what would happen if you
Made a large bang in a space um and what we can do is once we’ve measured it in the model we can then apply that to anyone’s voice so we record someone’s voice in a fairly dry condition like we do here and then by a process called
Oriz we transform them into the space and as you’ll hear what happens to my voice is it gets a bit basier and you can hear it gets a little bit louder and it’s not a huge change but it’s certainly noticeable okay so and and
It’s on me now and and and I sound much more basier he DRS his voice sound like in Stone Henge so you get a sense of what what kind of you can play around with these these these sort of kind of things um uh and actually that technique of all ization is
Actually all over the place in music production so it’s called convolution Reverb it’s nothing particularly new if you’re into computer games absolutely everywhere in computer gaming nowadays but it actually started off as a scientific testing technique is what kind of where it kind of started off it started off in
Physics so when I started off this sort of discussion of curv services I talked about the sewer and this Sparling effect and what I kind of came to the conclusion again not wasn’t sure at the time I was making the interview was this must be a whispering Gallery effect um
And a whispering I don’t know there anyone been to the whispering Gallery at St Paul’s Cathedral um so if you go one of my strong recommendations is go with a friend I went on my own it’s very hard to test a whispering gallery on your own
Um go early in the morning because it gets too noisy so go in very early in the day but a whispering Gallery this is upstairs in in St Paul’s it’s essentially it’s at the bottom of the Dome it’s a big curved surface and you go to one side of the wall and you
Whisper into it and then 30 m away on the other side it appears like your voice is jumping out the wall at your friends and it’s you know there’s Whispering galleries all over the place there’s one in Grand Central in New York for example actually once you know
They’re there you can find lots of places with Whispering galleries but this is one of the few ones which is mentioned in tourist guides so what’s going on with that is the sound is skimming around the edge of the wall and that’s what was happening in the sewer
The sound was skimming around the inside so it’s a whispering Gallery mode in the in the sewer um there’s several ways of describing how it does the easiest way is to go back to billyard balls you can solve it with wave equations if want but essentially if you imagine playing again
Playing a game of snooker I’m down at the bottom I’m playing my snooker ball I whisper into the walls my snooker ball goes up tangential the sound never gets to the middle it just sticks around the edge you just do angle of instances angle of reflection and it just goes
Around the edge and that’s the simplest explanation of a whispering Gallery uh that you can get so great to go and see um the whispering Gallery at St Paul because it kind of confirmed some of the things I thought was going on um but it’s much better to go to one where you
Can make a lot of noise so if you can’t you can go and whisper in it but they don’t tend to like you measuring uh if you make measurements like I do you have to start kind of wear hidden microphones and stuff and they do object to you
Shouting and they certainly don’t want you bursting balloons but in tburg that sort kind of Berlin place it’s got the same spherical thing it’s slightly smaller diameter but I bursted balloon so in that big rayome on one side I put um I found a jutting out bit of metal
And I stopped my digital recorder went to the other side and burst a balloon and this is what you hear I’m actually you hear is it doing laps so each time you hear a judder it’s the sound’s gone once around the Dome and you’ll hear it goes around quite a few
Times oh I play I thought it was going to play twice so each judder is another lap around the the Dome it’s a shame you can’t do it in some PS because it go it’ be further between them but there we go you can go and do it in some somewhere
Else um so Whispering Galls were something which really interested um people like Lord Ry and people like that and they sort kind of writing about this kind of you know turn of the 19th century kind of stuff um and it led to sort lots of discussions about what was
Going on in sort of kind of weird places this is a 1940s I think if I remember rightly uh article from the Journal of acoustic soci America which is the Premier journal in my my field and don’t worry about reading the paper obviously but it was talking about this bridge
Called Echo Bridge and uh it was saying well what’s going on there and essentially the arguments were about is it a whispering Gallery so the sound’s going a b c ba a when you chat or is it just an echo going a d c d a going
Horizontally so is it going round the bend or just horizontally and that’s what this argument’s about and they’re trying to how to measure it and how they’re struggling to work out what’s going on give you a sense of what it’s like you can go and visit it I this is
One I haven’t visited but I got something from YouTube um it’s really unusual it’s a tourist venue because it has a listening platform we’ve all been to viewing platforms to see views how often have you been to a listening platform this is purely down here to listen to the echo it’s quite amazing
And people like to do things like torture dogs there as I shall play it’s okay it’s all right baby you good boy there’s really nobody there what oh well we’ll leave that poor dog suffering on its own so I came back from you know I I saw
That online it’s not one I’ve actually visited that I’ve not been not been there unfortunately um and I wanted to work out what was going on so the people when they did it in the 1940s they you know they were really struggling but now we have computer modeling so actually
Another way to deal with Stonehenge is actually the computer model of it so actually olden days we used to build these scale models and measure them a lot in Acoustics we do a lot of computers as you do in all engineering and this is a finite difference time
Domain model that John sheer did for me of this and so what you’ll see is sound being created over here and on the left hand side and the question is where’s the sound reflecting is it coming back across the water at the bottom or is it going around the
Edge so there’s the sound going out you’ll see an aberration for the fin difference time domain model there we’ll ignore that doesn’t matter there you go what’s happening what where how does it reflect well some of it’s going along the water and some of it’s going around
The edge of top so this is one the reason I think they struggled is because the sound goes by both paths it’s not a question of one or the other it’s actually both paths and actually if you get them right the dimensions they arrive kind of back not too dissimilar
You know not too far apart and your ear integrates them so the actual answer to this problem of of what happens to the Echo Bridge is actually it’s not one on the other it’s both now if you like this effect you could go to Massachusetts but
Actually you can find lots of bridges do that next time you’re on a canal and you’ve got a very wide Canal there’s loads of them in castlefield for example in Manchester you can find this effect all over the place once you start kind of looking for it now so far se you lots
Of weird curved surfaces that have just kind of I’ve come across uh by accident it also made me think well my role normally is to design things you saw at the start those crispy bacon bits are designed so I thought can you design a whispering Gallery which isn’t like one
That exists so I came out with a prototype I’ve never built this yet maybe I should build it one side which is an s-shaped curve so the idea here is you you’re talking at the top on right hand side the sound skims around that top curve and then it jumps and
Skims around the other side of the bottom curve so you get it kind of skimming around both of them and the person who I put an arrow there because you couldn’t see them if they’re behind that would still be able to hear the whispering Gallery effect and so that
Was my kind of hypothesis maybe this would be a way of making Whispering Gallery which would be a completely different shape to what people had done before so computer modeler which is what I do I’m actually my background is in numerical modeling I actually did some
Modeling to see if it would work I don’t intend to take the graph apart in very great detail but on the left hand side is just a normal uh Whispering Gallery a normal curve so you’re looking from the left to the right of this left hand
Graph you’re in the middle of the of the Dome on the right hand side you’re on the edge of the curve and you see that rise that goes on in the level that’s the whispering Gall effect of the sound being concentrated around the edge when
The source is at the edge so that fact you’ve got it scoop up when it gets to near 50 m is the demonstration a whispering G is working there’s my right hand side being predicted using the same technique and you see the same scooping up effect showing how the energy is
Being consigned close to the sides so it should work and one day I’ll convince an artist to make it I’ll actually test it I’m actually in discussion with an artist now about making a whispering Gallery he doesn’t want this one unfortunately so I won’t kind of get to
Make it so that’s curv surfaces so if you want to look for things with aberration and and there’s lots of places which are undocumented look for Curves CU they focus they do weird things and then they play around with your hearing in sort of weird kind of
Ways now when I first thought of this idea of um writing a book called Sonic Wonderland the first thing I thought about doing was was you know about what’s called reverberation and the reason for that is kind of fundamental to architectural Acoustics but also because we have some really weird rooms
At sford University so this is our latest M if you’ve seen this one this is the latest anaco chamber at Salford so this is a room where every surface is absorbing the floor the walls and the ceiling and when you talk in there it’s a really odd effect if it sounds like
Your ears are blocked um it’s the place where there’s a s of meme that you can’t survive in there for 45 minutes and you’ll go mad and all that kind of stuff I’m afraid boring truth is you can very easily spend a long time in that place
Um and we do spend a lot of time in that place cuz your brain gets used to it uh but some people don’t like it some people when shown around go hm this this is nice can I now leave uh but it’s a great place to kind of to go into so
Because it’s all very absorbing it’s got no reverberation and it’s quite surprising when you do something like burst a balloon in there how little you get I’ll give you an example here here is a starting pistol going off in it I’m going to play it three times and it
Makes you realize what Hollywood does to your to to a gun to make it more interesting yeah oh there’s only two there don’t the third one that little click is the gun going off that’s and so when you when you actually in the real
Room a lot of the gun sound is the boom of the room it’s the room you excite the same is true when you burst a balloon a lot about what the balloon sound is actually the room reverberance in response so that’s what I’m interested
Is how the room responds and I can I can nip next door to this one at sford and there’s a room called a reverberation chamber which is it’s not that big a space it’s probably in terms of sort length and width kind of size of this
Room of this place it’s a bit taller um but it’s really reverberant so you go in there it’s a bit like walking into Cathedral so if you make a sound in there the sound kind of lasts for maybe depends out what we’ve got in there but
Let me say 6 seconds before dying away 10 seconds before dying away um and I kind of thought well that’s interesting there two very interesting rooms but maybe we could find rooms which are even more reverberant so what’s the most reverberant space so I have a sulfured
The deadest space you can get what’s the most Lively space I can find so I thought I was I event I should put an equation up there we go one equation um reverberation time is this measure of how reverberant stuff is and it’s basically you make a sound and you wait
To for it to Decay by 60 DBS and it’s that time which is the reverberation time so if I go to say Bridgewater Hall in Manchester which is the big classical music venue there or you go down to birming Symphony Hall which might be a bit nearer you here then the sound will
Last two two and a half seconds when the orchestra’s finished and that’s roughly the reverberation time if I’m in this space Oh it’s quite long maybe one 1 second one point something like that in this space if you go home into your bedroom probably. 3 seconds you know
That’s kind of typically what you get so what if we want is a big reverberation time and W as Clements are being worked in Harvard University to dve this equation there’s basically two drivers forget the constant there’s volume so big rooms have a lot of reverberation or there’s low absorption you want nothing
To absorb the sound so in this room we’ve got carpets us there’s even deliberate absorption on the walls I pointed out already all dampening the sound in here so what we want is a space that doesn’t have any of that so where it’s a space which hasn’t got any
Windows which is Big well how about a melum so quite a few of the places I’ve been to a mums um none of them had dead bodies in them oh actually one did I actually one did your dead body so this is Hamilton mosim you can visit it it’s
In Glasgow and it used to have the world record for the uh longest Echo and uh what you’re seeing there on the right hand side is a weird loudspeaker measure it and I visited it so when you go to acoustic conferences one of the funny things is is that quite often you have
Sort of weird visits to do and we don’t go off I don’t know don’t know what a normal physicists do but we also go off and do weird acoustic visits so this we went to hear this Echo as a day off from a conference internoise conference I
Remember rightly um so this is uh really great stories behind this the Duke of Hamilton was a really weird guy so he got buried in Egyptian sarcophagus which it was in here and all sorts kind of things and one of but unfortunately one
Of his um one of his uh uh I don’t know if it was his sons or grandsons lost all the money by gambling so the rest of the estate got hat got flattened but the mum still exists so we went to visit this and went to measure the reverberation
Time uh which is what this thing is doing here this is a weird do deedan loudspeaker which we used to measure spaces um and me and the restan said well that’s that’s good but actually it’s not that long is it this is a world record that could be broken um to give
You actual here’s a graph now that’s not from when we visited cuz when we visited there was quite a lot of people in the room and we’re absorbent so the better measurement is to get everyone out of the room and have an empty room so here’s a measurement from NY room um so
RT is reverberation time that’s what’s on the vertical axis and frequency give you a sense 125 Herz I don’t know trombo maybe uh 4,000 HZ Piccolo it’s this is basically the frequency range of a piano roughly and if you’re talking about speech it’s kind of around 500 1,000 we
Would worry about so we might say I’m going to pick the middle number here the reverberation time in that space is about 10 seconds it varies hugely all these very reverberant spaces have a lot of Base reverberation but I’ll pick the middle number for now it’s about 10
Seconds um that’s about St Paul’s Cathedral so there’s already a space which is almost as reverberant can we do better of course we can do better let’s go to a mosim which actually has the ashes of the artist Above the door I just remembered so it did have his body
In there so if you go to Oslo this is an Oslo and I visited it um and and it’s quite an amazing space um so there’s a very famous uh vand park with very famous sculptures in his brother was also an artist who mainly did stained
Glass and this was his studio and then became his melum what’s the the thing that most people go to see when it’s it’s not open very often um but I um go to see is the frescos the murals are quite amazing in this space um I’m
Trying to think what I can say what’s what’s the youngest person in the room some of them are quite explicit let’s put it that way um there’s all sorts of kind of dead bodies and skeletons all sorts of kind of weird stuff I mean this this guy was doing stained glass for
Churches had a quite a dark side or kind of quite an alternative side um so you go see the Fresco um but it has the most amazing acoustic in there and so you can find people recorded in there you find recordings you can find recordings on
YouTube if you want to look it up what’s the reverberation time so it’s the red curve there so you can see it’s a bit more than the Hamilton Mo’s lib so I have found found something that has beaten the world record so that was a kind of a good starting point but
Thinking 14 seconds I bet you could do better than that so you start looking at others places and um here’s a water reservoir there’s one in America which is even bigger than this but this is the one which is up in wormit in Scotland so wormit in Scotland’s up near Dundee and
Um I learned about it because there was someone did a tour of resonant spaces it was a you know a saxophonist um um called uh um John Butcher sorry I forgot his name he’s on there who went around playing to audiences in these various kind of different resident spaces and he went to
This Reservoir in wormit so I looked up and could find no mention of it at all uh and finally managed to track it down and it happens to be under the under the lawn of an architect’s house so when he bought the land to build his house on he
Got a free Reservoir with it and he showed me around it one day when I managed to get hold of him he’s very proud of it he doesn’t know what to do with it I mean I mean it is vast this kind of reservoir underneath the space
Um uh it was built because wormit which is near Dundee was going to be a big town but then the Great Wall struck and it never got filled up so they made Reservoir which is basically far too big so they never used it so it was always
Unused um but it’s got big volume lot of concrete and lots of Hard walls no windows um so it’s kind of very kind of uh very good for reverberation so I’m going to play a little bit of music in there cuz it’s this kind of these very space is
Interest musician so what can you do in the space You’ kind of basically got two choices so one choice is you can play really slowly think of whale songs you know play very slowly because the when you play a note in hereit it’s going to last half a minute before it dies away
So you’ve got to you know you got to go with the flow you got to play very very slowly or the other way is to play very very fast um so let me hit play you one of these pieces first of all So I said we play one of these pieces actually three notes from one of these pieces so that’s a commercial CD you can buy it’s it’s underground uh what’s it called it’s something from songs from the sistern chapel um by Stuart Dempster now so Stuart Dempster is a trombonist
He also plays the didy do he’s an improviser he’s a very good interview about playing in spaces like this he plays in the America one he said the problem with improvising in there is if you make a mistake because normally when you make a mistake improvising the note
Has the good grace to disappear in this place it lasts for another minute so it makes improvisation interesting so it’s a really fascinating topd demo so that’s one way of doing it to play very Serene meditative music the other way is to play really fast and you may have met
This before if you’ve gone to church when the or you let’s say you’ve got a wedding and everyone’s walking out the organist sometimes goes crazy don’t they play really really fast you can still you have this fog of sound builds up but you can still hear the tune coming on
Top and that’s because all the reverberation is at base and and the actual tune is a bit higher in frequency so you can still hear it so the other way which is what John Butch is going to do on hiso Sachs is just play lots of notes and just let the fog Build [Applause] so um the the husband who showed me around was you know said it’s a marvelous concert you know he was really great and the wife said it was completely unlistenable to that was the that was the kind of comment they made so I think they differed on their
Musical tastes um but it is quite an amazing space to be anyway so what’s the reverberation time in that space um so this is actually the Dan Haro system which is the America one because it’s a bit bigger so it’s got slightly long reverberation time and so looking at the
Mid frequency is what we up to 15 16 seconds so we’re certainly getting a lot bigger than that so I thought well okay so we’re getting somewhere but I wonder if there’re somewhere even better and there’s a there’s an organization called Subterranean britanica which specializes in going in underground Britain and I
Contacted them I I’ve emailed the top chairman of the you know whatever they called and said do you know of anywhere really big with really heavy walls and no windows which might kind of do this and they said you need to go to inch and
Down and that’s where you need to go and it actually had feared on One show about a month earlier um and it took a bit of Trace tracking down but I managed to get into the inch and down oral Depot so I’ll show you a moment but this is how
You kind of get into it so it’s quite a funny place to walk into because it’s it’s in the side of the Hill it’s up above uh iness and you wouldn’t know it was there and you walk down this tunnel it’s a bit like going into James Bond
Lair villain Lair and you walk down this long tunnel and then sudden to the left hand side you see the sort of pipe work and that’s how you get into the place you go down the pipes and this is how they used to maintain it is through the
Actual entrance pipes to give you a sense the pipe’s about that wide so it’s actually a bit narrower than uh kind of shoulder width it’s about 2 MERS long and you get laid down on that sort of thing and they s kind of shovel you through into the place like a pizza
Going into an oven um I was actually chatting to one of the guys who helps gets people in and out it so if you want to visit it by the way there is a place that you can about once a month they take about 12 people into it it’s
Possible now to go when I went it wasn’t generally open I I had to go for historic England to get into the historic Scotland to get into the place but this guy I think it was the same guy tried to go down that got halfway down
And scream blue murder to be pulled back out again so he as he hasn’t been into the tank cuz he’s too scared of the entrance but there we go I used to Cave so it wasn’t so bad and then when you get inside that’s what it looks like so
What was it doing why is that there well it was trying to protect the Royal Navy shipping oil during World War II so in the buildup to the World War II um uh the Cory F which is just below this is really important shipping point I mean
Nowadays What You Get There is cruise ships and oil um oril oil um oil refinery sort of kind of stuff but in those days it was the royal Navy had their ships and they were filling them up with oil and so they decided they need to make bombproof places and
There’s actually a series of these around the country um but this is the one that you can actually get into um so it’s qu of a kilm long 250 M long about 15 M wide about 18 M tall so actually St Paul’s Cathedral it’s actually quite a
Lot smaller than St Paul’s Cathedral but it was made bomb proof so that’s why it’s got such long reverberation time because basically what they did is they tunneled it out of the rock um and then they put shuttering in and pulled concrete down so it’s half a meter of
Concrete against bedrock and so there’s nothing vibrating in that wall at all which is where you get most of the losses of walls these walls are slightly vibrating as I talk and that’s the reason you’re losing energy on them there’s nothing then they sealed it so the reason the carpet’s absorbing is
Pores in them well they sealed this cuz otherwise the oil would see Power so there’s no pause it’s not vibrating and so it’s incredibly hard and reflecting it’s not nicest of places to work in this is all the um this is the leftover oil on the floor so everything you take
In there gets covered in rubbish uh this is supposedly cleaned um all this pipe work is to heat the shipping oil so it would go down the hill um so they could actually get it down the hill to the to the ships um so we went in there and we
Um kind of far a gun off and measured what the reverberation time is in the space and uh I got one of those for that which was what was mentioned at the start and actually today the guy was running me up from the place saying can
I get a copy of this we want to stick a certificate up on the wall in the tank so that’s what I’m doing when I get home so the longest Echo and we have an argum about that moment is 75 seconds so I show you the graph and I’ll come back to
My arguments with Guinness so the bottom one there is Hamilton which was the old world record this is the new world record so it’s the world record holder the argument was with with um uh was basically they had this longest Echo um um record now in my field which is
Architecture accuses Echo means a discrete event so it’s when you go echo echo that’s an echo where you can hear the word twice reverberation is this what happens in this it’s just a a blend of sound you don’t hear my voice twice you just hear a bloom on my voice so
Actually this is the longest reverberation time it’s not the longest Echo but I said to that to um to Guinness and despite having a PhD in the field they said you broke the record for longest Echo that’s what your certificate says go go away so I have an
I have a record for something which isn’t right but there we go um it’s still I still it’s funny I have the record because actually the room has record but there we go anyway so the reation time is incredibly long it’s about 40 seconds at Mid frequency I
Played a saxophone in there and so you know you play a note and it takes half a minute before it dies away now what you really need to do if you want to really get in there is you need to go get your trombone out because it’ll last 2
Minutes after you play a note before it dies away to nothing um don’t go in with Piccolo it’s easy to get a piccolo in there it’s smaller but it’s not as interesting so um uh so yeah so you get really extreme reverberations in that space and I did a calculation I did a
Paper on this for Journal um sort kind of saying this is interesting bit like sort of finding a new species we ought to S kind of have a paper on it and I did a calculation of how long the reverberation would be if the walls were perfect perfectly reflecting and it was
Pretty much the same number so for this volume of room you can’t make it more reverberant um but I I’ll end up by playing you a little bit of saxophone music in there so I’ve been in there quite a lot of time filming for for television this is another Channel 5
Program I think if I remember right this one um so you go in their film they spend ages filming you you get really cold and they say then can you play the saxophone and you you you’ve got five minutes to do it in so you pick it up
And play it quickly this is actually them filming me just twiddling the keys but the sound man picked up on his mobile phone so it’s not the best of recordings um there is one online of me doing it with a decent recorder but anyway I’ve not got that here with me um
But you get a sense of what it sounds like to be there and this is just me playing one instrument you may not believe this but everything else everything you hear is reverberation it’s not extra people Playing [Applause] Yeah that’s great and that’s we done