<&>Wellington Corpus of Spoken New Zealand English Version One <&>Copyright 1998 School of Linguistics & Applied Language Studies <&>Victoria University of Wellington <&>side one <&>2:32 right <.>now <,> last week we finished the lecture with a discussion of the um lincoln centre hall philharmonic hall in new york built by leo beranic and <,> the book that documents that we've um had a look at some of <.>the the halls there and the design criteria and we know there's failure and in <.>fact but <.>in about ten <&>3:00 years later they completely gutted it and um it went right down to the brick work and rebuilt new sides simply because they had tried time and again to adjust the acoustics now if everything <,> um <,> in beranic's design criteria had been right then um it would have been a perfect hall but there was one very important failing er which is the subject of the <.>lec lecture today um <,,><&>4 if you recall the er the design of that lincoln centre concert hall <,,><&>12 very approximately the seats stage you can see pictures of the <,> special <.>ceiling um <&>4:00 reflecting panels which were built into the hall so that if somebody was on stage here er the direct sound proceeded there and the first major reflection came in after an initial time delay which was fairly short because the path distance wasn't too long this was lower <.>th obviously than the basic er structure of the hall and this meant to er produce <.>i intimacy which could be rated <.>a as forty percent of the total hundred percent value for a good hall now clears throat there are two things wrong with this um reflecting system that had been added to the hall one of them was that all the um reflecting bits they weren't exactly that shape were exactly the same size and they had gaps between them they represented a grid with <.>sp air space in between so that produced the effect of um a grill which could absorb er and <&>5:00 destructively interfere with certain frequencies <.>wh so that meant there was a <.>t total distortion from this object um <.>a as well or perhaps related to that sound got behind it and seemed to get trapped so that you have er certain sound waves able to pass specially low frequencies pass the um reflection but then not <.>s adequately get back into the main space that was because of the the shape um of that constructed ceiling the other major thing that turned out to be wrong with it was something that was only discovered with er subsequent research and um howard marshall was strongly involved in that developmental work in the <.>s <.>seven sixties and into seventies <,,> now this <&>6:00 developmental work involved laboratory experiments and <.>i <.>w there are papers on this if you want more detail i can give the um specific references they're um in journals um journal of sound vibration and um um and i can't think of the other one at the moment um but they did things like this what they wanted to find out in a laboratory so that oh there's a pen word in a fairly small enclosed and probably anechoic chamber without any echo um they've very absorbing walls they would have a subject sit er in a position here with their ears <,> like that and they would play sounds from a loud speaker in the laboratory and then they would play delayed sounds <,> on another loud speaker somewhere else in the space and <&>7:00 there'd be a delay time here which would correspond to the initial time delay um in a concert hall in other words it would be delayed by an amount which would be equivalent to er a wall thirty feet or thirty metres whatever away okay and this sound would come here and the first major reflection in this laboratory would come in a certain time later <,> now what they discovered from these experiments <,> er was that there were certain places where this loud speaker was very satisfactory for the listener and certain places where it was very unsatisfactory and one of the places where it was least satisfactory was when it was directly over the head of the person um sitting in this space and i can't draw it of that diagram but just remember that fact um the direct sound comes from there from that loud speaker and another loud speaker is placed up there and no matter what the delay times or the <&>8:00 loudness of the reflections er that is unsatisfactory for the listener what the listeners turned out to really like um are er reflections which come in from an angle if you sort of are sitting here with your head loud speakers there and we're talking about where it would be in the just by waving my arms rather than talking in angles it's somewhere up there or up there on and those out of the um direct line there above um and coming in certainly well let's say voc yeah certainly coming in from a different angle not with your head straight ahead and two ears pointed towards the direct sound er it was much better if the first major reflection came <.>s from a different position <.>le voc was not in the same plane as that direct sound and that was of course binaural dissimilarity which <&>9:00 you all know about okay so laboratory experiments proved that um it was much better if the concert <.>hall er well in the laboratory here er that the other speaker <.>came had sound which came from er a different angle and therefore spread the image okay but <.>it's it's more complicated than that even <,,> they also measured how much energy you'd like to have coming from the side reflections so um <.>th this was very interesting in terms of subsequent design of the christchurch town hall and the michael fowler centre what kind of energy would would you like to have coming in as a major reflection and this is where i think the experiments went wrong and i'll just explain briefly why i think <.>that's if you can put yourself mentally in this position it's something like listening to a stereo isn't it er with one speaker there and the other one <&>10:00 somewhere else now everybody knows that you're not going to have <.>th a stereo with the speakers sitting on top of each other and then sit in front of it and expect to hear a stereo image you want to have binaural dissimilarity all the sounds coming from different angles now if you take your average clears throat laboratory um guinea pig in these experiments in the sixties they weren't musicians necessarily they were likely to have been colleagues um working in sound and scientists coughs put them in a situation like that and feed them two loud speakers and delay one and move it round what they're likely to enjoy most of all is that something that spreads the sound and sounds a bit like a stereo that <.>gives that means almost completely equal energy each side of the reflector <,,> okay the direct sound and the word from these two loud speakers they're pin points of sound and what would probably be ideal in the laboratory situation is almost as much energy going to the second loud speaker remember it's delayed in time by some er factor twenty thirty forty fifty <&>11:00 sixty milliseconds <,> okay so it could it could start to sound like an echo if it comes too um loud too late but basically it's going to be er an image spreading um device <,,><&>3 now if we have a look at the situation here on the transparency just a minute <,,><&>11 here we go sorry oh here it is it's on the piano clears throat <,,><&>5 this lower graph here at the moment is the one which you should concentrate on <,,><&>4 <&>12:00 <.>it's it's to do with the reflection level <,> that is the delayed speaker relative to the direct sound in decibels <,,><&>5 and this is time okay so um decibel level relative to direct sound um and the time after which it can come from the second speaker for a major reflection in a concert hall <,,> okay so you got um a situation here where they what they described as a preference range for the reflected loud speaker <,> and you can see that that's corresponds to or is even slightly above the level of the original sound that's that's where the sort of unity value goes across to zero um the reflected sound is the same loudness as the direct sound in that case <,,> if it's less <&>13:00 down ten decibels um <,,> it gets <,,> well it's not graded in the preference range and in fact there are two concert hall types mentioned down here small fan shape and a large fan shape hall those are the halls where reflections can't come back off the side walls do you remember um the models that we looked at last week they were usually very wide flat halls um <,> with er side reflections <,> um <,> were going to simply be er not <.>a a factor they would come in too late or too weak in relationship to the direct sound <,> so what beranic had originally calculated <,> as to be very important the initial time delay between direct sound and the first major reflection er <&>14:00 was also dependent on where it came from in terms of the um the er energy but in this case here what we are talking about is the intensity and time delay if it's too quiet if the major reflection comes in too late then it's simply masked by the direct sound it has no influence on the hall um and if it comes in er latish and too loud then there's an image shift which you couldn't get in a natural pen a natural acoustic and that is that you actually start to think the sound's coming from the other speaker the one with the reflection if it gets too loud then the direct sound's no longer the source point er <,> there's an effect there called the haas effect <,,> um which tells us <.>that <,,> at least <.>to to some extent we will always isolate as the <.>ori <&>15:00 original source er the sound that comes first but that's only up to a certain point and obviously when you get to plus ten decibels um direct sound and then ten decibels louder your reflections then your attention shifts and you start to take the delayed sound as par that's where the orchestra is it's no longer there on the stage it's actually coming from something near to you if you've ever been in um <,,> <.>a a space where there is artificial assistance for a speaker <.>or or something and it's a crude system where they have a speaker with a microphone on a lectern or something and then you're sitting at the back of the hall and there's a speaker behind you you see the person talking um but you hear the sound coming from behind you do you know the sort of thing i mean i mean it's <.>s simply that the source is not that person any more you might <&>16:00 be able to hear that person er but it's delayed by the distance whereas the the air sound travelling in air whereas the er er electrical circuits are travelling at the speed of light is coming through much faster to that speaker and then coming to your ears therefore you take that um as the sound the main source of the sound and what should happen in those situations in a church where there's very echoey um kind of long <.>rev reverberation and they're trying to have the speech heard is that they will have a system like this but they put in a delay so that the first thing you hear is the preacher and then slightly later comes the sound from the speaker behind you and so long as that speaker isn't too loud er you'll actually take the first thing that you hear as the source so this is um related to that and in fact what it's saying is that if it gets too loud um then the image will shift and you'll start to think that the person talking to you <&>17:00 is in fact the voice of god from above and behind that kind of thing <,,><&>4 okay now we'll just go back and show you why <,,><&>6 the energy for a fan shaped hall cannot conform to this <,> it cannot give you a lot of energy from the side or above <,,> and in fact the lincoln <.>ph the philharmonic hall er had this fan shaped component as well it wasn't very strongly fan shaped slightly fan shaped um but on the stage the energy was direct and then it comes off and hits the sides of the fan and it then continues as what they describe in the field as near frontal <,> lateral energy so <&>18:00 it's slightly off centre but it hits the side wall and then <.>go proceeds to go more or less parallel to the direct sound waves because of the fan by hitting the fan and then going straight ahead okay so you don't get lateral energy from a fan shaped hall and it was this lateral energy that they discovered was really interesting for a sense of envelopment in a concert hall and if you take your music beranic style um coffin which is actually longer and and <.>th thinner than that isn't it it's an extraordinary long thin building there's the stage and here's the audience out here direct sound and lots of reflections off the side walls cause the side walls are really close in those coffin shaped halls aren't they the shoe box effect so they have good lateral energy in fact quite accidental because they were just the design that was popular at the turn of the century or in the <&>19:00 nineteenth century 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