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In this episode of Sound Design Live I’m joined by the author of Rock and Pop Venues: Acoustic and Architectural Design and founder of Flex Acoustics, Niels Adelman-Larsen. We discuss room acoustics, reverb time, and sound system design.

I ask

• “This one factor, low RT at LF, has to be fulfilled in making a good sounding hall for pop and rock music. This is the single most important message of this book.”
  • Why is reverb time at low frequencies so critical to good sound?
  • But won’t that all be fixed by filling up the room with people?
• Why is the 125Hz octave band the most important to control?
• “The halls investigated in this book are in almost all cases over 1000 m³. With an ideal reverberation time for pop and rock music of 0.6 seconds for that size volume this yields a Schroeder frequency below about 50 Hz.”
  • “The only way to turn down the level of the reverberation is by placing absorption or diffusion on surfaces. The normal way about it, of course, is to find the appropriate reverberation time from figures 5.4 and 5.6 and calculate the amount of absorption needed in all active bands from acoustic specifications about different materials absorption coefficients at various frequencies.”
  • Can you walk us through how we can measure the reverb time of a music venue and make some quantitative judgements about it?
• “It is a fact that the more sound the PA system shoots onto the walls and ceiling, the more the reverberation of the hall is evoked.”
  • I know it can be difficult to generalize about some concepts, but is there a general guidelines around the number of independent arrays in a sound system? Is it better to distribute many elements around so that they are closer to the audience or to have few elements and attempt to cover the audience from those fewer strategic locations?
• What are some of the biggest mistakes you see people making concert venue construction and in converting existing structures into music venues?
• From FB
  • Michael Curtis
    • 1. Is a 12” deep absorption panel, with 6” of appropriately dense insulation with a 6” air gap behind the most effective and most economical broadband absorption panel? I see this propagated in studio world, but does it apply to larger scale rooms?
    • 2. In your experience, do air gaps behind absorption panels actually double their efficacy? In theory it puts the absorption where the wave’s velocity is at its highest, thus slowing it down the most. Does having a “full depth” panel work better?
    • 3. When designing rooms, is there a cost benefit framework you could walk us through when deciding where to invest dollars?
    • 4. What are some best practices for us sound system designers when we’re able to visit a venue first and check out the room?
  • ejc_audio
    • What is the most common, low-cost or high-ROI treatment that venues miss, don’t think about, or decide against when building or refurbing?

Notes

1. Rock and Pop Venues: Acoustic and Architectural Design
2. For the Best Concert Sound, Keep the LF Reverb Time Low
3. EBU Tech. 3276 – 2nd edition May 1998
4. “In these smaller volumes below about 1,500m3, MF and HF might become too loud if the hall is designed without some porous absorption or a highly diffusive interior.” pg132
5. Comment below with your venue’s volume and reverb time in the 125Hz octave band (or every band) and we can talk about their relationship.
6. Some of my takeaways
   • Some of the worst music venues have very unbalanced reverb times. eg. very low HF reverb time, but very high LF time.
   • If the room is completely dead and absorbs all of the high frequencies, you might as well stay home and listen to your really nice headphones because the show won’t be any fun.
7. Quotes
   1. And weirdly, had been none, no, no research done really on what is recommendable for acoustics room acoustics for pop and rock concerts, which is crazy to think about as a, there are hundreds of books on recommendations on acoustics for classical music since Sebine back in 1898 or something.
   2. that’s what I get out of and analyzing all these results of a lot of venues, a lot of River Up times, and a lot of venues, and a lot of ratings from all these musicians and sound engineers what do, and they, most of them think the same venues are good and the same venues are bad. So you can see what is characteristic for the venues that they all think are very good. And so it comes out that the 1 25 Hertz Arctic Band is just super crucial
   3. you cannot count on the audience fixing the 125 Hz octave band. That is so crucial.
   4. If the smallest distance in the room between two parallel surfaces is more than 18 feet, then you start to not have any mode problems at all.
   5. The louder we play an instrument, the more high frequency content there is.
   6. If we steal all the high frequency reflections out of the room by dampening the high frequencies, the musician cannot feel his own dynamics.
   7. the farther way you get from the reflecting surface, the wall or the ceiling, then the more base frames you will get absorbed from your porous absorber
   8. Human beings, we are not just equations in our head, our likes are not are not dictated by any equation.

Transcript

This transcript was automatically generated. Please let me know if you discover any errors.

[00:00:20.610]
Welcome to Sound Design Live, the home of the world’s best online training and sound system tuning that you can do at your own pace from anywhere in the world. I’m Nathan Lively, and today I’m joined by author, researcher and the founder of Flex acoustics, Niels Adelman-Larsen. Welcome to sound design live.

[00:00:39.100]
Thank you so much, Nathan. It’s a pleasure.

[00:00:41.490]
So Neil, I definitely want to talk to you about room acoustics and Reverb Time and maybe some products that you’ve been developing and sound system design. But before I do that, I’m always just curious about what people’s musical tastes are. So I’m wondering, once you get a sound system set up or you’re working on a sound system, is there a piece of music that you like to play through it that would help me get to know you?

[00:01:04.920]
I grew up in the dance music in the late seventy s. I would probably put on a piece by the Earth, Wind and Fire. Just get grooving a little bit. That’ll show, you know, how the venue works at the low end too.

[00:01:35.820]
So Neil, I wanted to dive in right away to help people to get to know you about what your work is. So let’s talk about the Eurovision Song Contest. So the Eurovision Song Contest is huge in Europe and a lot of resources have thrown it. It’s in a different city every year.

[00:01:55.920]
Correct.

[00:01:56.490]
And I know you participated in it when it was in Denmark. Tell us the story of how that happened.

[00:02:02.470]
Yeah, that was back in 2014. So it’s in the city where the year before person who won came from. So that was the Danish person in 2013 winning the Eurovision. And so it was held in Copenhagen by 2014 and it was in the venue that was chosen. It was close to the center of Copenhagen, so everybody would come in, buy airplanes and they would be easy out in the venue. So but they hadn’t thought so much about what what kind of venue that was. There was an old shipyard and they didn’t think much about what would a shipyard sound like when we thought, this.

[00:02:35.970]
Looks great, it’ll hold a lot of.

[00:02:37.270]
People, it’ll hold a lot of fuel and it’s got a 50 meters high ceiling, so why don’t we use this one? The thing was that it also held, the base was enclosed in that huge space. Nothing dissipated out of the venue that was all kept in there. So it was just bouncing around for a long time, actually for 13 seconds. 13 seconds.

[00:02:58.590]
Wow.

[00:02:59.470]
So that was the base frequency, 125 Hz. Octave band Reverberation time. And we had to do something about that because people would not understand what was played on stage with such a long reverberation time. It would just be a lot of muddy sound, right? And just the year before I had broken with a new product and new technology, which I call the Aqua tubes, which is inflated plastic tubes. So it’s essentially a huge piece of plastic that is inflated and then it’s a tube, right? As you can imagine when you play very loud music, then these inflated baffles, they will then rattle and shake and that means that the sound energy is being converted into mechanical energy and then into heat.

[00:03:50.490]
Okay?

[00:03:51.020]
They are absorbing, they’re actually absorbing sound. So it’s a sound absorber. And it was a perfect fit for this because we needed thousands of square meters of base absorption.

[00:04:01.330]
And it’s just temporary, right? They’re not making a permanent temporary.

[00:04:04.100]
If you can inflate it and it’s there, then it’s just the perfect piece of product for that kind of situation. So they bought 6000 was amazing. It was the first gig we got and I had just been making a few equations and a drawing and say, oh, this got to work. And of course I’d made a little bit of investigation in reverberation chambers and checking out the absorption covidian and so on. But from that it was so shocking just to walking into that venue, it was a huge venue. And then see 6000 something that had just been a thought in my head. It’s like, what, I think I might just leave because I’m not sure this will work. But as a matter of fact, we lowered that reverberation time to to 4 seconds from 13 seconds. Yeah. So that would you know, all of a sudden things started to sound much better and but I have a little fun anecdote actually about the steps into it really working out. We got the tubes in there maybe three weeks before the actual day of the show. And then my manufacturer in Germany, Garrett’s Company, they had done an amazing job on welding up these 6000 squares in no time.

[00:05:13.240]
And they had gotten it very good, so they didn’t deflate. So all weldings were nicely done. But there’s a certain amount of porosity in all materials, also in plastic. So after a week they conflated they needed to go up there and inflate all of these and have craze up and blowers and stuff. And we thought, hey, why don’t we put just a permanent little blower that’ll just constantly hold the pressure of those. So we needed to find out what kind of blower should that be and do we install that in this? Nozzle. Which was already there. So that was quick. And I had a friend, or a good friend who’s a mechanical engineer and a top drummer too, and we were checking out how can we do this, and we came up with a solution. We bought a few of these small blowers and we had calculated this should be enough to fill these enormous 50 meters long tubes. And so we put it here in my living room and turned on this little blower. It’s a tiny blow like this on one of these tube. Not a very long tube, but a ten meter long tube.

[00:06:13.650]
And then we left the apartment and said now it’s time for a beer. And we said let’s come back in half an hour or something. And we came back half an hour later and this tube had just pushed away all furniture and the whole room. Okay, this works. This really works. That was the way out and that was how we made that work for all those 6000 sqft. Which is 60,000 sqft, right? Yes. So that was how that was the premiere of that product. It was a lot of fun.

[00:06:40.860]
Wow, what a great story and a great success. We’ll come back and talk more about these products and more about acoustics in a little bit. Let’s take a little break from technical topics and just talk a little bit about career advice. I always like to start with this because especially during the pandemic, but even now there’s always going to be people looking for jobs in audio and so I wanted to start with how you got your first job in audio and then ask you a little bit about maybe some guidance you would have for other people. So how did you get started in audio? What was your first paying gig?

[00:07:17.440]
I should take it all the way from scratch, because I’ve always been divided between music.

[00:07:21.600]
And I should have mentioned at the beginning that you’re also a musician.

[00:07:24.150]
As right out of high school, I started a mechanical engineering bachelor’s degree and took a couple of years of that. And then I thought, I have to be a musician. So I went to Berkeley College of Music and I toggled between Berkeley College of Music and Technical University of Denmark for a couple of years and making a thesis on a bachelor’s thesis on acoustics. And I met a great Danish acoustician who would become my supervisor for that. And so I fell in love with acoustics. I have to say I was very close to take a job at the brilliant and Care measurement devices or acoustics and I had to turn it down because I could just feel if I said yes to an engineering job right at that age 25, I would desert some part of myself. So I became a musician for 15 years. I played 1200 gigs as I started out a jazz musician, which is where I have my beak have to say, I’m a complete fan of American heritage in music. I’m not a Brit pop dude, I’m American. You know, sure lose jazz and when it comes to pop, there’s got to be a fair amount of soul in there and like Whitney Houston, Paul Simon as his greatest ever, as, of course, Michael Jackson, of course, as big as pop star in my world.

[00:08:35.750]
So I just had to take the musician route and played a lot of jazz in the beginning that couldn’t make a living. So I made it into a cover band that was playing popular rock tunes and we made a new drummer. I was the drummer and made a good living for many years. And then it started to get a little bit boring because it was doing the same thing again and again. And I came to think about my bachelor’s degree in acoustics, which really had turned me on as well for the first time. I have to admit, nothing wrong with mechanical engineering, it’s just not a talented one. But I could feel that the acoustics was really grabbing me. And so I took then just one or two courses at the technical university and in just basic, basic acoustics. But it being on a master’s degree level, it was still being a musician, having played gigs for twelve years and not having seen an equation, it was like, what is going on? This guy was just filling blackboard after blackboard with differential equations. I was like, what? But at that point I had gotten to an age where I knew that at the exam there’s not going to be any differential equations here, would be normal equations, and then I could deal with those, okay?

[00:09:44.960]
And it just became huge for me. And I had a fantastic teacher, many fantastic teachers who just saw that I had maybe a little bit of talent there and they nurtured me whenever something was difficult on math, because that was far away, then I got a little bit of help and so on. And that was during those years that I invented this inflatable inflatable product that we talked about before. But I also did my thesis on room acoustics. So me having been a rock musician for so many years, played so many venues so many times, I knew that some venues were much better to play and the acoustic were much more suited for rock music and pop music than others. So I wanted to sort out what was good and what was bad and weirdly. There had been none and no no research done really on what is recommended for acoustics, room acoustics for Pomero concerts, which is crazy to think about as a there are hundreds of books on recommendations on acoustics for classical music since Sepine back in 1898 or something. And so that was really weird. So I started that whole thing and had a huge network among musicians, also very great musicians in Denmark and great sound engineers working in these venues that I played in all the time.

[00:11:04.440]
So it was easy to go to them, ask them, make assessments on what do you guys think about these venues, because if you want to take a scientific way into this. You got to have more than one opinion. It’s not enough that some guy says something, you got to have a lot of people saying the same thing. You have evidence, hopefully statistical evidence. So I just became totally immersed in that and and it has just been passion driving me now talking about ways into audience. So it’s just I’m totally passionate, driven. If I’m not passionate about something, I’m really traded terrible at it. Wherever there’s passion for me, that’s where I go. So that’s my route in career choice and I can’t make a nine to five job. It’s really difficult for me. Maybe having been a drummer for 15 years thinks I need to go out and I cannot sit behind a computer at a desk from nine to five every day.

[00:11:56.260]
You could have had a job, an engineering job and you said you know what, I need to try doing music. And then you did try doing music and you were not able to make enough money and so at that point you could have said you know what, I do have to do the engineering job so I can pay my bills. But instead you stuck with music and decided to figure out a way to make money at music. So it’s interesting for me that you decided to stick with it and try and make it work even when it seemed like it wasn’t going to work and make enough money.

[00:12:26.590]
That’s a very good point and I haven’t thought about it that way because that’s also the point when you walk away from improvised jazz music which is like where you use I have some talent and I can use myself as musician then into a category of musicianship where I’m not especially talented. Many dramas around who are more talented than I am. But the kick you get from having an audience liking what you’re doing, it’s just something by itself. It’s such a rewarding sensation that once you have it’s such a gift. You have to say that’s also why some musicians play for so little money because just the kick they get from going out there, it’s so meaningful to make a group of people it could be five or it could be 5000. It’s so meaningful when you’re doing that. It’s such a beautiful thing that you’re hooked to it. You have to do it again, I think. So that part of the musician thing was why I did not walk away from music altogether but drifted into a cover band. It’s still a nice sensation.

[00:13:31.960]
This is a good time to transition into this. It’s going to be backwards in the camera. IEM. Not sure.

[00:13:39.430]
No, that’s good.

[00:13:40.680]
So you spent these years playing in all these different halls and you found yourself wondering what is it about this that makes some of them good, some of them bad? And I’m using very general terms here because then you go on to not only do I don’t think I’m gain to get this in here, but it’s like study after study in here of all of these halls in terms of acoustics. But then you also interviewed sound engineers, musicians and audience members about just hey, whether or not they thought this hall was good. But then you also talked to them about why do they think the hall is good or bad? And you came up with a lot of interesting results here. But there’s one big takeaway here that can be summarized in a single sentence, which is you say this one factor low reverb time at low frequencies has to be fulfilled in making a good sounding haul for pop and rock music. This is the single most important message of this book. So Neil’s, why is reverb time at low frequencies so critical to good sound?

[00:14:45.050]
It’s because if you don’t get defined message as a spectator, as an audience, a very clear message, something blurred, then you are uncertain about what is being told to you via the music or via speaker. You know it from speakers too. Who’s speaking in a church maybe? And you barely understand the speech intelligibility. I would say there’s something called music intelligibility. Do you understand what is being tried to be conveyed from states to you as a listener? And if there is a long reverberation time at low frequencies, then because there’s a lot of bass level at bass frequencies in a rock consideration is high and it’s still pretty syncopated, then this whole syncopation which makes the music sound good in the first place, when that is lost due to the long rear brake chart, it’s just becoming muddy. The one sound has not finished before because it’s ringing out, it in the venue before the next one starts. Then what can I make out of it? All of that.

[00:15:48.380]
We can’t tell one note from the next.

[00:15:50.030]
Exactly. So our brain is like on overwork, we can’t figure this out. So we just resign as an audience and go to the barn drinks and beers and we’re not yeah, we just.

[00:16:01.280]
Talk to our friends because you can barely hear the music. That makes a lot of sense.

[00:16:04.600]
Exactly. Yeah, that makes more sense to talk to your friends about something else because this is not really working and it sounds far away. Exactly. It does. It becomes very distant. So that is the reason we cannot make sense out of the whole thing. And that’s why it’s so crucial to get that right in the venue. So that is actually now you mentioned low French reverberation. Why is that so important to have a low one? That is actually pretty ideal reverberation time in terms of seconds for a given whole volume. You got to have pretty much that reverberation time for that kind of music.

[00:16:39.200]
We just set this up for you because this was a huge this was a big surprise for me. Reading the book because you did all of these studies and then I thought you might just say it just always depends. But no, you came up with a graph that says if you know the volume of your room, then there is a specific reverb time in this 250 Hz octave region. And if you’re above that, you have a problem and you need to lower it.

[00:17:05.750]
Yeah, true. It’s actually the 125 Hz octave which is the most crucial. That’s what I get out of and analyzing all these results of a lot of venues, a lot of reverb times and a lot of venues and a lot of ratings from all these musicians and sound engineers. What do and they most of them think the same venues are good and the same venues are bad. You can see what is characteristic for the venues that they all think are very good. And so it comes out that the 125 Hz Arctic Band is just super crucial. And there are a number of reasons why that is more crucial than, for instance, the 63 Hz band and a number of reasons why it’s more important than the 250 Hz Arctic Band. And I can always talk about that.

[00:17:42.260]
Before we get into it. So I know one of them is that we have as sound engineers who are listening to this right now, they understand this as frequency goes lower and lower in our sound systems, we know we have less control. The sound starts to become more omnidirectional and it’s going everywhere and bouncing all over the room. That’s one thing that as sound engineers, we are really familiar with. So what’s another reason why the 125 Hz octave band is so critical?

[00:18:10.170]
Number one is that as a why is it more critical than the 63 Hz band? But that’s because it’s louder and it’s more busy. So you have a louder level of music going on there. So before that decreases to a sound level where it doesn’t matter anymore, it takes longer than in the 63 hours band, it’s quicker away because the sound level is lower. And part of that reason is that there are many more instruments happening in the 125 radioactive bands. And so not only is it louder, it’s also more busy because you have all the overtones from the bass PM in the keyboard bass, you have the bass guitar. All the overtones from the bass guitar is still in the 125. So they are also there. And you have the guitar in the 125, you have the male vocal in the 125. So they are fighting a lot for the room there. So if that is very blurry, then you cannot tell one instrument from the other. And then it just becomes this nonsense that we don’t want to listen to. Those are maybe the two main reasons why the 125 hertz is so important.

[00:19:17.650]
And then to talk about the 250, why is that less important? That’s because our speakers, we have more directivity and from the speakers than in the 125 hertz octave band. So you can aim the sound better at 250 where you want to aim it. Maybe you want to aim it at the audience. Of course you do, because that’s the people who want to hear it. That’s where we want to get the sound. Whereas the 100 and 2500 hertz October 63 are very omnidirectional. They go in all directions. You cannot aim at anything. The 250 Hz octopus already, you can aim much better at the audience. And so that one thing. Plus the fact that the audience actually starts to absorb quite a lot of sound at 250 and up.

[00:20:00.660]
This is another thing I was going to ask you. You say this is a problem, but won’t it go away as soon as the room fills up with people?

[00:20:06.760]
Well, that’s a $65,000 question. See, the easy question is no, because you don’t get a lot of sound absorption in the very low end from an audience.

[00:20:15.020]
Oh, really? Okay.

[00:20:15.650]
And it’s a crucial thing, and I’m glad you you put pointed it, because this have maybe an absorption coefficient of 0.2 into one.

[00:20:23.300]
That’s very low. Right. So absorbing coefficient from zero to one. One being like window, zero being exactly completely absorbed, like anecode chamber.

[00:20:31.920]
If you absorb everything, that’s an absorption correction of one.

[00:20:34.940]
Okay.

[00:20:35.150]
The other anecdotic chamber. Yeah, exactly. So you’re talking about reflection. So if you reflect everything, nothing is absorbed. But the open window is, as you correctly put it, is absorbing correction. One, you absorb 100%. The audience absorbs only 20% of the incoming sound at 125 hertz oxygen.

[00:20:51.170]
That’s really low.

[00:20:51.860]
At 250, it’s very low. It’s almost nothing. So you cannot count on the audience fixing the 125 horses. That is so crucial in what we’re dealing with here. But at 250, they already absorb 50%.

[00:21:03.220]
Oh, wow.

[00:21:03.650]
So it’s already more, it’s two and a half times more. And the sound is aimed down better from the speakers that cause the directivity is bigger at the 250, you can aim that down on the audience, who will then absorb quite a lot of it, so it’s not bouncing around all the surfaces before it hits the audience as the 125 octave. Those two factors together is the reason for the 125 octave being so crucial.

[00:21:29.250]
Talk about how you came up with some what are ideal reverb time, some ideal reverb times based on the volume of a room. And so I want to read this quote where you say the halls investigated in this book are almost all cases over 1000 meters cubed with an ideal reverberation time for pop and rock music of 0.6 seconds for that size volume, this yields a Schroder frequency below about 50. Just wanted to read that to give people an idea of what the average is that you’re looking at here. And as people are hearing that good, they should start to think about, I wonder if my room I wonder if the venue that I’m working at is above or below 0.6. Just as a medium that.

[00:22:15.210]
Can I just put one thing in here? Because it’s actually the lowest dimension of the room that’s going to determine whether there’s a spread of frequency, whether you have notes. And when you get to larger rooms, that’s one thing which would be great for sound engineers to know that in larger rooms, as what you said, there. So minimum height to the hole, if it’s above some 6 meters, which is about 18ft, right? If the smallest distance in the room between two parallel surfaces is more than 18ft, then you start to not having any mode problems at all, then we should not talk about modes at all. And so all the calculations of modes and on the mobile phones, all that, don’t use it just for venues which are bigger, maybe than 100 or 200 people, 300 people. So with more than 18ft ceiling high, don’t need to talk about modes anymore because that’s going to happen down at 40, 50. There’s nothing we can really do about it. Thanks for pointing that out, because that’s one thing we can omit and I’ll talk about when you sound. And so we should stick to the reverberation time.

[00:23:19.970]
I wanted to read one more quote which says the only way to turn down the level of reverberation is by placing absorption or diffusion on surfaces. The normal way about it, of course, is to find the appropriate reverberation time from figures 5.55.4 and 5.6, which maybe we can show in a little bit, and calculate the amount of absorption needed in all active bands from acoustic specifications about different materials, absorption coefficients at various frequencies. So that’s a mouthful. And I thought it might be fun, if it’s okay with you, maybe we could just walk through this in my office. I could take a measurement in my office. We can look at the reverberation time, compare it to your great idea, and that’s applicable to concert venues, but at least we can walk through the process. Is that okay?

[00:24:08.500]
Exactly, yeah, absolutely. Let’s do that.

[00:24:10.850]
So here’s a measurement that I took of my office before, but I’m going to take it again now to just walk through the steps and you tell me as I’m going through this if there’s anything you want me to do differently. So basically, I have a little studio monitor here in this part of my room. I have my measurement microphone over here. And I guess this is going to be the first question that people have, which is, is it okay for me to measure the stimulus through the sound system in the room or do I need some sort of like special acousticians dodecahedron, like sort of special speaker? What do I do? Is that okay?

[00:24:48.730]
I mean, that’s always a question. You would need that in a venue, you would want probably to go ahead with an omnidirectional sound source. But in a studio like this, if you were going to use your monitor mixers during your mixes, let’s see, let’s say it’s a control room in music studio, then there’s certain amount of idea behind measuring with the speakers you’re actually mixing on, because that’s the sound field that is created in your studio.

[00:25:16.050]
Okay? So in this case, it does make sense. Like if I was measuring my studio, okay, so I have my studio monitor set up. So I’m going to go ahead and take an impulse response here and this will take about 10 seconds. Got to save it. Okay, so now I’ve imported that impulse response and that measurement that I just took. And now you are saying that I should really look at the 125 octave band here. So these numbers are pretty small on the screen, but here on the right, it says T 300 point 64 and T 20 and T ten. So I should be looking at T 30. So zero point 64 is the time I got. So how does that relate to the ideal for this room size?

[00:26:02.100]
I said your room is more of control room size, control room, music studio kind of thing. So my book would not apply because I’m interested in venues for rock music. But what I can say is that there are some recommendations for that size of room and for the reverberation time in your room. And those are given by the European Broadcast Union. They have made many decades ago some recommendations on what should the ideal reverberation time be in the studio, in your size of room, and it’s probably around 0.30.4. I’m not sure how big your room is, but it would be 0.3. Was it a bigger room? It would be 0.4. So what we can say is, we can conclude that you are maybe almost twice as high as we would want it to be. And then an acoustic consultant can then from that knowledge, he measures your room geometrically and finds out volume, et cetera. And then he can calculate how much absorption material do you need. And to get from 0.6 to 0.3 at that octave band, you’ll know something about the product and which absorption questions this has in various frequency bands. And he can make some calculations or maybe even run it in a program.

[00:27:16.570]
Maybe an Odion is one of the programs you can use to make this calculation too. And then he’ll say if you put this and this, this is product there and there you’ll get your reverberation time from 0.6 to 0.3 and you have the ideal reverberation time for that kind of room, for that purpose.

[00:27:33.550]
Okay? Sound engineers out there, we can do this, right? So if we go into the rooms that we’re working in, we can take a measurement, get this time, which is reverb time, and the 125 Hz octave band. And we can compare that to the chart. And are you willing to share that chart with us right now or do you want people to get the best to see that?

[00:27:56.090]
Okay, what I can share is I think it’s even more interesting because that’s actually a standard that has come out, an ISO standard, okay. Because everybody has joined forces and made some suggestions to ideal. This is volume, this is cubic meters. And so for a given size venue, let’s say 1000 m³, then for rock music, which is the green area here, then you would want to have a 0.8 reverberation time at the 125 Hz octave or actually at TMIT. Okay, this is a little bit complicated, but at mid frequencies. So at 1000 Hz, you would want to have a reverberation time of 0.8 seconds. For a chamber music concept, you would want to go into the red area here. So in the same venue you would then want to have a much higher reverberation time, namely so something like 1.5 seconds, right? And so you would want to change the reverberation time in that venue from 1.5 to 0.8. From playing a Champion Music concert, you would want to have 1.61.5 at a rock concert, 0.8. So you will want to have variable acoustics figuring that out as ela doing that for you at the right frequencies and so on.

[00:29:17.410]
And, and sound engineers can go and see what is the reverberation time in this venue, how big is it? And they could use a book, my book brands to, to see what is the ideal reverberation time for, for rock music in this venue size. And then they could almost double by two and they would know what is the ideal reverberation time for a Champion Music concert in that same volume. So that’s how it works. But I would leave to the acoustic consultants to get the right materials to adjust the reverberation time. That’s a whole thing on its own as a whole profession. Acoustic consultants, like an acoustic consultant doesn’t claim that he can mix a concert. Don’t hope so. Some of them can, maybe very few. But that’s a fine craft. And I know people who are artists at this. We all know it’s an art on its own to mix a concert or mix an album for that matter. And that’s the same thing goes for nutrition, self, and the same thing goes for the acousticians, the acoustic consultants who have a whole lot of knowledge and not only years in school and a master’s degree in acoustics, but also a lot of experience on how do we get this in a nice way.

[00:30:27.740]
So I think we should leave that thing to the acoustic consultants about getting the right reverberation time in a given menu.

[00:30:34.560]
And do you have a slide there for the 125 Hz octave band as well?

[00:30:38.040]
But then you go by factors. So how much do we need to multiply this to get the right one at the right reverberation time. And so that could be we have to multiply at least one by 0.9 or 1.1 or something. Then you have the idea reverberation time at 125. But as you said, it’s in my book that graph that shows that ideal reverberation time. I would love all sound engineers out there to go out and check.

[00:31:06.710]
Some people are watching this on YouTube, some people are going to be listening to this and their podcast players. And what we’ll ask people to do then is take a measurement of your room and then comment on this post or on this video so we can see and we’ll make a comparison of different people’s room reverberation times and you could even upload your impulse response to other people could analyze it as well. But yeah, the number we’re looking for is the T 30 or the T 60 in the 125 Hz octave band.

[00:31:38.760]
Yeah, that’s correct. And together with the volume of the hole so with length height multiplied, then we can say what is the ideal reverberation time. I have to say one thing ideal reverberation time. Yes, but it can maybe go plus -0.1 2nd depending on the balance between the reverberation time at low end and high frequencies. So I can say that if you have a lot of reverberation at the High Frequencies, even in a Rock venue, then you can allow the reverberation time at Low Frequencies be a little bit longer. Because this High Frequency reverberation time just isn’t that’s another very important thing that I found just not too many years ago? How to substantiate that scientifically, and I think this is super interesting. Tell me if I’m getting too nerdy here ever. Okay, I have to say this because as out of my love for music and by many gigs on the stage behind the drum kit, when we really express music, when we are playing our instrument very dynamically, if you want to convey music, it’s going to be a lot of dynamics involved in your instrument. So playing Pianism move fortissimo dynamics, then it becomes a whole story that you are telling on your instrument, right?

[00:32:56.200]
Just an acoustic guitarist. You can make a whole adventure out of playing dynamically on the instrumental piano player as well. The louder we play, the more high frequency content is in that sound is in our sound on the instrument. On most instruments, the human voice as well, the louder we hear, the more high frequency content is in the voice. And so if the venue steals all that high frequency content by not giving anything back to you, just having a lot of high frequency let’s say it was completely filled with old sweaters. The whole venue.

[00:33:30.750]
Sure.

[00:33:31.270]
Which absorbs a lot of high frequency. Right. Then you would have a very dampened sound at high frequency, but not at low frequency. Low rate is completely unbalanced and that’s what unfortunately happens a lot of times and we really have to keep even. I think even a few acoustic spirits out there are not aware of this yet. And I’ve been fighting for 20 years to talk about the bass and now I’m talking since five years about the high frequencies. And so it’s just to say that if we cannot if we steal all the high frequency reflection out of the room by dampening the high frequencies, the musician cannot feel his own dynamics. He’s trying very hard to express himself as a musician, but he’s not succeeding. And there was one musician, a famous guitaristy in Denmark who, without knowing any of this 20 years ago, when I did my first investigation, he wrote in his answer in the assessments of the hole that in that hole down there and this is completely dead in high frequency. It’s like hitting a pillow. That’s the exact choice.

[00:34:31.690]
Nothing happens.

[00:34:32.970]
It’s not satisfying, nothing is coming out of it. He’s trying his best for 2 hours in a row and it doesn’t I.

[00:34:39.310]
Keep turning it off and it sounds worse.

[00:34:41.280]
Exactly. And if you try and think about an occasion where you went to a venue with nice high frequency envelope and nice high frequency reverberation, you can also remember, maybe from memory that the audience cheering and clapping becomes nice and lively. We on stage, the musicians hear that clapping and everything much louder. It becomes so reassuring for the musicians to hear that cheering and that clapping from the audience. And if the hole is very damp and that high French, they won’t experience that and the audience themselves will not experience it. It’s alienating sensation. Why didn’t I just stay at home with headphones on and my great stereo? Because it’s not a very social sensation to be at that concert in that venue with low hierarchy reverberation. And so we are social human beings. We’re going to that concert to experience something social and then that social thing is taken away from us. So it’s not so good.

[00:35:39.120]
You reminded me of two stories. One was when a circuitous soleil show came out and there was a news story about how part of the sound design was that they would take microphones over in this part of the room and pick up part of the audience reacting and share it over in this part of the room and generate more of this conversation. And so that’s a little bit of variable acoustics but giving people that sense of community and liveliness wonderful. The other story is I’ve worked at two small music venues that did the exact same thing. One was Villa Zebras Boys in Lisbon and one was 111 MENA in San Francisco. And what they decided to do as a cheap acoustic absorber treatment was they covered every wall and every ceiling in the entire venue, which is not hard because it’s very small, with two inch duct liner, which is cheap. And the result then is you absorb a lot of the high frequencies, but none of the low frequencies because you’re just attaching it directly to the wall. So there’s no air gap. The thing is two inches exactly wide. So it’s absorbing, it seemed to help a lot.

[00:36:48.550]
And it does help a little bit, but not in the low frequency.

[00:36:52.770]
Exactly. And so you can actually risk to make it worse by unbalancing the whole thing. And so that’s exactly true. We see it as people get the concept a little bit wrong still some people. But now there are books out here and recommendation and ISO standards. So if you can hold now the acoustic consultant responsible for what he’s doing, because he should know now the numbers that we need to get to in terms of reverberation times for various kinds of music in various volumes of rooms and at various frequencies. And so that’s why acoustics have developed immensely over the past two decades, actually. Yeah, we as audiences and musicians, everything we should say now we know that it has been uncovered what to do. So please, could you spend a few some money next time you do a renovation, please make sure that the acoustic consultant is up to date on these books and these standards and these solutions. I have to kind of just name drop a little bit my own solutions here, because the inflated baffle that we talked about in the beginning is actually ingenious. Because I didn’t even know in the beginning that we should not absorb high fringes.

[00:38:09.050]
It’s wonderful product in that sense. But then there are a number of reasons why some venues don’t want a lot of inflated baffles in the ceiling. It can look a little funny, but if it’s dark in the ceiling, it doesn’t really matter. But I’ve made another product which does the same thing. When you lower the reverberation time, push the button and you go from say, 1.2 to 0.7 seconds in some venue, let’s say that’s the two ideal reverberation times for classical music and rock concert in that given venue, then we do it correctly. We do it in the 125 horse socket band. That’s where we get that span. And we don’t absorb a lot of high frequencies in the dampened state for the rock. As we talked about before, that’s super important not to do that for the expression of music and audience. So there are solutions and there are knowledge. And so everything just points to a future where we get better sound experiences in the live concerts.

[00:39:02.630]
And let’s talk some more about this product because I know people have questions about products and how maybe they could do some of this on their own. And I know you’re recommending that people go to an acoustic consultant, but I know people are listening right now and they’re wondering what are these products? What are products that can actually help in the 125 Hz octave region? Because as sound engineers. I feel like we usually think there’s nothing you can do because you would need something that’s so big and so deep that it’s cost prohibitive. So can you talk about maybe tell a story or talk about some solutions for that low frequency region?

[00:39:42.080]
If you permanently want to lower the Robertion time in a venue because it’s just the rock venue, which is a good reason to have just one fixed Robertian time, you don’t want to have one fixed Robertion time. And how do we I don’t want to become unfriendly with all the acoustic assumes.

[00:39:56.360]
No, don’t worry about it.

[00:40:00.670]
Which is maybe not ideal, but if you use some of these, let’s say porous absorbers, so it could be some kind of mineral wool product. Don’t know about the US. But that’s used a lot here in Scandinavian Europe for acoustic treatment in offices and kindergartens and everything. But let’s remember that a kindergarten and we want to just lower all the noise. And it’s regarded noise, right? Unwanted sound in a music venue. It’s wanted sound. We pay money to get in there and listen to the sound. So we should be more careful about what we do frequency wise. But if we leave some cavity, air cavity behind from the wall out to where this porous mineral wool, for instance, is mounted, then you start to get more and more low frequency sound. It’s like a sine wave, right? If this is the wall and this is where then you have these sine waves, right? And if this is particle velocity, it’s particle velocity of sound. It’s definitely zero at the wall because the wall stops and it’s reflected. So it’s got to be zero there at the party here, a quarter wavelengths away. It’s the maximum.

[00:41:06.830]
It reaches a maximum, the particle velocity reaches the maximum, and then it comes to the zero again out here. And then the three quarter of wavelength, you have a particle velocity which is maximum again. So if I translate that into just more practical knowledge, then the farther away you get from the reflecting surface, the wall or the ceiling, then the more base frames you will get absorbed from your torus upsource. That could be a nice little thing to know. If you are going to put dry wall on some areas of the wall or the ceiling, then you could think a little bit about not mounting that flush to that wall because then it cannot vibrate. That’s the same effect of my inflated membranes, which is the tubes it shakes, it vibrates and thereby dissipates sound energy. And that’s the thing that happens with a dry wall fixed, not flush to the scene, but away from the reflecting wall. Maybe you have some joists and maybe you have a little bit of mineral wool in there. You can have some maybe do you have rock wool out there in this?

[00:42:16.810]
Yeah, I was actually going to let’s see if this will work. That’s full of rock wool.

[00:42:21.830]
Okay. Yeah, exactly. You have suspended rock wool back there and you have nicely lowered it from the reflective ceiling. So you get some low frequency absorption and you even have a thickness of that rock wall, which ensures that this very big wavelength of bass is absorbed. Because if your layer of forest material is too thin, then this huge sound wave won’t even notice. It’ll just go right through, like what’s happening in a tent. That’s why you’ll always hear the bass sound. If you have a lot of tents in a festival, you have this bass. But here, since your thickness of this material is pretty big, 10 CM slap you have up there, then you’ll make sure to actually repeat the propagation of the bass wave.

[00:43:07.310]
And engineers are comfortable with working with wavelengths. So let’s just say in imperial units first let’s do the speed of sound divided by 125 Hz is nine, so that’s 9ft, and then one quarter of that would be 2.26. So we need to ideally we would be 2.3ft away from the wall.

[00:43:29.880]
Yeah. And nobody can do that. But then, luckily, this is what I talked about, the wavelength and everything. It shouldn’t be taken to what is it, categorically. It shouldn’t be understood to categorically. It’s more a notion of the far away. So if you can have five to ten inch, seven to ten inch, seven to eight inches of cavity air cavity before you have your four inch thick Rockwell slap everybody knows, I think, but in the corners, that’s why we have corner ups over. It’s really a great place to to grab in smaller rooms, it’s really great place to grab the sound.

[00:44:07.280]
I guess I never understood that. I saw people doing that and I thought, like, why does that matter so much? But you’re saying that really does work. That’s where you want to absorb those base frequencies.

[00:44:16.060]
Exactly. You get a huge absorption cushion in the corners. So it’s like times two. Your absorption cushion is two times higher in the corners or even three up where the three meets, you’ll have three times as much sound energy. So your absorber works almost two to 3 hours.

[00:44:32.900]
Okay, neil a common question that I get, and that a lot of sound engineers have, is when they’re working, are coming in to do maybe a temporary or permanent installation in a room with bad acoustics and quotes. A common first question is should I try to do a small number of sources that are very strategically aimed and designed, or should I do a large number of sources and have them distributed so that I can get like, the speaker closer to people’s heads? So in your book, you say it is a fact that the more the PA system shoots onto the walls and the ceiling, the more the reverberation of the hall is evoked. And I know it can be difficult to generalize about these concepts. But is there a general guideline around the number of independent arrays in a sound system? Is it better to distribute many elements so that they’re closer to the audience or fewer elements? What can you tell us about this?

[00:45:25.370]
We have to be aware of one thing and that is that the number of discrete sources that we distribute also adds to decreasing the critical distance, which is a concept where beyond the critical distance you can experience reverberant sound, which is then a little bit less defined than the direct sound. And so the many the more sources, sound sources you distribute out in a room lower the critical distance and that’s unwanted. But that’s beneath a square root sign. So it’s not like twice as many sources gives twice as bad as short a critical distance. So it’s square root two. If you double that’s, the two and beneath the square root becomes 1.4 approximately. So we are fighting against at the same time as we get better directivity and better defined because we’re close to the speaker. Then you also increase the number of sources which decrease the gradient distance. So it’s damn it, we thought we had fixed it, but we haven’t quite fixed it. We have fixed it a little bit, but not quite. So it’s not as easy as that.

[00:46:29.680]
Unfortunately, there’s a great diagram in your book which maybe I can put up right now, later, if I can figure out how, which shows a sound system up with just like normal, I think, two sources and it’s going out into the audience. And then you define here’s the critical distance. And so if your sound system can only make it to half of the audience with the critical distance, then that is the reason, a justification for adding delay speakers so you can extend the critical distance all the way to the audience.

[00:46:59.270]
To be honest, I’m not an expert in sound systems and you should talk to someone else about that. I’m not a specialist on this, but I can say one thing. So critical distance is a little bit of a notion. It’s not all the critical distance, 22.7 meters than you have. But you can say one thing the lower the reverberation time in a given frequency band, the critical distance, the more, the longer, the farther away from the PA speakers you will have, the defined direct sound will be louder than the reverberant sound, which is blurry. So that’s also why that a few acoustic consultants have made a mistake and said, okay, so why don’t we make as short as possible the reverberation time. Let’s make it 0.1 or something. That’s got to be the best hall for rock music because we know this physical equation. But human beings, we are not just equations in our head, but we are our likes. And what do we like as human beings? It’s not dictated by any equation. So what we can find is that there’s this sweet spot of reverberation time. It shouldn’t be as low as possible in a venue.

[00:48:09.280]
That’s terrible. It’s terrible. You know how you get have you been in an ACO chamber?

[00:48:14.510]
You can’t stay there for too long, you feel bad.

[00:48:17.380]
Exactly. It’s a little bit creepy and you don’t want that feeling in a venue. And also the fact that especially the high, for instance, if you absorb all of those, as mentioned, then, especially on walls, that’s how we navigate as human beings. We have our ears on the sides and so side reflections from walls, what’s called lateral reflections, are super important for us to know what is going on around us. Oh, there’s a guy coming over with something. We get our cues of what is happening around us, audit cues from high frequency reflections from lateral surfaces a lot. And so also for that reason, we don’t want to dampen too much high frequency sounds. But now, we talked about the curriculum distance and this line away from the speakers. So just to say the short reverberation time is not the best, that’s the sweet spot, the ideal reverberation time for given size, volume, super.

[00:49:11.310]
So we’ve been talking about products here that especially ones that can help us in this 125 octave band. And so you sent me this report, the study that you did on this product that you’ve designed. And so right away, now, my eye is drawn to 125 octave band here, and I see that the coefficient is very high. So zero point 75. So this is really good. So tell me about this product, how did you design it and what gives it this very high coefficient in this band?

[00:49:44.310]
Oh, actually, when we talk about octave band, it’s actually the whole octave. So it’s both 160. That’s what we explained before, the mineral wool away from wall. So a thick piece of something porous absorb, which could be a rock wool slap at a given distance away from the wall. Now, this is a product where I can toggle between absorption and reflection. So this is for multipurpose venues where the next day, this is for the rock concert. You want to have this absorption cushion on a lot of surfaces because then you lower the rotation time at the lower frequencies and you will lower it less at high frequencies since the absorption cushion. So that is meticulously designed from my hand. And then you can say so, hey, Neil, you are failing because you only have 0.6 at 100. Why don’t you want to have 0.8 at 100? You could say that, and that would be true. I would love it to be one 0.8. But it doesn’t really matter so much because below 100 we are going into the 63 Horse band. And remember when I said that there’s not as much sound in there, I said the sound level is lower at 63 Hz band, but you just make a deeper construction, deeper cavity.

[00:50:58.230]
This one is exactly. And we can easily do that if some consultants are you anybody sound engineer come and says to me we need to get that 100 Hz as controlled as the 125 hertz therapy event. Then I would say no problem. We’ll just use another two inches as of your room on all surfaces. Then we’ll have that. Or we’ll put even a membrane absorber flush to the wall and then the porous absorb. Then we could do stuff like that. That’s what acoustic consultants are good at. They’ll come up with the small solutions to specific needs in a specific venue. Who knows, maybe in a venue revolution time may be rolling off already at 100 or maybe it’s twice as high. Then we have a problem. Then we would want to redesign this a little bit. But it’s super easy. It’s just making the whole construction a couple of centimeters an inches deeper. This product is the solution for multipurpose holes tuckling between acoustical settings every night. So this is for the Rock concert Tuesday night. Wednesday night you have a chamber concert with three celloes. Then could you scroll down this paper and see the this is the octave band.

[00:52:12.820]
So we go further down and see here you see the reflective mode, unabsorptive mode of the so you can imagine now we are absorbing a lot less sound in general and also in the 125 horse Arctic band. So when we absorb less sound in the room, we’ll have a much longer reverberation time. And that’s what we want for our Champa concert on the Wednesday night. Right. So somebody pushes the button or actually this is all programmed into the system. So for the whole calendar it will always have the perfect acoustics in the room for any given night in a season because we just program it for a whole season.

[00:52:56.320]
Do you have any photos or a video we could look at of the actual product? Or a room?

[00:53:01.020]
So these are the absorbers. You can see there are these rectangular holes where the sound is going for the Rock concert. So it’s absorbed in there. Then to reflect it, there are some flaps that closes and closes the hall blocks the sound from entering. Yeah, this is in a hall in Denmark. And so it’s quite simple system, but mechanically it’s not super simple.

[00:53:27.120]
The idea is simple how you did it.

[00:53:29.840]
Okay, got it. Exactly. This has been attempted many times but never succeeded because it’s not so simple mechanically to make this work. So if I can show do you think this is of interest? To show the two reverberation curves in that venue. This is a 2500 m³ venue. And so the ideal reverberation time for rock music at 125 Hz is 0.8 for that volume. And you see here, 125 volume is perfect. We calculated hot on this and use software and stuff to find out how much would we need. And it just turned out perfectly. And I should say that the punctured line here, the gray punctured line, is the venue before the renovation. So that was the reverberation time in the venue before we put the system in there. And as you can see now, we actually got a longer reverberation time when the product is closed. So nonabsorptive in the reflective state, we actually achieved a longer reverberation time in the hall. And we were all very heavily surprised because we didn’t know really what the stuff on the walls were doing. But it turned out that they were actually absorbing some sound in the entire frequency band, as you can see here.

[00:54:47.610]
And the classical professional players who have this hall also works for the Conservator in the second biggest city in Denmark, or who’s and players, they have played there many years and they came in and were just completely surprised by the change. And so the classical players like it much more now than they like. It was a nice chamber holding for.

[00:55:11.490]
Is that what the sound system on or with the sound system off?

[00:55:15.890]
The upper blue line is the reflective state of the Evoke, what I call Evoke, I call it Evoke, my new electricity.

[00:55:23.100]
But when you do a chamber concert in there, are you amplifying it through the sound system or not?

[00:55:27.630]
No, they don’t need to. It’s enough. That’s what classical instruments, they need the hole itself to amplify the sound. That’s why we want reverberation time there. That helps the sound level upwards. I just want to make a point here because these same classical musicians who were playing in the earlier hole as a non renovated hole, they now claim that it’s much, much better. So can you see here how much 0.1 2nd or 0.2 2nd change of reverberation time does?

[00:56:00.920]
No, I hadn’t thought about that yet. It’s such a small change. But it was huge for them.

[00:56:05.430]
Exactly. And that’s the point that we as sound engineers and acquisitions must not underestimate the ears of the musicians. Because if this is a huge difference for them, wow, that’s a big lesson for any acoustician out there because 0.1 2nd is a huge thing for these guys. Okay, so that also means if you think, then what would 0.4 seconds of change of reverberation time mean? So that means if you go from the upper blue line down to the new light blue line here, which is the setting of the open absorptive state of the Evoke system, then that should be even more than this 0.1 2nd change. And sure enough, this is as all the rock musicians and puck musicians who come into this venue, they totally love it. And that’s because of two things. One, we got the reverberation time at 125 to the exact spot, the ideal reverberation time for this volume. Two, we did not steal all the reverberation time at French, we left that. And that is what I. Get from this design. I do reflect enough high frequency reverberation to maintain this liveliness and dynamic dynamics in the music. That’s why I designed the product like that.

[00:57:28.980]
Some installations we do in the audio labs, so research for audio, they use this a lot because they can make these huge changes in reverberation time in the industry.

[00:57:39.050]
Like a laboratory.

[00:57:41.010]
It’s a laboratory so they can investigate. Maybe it’s a phone company who wants to investigate. Could we put some software in our mobile phone that will dereverize the signal? If the guy actually talks in his phone in the bathroom where it’s super reverberant, can we take that reverberation away digitally inside our phone to make the understanding much better at the other end of the so things like that is what they could investigate.

[00:58:12.750]
We talked about some of the innovations you’ve made and a lot of the great ideas you’ve had in this book. But what about some of the mistakes you’ve made? I’d love to know maybe what’s one of the biggest or most painful mistakes you’ve made on the job and what happened?

[00:58:27.360]
Yeah, my job has been many things along the way. And one of the jobs was, of course, going into the reverberation chambers to measure the absorption equivalents of these new technologies that I’ve been developing. And I just remember a very funny story about developing the tubes. So the inflated product, because of fire requirements, you need to use a very thin plastic. And I was in doubt, will this thin material ever absorb anything really low frequency wise? And I was in doubt just to kind of before going into finding any plastic that could maybe fulfill everything, I just made a quick little test. I was using these garbage bags that you use for gardening. So these plastic bags, it just inflated a lot of those with a blower and put into the revoltian chamber. And I got this amazing it actually works pretty amazing. Exactly. Yeah. But I have to say one thing. I got great absorption curve shan in the 63 Hz band octopus and the 125 Hz Octopus and the 250 and so on. So at that time, that wasn’t 2000 and I don’t know, six, maybe five even. I did not know where I thought the 63 Hz band was as important to control than the 125 Hz band.

[00:59:50.340]
So when I saw the results, I would say it’s great. It even worked in the 63 Hz band. And if it had not been that, I wouldn’t have carried on with the product development. But it turned out many years later that I was not able to measure the 63 spent probably in the chamber itself, but partly because of the chamber. And it could be that some people are better on measuring the we have some certified company here in Denmark. The only guys who are allowed to make a certified report, the one you just showed is a certified report from that chamber. But I was fooling around and I wasn’t very critical on my own measurements, so I thought, great, I have this great product for the 63 hearts band and 125. And then as many years later turned out, as I said, it was a mistake I couldn’t measure correctly, and I don’t think I would have carried on if I had not made that mistake. It’s not funny, really. So we got this product. Yeah. It’s weird.

[01:00:46.610]
I kept you going.

[01:00:47.840]
Yeah, absolutely. So two false right. Two false hopes. And then it canceled each other’s out and it all became fine. Because at the end of the day, we know now that we don’t need to absorb a whole lot of 63 and then IEM.

[01:01:03.900]
Sure someone else. I wonder if someone is going to try this out there. So if I fill my room with just a garbage bags full of air that will have some absorption?

[01:01:11.850]
Yeah, okay. Absolutely. For your sound studios out there, you want to try and put an inflated mattress as some of these air mattresses. You could be lucky. It has some impact in the 125 product. I know it’s very good in the 250, but it could also have an impact in 125.

[01:01:31.740]
Okay. I have a handful of questions here from my friend Michael Curtis. He’s very interested in this topic as well, because we’re both working on sound system, helping people optimize and design sound systems for their rooms, their churches, their music venues. So he says is a twelve inch deep absorption panel with six inches of appropriately dense insulation with a six inch air gap behind the most effective and most economical broadband absorption panel. I see this propagated in the studio world, but does it apply to large scale rooms? We talked about this a little bit already, and I can already say that ideally we would want more air gap. Right.

[01:02:13.450]
I think it’s a fair air gap. It was six inches. Right. Six inches air gap. It’s a very thick product. Mineral wool, we would assume it’s mineral wool. Right, yeah, it’s very thick. So because of the thickness of that, then the six inches air cap is fine because the total distance here is what counts, and there we have enough to get very low frequency. That’s fine. But I’ll say one thing, we don’t cope with the over absorption of high frequencies, which will happen because we will not absorb as much low frame. Even though it’s a very good low free broadband absorb, as you correctly put it, it still absorbs more base than high frequency. It absorbs a lot of high frequency and we don’t want to do that.

[01:02:54.310]
We need the right balance of diffusion and absorption.

[01:02:57.750]
Yeah, exactly. We should not absorb so much high frequency that this solution will do.

[01:03:02.910]
So Michael also says, in your experience, do air gaps behind absorption panels actually double their efficiency? In theory, it puts the absorption where the waves of velocity is at its highest, which we discussed, thus slowing it down the most. Does having a full depth panel work better?

[01:03:18.270]
It should be put in a way where he says, does it work better at low frequencies? Because that’s where we enhance. We’re not enhancing higher and mid frequency absorption when we make the cavity bigger. It’s just the base absorption. Which I assume he means, and that’s actually a good question. I think it has a little bit of impact, whether it’s full of porous absorption material, but I wouldn’t spend my money on that, because you have to double your investment. Investment? You don’t at all need to do that. It’s much better to just leave the aircraft.

[01:03:52.740]
Let’s see, when designing rooms, is there a cost benefit framework you can walk us through when deciding where to invest dollars? For instance, in sound system design, the longer the line array length, the more directivity we have at lower and lower frequencies, which helps us keep sounds steered towards the audience and away from the walls. You could also spend less money and use fewer boxes, but you would need more sound dampening to make up for the energy bouncing around the room. Is this something you’re able to collaborate on with the system designer for a new space and figure out can all of this be done in the ease platform?

[01:04:34.390]
Oh, I’m pretty sure it could be done in the east platform or the Odion platform as well, which is another more emphasizing on the absorption materials than the east, where the eases may be more emphasizing on the speaker systems, but I think both can do the job. And I would say if we’re just talking Taurus absorption, Rockwell, that’s not very expensive. You can get a lot of Rockwell for the price of one speaker. If you put that in a smart way in the right place in the room could be the back wall, if you treat the back wall correctly. But be careful not to over dampen the high frequencies, which you would do.

[01:05:11.080]
If you be clear about this. The back wall is behind the sound system, the front wall is in front of it.

[01:05:16.550]
No, good question. Very good. Thank you. It’s opposite the sound system. If you imagine the sound wave coming out of the speakers, let’s just imagine that all the sound is pushing through the venue, although we know the low frequency sound is going backwards as well. So then there’s a notion that we should probably very cautious about that wall where that whole sound wave hits the first, which would be the opposite end of the state of the stage.

[01:05:44.230]
In some rooms you might have a wall right next to the sound system, in which case the first reflection would be from that wall.

[01:05:49.840]
Okay, yes, very correctly. And then you got to maybe absorb some sound here, maybe diffuse would be better instead of because absorption is very often equaling. Exactly. So be careful not to over dampen the high frequencies. It’s a little tricky. That’s why acoustic consultants come in handy here.

[01:06:11.990]
What are some best practices for us sound system designers when we’re able to visit a venue first and check out the room? How can we best capture a usable impulse response? So we either do a rough acoustical model ourselves or hand off the data to a true acoustics expert and a large scale gig. We talked about this a little bit. We can measure an impulse response through the currently installed sound system. Right. So any other tips on gathering that data that we would send to acoustic consultant?

[01:06:43.550]
I would say that as we are in the preliminary phase here, it’s fine to use the PA system which is hanging there, or bring your own little PA system. That’s how I measured all the venues in this, but the 55 venues, two arena, London and Berlin and everything. I used a great sound system from one of these fantastic producers of speaker systems. And you can use the one which is hanging. I would say if you can just kind of do just one of the arrays, just not both arrays.

[01:07:17.060]
Really?

[01:07:18.650]
Yeah. I would use just one array that makes better impulse responsible. I’ve analyzed what impact is there. What does it mean whether you use the PA system or the Omnidirectional loudspeaker? According to all standards, acousticians need to use an Omni directional loudspeaker. But there’s no unique answer to that question. You can get a longer reverberation time and you get a shorter reverberation time with the PA system compared to the Omni duration.

[01:07:49.510]
We have one question from Instagram. So EJC Audio says, what is the most common, low cost or highest ROI treatment that venues miss? Don’t think about or decide against when building or refurbishing?

[01:08:06.650]
Okay, I’m going to make a great hint here, but IEM still going to say that it still needs a consultant to do this construction correctly. It’s not very expensive, so don’t, rather than doing this incorrectly oh, man. As of these building materials, because we’re talking big surfaces here in venues for several hundred people. So the cost is running up there. So the cost of an acoustic consultant is ridiculously low compared to that anyway. So in Denmark, we have these perforated chips and board plates, but I have to say, don’t use it in the venue without the use of acoustic consultant because he’ll make that work amazingly well. So that’s a great way to get great sound in rocks. But it’s just one of many products you’ve got to put together to get the final solution. That’s how acoustics work. You don’t buy a final solution. It’s building materials that acousticians and architects come together and blamed around and then boom, you have what you need.

[01:09:07.580]
Neil, where is the best place for people to follow your work? Maybe at Flexacoustics.

[01:09:15.090]
Yeah, absolutely. Flexacoustics.com is where products are DoD and available I have on LinkedIn and on Facebook, person and LinkedIn as a person. And people are very welcome to hook up with me there. I really hope you do that. That would be great.

[01:09:32.560]
All right, neil, thank you so much for joining me on Sound Design Live.

[01:09:35.620]
Thank you. Nathan has been thrilled and it’s been so great to talk to you all.