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In this episode of Sound Design Live, I talk with the Associate Professor of Electroacoustics at the University of Derby, Adam Hill. We discuss managing sound exposure and noise pollution, diffuse signal processing to cure power alley, and the effect of stages and other boundaries on directional subwoofer arrays.
- Your presentation at this year’s Live Sound Summit was called Managing On-Site Sound Exposure and Off-Site Noise Pollution. My takeaway was that you came away with more questions than answers, but there were a couple of interesting moments I wanted to follow up on:
- If I am required to measure audience exposure during my event and the regulation states that it must be measured at the loudest point in the audience, but there’s no way for me to practically keep a mic there through the show, walk me through how to set up a measurement at FOH to accomplish the same thing.
- From the research you got from NASA you wrote: Note of caution for 50-60Hz, due to chest resonance, causing whole-body vibration (annoyance and/or discomfort)? Is this something I should be watching out for with my system calibration? If there’s a resonance at 55Hz, could that unconsciously make someone feel bad?
- Can you talk about what Vanguardia and SPLtrack are doing around off-site noise pollution?
- Why is it illegal to fly subwoofers in Amsterdam?
- I took the WHO hearing test and got a 79, which is supposed to mean I have good hearing. What did you score?
- Diffuse Signal Processing (DiSP):
- While a ground-based centrally distributed subwoofer array is a common and straightforward solution, it can be impractical and unsafe in certain situations (which is a topic for another day). Often a left/right subwoofer system (ground-based or flown) is a better choice. The problem with a left/right configuration is that there will be severe comb-filtering, causing inconsistent horizontal coverage. To avoid this issue, the left/right signals must be decorrelated. Existing approaches involve unique EQ applied to each side of the PA (which isn’t great from an efficiency viewpoint) or the use of allpass filters (which generally result in a reduction in audio quality).
- I know you intended this for small rooms, but is it possible this could fix power alley for larger sound systems with uncoupled subs?
- Subwoofer positioning, orientation and calibration for large-scale sound reinforcement.
- Based on these results, it is evident that subwoofer placement directly underneath the stage can almost eliminate any advantages gained with cardioid polar patterns; the low-frequency SPL on the stage is virtually identical to that in the audience (Figure 22). Moving the subwoofers two meters forward so that they are not underneath the stage results in much lower SPL on stage while preserving the audience area response (Figure 21).
- Elliott Clarke: Is he aware of male/female hearing differences (and hearing LOSS differences), as per Loreen’s LSS talk?
- Where is the medical hearing research heading (or currently at) for dBC/music exposure (rather than constant dBA industrial noise)?
- Does he think we will reach a sensible compromise for impactful/powerful live shows, within safe exposure limits *and* environmental/off-site concerns?
- Matty Luka Sokanovic: Ask him if there is any 3D acoustic modelling softwares that you can drop your own models into! That are priced reasonably that is..
- Elliott Clarke: Is he aware of male/female hearing differences (and hearing LOSS differences), as per Loreen’s LSS talk?
Any directional low-frequency system whether in a single box or gradient or end-fire approach isn’t going to play ball when underneath the stage.Adam Hill
- All music in this episode by Liam The Villain.
- Decorrelation of Signals Demo
- Software: EASE, CATT Acoustic, Odeon
- Fear and Loathing in Las Vegas
- An audience that is in front of a ground-based subwoofer system actually causes resonances within the audience almost like standing waves and room modes.
- It’s been shown that someone having the perceived control of an annoying noise lowers the annoyance. So what they do, for Vanguardia, they create a hotline so all you have to do is pick up the phone.
- There was never a subwoofer in the air during that test.
- I’m convinced that us audio engineers are able to cheat these (listening) tests.
- We’ve come up with a way to decorrelate two or more signals that are initially identical in a way that you can’t perceive it. You shouldn’t hear a difference in the tonality, but statistically, they are decorrelated. Run those through your LR subwoofers and you’re not going to get the coherent interference that causes the difference in tonality from left to right in the audience and the power alley.
This transcript was automatically generated. Please let me know if you discover any errors.
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 the associate professor of electro acoustics at the University of Derby, Adam Hill. Adam, welcome to Sound Design Live.
Thanks for having me, Nathan.
So, Adam, I definitely want to talk to you about a bunch of stuff. We got a lot of questions, managing sound exposure, noise pollution, diffuse signal processing to maybe cure power alley. I don’t know. And the effect of stages, near gradient arrays. But first, once you have set up a sound system, what’s maybe one of the first listening tracks that you want to put on to hear something through it?
For years, my track was Broken-Hearted Road by Sonny Landereth. About a year ago, I switched over to three songs that I always listen to. One was stolen from my now colleague John Burton, which is Teardrop by Newton Falkiner.
So, Adam, how do you get your first job in audio, like what was one of your first paying gigs, first paying gig? That was my mom’s fault.
Yeah, thanks, Mom. Really, it was not on purpose that I ended up in this industry. You know, I was even at the age of about 17, 18, I was pretty convinced I was still going to be a musician. I had luckily enough musicians in the family to tell me, you know what, if you’re good at something else, you should probably do that. But it really came down to a finished high school. And my mom was like, well, you know, you need a summer job.
You need to do something. She’d already kind of pressured me into signing up for university. So I was going to do that. I was going to do electrical engineering that fall. But she said, look, you’re not bumming around this summer. You’re doing something. And she said, you do realize that you like music, you like live events. There are engineers who have to make this all happen. And I never had any idea. I never even crossed my mind that, oh, yeah, there’s a lot of people who work in this industry, but yeah, that was it.
So I thought about it and said, OK, I sent out a few emails, which especially back then I don’t think anyone checked their emails, just got nothing. But I thought about it like, oh, you know, I had been playing in my dad’s band since I was about 10 years old. And obviously we do maybe a dozen gigs or something like that. But we kept coming across. This guy named Gary Gand and Gary runs Gand Concert Sound, which is located just outside Chicago.
It’s a company that had been running since the mid 70s, still is running. And I said, oh, yeah, I know Gary. And so I asked my dad, like you, you’ve got Gary’s contact information, you know, mind calling him up and seeing if he could have a chat. So we got hold of Gary. Gary invited me over to his house one night and basically sized me up, you know, showed me a few of his guitars, asked me a few questions, see if I knew anything about sound, and then basically said, look, I’ll give you a shot.
I’m not going to pay you much, throwing you in the deep end. If you can’t swim, that’s your fault. And in a way, I went so that summer. Yeah, it was brutal. I had all the worst jobs, you know, testing about a thousand explorer cables and repainting the lift gates on the trucks, cleaning off your big analog multicar snake after it came back from a circus gig, you know. Yeah, all the good stuff.
But that’s where I started. And when I started, it was just a summer job. That was that I was going to, you know, make a few bucks, you know, maybe go to a few gigs if I was lucky and get paid for it and then go off to university and do something else. Sure. And then whenever work that’s probably almost 20 years ago now, you know, here I am. I’m still doing work for, again, concerts, sound and still involved.
That’s amazing. Your first job? One of my colleagues, Rob Lizzo, at the time, about a month in, he said very little to me the whole time. I think he was kind of saving me up from a distance. And he came up to me after about a month, just looked at me and said, You’re still here. I am like, you’re doomed now. Yeah, it’s like telling me you’re never going to escape.
Looking back on your career so far, what do you think is one of the best decisions you made to stay happy and get more of the work that you really love?
I think the best decision that I made was to stay in academia, actually, which is probably maybe not the usual answer that that you’ll get for from interviewing people on this podcast. But basically, when I ended my undergrad degree, I knew a lot about electronics, electrical engineering, and the plan was right. I’m going to go back and work full time and live sound. And I thought about it. I’m like, OK, I don’t really know much of anything about acoustics.
So I started snooping around and I found that if you go to the UK, you can do an entire master’s degree in a single year.
So I thought that was pretty cool. I’ll I’ll take a year off.
I’ll go live in the UK and learn a bit about acoustics and then come back and do live sound. So I did that. Learned a lot about acoustics at the University of Edinburgh, you know, the proper physics and mathematics behind it. And then happened to be just get in touch with this professor at the University of Essex and Malcolm Oxford, who you probably don’t know him in and live sound. People probably don’t know him, but the name is absolutely legendary and more of the academic side of audio engineering.
Yeah, he’s spent fifty years working on power, AMP designs, working and all sorts of digital signal processing routines. He’s really kind of behind the scenes, touched quite a bit of the technology we used and he convinced me to go to a PhD. So at that point I kind of had to make the decision right. You know, do I go the academic route? Because if you do a PhD, I think you’re you’re pretty much overqualified for, you know, sticking it out as a live sound engineer.
And I’d be. I’d be standing so far away, you just love it so much. OK, sorry, go ahead. But I think you’d you’d also be stepping away from the core of the industry for such a long period of time that, you know, I think it would take some time to get back into the full time groove of it. But I thought about it and said, well, you know, in the summers that I’ve spent with and still doing summers, probably about four or even five months a year full time with them working in the warehouse, going to do gigs.
And, you know, I said, OK, the gigs are great. I love those. You know, I live for that. But the warehouse work is just really monotonous. And I was getting pretty bored with it. And it just kind of said, look, you know, I’m not sure if I’m going to be happy doing this for the rest of my career, need maybe a bit more of a challenge. So the academic world seemed to fit with.
That’s where I can still kind of keep a hand in life sound. You know, to this day, I still go back, you know, at least a month every year and go work for Gand. But it kind of allowed me to work more on the research side of things and teach the next generations of engineers. So I did the PhD and then the University of Derby, which is smack in the middle of England.
If you’ve heard of the car company Rolls-Royce, that’s for Rolls-Royce is from that’s going on for they were looking for a lecturer who had a background in life, sound, understood music, understood acoustics, understood electronics and was research active. And there aren’t many people in the world who who take all those boxes. So it just it was the right place at the right time. And I’ve been with Darbee for almost nine years now.
All right, Adam, so we just wrapped up a live sound summit. Your presentation was called Managing on Sound Exposure and off site noise pollution. And my takeaway from your presentation is that you ended up raising a lot more questions than answers during this entire process. And that’s because it’s this big project that’s never been done before and you’re trying to bring together all these people in the world. And so the first thing you guys did is just like, hey, what are all the things we don’t know?
What are all the questions that we have? But there were a couple of interesting moments that I wanted to follow up on. So you mentioned that most of the regulations about on site noise exposure have to be measured at the loudest point where someone would experience that noise exposure. So I’m wondering, how do you do that? If I’m required to measure audience exposure during my event and the regulation states that it must be measured at the loudest point in the audience.
And I’m not going to somehow, like, figure out how to get a microphone into that mosh pit, then walk me through how to set up a measurement, a front of house that could accomplish the same thing.
Well, in practical terms, I’ll talk about what’s possible at the moment and most software, most bits of software. And I’m thinking Tunisie or Tennesee within smart or, you know, the stuff Smart’s working on, kind of separate from Tennesee. The terminology will differ between the software, but it’s a correction factor. You add in to your measurement feed coming from the microphone. So what you can do is before anyone gets there to the gig, you can walk around the venue with the sound level, meter, whatever you have handy.
Hopefully it’s calibrated ideally and you identify that loud as part of the audience, wherever that may be, and take a measurement and then keep the signal going through your system the same and go to front of house where your measurement location is actually going to be during the show and take a measurement. The difference between those two sound pressure levels, that’s your correction factor. You plug that into the software and then it gives you the best possible estimate for what the level is during the show at the loudest location based on your front of house measurements.
So I’ll say it’s imperfect because what that doesn’t take into account is any affects of the audience. So high frequencies, the audience will provide the absorption, low frequencies. There’s been some really interesting work done by Elayna Zabbaleen, who’s now at dB, where she found that an audience that has that is in front of a ground based subwoofer system actually causes resonances within the audience, almost like standing waves and remotes. OK, so you may get some, you know, a couple of dB difference throughout the audience at low frequencies.
So you’re not going to pick up on that with your correction factor. But it’s a quick and easy way of saying, OK, give me an estimate of what’s going on. At the loudest point, if you look at the regulations, that’s what they recommend. But it’s a frequency independent correction. It’s not looking at active bands or third active bands. It’s just one overall dB or dB measurement. And that’s it.
OK, so let’s talk about NASA. This is kind of fun from your research that you got from NASA. You wrote that.
Well, I’ll just read what you wrote. Note of caution for 50 to 60 hertz due to chest resonance, causing whole body vibration, annoyance and or discomfort. So is this something that I should be watching out for?
With my system calibration, let’s say if there’s a resonance of fifty five hertz, could that potentially cause some, you know, uneasy feeling unconsciously in in my audience and should I, like, try to avoid those resonances?
I think at the moment, as a designer, it’s not something that you need to do anything about because there’s still too many questions that are unanswered about this. I can tell you from experience when I’m tuning system and I walk right up to a ground based subsystem and I’m right there standing in front of tens of meters worth of subwoofers. Yeah, my eyeballs are rattling, my teeth are shaking. I can’t see straight. And I’m convinced that everyone will have a slightly different reaction to this.
You know, it just might be I have a certain reaction because the proportions of my body are a certain way. Someone else is different. Sized to me might be different. So I don’t think it’s a one size fits all sort of thing. And I quote the NASA research because that’s all we have to go on right now. There’s just not anything out there on the level of low frequency we’re being exposed to. There’s plenty on lower level, low frequency where they say, oh, you know, it’s not a problem because you’re talking 60, 70, maybe 80 dB.
We’re not talking 60, 70, 80 dB. We’re talking front row of the audience, getting on average between 120, 130 dB. See, at peak, we’re exceeding 140 dB. See, and the only people who have even started to look into this is NASA.
Can you talk about what Vanguardia and SBL Track are doing with off site noise pollution? I just thought this was really interesting and I thought, you know, people should know about it since they’ve been doing it for years and it sounds like they’ve had some success with it.
Well, it’s it’s something that once you hear about it, you’re like, oh, yeah, that makes a lot of sense. Vanguardia and dB control and the guys that SBL track. So I should say Vanguardia and SBL Track are UK based companies and dB control is based in the Netherlands. So if you’ve done any sort of festival work in those areas, you’ll know these guys. But their main method of attack to minimise annoyance off site is actually communication.
It has nothing to do with engineering the sound system or, you know, telling the engineers to turn it down constantly. I guess the first thing they implement is a communication protocol, and that’s communication with all stakeholders involved in an event. So they bring on board the people who are managing the event, the system designers, the sound engineers, even in some cases the musicians, depending on what the event is, but also bring in the local community.
And that’s really the important bit, because in the run up to the event, they can distribute flyers or send out some method, find some way to alert the local community that, look, there’s an event that’s happening. This is when it’s happening. This is what we’re doing to limit the noise coming to your place. And if you have a problem, here’s how you can get in touch with us in the run up to the event and during the event.
And it’s that during the event method of communication that I think is really helpful because you’re sitting in your house and let’s say your neighbors are having a party next door. You know, the thing that probably drives you more crazy than anything else is that you have no control over that, aside from angrily pounding on the door, you know, and, you know, making a war with your neighbors. You don’t have control over that sound. And this is backed up by loads of research, really, where it’s been shown that someone having the perceived control of an annoying noise actually lowers the annoyance.
So what they do is they pour Vanguardia. They allow they create a hotline. So all you have to do is pick up the phone, call this number and say, look, here’s where I live and it’s too loud, it’s annoying. And they’ll say, OK, great, we’re going to contact the people in control of the sound and we’ll get this sorted. Now, whether they do that or not is almost irrelevant. Sure. Because you’ve told someone who has control over this.
And so in your mind, it’s going to be sorted. Even if it’s not, it’s all psychological and therefore kind of taking it a step further. The guys at SBL Track, which is run by Chris Beale, they’ve created an app that any local residents can have on their phone free to download. And if they have a noise complaint, they send a text message. It pings the crew at front of house and they see on their display where on the map it’s coming from and the message.
And if the front of house engineer wants to reply back, they can text right back. And there’s that direct line of communication. But it’s the same idea. It’s giving people the perceived control over the sound. And in almost all the cases, it is significantly lowered complaints.
Why is it illegal to fly subwoofers in Amsterdam? This this is a very frustrating story. What happened was as if you’ve ever visited Amsterdam or if you live anywhere near Amsterdam, you’ll know that over the past maybe 10 years, there’s been an explosion of outdoor music events there in the summers. It’s just one of the places to be for a good music festival. And they do loads of good events outdoors there and indoors for that matter. But the city of Amsterdam, again, if you’re familiar, is not the cheapest of places to live.
So if you’re living in central Amsterdam, you’re paying a premium to be there and you’ve probably been there for quite some time. All of a sudden, with all these events popping up, you’re having some very annoyed rich people. And so they’re going to the city saying, what are you doing? Well, I can’t live in peace here anymore. You know, sort it out, fix it. So what Amsterdam did was they said, OK, we’re going to learn more about this.
So they didn’t just slap a regulation on it. They said, we’re going to learn some more about this. We’re going to figure out what we can actually do to have both sides of the situation live in harmony so we can have the festivals while also keeping all our rich rich residents happy. So they got in touch with the local audio firm who does system design as well as research and product development. And they know their stuff. And they said do a study and tell us what the best available techniques are for system design to minimize noise pollution.
So they trailed a bunch of different systems. They found this big field just outside the city. They took loads of measurements. It was a fairly well constructed experiment as well as any outdoor effectively shoot out as well as it could be designed. And they tracked the weather and all that sort of thing. And then from the data, tried to draw some clear conclusions. And what happened was that one of their conclusions was saying if you fly subwoofers, the sound propagates further and causes more noise pollution.
And they see me to point out that, yeah, that’s what our data showing. And so I looked at it and there are a number of other people know colleagues who are working on this as project looked at it as well, critically looked at the data and said, well, we can’t see that. More importantly, we looked at what systems they tested and they didn’t testify, for example, first, that there there’s never a cell before in the air during that test.
And the argument was that, oh, well, we used the Dask system, which goes down to 35 hertz. And so I pulled up the old Vidor’s documentation of how something comes out at 35 hertz, but it’s, you know, whatever, 30 dB below everything else. And so the data, they didn’t have good enough signal to noise ratio on their data to give anything conclusive. Although I’m not knocking the whole report, I think there were some really good observations made in that work and know it’s not slating the whole thing.
But then that one specific area, they draw a conclusion where a conclusion should not have been drawn. Unfortunately, what happened was that that was the conclusion Amsterdam took that and said, oh, OK, I can’t fly subwoofers because those send the low frequencies really far. And they said, fine, that’s the new no fly zone. Subwoofers, the end. Wow.
I’m also just impressed at how quickly and almost like efficiently they were able to make that happen. Normally it seems like any anything else we try to get done for the auto industry is takes forever and is a big hassle.
Adamu, like the World Health Organization hearing test app, I tested it out as well. And it’s interesting, instead of your normal test that has some sign tones at different levels and you see if you can hear them, this one is just a recording of a person reading numbers with different amounts of relationship to background noise and then you get a score. So I took the test. I got a seventy nine, which is supposed to mean I have good hearing.
So what did you get.
I got an eighty six. Oh, but there’s a big but there. I know my hearing, especially hearing and noise is not an eighty six out of 100. It’s not. I’m convinced and I’ve had chats with a lot of people who were kind of very closely involved with hearing health. I’m convinced that US audio engineers who are trained to listen critically are able to cheat these tests. We’re not we don’t fit the the kind of forum of the general public or general people that unless you’re admitting that which is which is why you got higher score than me.
Well, yeah, but I couldn’t avoid it. It’s you know, it’s we critically listen, our job is to pick out these little yellow, unrecognizable details and audio that no one else will hear, because I know, you know, that’s my big bit of hearing loss. It’s not revealed in terms of frequency loss. It’s hearing a noise. And if I’m in a busy environment trying to hear a conversation, I really struggle. And it’s called hidden hearing loss.
And it’s something that’s less easily tested for. But so I think the test is useful and interesting to take. But if you’re an audio professional and a good critical listener, I would lower your score probably by about 20. Oh, wow.
OK, shit. And maybe I don’t have flittering as I thought.
So, Adam, you love talking about diffuse signal processing. If you look up Adam Hill in the a library journal, there are a bunch of papers on this subject. So to dive into it, I’m just going to read this paragraph from your website so you don’t have to explain it all again. And I just I kind of want to talk about the practical implications of this. OK, so here’s what you wrote. While a ground based, centrally distributed subwoofer array is a common and straightforward solution, it can be impractical and unsafe in certain situations.
Often a left right subwoofer system, ground based overflown is a better choice. The problem with left right configuration is that there will be severe combe filtering causing inconsistent horizontal coverage. To avoid this issue, the left right signals must be dB correlated. Existing approaches involve unique.
You applied to each side of the PEO, which isn’t great from an efficiency viewpoint or the use of all past filters, which generally result in a reduction in audio quality. And so I’m just wondering, could this fix Power Alley for large sound systems? I know you have a design for your thinking. It’s intended for smaller rooms, but what about you uncoupled subs that we that we use on shows to correct one point?
It actually is designed for big systems. That was the initial intent. It was actually kind of an extra application that I just dreamed up with my PhD student, John Moore, who did a lot of the work on this to test it in small rooms. But yeah, to go to your question, yes, it can deal with power early and deal with all the kind of notches in the frequency response you get along with it. Basically, without explaining the whole thing.
You can follow the link to my blog to kind of get the full in detail explanation of how it works. But we’ve come up with a way to correlate to a more signals that are initially identical in a way that you can’t perceive it. So if I’m turning the Decorrelation on and off and you’re just listening to the signal over headphones, you shouldn’t hear a difference in the tonality at all. But statistically, then those signals will be correlated. So the idea is that run those through your left are left right subwoofers, and you’re not going to be getting that coherent interference that causes the difference in tonality from left to right and the audience and will then not cause the power rally, which is that big bass buildup you get right down the middle of the audience.
So that really was the initial focus of this research. That’s what we wanted to solve. And I’m fairly confident we’ve come up with an algorithm that can do it.
Oh, cool. So how long before we can get a demo from you? That is low latency.
It’s on my list of things, not just a question of when to get around to it. I, I know what needs to be done and I’m I’m pretty confident that it can be done. I’m shooting for a few milliseconds latency at the moment. We’re looking at thirty, forty milliseconds which isn’t going to work for life sound. So that’s the last thing on the list really. I’ve been having informal conversations with people in industry manufacturers about it and implementing it.
Nothing concrete at the moment, although there’s a completely different application then I can’t talk about at the moment on the other side of the world. Yeah, secrets. But it has nothing to do with live sound. It’s it’s a completely off the wall application of it. So it’s getting out there. And to be honest, I mean, looking at my email inbox, I’m at least getting one or two messages every day from someone in the industry saying, hey.
I’ve heard you’re working on this one. Can I have it? So, yeah, there’s the demand, I think there and I think enough engineers are open minded enough about taking this approach, because let’s be honest, what we’re doing is we’re messing up our signals to make it better, to make the listening experience better, which I think for some people doesn’t quite fit too well.
Sure. And that actually makes me a little bit more happy about it, because let’s imagine that it’s available already. There’s going to be plenty of people who reject it, and then there’s going to be plenty of people who see it as like that. Now, this perfect solution, which I think is cool, you know, and so then those early adopters are going to go out and test it out and eventually we’ll find out, you know, if it’s going to be accepted in the long run.
Yeah, that’s it.
So I’m hopeful with it. I think it’s something that at least needs to be tried in the industry.
I want to mention one more application that you and I talked about previously. So I showed you my main subelement alignment calculator that I’ve been working on. And then we got into talking about this decorrelation of signals and it came up that you could use this in just the tiny crossover region between these two boxes, between main and sub. And so if you just correlated that tiny area, then you could potentially stop worrying about main subelement. You would still want them to, you know, arrive at the same time and not like cycles and cycles late.
But it could save us from some of the more drastic effects created from bad means of alignment’s.
Yeah, if you focus this decorrelation on the crossover region between your mains and your Celebes, which is entirely possible with diffuse signal processing, it’s you can be frequency selective or you can apply to all the frequencies. Doesn’t matter. You can choose. But if you just focus on the crossover region, that’s the area where you have a huge amount of problems, especially if you have ground based cell buffers of getting the mains and the subs to play ball. And you’re looking at some of the line arrays out there these days.
They’re going down to 50 hertz or below. You know, they’re definitely kind of moving well into the subwoofer range. So you need to sort that out. And if you can correlate those two elements in that specific frequency region where they overlap, then time alignment is less critical. And we talked about it earlier. But I’m not saying that you shouldn’t timeline. I think you always are going to have to timeline. That’s really the name of the game of system design, but it makes it a little less sensitive.
So if you’re a little out in certain areas, you’re not going to be getting massive peaks and dips in the frequency response. Sure.
This is the sort of crossover alignment is that, hey, you can only be aligned in one point, so why do it at all? You know, doesn’t does it make a whole lot of sense? Because then you never know really where you’re aligned and where you’re misaligned. But it sounds like it would then allow you to make that alignment work for a much larger portion of the audience.
That’s the idea. These days, everybody sees this and things feel different and people go home and everybody sees how many people listen as we reminisce. Let’s talk about subwoofer positioning. So I wish we had time to dive into a lot more of the writing and research that you’ve done. But I picked out this one that was interesting for me called subwoofer positioning orientation in calibration for large scale sound reinforcement. So part of the study was looking at how stages affect the predictions that we do in our modeling software and then how they should how our sciberras should perform in the real world.
And one of the things you wrote is based on these results, it is evident that a subwoofer placement directly underneath the stage can almost eliminate any advantages gained with cardio polar patterns. The low frequency SBL on the stage is virtually identical to that in the audience, moving the subwoofers two meters forward so that they are not underneath the stage results in much lower speed on stage while preserving the audience area response. So this is interesting. What I’m taking away from this is that particularly is is it all directional rays are just gradients of a phrase, don’t work under the stage, don’t have the same result that we expect, and to get them to work as we expect, they need to be at least two meters away from the stage.
Well, the paper that you’re talking about, that was from about 10 years ago and the findings presented in it were purely based on simulations. Now, the good news is that since then this has been tested. I had an undergraduate student a few years ago do these tests, so we put a directional subwoofer on its own, took some measurements around it in the virtual state while the stage area, the pretended stage area and the audience, and then plopped a stage on top of it and see what happened.
And the results from those experiments almost perfectly lined up with the simulations. And that was a single unit that was cartload that basically turned into an army directional unit when a stage was placed on top of it, when you kicked that unit out by about a metre in front of the stage. And then we tested it with even less and the effect was about the same. It regained its cartload response. So from the research that research and other smaller experiments done by myself and others, any sort of directional low frequency system, whether it’s in a single box or whether it’s a gradient or an end fire approach, isn’t going to play ball when underneath the stage.
So you have to get it out as much as you can in front of the stage. Now, whether that’s a metre, two metres, half a metre, as long as it has some sort of breathing room, then it has the ability to achieve the cartilage response. If you chuck it under stage, there’s no point having to do it. It’s going to be IEM.
It’s interesting to say that because I recently heard a story from Mira Ramirez talking about how a student had a question about this at a seminar he was teaching in Iceland. And so they decided to put a gradient array on a dolly or wheels somehow. And then they had a rope and they were able to, like, measure it and pull it closer towards I think it was a boundary I came in for as a wall or a stage. And until they saw the results change in front of the array.
And it was when they got close to a meter that they started seeing the results change. So it’s cool to to hear you’ve had.
And I’m glad you mentioned the boundary effect as well. I mean, this is something that’s been known since the 1950s with Richard Waterhouses research. You know, we’ll know the Waterhouse effect. At least some of us know where you get towards a perfectly reflected boundary. You get plus six dB in some cases. But if you read his research a bit closer, he also looks at dipole units where his version of a dipole unit is basically ah, and fire cardioverter without the delay, I should say, gradients.
No, don’t fire a gradient. Turei Without the delay, just the reversal. And what he found was if you back this up towards a wall, it just kills your output in front. And I’ve had this happen to me before, years ago with my colleague Adam Rosenthal. We were doing a gig at the Auditorium Theatre in Chicago and we were using Naxos 18 subs at the time. So cardio boxes and the only place we could place these were right in front of the proscenium.
And so it was right up against the wall. We flip the switch with the system. There’s no I’m just looking at the amps and the amps are slammed like there’s definitely electricity coming out of these things. But we were getting nothing acoustically and we thought about it. And this was still early on in my career. I didn’t have like a proper, proper knowledge of it, but just through experience. And we turned off the rear drive unit, the it became nominee, and all of a sudden, boom, you had left once again.
And a number of years later, when I was learning about Waterhouses research and I’m reading through his paper like that, yeah, that’s what happened.
We had heard stories too close to the wall and it was canceling itself out effectively. What happens is the direct sound is canceled by the reflection off the wall. So it’s the same thing, which is why even when I have my subs out for a ground based system in front of a stage, I have to battle the staging people to not put a stage skirt up. And this is my welcome to my world in the summer and the Chicago festival scene.
You know, one day I’ll take down the stage skirt and have a talk to the staging people and say, look, you know, my speakers aren’t going to work right off that stage skirts right behind the skirt, does it? I’ll take it down. Yeah. Yeah. If it’s not acoustically transparent, look at the same thing. It’ll destroy the cardio subs. And the next day I rack up to the site for day two of the festival and the stage will be back up because it looks like to.
I know. I’ll fix that. Yeah. So it’s part of my routine. Every morning I have to go take off the stage skirt again. So my subs work. But yeah, it’s stage skirts are also really important to keep an eye on because if they’re right up against eukaryotes, I don’t know which they described as acoustically transparent though I got to test them all.
I talked to John Burton about it because John has wanted to do a test not only on this, but he wants to know what happens to this scrubbed material when it gets wet. And I’m sure a lot of people have experienced that when it starts to rain. I’m not talking about subs now. I’m talking about the banners that get flown in front of our eyes. All is well and good until it rains and all those tiny little holes fill up with water.
So John wants to do a big study on this, not only for low frequencies, but for the high frequency effect or just do in the morning or, you know, water in the air.
Yeah, yeah. So my answer is, I don’t know. But I know the stage skirt’s used at the fest’s I work in Chicago are not at all transparent. They’re sheets of plastic. OK, so they need to go.
We have a couple of questions from Facebook. Elliott Clark says, Where is the medical hearing research heading or currently at four dB music exposure rather than constant deba industrial noise? So I guess what he’s referring to is that so many of our regulations refer to dB standard, right?
That’s right. All of them referring to dB standard with most of the industrial noise, will have dB limits as Peake’s. So in terms of the research for our sector, for a music based noise, as far as I know, there is little to no research.
There are some interesting projects that are more in the early stages in the Netherlands looking into this, looking into the health implications of low frequency sound as quantified by dB. The guy to talk to about that is Marcel Cuck from dB Control. He’s currently part time doing a Ph.D. at a university in the Netherlands looking into this.
So he’s really, as far as I’m concerned, at the authority on this at the moment. But he’ll be the first to tell you that we don’t know much. There just isn’t the research. And when Marcel and I and others from the live event community travel to Geneva and are at these meetings at the World Health Organization, it’s about four of us in a room of about 50 people. And we’re the only ones who really seem to have any clue as to what we’re really talking about when we’re talking about 140 dB at low frequencies, I think most people don’t believe us.
We get some eye rolls. We get some distinguished professors from Europe kind of basically pooh pooh the whole thing, saying it’s not a problem. And really we’re saying, look, we go to these events, we work there. We’ve stood there in the audience. And, you know, we refuse to accept that this is perfectly safe. But at the same time, I can’t sit here and say anything definitively. I can’t say that’s definitely dangerous, but I can’t say that it’s definitely safe.
I’m saying here are all the questions and we need to do more research on it.
So Elliott would like you to continue to extrapolate into the future concerning the safety, he says. Does he think we will reach a sensible compromise for impactful, powerful live shows within safe exposure limits and environmental off site concerns?
At the moment, there are two separate things what’s going on with the show is purely looking at sound exposure on site. They don’t consider and make it a point now to consider anything off site because that would get messy. And that’s pretty much my answer. It’s going to get messy. What I hope and having gone through this work with a US and kind of releasing this big report with sort of what we know and what we don’t know, I’m fairly confident we can achieve the levels we want to achieve and the impact we want to achieve at live events.
I don’t think we’re going to be coming out and saying you have to turn everything down. I hope we don’t have to say that because I like loud sound more than most other people, probably.
But I think it will be causing maybe some slight changes to practice, for instance, when you can try to fly yourself Bofors instead of putting them on the ground or at the very least try to maximize the distance between any loud speaker and the closest audience member. So you don’t want to have someone yell within arm’s reach of any loud speaker know, especially looking at the subwoofers and air front fills their close, but they tend to be at a lower level anyway.
So you can make that work, but effectively it’s protecting the people closest to the P.A. That’s the main thing. And if you can maximize the distance they are away from the closed speaker, that means you have less to worry about and then you can get the level you want to front of house without killing the people out from up front. And that’s the main thing. So I think there’ll be some suggested changes of practice were practical for off site. I think there’s more research to be done along the same lines of what they did in Amsterdam, but just doing slightly more controlled and in-depth experiments to make sure that your conclusions are are robust.
But again, this is what we try to kind of hammer home with the WHL. We think that it has to start with system design. And what we’re trying to avoid is regulations coming out and then causing us to scramble to meet those regulations. What we want is for the discussion to start with finding the best practice for system design and then craft some regulations around that. So that’s what we’re looking for.
But I would really hope that none of this actually impacts the exciting live event experience that we’re delivering to people on a daily basis.
Is looking for some software suggestions. So they say ask him if there is any 3D acoustic modeling softwares that you can drop your own models into that are priced reasonably, that is. Define recently, yes, I wrote back to him on Facebook and said, do you mean like different than something like your eyes? And he didn’t write back. So I’m not sure what exactly he’s looking for, thinking of. But maybe you could just list a couple of your favorite software that allow you to bring in models from the outside.
Well, for what we do, which is electroacoustic, it’s designing sound systems and putting them in an acoustic environment. As far as I’m concerned, there’s only one accurate piece of software out there right now, and that’s is is brings in the proper loudspeaker data from the manufacturers and gives you, from my experience and talking to the others, the most accurate estimation of what that sound system will do in that room. You also have Cat Acoustic, which I’ve used a little bit, but I lost interest because it doesn’t go down to the low frequencies nor disease for that matter.
And you have Odean and Oden’s really great for pure acoustics and designing kind of great concert halls. But you really I find myself I keep going back to ease, and that’s what I teach my students with because they are the most accurate with loud speakers. But it’s going to cost you it is expensive and that’s you can’t really avoid that. As far as I know, there’s no free software out there at the moment that that does kind of the full package.
So a couple of short questions for you to wrap up. What’s the one book that has been immensely helpful to you, Adam?
There’s only one book that I’ve ever read more than once, I’ve only ever read one book. If it was my my teenage self talking to you, that would be a true answer, probably. No, I love reading. I’ve got bookshelf after bookshelf of books. I devour them. But the only book I’ve ever read twice is Fear and Loathing in Las Vegas, for sure. And, you know, I’m not saying that this has taught me how to live my life or anything because I think I’d be dead by now if I was following those examples.
But it taught me to laugh at life, not take anything too seriously. So important, you know, and I think that’s, you know, that’s something that you read Thompson’s work and, you know, yes, he’s he’s outraged by all these things he’s saying and commenting on it. But at the same time, he’s just being absolutely ridiculous, you know, and having fun in life. And I think that’s important. You know, we talk about these things and we’re serious about audio and all these important things, but ultimately we’re providing entertainment and we’re here to help other people have a good time.
And we have to have a good laugh all the time, really, you know, and be a little bit serious.
Adam, where is the best place for people to follow your work?
The best place is probably checking in maybe on a monthly basis to my website. My website is where once I’m allowed to, I’ll post my publications so you can read my papers. It’s usually about six months to a year delay before I’m allowed to put them up for email me and ask me what I’m working on.
I don’t know. Yeah, I’ll pull you in and you’ll never escape. Well, Adam, thank you so much for joining me on Sound Design Live.
It’s my pleasure. Thanks for having me.