Episode #22 - The Evolution of Acoustical Testing & Product Innovation

In this episode, we explore how acoustical products are conceived, tested, and refined through the lens of Riverbank Acoustical Laboratories and one of the most forward-thinking voices in acoustic design.

We are joined by Eric Wolfram, from Riverbank, and Zackery Belanger, Principal of Umbel, a Detroit-based studio specializing in shaping objects, surfaces, and rooms for acoustic performance in any material.

 

 

Adam Hritzak, Brand Champion, Catalyst Acoustics Group

Hi, and welcome to Catalyst Conversations. In today's episode, we explore how acoustical products are conceived, tested, and refined through the lens of Riverbank Acoustical Laboratories and with one of the most forward-thinking voices in acoustic design. We'll discuss how product aesthetics have evolved, how testing methodology shapes product outcomes, and what the future holds for acoustic innovation across industries.

Joining us today are Eric Wolfram from Riverbank and Zackery Bellinger, Principal of Umbel, a Detroit-based studio specializing in shaping objects, surfaces, and rooms for acoustic performance in any material. Zackery brings deep experience across the built environment from products to concert hall design, and is widely recognized for his research, teaching, and his influential essay, Acoustic Ornament. Now let's move on to today's conversation.

Eric Wolfram, Laboratory Manager, Riverbank Acoustical  Laboratories

Hello everyone, my name is Eric Wolfram. I'm the Laboratory Manager of Riverbank Acoustical Laboratories. I'm also the current Chair of the ASTM E33 Committee on Building and Environmental Acoustics. With me today is Zackery Bellinger. Zackery, tell me a little bit about yourself.

Zackery Belanger, Acoustician, and Principal of Umbel

Hi, Eric. Yeah, really, really nice to be here. I'm an acoustician, and I also get into research and design. That's it in a nutshell.

Eric

So, Zack, how did we first get connected?

Zackery

That's a great question because it was a while ago. I think I was going to Riverbank before I met you. And I feel like we might've crossed paths somehow in the Chicago acoustics circles. I definitely remember when I met you when you became the director at Riverbank.

Eric

Yeah. And I remember you were bringing us a lot of very interesting, unique, like felt sculptures and really just creative, acoustical treatments. And I, the way I remember it, correct me if I'm wrong, but you were early in that, in that world, the world of, you know, the felt, suspended objects and sculptures.

Zackery

Yeah, I think so. I should be careful because I am not an expert in the work of everyone else. Whenever you dig deep into these things, you always find that somebody else was thinking about this before you were. But yeah, I would say that I was really drawn to the elements that affect our rooms that also have a really high visual impact. I've always been drawn to that as opposed to the things that were being more hidden or more minimized.

Eric

And then that felt fixture phenomenon exploded. At this point, it's everywhere. I like to go to NeoCon in Chicago, and there's a number of companies that are doing that, and they're just really beautiful, creative designs and things like that come out of it.

Zackery

Yeah, I mean, even in my career, it's been about 20 years, I think, that I've been doing acoustics, but the explosion of felt in that world has been really amazing to watch. I think there's a number of things that probably came together all at once for that to happen. In particular, the visual aspects of it, it just seems like people are ready to start seeing more colors, more sculptural forms, things that are more visually interesting.

But I could turn that around to you, too, because you're the one who sees the products coming all the time through the laboratory, right? So, did you see this definite rise of more colorful, more visually interesting things coming through?

Eric

Yeah, definitely. The early, so I've been running the lab for maybe going on 13 years now. So, in the early times, you know, office screens, ceiling tiles, fabric-wrapped wall panels, and we still see those things. But that was the bread and butter. That was the majority of things that were coming through were some iterations of that, and then you had other creative designs and phones and things on top of that. And the way I remember it is you were early with the felt designs, which was really interesting. It's unique and has the creative aesthetic, the visual aesthetic to it. And then we started seeing a lot, a lot of felt come through.

There are challenges to it from the lab's point of view. The installations can take a little bit more time. They're a little bit trickier to assemble and install. But maybe on the positive side, there was infinite variation, which is positive for the lab when there are potentially infinite types of configurations to test.

Zackery

Yeah, absolutely. And I can see that, as compared to laying tiles in the ceiling grid, which, as you mentioned, is still there, and I think a lot of acoustic products are still from that era of the gridded ceiling or the hanging wall panels. And it's nice that, that part of the product industry is still seemingly strong because from the standpoint of an acoustician who just wants our, our buildings, our architecture to sound better. The more options that interior designers and architects, and building owners have the better, as far as I'm concerned.

Eric

And so, your relationship early on with the company that sponsored your work was, so you were not directly an employee, you were working as a consultant, which I thought was a very interesting and kind of pioneering thing too. A lot of acoustical consultants kind of point towards architectural design and or building acoustics, noise control, know, kind of serving the project of a building. And I think you were looking at serving a product manufacturer, and they're helping them answer their questions, helping them understand the impact of their products on the space, and helping their customers to make sure that what they were installing would work for them.

Zackery

Yeah, in that sense, I've never really stepped outside of the role of consultant. I've never been an employee of a manufacturer. And I think a lot of the consulting world stays away from working with manufacturers directly simply because they need to maintain an unbiased approach. If they simply put, if you want your client as a consultant to know that you don't have any stake in any particular product manufacturer, the best way to do that is to just not work for any product manufacturers.

But I didn't really plan this out, but it just kind of happened that way, through meeting people and networking and life in general, I noticed that some manufacturers really do want to understand their products better. They want to develop products with the input of a consultant. And so that has really organically turned into a big part of the work that I do and the work that my team does because we just have seen this great need for it.

And we do have to be careful about it. You have to do it with integrity. You have to be honest with the manufacturers that you're not there to sell products. You're there to help their products be successful in their application.

And I think that with the right manufacturers, that's actually a really nice, that's a really nice arrangement. You have to tread carefully, but I think it's important work.

Eric

Yeah, so let's talk about what we've seen the evolution of these acoustical products. How have you seen things change over the course of your career?

Zackery

Yeah. The primary thing is the visual aspects. mean, it really, when I look back, it's like, you could say that the first decade was dominated of my career, which would have been the aughts, or the 2000s. The first decade of my career was really, I think dominated by a lot of the more traditional acoustic products, which we've mentioned, ceiling tiles and hanging wall panels, a lot of fabric-wrapped fiberglass panels, that sort of thing. And, then felt showed up.

Eric

From an acoustics point of view, acoustical ceiling tiles, fabric-wrapped two-inch thick wall panels, are excellent. They performed great. They did the job perfectly.

Zackery

Yeah, they still do. They're still an option, and some people still really like them. You know, they have, especially if they're done carefully and with an attention to detail, they can be very, very nice solutions. But then all of a sudden felt shows up and a PET felt in particular. I don't really know the history before, but before this, but in, in about the second half of my career, the teens, I just started seeing it everywhere. And I think that it's been really good for the acoustics industry. Not only are more people sending stuff to the laboratory, like Riverbank, but I think it just really opens up the design possibilities because if your goal is to minimize or your goal is to hide that which changes the sound of our room, you're going to have very limited options, and you're going to resist those options.

But if you embrace that you're going to see it and you have options that are visually interesting, then it just really, it just really opens up the possibilities. It's been a really nice change. It's been remarkable, and it gets me very excited about acoustics in general.

Eric

There was sort of, I don't know if it was like a meme in the 2000s that every restaurant, you know, was renovating and just the interior designers were just so excited to be taking out the acoustical ceiling tile, right? But then they had this problem. And one of the things I've said is one of the positive sides about that era is we stopped having to explain why acoustics was important because they were doing such a bad job of like building these like kind of nasty reverberant restaurant, so everybody knew, everybody already knew this was a, there was a need for something in here to absorb sound and then cue like all these new types of products that gave the designers and the architects something they liked to look at, but then also performed well.

What are you seeing in terms of, you know, we talked about the advent of the felt and the felt fixtures, but how has that evolved over time? Maybe even in the last five, 10 years, are there trends or changes there?

Zackery

Yeah. What I'm noticing is that acoustics is starting to integrate into other product realms, let's say. And also, there's a lot to talk about when it comes to the non-product realm, but I think this track about products is a really good one. For instance, lighting, the integration of acoustic performance into lighting is extremely new. And it is something that I think, in retrospect, was obvious. It's kind of surprising that it took as long as it did for it to happen. But now it's a major product sector. What I want to make clear here is that I don't think of something like acoustic lighting as being attaching acoustic products and materials to lighting and really just adding those two things together.

When you really start to get into what's happening in a room, the physics of it, you find out that every element in a room, whether it's a light fixture or a chair or a plant or a book, every element in a room has an influence on the acoustics of a room. So already light fixtures were influencing acoustics, and it was probably just a matter of time before, the lighting designers started to ask, how might we evolve this? How might we design lighting so that it has more and more influence, and eventually it pushes into the category of acoustic product?

So, I think that view is important to recognize because I think we'll probably get to this a little later, but it forecasts or foreshadows where acoustics is going. When you think about the fact that everything has these properties.

Eric

I remember the first time I heard, ‘test some acoustic lights’. The what now? Yes, it's a real thing. And they're super creative in the way they integrate lighting elements with a texture of acoustical materials.

Zackery

And I would like to add something else while we're on it, which is that I think there also might be something of a reckoning happening with acoustic products being part of the solution, because one of the really great things about acoustic lighting is that there's another reason to have these objects in your room. And so, you can design for your lighting needs for your lighting layout. And then a lot of acoustic benefit comes along with that.

But it doesn't necessarily mean that all of the acoustic benefit comes along with it. So, then you've got lighting manufacturers also making unlit baffles, and you've got designers reaching for multiple product lines and mixing them together, which is really interesting from a design perspective. And so, when you start to merge acoustics with other realms, with other functions, you sometimes have to admit that you aren't going to necessarily get it all in the same place. And that also feels like a very healthy trend to me.

Eric

Yeah, that's an important point. And it's kind of related to the whole movement with Array NRC. Early on, through the ASTM E33 committee, we developed a new approach in this test method, ASTM C423, which allows us to create a single-number rating for arrays of suspended objects. There was resistance and pushback at this originally because there's a fear that if we give baffles an NRC rating, if we give acoustic lights an NRC or baffle arrays an NRC rating, that someone will assume we can pull down that NRC 0.85 ceiling tile and then put up an NRC 1.15 or 0.95 acoustic light fixture, a single pendant or four pendants, and that this would be an improvement.

What was sort of lost in that single number rating was just an understanding of it as units of sound absorption per unit area. And one of the things I worked on over the last few years is trying to educate and raise awareness of this. It's not really necessarily the percentage of sound absorbed, although that is a helpful way of thinking of it. It's not wrong, but maybe a next-level way of thinking of it is units of sound absorption provided by this object or set of objects per unit area. And that's exactly what we're doing when we publish Array NRC in our test reports. Now, Array NRC makes a lot of sense for certain things.

Whenever we're creating kind of a false texture, a false surface with a set of suspended objects, Array NRC is perfect. It's almost obvious that that's the right approach. But there are other types of things, other types of treatments. We talked about acoustic lights, pendant lights, and where it's still not a surface. It's still not a plane by any stretch of imagination.

As a consultant, what's been your experience with Sabin’s per object versus array NRC versus the struggles out there in the field?

Zackery

Yeah, by the way, congrats on the Array NRC thing. I know that was a lot of, was a long time, a lot of work and a lot of effort went into getting that, launched and yeah, what I've defaulted to, I, one of the other nice things about working with manufacturers is that I, have a lot of opportunities to talk to architects and interior designers, and I have found myself really just taking the education side of this really seriously. And I'll straight up tell an architect or an interior designer that NRC was a terrible name, noise reduction coefficient, way back in the 20th century. We should have just called it absorption per square foot. I tell them that, and of course, we could debate that. It's just that the name NRC does have some connotations that are easily lost in the design process, and people tend to just think of it as a rating where higher is better.

And you're absolutely right, that per area part gets lost. And so, I do encourage architects and designers, when they see NRC, just think absorption per square foot. And what naturally follows from that sort of thinking is how many square feet do I need, right? And then if you add objects into the mix, now the square footage isn't very clear. And so, Sabin’s per object makes a lot of sense, and the Sabin being a unit of sound absorption.

If I have a captive audience for a little while, I will usually start by explaining what the Sabin is, and then I will say, this is where NRC comes from. And if you're dealing with an object like a light fixture, maybe Sabin’s per object is best. If you're dealing with a surface, Sabin’s per square foot is best, which is also known as NRC. And I think Array NRC kind of nicely links those two situations in a lot of cases.

Eric

And the issue has been that the Sabin’s per object is the right answer for a lot of discrete object absorbers. It's very hard to use unless you're an acoustician and you're doing room calculations, saving reverb calculations. That's what an acoustician could use it for, challenging for an architect. However, one might say, if you're an architect and you're not an expert, maybe you need to reach out to someone that can help design the space. One of the challenges with the discrete object absorbers is that we're sort of in the deep end of the pool in terms of sound absorption and what these results mean, and how they can be used. It's in the more complicated, maybe much more complicated side of room acoustics.

Often, the types of spaces they're used in are maybe they're not necessarily often used in concert halls and recording studios. They're maybe in more of the general-use type spaces where an architect may feel they don't have the budget for a consultant.

Zackery

Yeah, that's right. And I think that is a really important point that not every project can afford or even really needs a consultant involved. And I think this is where a basic understanding of what a Sabin is and why, discrete objects should be thought of as Sabin’s per object, and surfaces can be thought of as Sabin’s per square foot, rather than NRC or as a way to think about NRC, is that once the designer recognizes that everything has some absorption associated with it, they can actually correlate fairly easily what might have high absorption or low absorption.

For example, a really cushy, big foam chair is going to have more Sabin’s, or it's going to absorb more than a steel chair would. Neither one is zero, but I would argue that they do. One has more, and that's pretty intuitive, and an architect who can't afford an acoustician on a job or is just working on a project that just doesn't justify that cost can absolutely still understand that a big cushy chair is going to absorb more than a steel chair. And they probably already do understand that at some level.

And so, they can still make decisions, generally speaking, about the direction in which they're designing. If you have a blank wall and you're thinking about putting shelves in a bunch of books, go for it; that shelves in a bunch of books will have more absorption than a blank wall would; you don't necessarily have to have all the numbers or the acoustic expertise to make that decision.

What's nice is when you've got the understanding or the training involved in that process, and you can quantify everything, and you can really make it, you can really set solid goals, precise goals. In my opinion, that's like the nicest way to work. It's just that not every project can afford that sort of help.

Eric

And it's nice that there are, like yourself, independent consultants available that could fit within the budget of these sorts of projects, I think.

Zackery

Yeah, I agree. think we also do, mentioned that my team does, we help manufacturers, but we also take on projects just like any normal consultant would. That mix is really nice, honestly, to be able to do a project here and then help with a manufacturer there because it's all just trying to make our architecture sound better.

Eric

So, a lot of people ask me sometimes, What's the weirdest thing you've ever tested? On the transmission loss side of things, one of the things we always, the first thing that comes to mind is that we had a customer ask us to test a mesh retention barrier. You see this at construction sites. They put it up along the periphery, and it's meant to just stop erosion and waste materials from getting into the street and the neighbors’ property, etc. So, we had someone ask us to test a wall of just that, which is totally permeable, open. So, one of those, like, why are you asking us to test something that has no performance at all? Well, sometimes you want to prove that it has no performance, or sometimes things have a surprising result. On the absorption side of things, so I actually, one of your projects is in my list of most unique or weird quote unquote items, which is your chair sculpture. Do you want to tell us a little bit about your chair sculpture?

Zackery

Sure, yeah, it's right behind me, actually. Yeah, this is brand new, and we, okay, so it is 24 stacking chairs from the 1990s. And if you're familiar with furniture of that type from that time period, they're basically formed plastic backs with steel rod frames. Stacking chairs are designed to be minimal in material and footprint, and to basically be stored out of the way in a closet when you're not using it. And my work over the years has really started to move into things with milder effect, surfaces and objects with milder effect, not necessarily chasing the highest NRC possible, but asking what the value is and what the design possibilities are in the lower realms of performance, because everything adds up in the end to give you the room you have.

I find that if you can be open to the design possibilities that aren't just competing at the top end of NRC, that a lot of really incredible stuff can come out of that. So, we decided just to take these chairs and test them at Riverbank to see what they do. And instead of putting them in a typical configuration or the stacked stored configuration, we laid them out in a more interesting sculptural configuration on the floor. And they're now hanging on the wall behind me in my studio, and we use them as a sculpture, and we also just take them down when we need them. But the idea is to take something that was meant to disappear and to make it very intentional acoustically, and to try to understand what its influence has on the room.

Not to our surprise, but maybe to the surprise of people who haven't thought about acoustics in this way, their effect is significant. It's not high, but it's not zero either.

And to me, the fact that you can take chairs that were really designed to disappear and you can have them be both visually and acoustically impactful, I think it begs a lot of questions about where acoustic design could go in the future.

Eric

Yeah, you make a really good point about the high end. Talking about sound absorption testing, the high end of the NRC spectrum. Now, there are definitely situations where you want 1.0 NRC or close to 1.0 absorption coefficients, recording studio, first reflection on the sidewalls, that sort of thing. Yes, you need very high sound absorption or places where you are concerned with a really bad slap back off the rear wall. You want a high ratio of sound absorption on those surfaces. But one thing you've said, and we've talked about over the years, is that not everything needs to be a 1.0, and there's this huge opportunity with medium NRC performance that if you have more area of these materials and they have great visual interest in the space, they add a lot. know, if we're talking about like a 0.5 NRC, that's adding an average of half a Sabin per square foot of material. If you're using twice as much square feet of that, it still has a very big effect on the space. And so, we run into that as a lab, where we'll have customers where they have a really interesting, unique product. And it's something kind of different we haven't seen before. And the test result is 0.75 NRC. And they're all, this is it? What are we going to do? This is not great.

No, compare yourself to zero; to not having that treatment would be zero. So, in a lot of situations, a 0.75 would be perfectly useful and helpful.

Zackery

Absolutely. Especially if you love the way it looks, if it's doing something else, what we can see, this was a blank wall behind me beforehand. And what we did was take something that's highly functional for us, a bunch of chairs that we use and need, and make it acoustically beneficial and interesting. And even when the absorption results are on the low end, it's still a positive force in the space.

I think about that quite a lot. I wonder what a furniture manufacturer would do. Like I said, this is kind of a new experiment for us, but what would a furniture manufacturer think about or what design possibilities does this open up if the furniture they're making can be configured in ways that is intentionally beneficial to the sound of rooms?

Eric

So, where do you think things are going next? What do you think is down the pipeline for acoustical products?

Zackery

That's where I think it's going. I think that embracing hard materials and shaping and the seeing of the space as a whole rather than just maximizing the performance of each square foot, I think that's where it's going. And I should be careful and say that...

There are examples. Acousticians work all the time on rooms as a whole. They get this. But I do think that the dominant mindset in the architecture world is that acoustics is about the products you add, and those products do little else than just make your room sound good. And it's an extra line item on the budget, and you have to have the money to have it. And I think that we just went through a period where manufacturers invested heavily in getting that performance and that high performance, and then into visually interesting territory. And I think the next frontier is reckoning with the acoustic effect of everything else and asking how would the design of a chair change if we're also thinking about its influence acoustically. And I don't necessarily mean foam chairs, I mean, how might a designer shape a hard chair just to give it a little more influence on the room?

When I think about the future of acoustics, that's the part that I really get excited about. I think you could say it's an embracing of the mild effect. Intentional acoustic influence, and this is something that parallels how we feel about the visual realm. I don't buy into pitting light and sound against each other at all. I think there are some similarities, and they're quite different.

But one of the things I love about the visual world is that when somebody arranges, when they design a space to look the way they want it to, they think about the volume, the dimensions, the materials, the furniture, the lighting, they think about all of the elements and how they come together as a whole. That I think is the way we should be thinking about acoustics. Not just, not just how do we add something that will fix everything, but how do we assemble all of the right things? And that includes things that were never meant to be acoustic and things that were highly engineered to be acoustic. It can all be part of the you know, the same vision, the same overall goal.

Eric

I think you said it once, and it sticks with me, that everything is acoustic.

Zackery

That's right. Yep, it is.

Eric

Cool. So how can our listeners connect with you, Zackery?

Zackery

Well, I'm based in Detroit, and I have a great and talented small team here. We just rebranded, and we're known as Umbel, U-M-B-E-L. So, they can find us at umbel.design. And that's probably the best way.

Eric

Great, anything we missed, anything you want to cover that we didn't talk about?

Zackery

One thing I think we should least mention is the novelty testing program.

Eric

Oh yes, which is related, I guess, yeah, that's related to the themes we're talking about. So, I'll give a little background on what it is. So, as a lab, most of our work is sponsored by various entities that are basically paying the lab to run the testing. And then we deliver the data. They own the rights to that data. That's what we mean when we say this is the sponsor of this test.

They basically own the rights to that data, which is challenging for a lot of acousticians who want to call the lab and hope that we can share data. In a former life, I was an acoustical consultant. I remember just how hungry you are as a consultant. You're hungry for data and information, especially about things where there is no sponsor. There is no one that's going to pay the lab to run these tests on something really, really unique or general.

So, we started the novelty testing series a few years ago, and basically, things that consultants have asked for that are non-products, that are, for example, we did a fresh sod. We ran a sound absorption test on fresh sod.

One of my favorites, we did both pine trees and the Christmas tree variant, so you can see the impact of the tinsel and the Christmas ornaments on the Sabin’s per object of the same exact trees. So that was kind of fun.

Actually, my number one favorite is the egg carton series. So, there is a meme out there, and there's sort of different levels to this. If you want to make a wall or a surface, quote unquote acoustical, you add egg cartons to the wall. This was like a Hollywood, you see it in movies, thing. But then, acousticians rightly went out; this is kind of a myth, just putting up egg cartons on the wall isn't going to solve all of your acoustic issues. Well, I think where this may have evolved from is there is something called egg crate foam, which is a style of foam where it has like almost like little pockets for eggs. And in the architectural space, we would maybe call that egg crate foam. And then maybe someone hears that and thinks, We can put egg cartons on the wall, right? They're thinking of the cellulose, hard surface egg cartons. And then that somehow gets translated into movies showing someone with a makeshift recording studio with egg cartons on their wall or the egg trays.

So, we did a series where we tested egg cartons, and here's the thing: if you use just the tray, the absorption performance is really, it's fairly low. So, the acoustician community is correct that just the trays - fairly low performance. However, if you if you use the entire enclosure like you would get at the grocery store with the enclosed egg carton tray and the lid, you're creating a small Helmholtz resonator. And so, we tested a whole amount installation of those egg cartons. And then I think someone on our team had the idea of what about the other way? Because we started it with the egg trays up, right, in the classic Hollywood presentation. But wait, what if we flipped them? So, we tested that. Now the frequency performance shifted a little bit because the vents were up, right? So, then the next step was we split half up, half down, and created a pattern. And then that took that frequency response and leveled it out.

And actually, if you want to, I wouldn't recommend it for a really high-end performance thing. It actually performed in that kind of mid-performance range. I think it was 0.65. I don't know. The reports are on our website under Education references. So, we'd like to do more of these. The past year, we have been absolutely overflowing for the past year, so we just have not been able to give bandwidth to the novelty series. It's coming back. One way or the other, we're going to restart this novelty series in 2026.

Zackery

Yeah, what a great program that is, I have to say, just to help us understand the performance of things that, like you said, no one's going to find. So yeah, that's one of my favorite things about Riverbank right now.

Eric

Cool, thank you. More to come. All right, well with that, we'll catch you later, Zack.

Zackery

OK, thank you. This was a lot of fun.

Adam

Thank you both for joining this episode and sharing your insights. Your combined perspectives highlight the ongoing evolution of acoustical testing and design and how innovation continues to shape the built environment.

And to our listeners, we thank you for joining us for another episode of Catalyst Conversations. Be sure to subscribe for more discussions featuring the experts driving the future of acoustics, noise control, and vibration management. Until next time, thanks for listening.