Reverb: The Evolution of Architectural Acoustics

Roman Mars:
This week was a hard one for a lot of people, myself included, and it feels a little strange to put out a story that has nothing to do with the election or with politics because that’s all everyone around me is talking about. But I hope this architecture-centric episode will be just what some of you need right now. Our mission is to show you the human thought and care that goes into designing the built world around you. This 99% invisible work will keep going, and we’ll keep going, to present it to you with care and so much gratitude that you’re out there listening.

Roman Mars:
This is 99% Invisible. I’m Roman Mars. And I’m sitting in a tiny little room with this microphone right up to my mouth so that the sound of my voice is transmitted directly from me to you. There’s no sense of the room that I’m in. When I stop speaking, the sound stops. There is no reverberation, no reverb.

Avery Trufelman:
Roman and I are both talking in rooms outfitted specially for recording, rooms that sound good.

Roman Mars:
That’s producer Avery Trufelman.

Avery Trufelman:
Because if I step outside this tiny, completely padded studio… Okay, it’s still quiet because I’m inside, but I’m going to walk around a little bit so you can hear the architecture around me. You can tell now that I’m in a bathroom. Or you can tell if I enter the stairwell outside our office. And if you’re not listening in headphones, my voice is bouncing around your car or whatever room you’re in. Whatever you’re hearing, sound is affected by the architecture.

Roman Mars:
There are two main ways to control the sound in a building. Active acoustics and passive acoustics.

Avery Trufelman:
Passive acoustics are the materials in a space, like the padding in the studio room. Carpeting and drapes are also absorptive materials that soak up sound. Glass and porcelain, on the other hand, create more reverb.

Ashley Hanson:
Essentially, if it’s shiny, it’s going to be reflective, is an easy way to interpret that.

Avery Trufelman:
This is Ashley Hanson.

Ashley Hanson:
My name is Ashley Hanson. I’m the design services manager at Meyer Sound.

Roman Mars:
Meyer Sound is a company that mostly makes active acoustics, which is to say speakers, amplifiers, and other electric sound equipment.

Ashley Hanson:
People probably have run into our products, they just don’t know that it’s Meyer Sound.

Avery Trufelman:
Meyer Sound makes a lot of the big speakers hanging off of the ceilings at concerts and Broadway shows. But their products are also in a lot of unexpected places.

Ashley Hanson:
Cruise ships, restaurants. We are in some corporate headquarters, educational facilities, airports.

Roman Mars:
Over 600 Meyer Sound speakers were used when the Pope spoke in Mexico.

Ashley Hanson:
One of the things I tell people in general is, if we’re doing our job right, you might never notice that we’re even there.

Avery Trufelman:
And that’s part of Ashley’s job at Meyer Sound, to make sure the sound equipment is effortlessly integrated into a building, using both passive and active acoustics, materials, and electronics.

Roman Mars:
But often in architecture, what looks the best is at odds with what sounds the best.

Ashley Hanson:
Of course, you don’t necessarily want to always see the big black speakers somewhere. And so, we have to get creative.

Roman Mars:
We like our speakers out of sight. And we also like high ceilings and long glass windows, which makes spaces sound really reverberant. So, architecture is a puzzle for Ashley and her team to solve.

Ashley Hanson:
Whenever we see rooms that have curved walls, we kind of cringe, especially if they’re out of glass. Oh, that’s pretty. When we approach spaces, there are things that, although they’re beautiful, we know are going to definitely put pressure on us to come up with creative and unique ways to appease the visual and sonic needs of the room.

Avery Trufelman:
So it depends on what you’re trying to do in that space. If it’s a venue for the symphony or the opera, you want the sound to be big and resonant and echoing. Or a cafe or a place with acoustic performances, a little reverb is nice. But if you’re trying to hear a lecture or a reading or say, have a meeting, you probably don’t want much reverb at all.

Roman Mars:
But we haven’t always been able to precisely control the acoustics of a building. Sound, until fairly recently, was a somewhat mysterious element in architecture.

Emily Thompson:
In the late 18th century, there are all sorts of different theories about how to get good sound, but half of them contradict the other half and no one really knew what to do.

Avery Trufelman:
This is Emily Thompson. She’s a history professor at Princeton and a scholar of sound technology. And she says at the turn of the 20th century, architectural acoustics are pretty much a roll of the dice.

Emily Thompson:
Architects begin to fret that they don’t really know what they’re doing with this aspect of their designs. And it was all kind of left to chance. And if you were lucky, your theater would sound good. And if you were unlucky, it wouldn’t.

Avery Trufelman:
And in 1895, Harvard University was very unlucky.

Emily Thompson:
The university had just completed building the Fogg Art Museum and it had a lecture hall, where there was so much reverberation that they simply could not hold classes in that room. You couldn’t understand the speaker because there was so much reverberatory confusion of sound.

Roman Mars:
Harvard had just wasted a lot of money on a completely useless room. Sound had ruined it. And in an attempt to save the space, they enlisted the help of a rookie physics professor who had some time on his hands.

Emily Thompson:
So, the president of Harvard asked this young physics professor to figure out how to fix that auditorium and make it usable teaching space.

Avery Trufelman:
This professor’s name was Wallace Sabine, and through this task, Sabine would eventually become the father of architectural acoustics.

Emily Thompson:
This sent Wallace Sabine onto an investigative path that actually took several years collecting data.

Roman Mars:
Basically making sounds in rooms and timing the reverb.

Emily Thompson:
He would take measurements of the different reverberation times in different rooms all over campus. And in order to do this under the quietest possible circumstances, he tended to run his experiments in the middle of the night. And he would change the reverberation time within a given room by bringing into it various sound-absorbing materials.

Avery Trufelman:
Sabine was a perfectionist. He threw out over 3000 measurements after determining that his own clothes had a small effect upon the sound of the room. He started all over again, taking measurements in the dead of night, but now wearing the exact same outfit every time.

Emily Thompson:
Meanwhile, the president of Harvard is waiting and waiting for this lecture hall to be made useful again. At one point, he finally says to the young professor, “It’s time for you to tell us what to do here. Enough is enough.”

Avery Trufelman:
And that night, feeling nervous under pressure, Sabine pores over his notebooks and has a breakthrough.

Roman Mars:
Looking at all his measurements, he starts to notice a trend, a mathematical relationship between the size and materials of a room in its reverberation time, a relationship so steady that you can make a formula out of it.

Emily Thompson:
He discovers a mathematical formula that connects the architectural materials of the room and the behavior of sound within it. And this is a formula known as Sabine’s formula now, that really enables people to be able to predict the reverberation time of a room based on its design.

Avery Trufelman:
Sabine’s equation allowed for planning. Suddenly, you could manipulate the reverb of a space by changing the materials the room was made of.

Emily Thompson:
So that then you can take any sort of architectural plan. You know the dimensions, you know how many square feet of plaster or wood or glass or upholstered seats fill this room, and you can just kind of plug and chug and the formula will churn out a predicted number for the reverberation time of the room.

Roman Mars:
Sabine’s formula helped architects design for as little or as much reverb as they wanted.

Avery Trufelman:
Architects could now control the sound of a space. They could make big rooms with very little reverb. And so, they begin to do just that. And the most remarkable early example of this was Saint Thomas Church.

Emily Thompson:
Saint Thomas Church, which is in New York City, not far from the Museum of Modern Art.

Roman Mars:
The architects of this church wanted to build it in a neo-gothic style, basically to make it look like a European cathedral, made of stone with high ceilings and stained windows.

Emily Thompson:
But while they wanted this building to look gothic, they realized that a gothic sound would not work for a modern Protestant service.

Avery Trufelman:
They wanted to hold a much more sermon-focused service, not just a medieval mass. It needed less reverb so parishioners could understand the words. So, the architects turned to Wallace Sabine to make a sacred space that would be clear, calming, and reverb-free.

Roman Mars:
Sure, Wallace Sabine could add felts and padding to the building, but he thought that didn’t fit the feeling of a church. He worked with a tile maker to come up with special sound-absorptive ceramic tiles with porous surfaces. He called them Rumford tiles.

Emily Thompson:
The Rumford tile, they named it after a physicist who had kind of been interested in solving practical problems, and it’s a substantial architectural material. It’s not a matter of just hanging drapes or tacking felt onto a surface. It’s much more integral. So, with Saint Thomas Church, by using these sound-absorbing tiles way up in all the ceiling volts, they had the gothic look without the gothic sound.

Avery Trufelman:
Saint Thomas Church was completed in 1913. It’s definitely not modern-looking, but it was a landmark modern-sounding building, completely engineered and formulated for environmental control, thanks to the Rumford tile.

Roman Mars:
Sabine worked in public and private spaces all along the east coast and came out with more products to accompany the Rumford tile.

Emily Thompson:
And he passed away in 1919, right really at a moment when a much more pervasive interest in controlling environmental sound would come to the fore.

Roman Mars:
The roaring ’20s, it got that name for a reason.

Emily Thompson:
It may very well be the case that it was louder in the ’20s than now. This was an era when cars and trucks did not uniformly come with mufflers.

Avery Trufelman:
There were these new, unfamiliar, unprecedentedly loud sounds of cars, of trains, of industrial machinery, of construction, of skyscrapers rising everywhere. And in the crowded city, an escape was hard to find.

Roman Mars:
Sound crispness and clarity could provide calm and control. It meant a complete mastery of the environment.

Emily Thompson:
And so, the desire to control sound within interior spaces is in part a kind of a drive to create refuge from the noisy tumult of the world outside.

Avery Trufelman:
Rumford tile launched an industry. By the 1930s, dozens of different corporations were manufacturing and selling vast quantities of acoustic building materials, with names like Akoustolith, Acousti-sellotechs, and Sabinate.

Emily Thompson:
For those who could afford it, whether you could buy a soundproofed apartment or just enjoy quiet offices or theaters.

Roman Mars:
Quiet became a luxury commodity.

Avery Trufelman:
Acoustic materials were so advanced that Sabine’s formula couldn’t apply anymore.

Emily Thompson:
By 1930, you’re really able to create spaces that simply didn’t exist in the 19th century. Sabine’s equation doesn’t work particularly well. It was a product of the world in which he did his investigation, which was still that 19th-century world filled with glass and wood and plaster.

Avery Trufelman:
All this new acoustic technology was able to create a level of silence unprecedented in Sabine’s time. Finally, it was quiet. Too quiet.

Roman Mars:
But as the 20th century went on, people became disenchanted with the idea of completely closed-off spaces with dampened acoustics. They wanted to let in air, light, and sound.

Emily Thompson:
Interestingly, by the 1970s, some of the cultural factors and the aesthetic preferences of people, with respect to sound design, had changed since the early 20th century. And in some of these spaces, including Saint Thomas Church, they actually decided they wanted more reverberation than this material engendered. So, in some cases, the porous surface of the Rumford tile has been painted over to kind of seal off those pores and to make it more reflective of sound.

Avery Trufelman:
And these days, we want our architecture to have a range of reverb. Now, one single room or venue can accommodate a lot of different kinds of sounds. And that’s possible using not just passive acoustic materials like the ones Sabine pioneered, but also active acoustics.

Melody Parker:
Using microphones and loudspeakers and digital signal processing.

Avery Trufelman:
That’s Melody Parker, an acoustic engineer at Meyer Sound. And they have this product called Constellation.

Melody Parker:
And so what Constellation allows you to do is to create multiple environments in one space.

Roman Mars:
It basically allows you to manipulate the sound of the room completely digitally, through a system of many tiny speakers and microphones.

Avery Trufelman:
“Where are the microphones?”

Melody Parker:
“Throughout the ceiling. They’re really small. Let’s look.”

Roman Mars:
Melody showed Avery the test room for Constellation, inside Meyer Sound’s headquarters in Berkeley. It looks like a very small theater. It’s a room with a low reverb time, thanks to much acoustic padding, but it’s outfitted with a variable active acoustic system, where tiny microphones capture the sound and the speakers play back those sounds to mimic the reverberation in different-sized rooms.

Melody Parker:
“I should demonstrate.”

Avery Trufelman:
“Yeah.”

Melody Parker:
“Okay, so I’ll grab…”

Avery Trufelman:
Melody took out an iPad and activated different settings, which completely changed the sonic shape of the room.

Melody Parker:
“And I’ll do a dramatic demonstration. This is what it sounds like with a very long reverberation time.”

Avery Trufelman:
Melody played the clave to demonstrate the reverb time. This setting was called Sacred Space. And it gave this tiny room the sound of a cathedral. And it’s one thing to hear a reverb effect in a song or a podcast. It’s another thing entirely to experience a reverb effect in a room, in real life, in real-time. The echo completely changed my perception of the space. Then Melody took the reverb completely out of the room, just entirely, and suddenly, it felt stifling, like I’d been muzzled or something. It was hard to breathe.

Roman Mars:
And those are some of the most dramatic settings on Constellation. There are lots of subtle changes that a client could make to a room.

Melody Parker:
They have the ability to change the length of the reverberation, change the strength or the loudness of the reverberation, and to even change the perceived height of the room and the perceived width of the room.

Roman Mars:
Constellation and its competitor sound systems are expensive, so they’re not common exactly, but they’re in a lot more places than you’d think, like a number of big venues all over the world and in classrooms and offices, restaurants that use so-called variable active acoustics so they can adjust the noise level to keep it in a pleasant hum, regardless of how many people are in the space.

Avery Trufelman:
And the architectural implications of this are fascinating. Of course, architects and acousticians still have to pay attention to the passive acoustics and the building materials, but there’s a lot more design flexibility now.

Ashley Hanson:
Yeah, we actually have an interesting one that we’re working on for a tech business where they took over an old factory.

Avery Trufelman:
That’s Ashley Hanson at Meyer Sound again.

Ashley Hanson:
And so, the challenges in that space, it’s that the factory’s all brick and exposed and beautiful and have these high ceilings.

Avery Trufelman:
And she says a combination of active and passive acoustic systems help architects repurpose old buildings.

Ashley Hanson:
We’re able to take spaces that would never be used for certain applications and make them great for all sorts of different events. And that wouldn’t happen before. This office space in this old factory would just be a reverberant nightmare. No one could focus, and they probably wouldn’t have purchased it for that.

Roman Mars:
Buildings like Saint Thomas Church mark the beginning of our quest to control sound in the built environment through passive acoustics. Now, a hundred years later, with advanced active acoustics, we can separate sound from space. Warehouses can be made to sound like opera houses, and opera houses can sound like small clubs. It’s just a matter of how much reverb we want.

Roman Mars:
In this episode, we featured some actual sounds from New York City from the 1920s and 1930s. You can find them on this incredible interactive website that Professor Thompson made in collaboration with the University of Southern California. It’s got a map of New York and you can click around it to see what it looked like and what it sounded like in the 20s.

Emily Thompson:
And the easiest way to find it is to go to ShutOutTheNoise.com.

Roman Mars:
Seriously, check it out. It’s super cool. ShutOutTheNoise.com. Special thanks to Ben Strange, Alex Stoll, and everyone at Meyer Sound.