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How does one become one of the country's top experts in acoustics design? Ask this question of a child "What do you want to be when you grow up?" and chances are you will be hard put to find one who would answer loud and clear "An acoustician!" Even Bob Mahoney, acoustics designer of The Ellie, didn't give that answer as a boy growing up in New York. Acoustics, after all, is a complex field, even for adults who love the sound of a great concert hall.  Mahoney's journey to acoustician wasn't simple and direct, as we learned during a phone interview with FanFaire a couple of weeks following the opening of The Ellie.


It all started with music. "I started out, as a lot of people do, with studying piano as a child. Then I went for an undergraduate degree in physics. But I missed the music, so I took courses in Juilliard for a couple of years, and then went to architecture school."

He could have ended up as a full-time musician (he studied piano with Alton Jones at Juilliard, and for nearly 20 years played the horn with various chamber and symphony orchestras) had he not gotten involved with the Recording Department of the Juilliard Opera Center. That was about the time Maria Callas was doing her famous master classes. "I was involved in taping all of them. And in fact, those tapes were the basis of 'Master Class' - the Tony-winning play by Terence McNally."

Obviously, it was an experience he never forgot. A full semester. "Oh, it was fabulous! She was so charming. Many of the humorous moments in the play - it was amazing to see and hear those the first time - really happened."

That started his fascination with acoustics. "Actually the Recording Department at Juilliard was called the Acoustics Department. But it really was primarily involved with recording. In the course of doing things like hanging microphones, I got to see the bowels of the opera house there and was fascinated by how all that was put together. So, I decided to go to architecture school at the University of Colorado."

Why Colorado? "Oh, I was just glad to be in another part of the country." Wanderlust.

"I did architecture, but I still wasn't thinking about acoustics consulting until I got out of architecture school and there was a job opening with Christopher Jaffe's office in Denver. That was my first job." (Jaffe was then already an internationally known innovator in architectural acoustics.)

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Photo courtesy of Bob Mahoney Music, physics and architecture - what a combination! There couldn't have been a more perfect background for what has turned out to be a life's work in acoustics. In 1992, Mahoney hit the road on his own. His first big project was the reconfiguration of the Ahmanson Theater in Los Angeles.  It was there that he first met Peter Lucking, lead architect of The Ellie, who was then a consulting architect with Theatre Projects Consultants. They stayed in touch with each other, developing a working relationship that has grown stronger through the years.

His connection with Semple Brown Design goes back to the late 1980s when a number of his classmates from the University were working there. He did his first project with the company in 2001 - the Kenneth King Academic and Performing Arts Center, almost literally across the street from The Ellie. He has since worked with Semple Brown on several academic projects, i.e, performing arts facilities on college campuses mostly with Peter Lucking, and mostly in Colorado - e.g., Mesa Stage College, Aurora Community College, and a few high schools. 

Just like Peter Lucking, The Ellie is Bob Mahoney's first opera house, if one does not count the opera houses that he has worked on in an academic context, which are designed on a totally different scale, such as that at the college in Tuscaloosa, Alabama.

For Mahoney, designing an opera house is difficult and challenging. He explains, comparing an opera house to a concert hall: "I think an opera house is more difficult to design than. In a concert hall, people recognize the primacy of the acoustics. And there are only a limited number of other disciplines that have to be reconciled and that force compromises, such as lighting.

"In general, in a concert hall, the acoustician has a lot of influence over virtually every surface, on or to the side of, above, behind the singers or the orchestra. All these surfaces are part of the palette. On the other hand, literally half the house is out of your control because you have to accomodate the set design. You have to reconcile things with the set designer, the director... and there are so many other elements." 

"But surely you have control over the stage ceiling, the curtains, the floor?" we asked him. "Actually, not even that. Because it's entirely possible that a set designer will take out all of the curtains. In fact, that actually happened at the Ahmanson. When the musical Amadeus played, the set was made out of glass." A very highly reflective surface.

"And in an opera house," he continued,  "you of course have to consider that the balance between the orchestra and the singer is very delicate. It's very easy for an orchestra to overwhelm the singer."

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THE BEST (AND WORST) SEATS IN THE HOUSE: Opera House Acoustics 101

In designing the acoustics for an opera house, one aims to achieve the right blend of direct sound, reflected sound, and reverberation. What is the key combination, if you will? Mahoney explained, clearly and patiently: Strictly speaking, direct sound is sound that has suffered no reflections at all on its journey from singer to listener.  If you can see the sound source, you'll have direct sound. There's nothing intervening. So, in an opera house, if you're on the orchestra floor, you'll have direct sound from the singers, but not from the orchestra - as a rule, because if you're high up in the balconies, you can see the orchestra in the pit. That's also why offstage voices sound like they're offstage - there is no direct sound in what you hear.

"This is a fine technical point, but in terms of common acoustical usage, direct sound is the sound that comes without any reflection as well as any sound that comes in a very short time window thereafter. So, we do allow for some reflections as long as the path length difference is quite small. That's really the key part. In an outdoor space you have direct sound but virtually no reflections at all so the acoustics are usually terrible for singing. So, the first reflections are really, really what I concentrate on."

The conversation inevitably turned to where, acoustically speaking, are the best and the worst seats in the house. Is it true that the sound is most beautiful at the very, very top of center upper balcony? "Oh yes, for most halls. That's because the seats in the top balcony not only have great sightlines but they are close to the ceiling as well. So, the direct, unreflected sound is immediately reinforced by strong reflections from the ceiling, which having traveled a path that is just slightly longer than the path of the direct sound, arrive at your ears just a small fraction of a second later. These sounds - direct and completely reflected - combine to give you excellent clarity. And the worst seats traditionally are in the center orchestra. They're the farthest from any reflective surface." Center back, middle, or front? - we asked, making sure we can locate with pinpoint accuracy the seats to avoid at our next opera. "Well, mostly center center." And how about the seats under an overhang, such as under a balcony - is the sound blocked in that area? "Yes, especially if the designer was using reflectors overhead that you can't see. But in The Ellie we used the side walls of the audience chamber just downstage from the proscenium line that the people under the balcony can see. Do you remember the panels with the kind of a sawtooth geometry? They provide a useful reflection. That's why they're that shape."

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In designing The Ellie, acoustics was always the number one priority. Robert Mahoney and Peter Lucking talked acoustics from day one. "Peter's a wonderful guy. And the nice thing about working with him is before he even drew anything we were talking about the acoustics. Peter is quite exceptional in that regard. Oftentimes, an architect who has, shall we say, a very strong architectural reputation, but not necessarily much experience in the performing arts, they will say, 'Here's my vision. I'll make a few changes, but nothing significant.'" And the acoustician would have to fit into that vision, which can be very restricting. Of course there was none of that in this case. "In fact," said Mahoney, "the very, very first exercise that Peter and I worked through was to define areas where the reflectors really needed to be. And that gave rise to the ceiling design, which has gotten a whole lot of attention."

But actually the starting point in designing the acoustics for The Ellie was defined by the pre-existing facade. "In this instance, we had an existing building; so the starting point was to really understand what the boundaries of the dimensions could be - obviously no greater than the existing building. And as big as that is, that was quite a limitation, especially in terms of the height. So, I'd say the first order of business was to get some sense of the necessary seat capacity. Was it a 1200- or a 2400-seat house?

"The second was the commitment that it would be for unamplified sound. And the third was recognizing that because it was for unamplified sound, we could not have any deep balconies. We needed balconies to meet the seat count yet still keep the house intimate. We quickly saw that the balconies would have to be shallow and stacked vertically but not directly above one another. Do you remember that as you went up, each balcony was a little farther from the stage? That's so that we wouldn't overshadow the seats underneath. And once we had that done, we looked at the vertical arrangement of spaces. And that's when we had the study that said: These are the boundaries of the ceiling reflectors, they can't be any higher."

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The ceiling reflectors as well as the panels on the side walls are made of cherry wood. "There is nothing specially unique acoustically about cherry. It was a visual concern. It's just beautiful, and it changes color over time, becoming darker and richer." This steered the conversation to a discussion of acoustical materials. An acoustician like Mahoney must keep up with advances in materials, we surmised. "Yes," said Mahoney, "but what is even more important is not only the materials themselves but how they are attached to the rest of the building. For example, wood that is very thick behaves very differently from wood that is very thin with a big air space behind it. The shape of the room surfaces, as well as the mass and the stiffness of the materials used, are also very important."

Noting that wood is used rather extensively in The Ellie, we asked if it is frequently used as an acoustic material. "Well, we use it on critical surfaces. But you know, even the greatest classical halls used mostly plaster. If you look around La Scala, you will notice that the walls are all stucco or plaster. The details may often be wood, but the walls themselves are plaster. Also, when you look at the ceiling in The Ellie, what you see are the wooden reflectors. What you cannot readily see is the actual ceiling that is the acoustical envelope, which is made of multiple layers of gypsum board. We couldn't use anything terribly heavy because the roof would not carry extra weight. So that was a limitation. Gypsum board is a pretty good reflector. And the more layers you use the better it gets."

How then does one control reverberations and echoes? "One way is to absorb the sound enercy outright, with a good absorber such as fiberglass. Fiberglass is a good absorber because its interstitial spaces are rather small scale. Thus, when a sound wave hits it, the viscous losses of the air as it tries to push through those spaces is what absorbs the acoustic energy. The rear wall, for example, is circular and that of course is a focusing surface, so that even if it absorbed say 80% of the incident sound energy, the remaining 20 % comes back and all ebb together somewhere in the center orchestra.

"There are other tricks you can play to suppress the echoes. But they're difficult. For example, the walls can be tilted out of plumb so that the reflection doesn't travel a great distance before it is absorbed by the audience seating. And indeed the walls at The Ellie - those sawtoothed walls- are tilted forward out of plumb, not enough that you can see, just seven degrees off the vertical."

We then asked Mahoney about the acoustical role of the movable walls in the orchestra pit. "The space under the stage is really a very big room, about as deep as but not quite as wide as the stage. And that room has a lot of absorptive materials on the walls. So, when the towers - which you might think of as vertical slices of wall that, instead of sitting on the floor in a solid fashion, are on a caster base so they can move around - are fit snugly together, all of that absorption is excluded from the pit. However,if you space the towers apart just a little bit, some of the orchestra sound leaks out and is absorbed. If for example, you had a piece that had a great deal of brass, that was overpowering the singers, just spacing those towers a little bit will make the brass sound a little weaker, which would help restore a proper balance with the voice."

The orchestra pit is on two lifts, one bigger than the other, which can park or stop at the same elevation. "But in this particular pit, you don't need to stop them at the same elevation. You could have a pit like Bayreuth's that steps down as you move farther upstage. The upstage wall of the Ellie's pit is of course made of movable towers. So, if the conductor wanted, he could put the low brass and the percussion way under the stage. What was the phrase that Wagner used, the mystic gulf? We can achieve that. But of course that sort of pit for a Mozart or a Rossini opera would be awful.

"In fact for the gala, we were incredibly lucky that we have those movable towers because Opera Colorado had sold the seats on the big lift, and so we had just the small lift - but we had a big orchestra. So, we were able to push those towers farther upstage and get everybody in there.

The movable walls are made from a lightweight composite panel that was developed for orchestra shells, while the permanent walls of the large room that surrounds the pit are covered by a material called tectum. "But the other thing we did in The Ellie that is very common in opera houses is we installed a solid wall behind the conductor," Mahoney said. "It does a number of things. It doesn't allow air to pass through it and it shields the patrons seated in the first row orchestra from the musicians who are so close to them." That wall is made of plywood.

Obviously, the performance hall of an opera house, especially in the middle of a busy city like Denver, has to be shielded from all sorts of extraneous noises. Bob Mahoney of course saw to that. The hall is enveloped by a one-foot thick concrete wall. "There's a lot of data that's published on how concrete, a practical material, performs acoustically. Given that we are in the middle of the city and the lobby walls are punctured by a lot of glass, we knew that sirens and other urban noises would be quite audible inside the lobby. But we wanted to make sure they were inaudible inside the house. That was a another consideration that shaped even the earliest visions."

But sirens and other street noises are not the only undesirable sounds inside an opera house. People often forget how many sources of noise are inside the building itself. "You know, a big part of what I do, which is not all very glamorous, is to keep all the bad sounds out,"Mahoney acknowledged. "Certainly the kitchen is annoying and the air conditioning noise can be horrendous. There are all kinds of pumps that are really extremely noisy. There are elevators and motors, scene shops in the basement with all the power tools.  Even the lights in the underbalcony area have little transformers, so those were all collected together and segregated in the soundlock. When you're in the soundlock and listen carefully you'll hear that hum. You won't hear it inside the Ellie, though."

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By now it should not be difficult to understand that the shape of materials shape the acoustic quality of an opera house or a concert hall. And the choice of the lyre- over a shoebox- or a horseshoe-shape configuration for The Ellie was a critical decision in which Bob Mahoney, not surprisingly, was a major player. He explained the decision this way:

Mahoney in Kodak Theater,
one of his recent projects

"The lyre-shape has a number of really good advantages over the shoebox shape. I'm sure you've experienced this in places like Boston's Symphony Hall - if you are on the side balconies farthest from the stage, it's very hard to see the performers."

The obvious conclusion: a sightline problem is usually also an acoustic problem. But what about the horseshoe configuration? "The horseshoe or lyre configuration is advantageous acoustically because it pulls the balcony fronts away from the side walls and brings them closer to the middle of the house, effectively narrowing the hall. In inexperienced hands, the sightlines of the lyre shape can prove very difficult to solve. The other thing is that the dimensions of the proscenium opening generate many of the other dimensions in the house. Originally, the Denver Performing Arts Complex wanted a 65-foot wide proscenium. And I had to argue quite forcefully to make it only 55 - that's still as big as the Metropolitan Opera and much larger than places like Covent Garden." Not surprisingly, Mahoney carried the day.

Interestingly, shape, but not the singer's, also influences what the singer hears of him/herself on stage. How much of the reflected sound from the hall actually should come back to the singer? "That is an excellent question, because obviously the singer has a limited energy budget. And you have to decide what proportion goes to the audience and what proportion comes back to the artist. Mainly what the artist should hear is kind of a wash of sound that comes back as opposed to one strong reflection that comes back as an echo. And the easiest way to do that, and what we've done in The Ellie, is to use balcony fronts that are convex; and since they don't align vertically, they're not all equidistant from the singer. Each one of them sends back some energy to the stage, but at a different time than the others do. So that gives the singer an impression of a wash as opposed to one single reflection."

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The ultimate reality test of course came on opening night. "But surely," we asked Mahoney, curious about the technology used to measure the quality of sound, "you must have run some kind of preliminary tests?" "Well," he replied, "the the instrumented tests that I do are only to see how accurate the predictive models were. So, in a sense it's mostly for professional interest.  The only meaningful question once the hall is done is 'Do you love the sound?'"

But how was it done in the old days, we asked, having in mind Europe's oldest opera house, Teatro di San Carlo in Naples, built in the 18th century, its acoustics praised to this day. "Well, to tell you the truth, I think they used full scale models. And if the hall was no good, they tore it down.

"You might enjoy this," he continued, obviously eager to share a book he was reading. "There is an excellent book, by Edwin O. Sachs, reprinted not so long ago that was originally published in the 1880s. It's a 3-volume study that gives the history of each of the opera houses then extant, with beautiful drawings. And it has a survey that measured the average life of the opera houses. In the one hundred years preceding the book's publication, opera houses lasted just 18 years on average - before they burned down!"

"Surely, The Ellie will live much, much longer than that!" we interjected, remembering what we had been told - that The Ellie was built to last a hundred years and more.

Mahoney continued, in typically mild-mannered fashion: "But years ago they used to use these great big organ pipes. They would essentially make the sound as loud as they could stand it and they had a stop watch to see how long it took to for the sound to die down.  You still see people doing something like that. I see it all the time because I do a lot of work with pipe organs. People in churches will come in and clap their hands and they time the decay with their wristwatch. But if you make a quiet clap, obviously it disappears sooner than if you made a loud clap. So that doesn't work. In the past, acousticians used shotguns and balloons, made a tape recording and did a graphical output to measure the slope of the decay. But that is very difficult to repeat. So now we use a very sophisticated digital signal processing.

"The ultimate test is truly subjective. If nobody liked the hall but the numbers were good...." " like the doctor saying," as we took the liberty of finishing his sentence for him, "the surgery was technically successful, but the patient died."

"But there were inklings beforehand that we'd achieved the crystalline clarity we sought. Once the scaffolding was down and the seats were in, we were able to converse from the stage to the top balcony. And even from the gallery farthest upstage of the house, we could have a conversation! We had to project of course, but we didn't shout. And I thought, that really bodes well," related Mahoney, adding, "Later, we had a hard hat concert for the workers - we had some local talent - and that was very reassuring. But until the really big names came out, we didn't know for sure."

We were most surprised to learn that the acoustician's domain extended well beyond the performance hall. There was need for Mahoney's expertise in the lobby for which the decision was made not to mute or muffle the sounds. The lobby's mostly hard surface, said Mahoney "was a conscious decision on our part. I think it's so much more festive." We was referring of course to the sounds of laughter and lively conversation one hears before a show and during intermission.

His expertise was called into service in the Chambers Grant Salon as well. "It's also for pre-event lectures, demonstrations, chamber music, and combos. So, I had a hand in that too." And he added, "As well as all of the singer's dressing rooms, because they warm up there."

The acoustician's job indeed gets more complex everyday. Before this interview, we had no idea how much work it took to make sounds sound good.

"You know, I am so very happy with the outcome of the project," Mahoney said in parting, adding with great modesty: "Again, I have to give enormous credit to the architect. The main thing we wanted to do was to make a place where the performers felt they had an ally, that they could really give their best, where they could take risks." And the audience could have an experience they would never forget.

The bottom line: what Bob Mahoney hoped to have accomplished with respect to acoustics in The Ellie was that the person sitting in front row orchestra, heard essentially the same beautiful sound as the person sitting in the very top balcony. On opening night, everyone was his ally, the singers gave their best, and the audience's happy consensus was that he succeeded as Mahoney, acoustician and most adept master of complexities, always does - with flying colors!

[Update: Since this interview and following several more performances in The Ellie, some minor acoustical adjustments have been made. About half the absorptive panels have been taken out of the back of the house so that the sound onstage is noticeably brighter, and changes in the pit have been made in response to the musicians' need for more elbow room.]

CLICK HERE for a sampler of Bob Mahoney's recent and upcoming projects.

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