Concert hall acoustics in the 21st century: Interview with Sam Berkow

Sam Berkow is the founding member of SIA Acoustics and SIA Software Company, Inc. He is best known as the acoustical designer of performing arts venues and recording studios and as the developer of the SIA-Smaart acoustical measurement system. Sam enjoys a wide range of musical styles, and believes that modern performance spaces should support this wide range of performances, without acoustical compromise!  Sam began his career in acoustics under the tutelage of Russell Johnson. He has also engineered and produced music for bands and musicians, as varied as Steven Bernstein, Frozen Concentrate, Ali Jackson and Wynton Marsalis.

When you’re working on a classical music hall or theatre, what are the objectives that clients ask for most often?

Almost all clients ask for “great acoustics”. However, few understand what it takes to further define and achieve that goal. When I started in acoustical design in the early 1980s, we would hear clients start by saying “The room needs to be a great place to listen to music”. Then in the 1990s that became: “The Halls needs to be a great place to perform and listen to music”. In the 2000s the priorities have evolved to become: “The room needs to be a great place to perform, listen and record/broadcast music”. With Jazz at Lincoln Center and other arts organizations, their broadcasts mean they can reach many times the audience in the hall.

Back when I started, we developed a decision tree to help clients understand the choices they were making. The first layer of that decision tree was the split between those halls being designed for truly acoustic, non-amplified music and those designed for amplified music. That has radically changed. The halls that have been designed in the past 15 years or so and almost all halls going forward for the foreseeable future, have a new set of underlying priorities: they must support high quality amplified performances, even if they are home to an orchestra performing unamplified concerts. Also the needs of recording and broadcast must be addressed in the design of any new concert venue, as every venue has become a broadcast facility to at least some extent.

While this evolution does not sit well with some traditionalists, it has become the standard, as even orchestral Pops concerts often require amplification. Also the quality of professional audio gear has increased dramatically, and when properly designed, setup and operated in well designed, tonally balanced rooms, many of today’s systems can provide very high quality listening experiences.

What are the most important things that clients don’t necessarily ask for, but you think are crucial for success?

When clients ask for “great acoustics” and are looking to build a venue where performances are either unamplified or “lightly amplified”, we help them to understand that they are really asking for a set of well defined goals, each of which presents its own challenges. These include:

Quiet: Great venues are quiet. Really quiet. This means that a venue featuring unamplified music must be isolated from intrusive noise. In most cases this means that the concert hall will include box-in-box construction or be surrounded by lobbies and other noise controlled spaces. The air-conditioning system must also be designed for low noise performance. Addressing just these two items can increase the cost of a venue by millions of dollars. One funny story is that during a meeting early in a concert hall project, the mechanical engineer decided that he would speak his mind. “These acoustical guys have us designing the HVAC to be so quiet that the audience breathing will be at the same sound level!” We replied that orchestral audiences get quiet together, to listen to quiet moments, they will even collectively hold their breath!

Tonal Balance: We have all heard rooms that sound “boomy” or “tinny”. These are rooms that are NOT tonally balanced. In general, to achieve tonal balance, we look at the decay rates of sound in the space. In a tonally balanced room, the lower frequencies (the octaves below middle C) will decay about 1.35 times the decay at mid to higher frequencies (two to three octaves above middle C). Most materials either reflect most sound or absorb high frequencies easily and low frequencies inefficiently! Without carefully selecting both the materials used and the way that these materials are mounted, it is easy to create a boomy or tinny acoustical environment.

Uniformity of Sound: Ideally everyone in the audience will hear/experience a similar sound in terms of tonality, impact and envelopment. Of course, this is never truly the case. However, designing the hall to eliminate deep under-balcony spaces (where, if not properly treated, low frequencies can muddy the sound), can go a long way to getting closer to this goal.

Stage Acoustics that both project sound to the audience and allow the musicians to hear each other AND support recording! – That’s a mouthful! For orchestral halls, the need for cross-stage communication between musicians is critical (this allows musicians to hear other parts of their orchestra). However, strong reflections that can be understood by the brain, a favorite way to create cross-stage communication between orchestral musicians, are NOT conducive to clean recordings.

When smaller ensembles are on the same stage, the long reflections required by a full orchestra are not helpful. The modern approach we have adopted is to incorporate more diffusive sound scattering materials into the areas around and above the stage. The increase in diffusion results in a stage where both small and larger ensembles can hear each other and microphones are not subject to strong reflections that often cause unwanted change in the tonal response.

Lastly, in many modern halls, “light amplification” is used. This term refers to the case when the sound from the stage is a significant part of what the audience hears and the sound system is used to create balance between instruments and increase the volume of the human voice. Audience expectations for the human voice have been greatly increased as we listen to movies, television and radio.

How, and how much, do the objectives set by clients vary for different types of music? How much do they vary just according to the clients' individual taste? And how does any of this affect the methods that you use?

When we start a project, we often visit a number of venues with our client and members of the design team. We feel that having common listening experiences is critical in being able to talk about the sound of various halls.

For different musical types, there are some specific requirements and configurations. An example is: for opera, balance between the vocalists on stage and the orchestra in the pit is a critical requirement. So we try to create a pit where musicians can hear each other and the sound can project to the audience, while the sound from the front of the stage is also projected forward to the audience. To achieve these items, we use diffusive surfaces within the pit and reflective eyebrows above the stage on the audience side of the proscenium, and when possible we add a reflective surface above the stage on the stage side of the proscenium.

I think it's important to note that in the traditional European concert hall, the orchestra performs on a platform in the same air volume that it shares with the audience. The concert hall was NOT asked to be a theater or opera house or support ballet. The idea of a multi-purpose hall with a proscenium being used as a theater and concert hall is a mostly American invention. It was only in the 1970s and 1980s that a significant number of new American halls positioned the orchestra in front of the proscenium. When I mention this, I am often asked about Carnegie Hall (which has a very large proscenium). While the proscenium at Carnegie is a prominent architectural feature, it is so large that the air volume of the space in front and behind the proscenium act as one large air volume – achieving the European standard and design goal of the orchestra and audience sharing a single volume of air.

When clients have a favorite hall, we try and measure that space to see what the acoustical response is. We try and determine how their stated preference for a space relates to the measurements and then how we can achieve a similar result in our design. We put tremendous faith in acoustic measurement as a tool to help us document, quantify and understand what we are hearing, as well as a way of comparing architectural design elements.

Are there any particular techniques and/or materials that you think are new and exciting? Or toys that you can’t wait to get your hands on?

I am always excited to see what predictive tools people are developing. I have been very active in developing acoustic measurement tools, and as the next generation of tools is becoming more practical, I think we will be seeing better studies of the three dimensionalfields being generated in our concert halls.

We see large numbers of people starting to manufacture a wide range of acoustically diffusive surfaces and this gives us a range of options. Some of these surfaces are really interesting in the range of frequencies they are able to diffuse.

New sound systems continue to get better, with lower distortion and better directional control. The current state of the art with systems that adapt to room designs is really intriguing. We have been playing with them, but have not used them in a permanent install... yet.

And of course, there are all sorts of new musicians playing amazing new music. I'm fascinated by musicians who merge classical, jazz, rock and other influences, such as Joshua Redman, Yo-Yo Ma, Christian McBride, Ted Nash, Ali Farka Touré, the band Tinariwen, Wynton Marsalis, Herbie Hancock, John Zorn, Stephen Bernstein, Henry Butler, Edger Meyer, Arcadi Volodos, and many many others. This is what makes our work so much fun!

What should an ordinary audience member listen out for when evaluating how good a hall is and where the best-sounding seats are likely to be?

I would start by avoiding bad seats. I had heard that La Scala was one of the great sounding opera houses in the world. My first night there I was given a seat in the very rear of a box and I couldn’t really hear anything – the sound was muffled, and weak. At intermission, I mentioned this to my host, who arranged for me to sit in the front of the box for the second half, where the sound was glorious. For classical music events, try to avoid sitting under an overhang (more than three or four rows) or next to a wall, or deep in the back of a box. If the hall is fan-shaped, I try and sit further back in the orchestra (as the fan shaping tends to push side reflections further to the rear of the orchestra). If the hall has a shoe-box shape, I try to sit more in the middle of the orchestra level seating. In unamplified venues and performances, seating behind the orchestra is interesting in many ways, but rarely a tonally balanced listening experience.

What are the particular challenges if a space is going to be used for both classical and non-classical music?

As I mentioned earlier, it is true that now, almost all classical halls music halls support a range of amplified productions. The Disney Hall in Los Angeles opened with little support for amplified music, but more than 50% of the performances presented the first year required amplification. This resulted in a multi-million dollar effort to retrofit some adjustable acoustical absorption into the space.

To address this dichotomy, I think there are a few items that require attention:

a) First, how much sound from the stage will the audience be hearing? In Jazz venues, this is very often a large percentage of performances. For heavy rock shows, the sound system simply overpowers the stage sound. This information helps us determine both what the stage acoustics should be and how the halls walls and ceiling should be treated (or at least including retractable treatments). Consider the new SFJAZZ Center. This 800-seat venue presents a wide range or jazz performances, as well as chamber music and other non and lightly amplified events. To address this we designed a venue that has a large diffusive canopy above the stage and an acoustical diffuser in the lower portion of the upstage wall. This diffuser can be covered by a set of retractable acoustically absorptive panels to reduce the amount of energy on stage for heavily amplified events. Sadly (for me) all of these diffusive elements are hidden from the audience by wood slats.

b) How is the sound system designed and operated? Relatively few systems are really well designed and even fewer well-tuned. However the number of both of these categories is increasing! On the design side, systems that reduce the amount of off-axis low frequency energy on stage should be used. In the SFJAZZ Hall, the low frequencies are controlled by used a five element cardioid subwoofer array. This means that the five boxes reproducing the lowest frequencies are set up in a way that results in much less sound hitting the stage, which in turn makes it easier for musicians to hear each other and for microphones to respond to subtle tonal changes.

Do you prefer working on new build or on refurbishments? What are the joys and challenges of each?

With new construction projects, you face problems such as “what do we want/need to build?” and how these items are prioritized. With renovations, there is always the unknown. In one case, digging down through the basement of a building, we hit a river (yes there are rivers below some of the buildings in midtown Manhattan!). While you can study existing buildings, there are often things you cannot see until significant demolition has been done!

There is a very different kind of pride one feels in being part of the continuing saga of a storied historic venue or kicking off a new venue. In either case, the excitement is real and very moving. One of the greatest thrills I have experienced in my personal and professional life is helping visionary leaders such as Wynton Marsalis at Jazz at Lincoln Center, Nick Forster of eTown Hall and Randall Kline of SFJAZZ fulfill their dreams for building a venue to move their vision for their organizations forward.

What classical-related project are you most proud of? And what’s been the most problematic?

I consider the concert halls and venues at Jazz at Lincoln Center modern classical venues, supporting both unamplified performances and lightly amplified events. In Rose Hall and The Appel Room, the audience hears a great deal of energy from the stage and the tonal balance is critical to the success of these rooms. Working with Wynton Marsalis on the design of the JALC facility has inspired me, personally, to strive for excellence in everything I do.

I loved working on eTown Hall. This is a small facility in Boulder, Colorado. We took an older abandoned church and turned it into a 220-seat concert venue designed to support acoustic music. The facility also includes a substantial recording studio, some post-production audio and video rooms as well as the eTown offices and a community gathering space. This venue was built on a very tight budget and has become a home for great musical experiences! I am extremely proud to have become part of the eTown community (see www.etown.org)

The new SFJAZZ Center is a dream come true: an 800-seat venue and a 70-seat venue in one building. The range of music they present thrills me (I try and attend as often as possible). The room has a great sound, an intimate feeling that is shared by audiences and performers.

Which are your favourite halls? Is there anyone’s work you particularly admire?

I love the great European Halls for orchestral concerts. Is there a better hall than Amsterdam’s Concertgebouw? I love the 6000-seat Greek Theater in LA for amplified events and I have heard some wonderful performances at the Hollywood Bowl (Gustavo Dudamel’s Carmina Burana really impressed me this past year). The Meyerson Symphony Center in Dallas and its sister room, Birmingham Symphony Hall, remain favorites.

I was very lucky to have worked for and with Russell Johnson, who was a mentor to me in the acoustical design of orchestral concert venues. I was also lucky to work with, and become close friends with, Don Pearson, who was a master sound system designer and system engineer. Sadly both of these legends have passed on.

For Jazz in a small venue, in NYC we have the Jazz Standard, a wonderful basement club, where the food is great and the music is greater! And every Jazz fan should make the pilgrimage to Preservation Hall in New Orleans.

On the subject of Russell, one of my favourite concert halls is Müpa in Budapest, where I remember being able to hear the decaying notes of a harp in the middle of a full Wagnerian orchestra in Das Rheingold.

In the traditional model of a concert hall, intelligibility and reverberation are diametrically opposed. Russell was seeking a model that would let you have both. The way he achieved this was to develop a theory of coupled spaces. If you're sitting on a centre line and the side wall is 10 metres one way or the other, the reflections will come in a nice short time; they're just going to build up the strength of the tone and going to give you the sense of envelopment. If the hall is too wide, the reflections come too late and they turn to mud. So it's better if the room gets narrower as you go back. But that's at the expense of seat count.

Russell's other big thing was making rooms quiet. The need for quiet in halls is something that's getting overlooked now – the problem is whether we can afford to make a room really quiet. In one South Carolina church I worked on, where the older congregation couldn't hear the words of the service, they thought the choice was to spend mega money rebuilding the room, or buy a new sound system.  I demonstrated that by simply turning off the aircon they could substantially improve perceived intelligibility. The cost of lowering the noise level of the aircon was only a tiny fraction of the other options.

I remember going to see Pierre Boulez at Carnegie Hall with Phil Lesh, bass player of the Grateful Dead [who at one point held the record for the loudest rock concert in history], who was a contemporary classical music fan. Boulez was doing Webern's Six pieces for orchestra, and there's a section where the double basses are tapping the strings repeatedly, really quietly, which he repeated three times. After the show, I asked Pierre why, and he explained that he started doing this because halls aren't quiet enough and he often found that the audience simply doesn't hear the first repeat. Phil whispered to me, joking: “why doesn't he just turn it up?”!

There are questions we face as designers of halls.  For example, with many modern halls being seen as part of an urban renewal project rather than primarily as an artistic space, what are we building? It's like some of the new baseball stadiums: they're a great place for corporate entertaining, but are they a good place to watch a ball game?

In a modern concert hall, what we do architecturally is to do everything we can to enable musicians to hear each other. That's what enables people to have a real expression on that stage and a musical experience in the hall.