Multi-use performing arts centers were once considered pariahs of the arts community. Through the use of adjustable acoustics systems, these types of halls can now adapt to different types of performance without degradation in sound quality and are comparable to many concert and single-purpose halls. My passion for the complexity and artistry required in the acoustic design of these spaces is revealed within this book. I wanted to dispel the many myths and use evidence-based design (not just theory) to prove that outstanding acoustics can be achieved in multi-use performance spaces.
I guide the reader from planning of the initial concept through to the final tuning, which is the featured chapter in this piece. The text is a tool for architects, acousticians, musicians, and students in addition to the general public.
Chapter 17: Tuning The Hall
Adjustable acoustic systems in a multi-use hall are most effective when they are set at the appropriate position for a particular program. Tuning the hall is the process of determining the optimal position for the musicians on the stage, as well as the shell, banners, and drapes for each type of performance or rehearsal. Calculations and modeling can determine rough, general settings, and measurements can then prove the impact on reverberation time, early reflections, and other acoustic criteria. Tuning the hall to its optimal settings requires the use of live musicians both onstage and in the orchestra pit.
A Collaborative Process
The process of tuning is one that has developed over many years through evidence-based results in dozens of facilities. No two halls are identical. Every hall has unique systems and attributes, so it is not possible to pinpoint one methodology that achieves optimal sound in all halls. That process itself is collaborative and team-based, much like the initial design of the hall.
Questions must be asked. The acoustician must listen to opinions and integrate the observations of musicians, experienced listeners, and other team members. During the tuning of Alice Tully Hall at Lincoln Center, my team gathered input through the distribution of written questionnaires to faculty, board members, and experienced listeners. At other halls, we were less formal and asked musicians specific questions about shell settings, musician positioning, and the way the hall responded to drape settings.
I believe that tuning a hall is similar to tuning a piano. The piano tuner begins by forcing the string out of tune and then slowly brings it into tune.
The basic approach begins with the acoustic banners fully extended in the hall. Gradually, the banners move to a position with an improved condition. Start with the instruments fully upstage, and gradually move them downstage into more optimal positions so as to hear the differences and understand how the hall is working. Interestingly, the same methodology of tuning is used for tuning electronic enhancement systems. With electronics, the RT is set for unnatural longer and louder reflections, and then they are backed down until the sound is natural and comfortable.
Preparing For The Tuning: What To Know
Many technicians and musicians have been gathered for the tuning, and the acoustician must be prepared.
Be familiar with all calculations and measurements before arriving. This includes checking ceiling reflector angles, ray tracing or CATT models, RT measurements, and background noise measurements. Study the drawings for acoustic drapes and banners. Know how they are labeled, where they are located, and how they are controlled. Have a thorough understanding of the control systems. Know where they are located and how they work.
What To Bring
Do not assume that drawings will be provided by the facility. Bring half-size drawings of key items. A flashlight and a 50' tape measure will be invaluable in addition to tuning tools, including the angle meter, meters, and acoustic balloons. Don’t forget to bring a camera to document the process.
What To Do
Before the tuning event begins, speak with the technical director or manager to get an accurate feel for what works, what doesn’t work, and what issues or problems have occurred in the facility. Create a tuning schedule and review it with the technical director or music dean. Confirm when groups will be in the hall and what accommodations they will require. Try to get as much community involvement as possible. Utilizing local high school bands or community chorus groups during tuning generates excitement about the new facility. Gently discourage groups that will not be helpful in the tuning process. Schedule acoustic measurements as well as breaks.
When you arrive for tuning, set up a tech station at the center of the hall with power outlets, chargers, laptop, drawings, and chairs to create a command center. Make sure a stage crew is handy, and be aware of their onsite schedule and union requirements for breaks.
Click to the next page for more!
Setting The Shell For Tuning
Setting the orchestra shell is the most time-consuming and complex part of the process. The shell has many functions; it must work acoustically, be visually attractive, mask backstage and offstage areas, allow access to musicians, allow for air flow, etc. The first step is for the theatre consultants to check the shell to ensure it is hung on the correct line sets, that the angles of the ceilings are close to our recommendations, and that lights in the ceilings are set and working correctly.
Next, bring the ceilings into the stage level, one at a time, for visual inspection. The acoustician must check for warping, delaminating, damage, and sighting down the leading and trailing edge to see that edges are straight and true.
Ceiling Angles
It is important to assess the angle of the reflector face as it relates to the stage floor. This is easily accomplished when the ceilings are lowered to about 4' (1.2m) off the floor. Check the difference in height off the stage floor for the leading and trailing edge of the shell (upstage/downstage) from that which is on the drawings. Trust the angle that ray tracing and CATT models suggest, even if it looks wrong.
Typically, the angle of the large (downstage) part of the face of all three reflectors is set at 15° to horizontal as a starting point. The rear part, or the back third of the reflector, is the curved swoop that sends energy back to the musicians on stage, and the front two-thirds of the reflector sends energy out to the hall. We investigate the first two-thirds because the rear is not angle-specific.
Each ceiling piece is a three-way valve, in a way, that operates in the time domain and in the energy domain. Sound is blended on stage to become homogeneous, directed out to the audience, and vented to the upper volume of the stage house in order to reduce the loudness of brass and percussion.
Choral Reflector
The ceiling piece located furthest upstage is the choral reflector, since the orchestra usually plays forward on the lift. Here the angle setting is steeper—up to 20° or 25°—so that choral sound is projected into the audience chamber and does not get overpowered by the orchestra.
Next, determine the height of the ceiling reflectors from the floor. Using the calculations as a guide, take a 50' tape measure to the leading edge of the shell, and fly it out to the calculated height to determine the starting point. The ceiling reflectors must pass the visual and listening tests. When lights are in the shell ceilings, the lighting variable is removed from the equation. If lights are centered between the ceilings, the process becomes more complex as lights will need to be masked, angled, and set.
Forestage Reflectors
In many halls, the shell starts with the forestage reflector, or the eyebrow piece. This extension of the orchestra shell ceiling has a slightly different function than that of the onstage reflectors. Forestage reflectors are located forward of the proscenium, and the volume above is designed to be part of the overall acoustic volume of the hall. The sound that travels through the reflectors is not lost in the stage house. It contributes later in time to the overall acoustic energy, or loudness, and drives the upper reverberant volume of the hall. If the forestage reflector is too tight, the upper volume is starved of sufficient sound energy and cannot create the proper level of reverberation. This will result in too much sound directed down to the audience and musicians, strings that are far too bright and harsh, and weak reverberation that lacks envelopment. Often, forestage musicians have a hard time hearing themselves and each other if the forestage reflector is too open, and there is already a strong reverberant field and great envelopment.
The first of the two reflectors (the one closest to the proscenium) should be set at about 20° to 25°, and the second reflector set at 15°. Utilize ray tracing to determine these positions. Sometimes, a winch is in place to provide vertical movement for the forestage reflector. This allows the array to move up and out of the way of lighting angles. If this is the case, the trailing edge of the reflector should start 30' (9.1m) off the stage. At times, the forestage reflector is fixed in position and the winch eliminated to save money on a project. This was the case at Dell Hall at the Long Center for Performing Arts in Austin, TX. Here, we set the fixed forestage ceiling reflector at a higher position than optimal, about 35' to 40' (10.7 to 12.2m) off the stage. This works, but a movable forestage reflector on a winch is preferred. Note that the angle of the forestage can be pre-set from calculations so angle adjustability is not normally required.
Click to the next page for more!
Shell Tower Settings
Orchestra shell towers, in conjunction with shell ceilings, support the orchestra and chorus with strong reflections that improve hearing, support blending, support reverberation, and project sound into the hall. Their acoustic, aesthetic, and practical design is discussed in detail in Chapter 10. Here we put them into action.
Set towers according to the theatre consultant’s design drawings, but don’t permanently mark them on the floor yet. The tower closest to the proscenium is tricky because too large a gap allows the audience to see into the stage house. Instead of dropping soft goods into that gap for masking, adjust the angles of the wall to be slightly more offstage so the line of sight is blocked adequately.
As with every adjustment, moving the towers too far offstage affects other criteria. The gap between the towers and ceilings should not exceed 24'' (0.6m) or else the positive wall/ceiling reflection pattern will be negatively affected. Visual appeal is also lost if the gap between the walls and the ceiling is uneven or too large. The 24'' (0.6m) gap allows the towers to come offstage at the fire curtain and looks good from locations in the audience chamber.
Tuning Adjustable Acoustic Drapes And Banners
As with all halls, the reverberation requirements of the symphonic orchestra are ill-disposed to amplified music and Broadway productions. For the most part, a hall should be at the most reverberant with a reverberation time of at least 2.0 seconds for classical symphony and choral music. A question presents itself: Why not leave all the drapes stored and go with max RT for symphonic tuning? There are three factors involved in this answer.
First, it is best to start with all drapes deployed to see how the room reacts and how the energy from the stage fills the room. This allows the acoustician to hear the direct sound more clearly with less cover from the reverberant field.
Second, leaving some drapes deployed provides a vital simulation of the audience condition during rehearsals. This allows the acoustician to learn how much drape to deploy to accomplish the best sound.
Third, the upper balcony seats can be a bit too reverberant. The deployment of one to three upper rear drapes might be necessary even in concert mode with audience.
Motor Controls
The advance of software programming technology for motor controls leads to a temptation to produce an unlimited number of tuning options. Avoid this mistake. Primary end-users have limited time and experience setting the system, and there is a big risk of using incorrect settings. Select controls that are designed to be intuitive to users and the tech crew and that list the type of programming being performed in the hall rather than using complex and confusing presets.
Examples Of Presets:
Symphony setting: All drapes and banners are stored except for the upper rear drape at the rear of the balcony.
Opera setting: some ceiling banners are deployed.
Amplified music/voice setting: All drapes and banners are deployed.
As much as we wish for fine-tuning control of individual acoustic criteria, such as reverberation time and early reflections, remember that acoustics aren’t controlled that acutely with any device. Acoustic banners work well, but they are a rather blunt instrument. At most, there should be one preset in between the stored and deployed setting. Many settings can be grouped together rather than individually controlled. Overly complex control systems are expensive, provide no real value to end users, and may not even be used!
Essential Features Of A Control System
Control pendant: This allows drapes to be controlled by a technician standing center stage and watching the drapes move. A duplicate control system exists in the control room.
Touchscreens and presets: These must be based on intuitive thinking rather than machine language.
Visual guide: Since drapes and banners are not always visible to the technician, it is helpful to have a numerical readout of the percentage of movement for drape positions.
Rehearsal Mode Versus Performance Mode
Since tuning of the hall occurs during rehearsal, consideration must be given to the different conditions surrounding a performance. You will need to account for this discrepancy when you complete the settings for the hall.
Plan to set the drapes so that sound is over the top, that is, too reverberant, too big, too lush. When the audience enters, the hall will settle down and come right in to line. Rehearsal mode should be 0.2 to 0.3 seconds more reverberant than optimal, to accommodate the impact of an audience. An audience also reduces direct energy and reflections. If you tune the hall during rehearsal mode for optimal sound without an audience, it will be low in reverberation, lack brightness, and lack loudness in performance mode.
The book can be purchased at CRC Press online here or on Amazon.com for Kindle and hardcover.
Stay tuned for Part Two!
Mark Holden is chairman and lead acoustic designer at Jaffe Holden Acoustics, located in Norwalk, CT. He has collaborated on hundreds of diverse performance and exhibition space designs throughout the world. He thrives on the creative design processes that call on his unique skills as an engineer, physicist, communicator, and former jazz musician to create superior acoustic environments. He lectures at universities across the United States, including Harvard and the University of Miami. He is a member of the National Council of Acoustical Consultants and elected fellow of the Acoustical Society of America.
For more, download the March issue of Live Design for free onto your iPad or iPhone from the Apple App Store, and onto your Android smartphone and tablet from Google Play, or read the interactive PDF.