Now Hear This: High School Acoustics


This is my first in a series of occasional ramblings about acoustics and sound. In our experience, performance venues fall into three or four broad categories of cost and acoustic performance: high schools, colleges, professional, and world-class. World-class facilities have familiar names such as Lincoln Center, Carnegie Hall, and Bass Hall. Here, as one would expect, acoustic quality is at the highest possible level, without compromises on air system noise (dead silent). Sound isolation to the exterior noises is almost 100%, and musicians, audiences, and management are extremely satisfied. Costs typically run over $500 per square foot and might reach over $1,500 in cities like New York or Boston.

Virtually no high school can afford a $100 million performance hall, but perhaps they really don't want the operational costs and maintenance of such a “white elephant” anyway. These facilities need a flexible performance venue for the wide variety of performances and rehearsals, at a very modest cost, and one that is durable and easy to operate with limited staff and budget.

High school acoustic performance, while admittedly on the opposite end of the acoustic quality spectrum from world-class, has improved in recent decades, blurring the boundaries with higher education spaces. High school boards are demanding spaces that work for a wide variety of performances, from the chorus and band, to Broadway-style productions, to hosting the local symphony and community theatre company.

No longer is the café-gym-atorium the model, with its low ceiling, flat floor slope, tiny stage, and wide fan shape that many of us sat in a few — well, more than a few — years ago. These spaces were acoustically and theatrically poor, lacking intimacy and contact between performers and audiences. Loud sounds of bands and orchestras overloaded the halls, making for shrill and harsh sounding spaces, and the low ceilings made them dead sounding. When the high school musical was staged with minimal PA from a local music store, the feedback was ear splitting and words unintelligible to all but the singer's proud parents.

Sound quality expectations, in some ways (and yet not in others), have been raised by the plethora of high tech surround sound systems in everyday homes and cars. Ear buds and iPods raise the expectations of performance venues far beyond that of just a generation ago. Audiences and performers may not know how to actually get good sound quality, but as a Supreme Court Justice famously quipped, “I know it when I see (or hear) it.”

To meet these demands of higher quality spaces, design teams (acousticians, architects, engineers, project managers) are designing a number of raked floor halls, possibly with a tiny balcony, a partial orchestra pit, partially rigged stage house, and even a modest orchestra shell. The shell might be equipment that is bought from PTA funds at a later date, and the sound and lighting may be minimal to start, but some of these venues rival many small colleges and university auditoria in capability and acoustic quality.

How do we approach today's high school with a modest budget but big expectations? There are a few things to consider. We have to provide adequate acoustic volume in the hall, at least 300cu-ft. per person, which equates to a minimum ceiling height of 40' to 45'. There is no substitute for having enough volume in the hall. Without it, the hall is overly bright for amplified events and too dead for the classical programs.

We use two layers of drywall with some modest shaping. This goes a long way to improving the sound of a hall over flat walls with a single layer of drywall. Also, the air systems need to be quiet but need not be dead quiet. Using conventional air handling units (AHU) and variable air volume (VAV), AHU systems with low first cost and high-energy efficiency can be quiet. Remote locations of oversized VAV boxes and duct lining down stream inside oversized ducts will keep things quiet if the main AHU is remote (don't put it on the hall roof!).

Avoid fan-shaped plans. They send all sidewall sound reflections away from the audience and into the back corners, near the entry doors — good for the usher stationed there but not for your audiences in the rest of the room. Think rectangular!

Provide for future technology, sound systems, and lighting systems, even if only power and cableways can be provided now. Get catwalks in the ceiling with the basic building, leaving the ceiling mostly open for future sound systems, theatrical lighting, and other gear (video projectors, house lights). Acoustic reflectors can be hung later, if needed.

Modest acoustic drapes that are simply walk-along, heavy, gathered velour on the side walls will allow the room to function (when stored) as a modest concert hall, and when deployed, as a Broadway-style house for amplified musicals.

What does that mean for tomorrow's new and renovated higher education facilities? We believe that these lines are blurring with professional or municipal class facilities. Town-and-gown halls that double as the home to the city opera, ballet, and symphony orchestra have been built in many communities, and many are located on the university campus for use by faculty and students.

More on all that another time.