The Music Center At Strathmore - variable acoustic controls

February 4, 2005

The opening of The Music Center at Strathmore was celebrated with a gala concert by the Baltimore Symphony Orchestra on Saturday, Feburary 5, 2005. The second home for the BSO, this concert hall was designed by William Rawn Associates of Boston, along with acoustician, Kirkegaard Associates, and theatre designer and consultant, Theatre Projects Consultants (TPC). The hall features world-class acoustics for symphonic and classical music with the added benefit of allowing the room to be adjusted to create an exceptional acoustical environment for a wide range of other types of musical performance both un-amplified and amplified.

The following article discusses the special acoustic elements and unique control system. It was written by Michael Nishball, Director of Technical Production for Theatre Projects, who led the equipment design team.





A concert hall design these days invariably has numerous motorized acoustic devices to diffuse, focus, absorb, and enhance the naturally produced sound coming from the concert platform. These devices appear deceptively simple but are often very complex.

For sound absorption we often utilize fabric on motorized or manual curtain tracks, fabric on motorized rollers in a banner configuration, and rigid fabric wrapped panels in all types of movable configurations. Sound diffusion and focus is aided by the use of various reflecting surfaces, such as architectural features of the room and suspended reflectors made from a wide range of materials. These devices have been among the primary techniques utilized by many of today's acousticians. To that end I have been fortunate in my practice at Theatre Projects Consultants (TPC) to work along side many of these fine acousticians in developing the machinery and controls for variable acoustic devices in both large and small projects.

The Music Center at Strathmore in Montgomery County Maryland has a particularly complex and grand array of variable acoustic devices that required a control system that could organize, display, and execute the movement and position status of 110 electro mechanical elements. Working with the acoustician for the Music Center, Kirkegaard Associates of Chicago (Larry Kirkegaard and Carl Giegold), TPC specified these devices and the control system. The control user interface had to store and recall large amounts of data and be immediately operable by a technician with a reasonable amount of training.

Following the successful bid by JR Clancy on our performance specification for the variable acoustic controls, Larry Eschelbacher and his team began to discuss and refine TPC's design criteria for the controls.

A common push button approach is taken to controls when positioning tracking fabrics, banners, and acoustic panels that move in one axis. This axis of movement is either open/deployed into the auditorium or closed/retracted into storage out of the acoustic volume of the hall. In more demanding control designs these absorption elements may have several intermediate positions representing a percentage of absorption that must be calibrated and displayed by the control system but this again is considered one axis of movement and visualized simply.

What the Strathmore controls required was an organizing system to access and visualize 43 individual acoustic reflectors each having three axes of movement in addition to numerous absorptive elements, concert lighting hoists and speaker hoists. One Acoustic Panel Reflector (APR) with three axes can create an unlimited number of positions or attitudes. Combine this one APR with the other 42 APR's in a stage canopy system and the profiles you offer the acoustician and the performing artists are limitless.

With enough processing power and Mr. Eschelbacher's expertise we set out to achieve a user control interface that could recall and display real time APR canopy system moves with pre-visualization of any configuration. We succeeded with an industrial grade 15" touch screen, programmable logic controller (PLC) and graphic language that are stunning. With its positioning accuracy and resolution it is unlike anything that has been done before.

By importing digital images of the hall and being able to zoom, orbit, pan etc. within the visualization display the APR's on screen can very accurately mimic what is onstage in the current position and display what the preset target position will be for one or all of the APR's.

This is particularly effective serendipitously. For as is the case in many cutting edge endeavors such as this we did not realize until the 1/2" acrylic reflectors were rigged and unwrapped that the combined clarity of the material and the concert lighting made it difficult to accurately see exactly what attitude the APR's were in. We began to rely on the Production Control Panel's (PCP) superb graphics to preview new system presets backstage.

The PCP contains the full visualization display, as well as the preset and status pages for the system. Also integral to the system is a remote pendant controller with a 9" touch screen and momentary operators that quite easily move one or all of the acoustic devices in the system from any line-of site location on the orchestra level.

Within minutes a conductor, technician, or acoustician can sit in the house, select and execute a preset from previous rehearsals or build a new one to compare its effect on the music being produced. Complex reflector arrays that would take inordinate amounts of time to achieve now take minutes and are accelerating everyone's understanding of the acoustic potential for the hall.

The APR hoists are a solid refinement to a 1992 unit designed for Davies Symphony Hall in San Francisco by stage engineer, George Van Buren, and still in service today. The hoist is very compact and portable by achieving vertical travel with a conventional moving drum and the various reflector attitudes with four lead screws deflecting the lift-lines within the footprint of the hoist. The 6'6" x 6'6" reflectors weigh 125 pounds and are safely suspended with 1/8" wire rope at the corners. Borrowing from the world of aviation, the complex movement of the APR's is categorized as a "roll" axis in positive and negative degrees from level and a "pitch" axis in the same manner.

What is remarkable and a significant improvement to the Davies control system is the precision of the feedback in elevation (feet/inches) and attitude (degrees to one decimal place). This data is available on the status screen then validated by the three-dimensional visual display that makes it a powerful diagnostic tool.

The design and execution of a complex performance equipment control system for multiple acoustic devices require uncommon experience, knowledge, and forethought from the team of acoustician, theatre consultant, and contractor. It was a pleasure to be part of such a team for the Music Center at Strathmore.

Michael Nishball
Director of Technical Production
Theatre Projects Consultants

The Music Center At Strathmore - variable acoustic controls
Credit: Alan Karchmer/Esto
The Music Center At Strathmore - variable acoustic controls
Credit: Theatre Projects