Variable Acoustics

Modern halls and churches come in all shapes and sizes, and the push for these spaces to be multipurpose spaces creates acoustical challenges. From music requiring long reverberation times, to dramatic performances that require greater articulation and ambient warmth, a venue must often accommodate performances with conflicting acoustical requirements such as music versus drama. The acoustic properties of a space depend on its reverberation time, volume and the physical makeup of the space. If a space is reverberant enough for classical music, intelligibility and localization of the spoken word can be compromised.

In the past this issue has been addressed in a number of ways. The most common way is that the room is designed to its longest reverberant quality (typically for music) and then the room has sound absorptive banners or panels added to shorten the reverberation time for speech based events. While this can work well, it requires a fair amount of time to adjust a large room and does not allow for a performance venue to be “quickly turned” from one type of event to another.

With electronic enhancement, the acoustic performance of a venue can be very quickly altered to best suit the event. An electronic acoustic enhancement system can be an effective means of resolving sound quality challenges in ways that traditional architecture can’t easily accomplish, the drawback is the cost. To appreciate the complexity of the system and the cost we must look at the “electronic architecture” of these systems.

The electronic enhancement works just the opposite of architectural adjustments. In the case of the room that is architecturally adjusted we start with a “live” room and shorten the reverberation time; for the electronic room we start with a room with a short reverberation time and then liven it up electronically. To liven a room up electronically we need to locate a large number of loudspeakers around the space, the bigger the space the more loudspeakers. Each of these loudspeakers usually needs its own acoustical signal shaping processor (DSP – digital signal processing) and its own power amplifier. The goal is that each loudspeaker needs to simulate the sound field that would have been reflected off a surface into your ear.

When you think about the last great sounding room you were in, there were many, many surfaces that reflected sound into your ear. The more loudspeakers the better the enhancement, the more expensive the system.

Four systems that we would consider when designing a space using variable acoustics come from:

The maker of the Lexicon Acoustic Reverberation Enhancement System is located in the Boston area. LARES began as a Lexicon product. The system uses a time-varying technique to shift the output in time enough to maintain stability but not enough to introduce tonal coloration.

Based in Sierra Madre, California, and Western Canada, LCS makes the Variable Room Acoustics System. VRAS. The VRAS system acts similarly in acoustically coupled spaces. The processing hardware is the LCS matrix system with an interface written in the BeOS operating system.

Based in Garderen, Netherlands, the ACS system uses a large number of microphones “typically 12 or more” in microphones arrays. The arrays create specific coverage patterns for the input side of the system. The ASC hardware system is based on a card-cage configuration.

SIAP, developed by SIAP B.V. at Uden, Netherlands, typically positions microphones close to the source of the performance (within 26 to 32 feet). SIAP offers only enough energy to make up deficiencies in the natural sound. The hardware system is a remotely controlled card-cage configuration.

So the short answer is yes we can change the acoustical feel of a space very quickly but does the project have the budget.