BAI, LLC

by Charles R. Bonner
President
BAI, LLC
Consultants in Acoustics and Audio-Video Technologies

Introduction:

The acoustics of performing arts venues, as perceived by audiences and critics, is a confluence of the natural (i.e. non-amplified) acoustics of the spaces, and the sound systems serving the spaces (to the extent that such systems are employed). Some events, such as orchestral performances, rely upon natural acoustics, with varying results from venue to venue. Other performance types such as Musicals, Plays, Pageants and the like rely on sound amplification. Such amplification works together with the room acoustics to produce specific results. Touring shows generally bring their own sound systems with them; the same system is used for every venue toured.

Natural Room Acoustics Elements:

In its most basic terms, the acoustics of a venue is represented by the following elements:

• The loudness of the direct sound as observed by the audience (the shortest line-of-sight distance from sound source to listener);
• The timing and loudness of the early reflected sound energy from walls and ceilings;
• The timing and loudness of the late reflected sound energy from walls and ceilings;
• The ability, or the lack of ability, of the walls and ceilings to reflect low, mid and high tones, ;
• The feature known as reverberation time, which is a confluence of all of the above attributes, and finally;
• The background noise level loudness that is generated by mechanical equipment and air delivery systems.

The ability of the spoken word to be audible and intelligible to the audience is controlled by the loudness of the direct sound as compared with the loudness of the reverberant sound energy in the room. If the loudness of the sound source is not audible, intelligible or pleasing to the listener because of room acoustic effects, sound amplification systems may be and frequently are used. In some cases, the loudspeaker systems may simply increase the direct sound loudness as compared to the reverberant loudness, with only small amounts of amplification. There are limits to the amount of amplification that can be achieved; the theoretical limit that applies to amplification is reached when the loudness delivered by the source to the microphone is equal to the loudness delivered to the audience by the loudspeaker system.

21st century audio technology that comprises sound systems for Performing Arts venues has developed from meager beginnings during the decades from the 1950′s to this day. Development of loudspeaker systems advanced, thanks in no small part by sound equipment manufacturer, acoustical consultants and the increasingly rigorous demands of the touring sound industry.

Sound systems for the Performing Arts are broadly classified into two principal categories: (1) sound amplification systems, and (2) electronic enhancement of room acoustics (which is referred to here as electroacoustic architecture, or  as later described).

Traditional Sound Amplification Systems:

In its basic form, a sound amplification system is a vehicle that is used to amplify a sound source, which may be generated by people, musical instruments, compact disc, DVD or other sources. If the loudspeakers are sufficiently directional, such systems can partially overcome the effects of excessively reverberant acoustics. Such systems tend to function within the acoustical environment that is presented to the loudspeaker systems. Reverberation time and other acoustic parameters work together with the directionality of loudspeaker systems to produce a specified and predictable result.

The technological advances that have occurred in the most recent past include the following elements:

• Loudspeaker systems which provide extended response and narrow beam patterns, which reduce the influence of room reverberation upon audio quality, some of them are available in configurations that permit digital control (or steering) of loudspeaker response and beam widths;
• Digital control of such loudspeaker systems;
• Digital routing of audio signals point to point within sound system electronics, avoiding cumbersome and trouble-prone manual patch panels;
• Digital mixing of audio sources, enabling instant audio scene changes at the touch of a button;
• Very high quality UHF wireless microphone systems;
• Infrared Assistive Listening Devices for the hearing impaired.

These and other technology upgrades have made sound systems more adaptable to today’s changing requirements for sound amplification. Touring Broadway shows (like The Lion King) can and are produced with complete (and hands-free) computer controlled sound systems, and school auditoriums around the country can easily be operated by today’s digitally-qualified students.

All of these advances increasingly optimize sound system performance, even in acoustically difficult rooms.

Electronic Acoustical Enhancement Systems:

Electroacoustic architecture, on the other hand, uses many (in some cases over 100) loudspeakers and multiple microphones located strategically to either side and above performers and audience to create a specific acoustical environment that the venue does not provide naturally. This technology has been under development in Europe and Asia since the 1970′s, and has only been introduced in the U.S. within the past five years (2003-2008),

The microphones used in these electroacoustic architecture systems receive the natural sound by orchestras, bands and choral ensembles, digitally process this sound energy, and reproduce an enhanced electroacoustic signal via the loudspeakers. This energy, in turn, re-enters the same microphones, is processed again and reproduced again. This chain of regenerative signals continues to occur until the perceived acoustical characteristics become inaudible, thus creating reverberation and individual electroacoustic reflections that are unique to the rooms in which the technology is installed.

The loudspeakers and microphones are customarily concealed within the architecture of the room, and are therefore invisible to the performers and audiences alike. Invisible subwoofer loudspeakers can be included as an acoustical warmth enhancement tool. These systems include combination or a-la-carte features that encompass many natural acoustical attributes, at the touch of a single button:

• Reverberation Time (short, moderate, long);
• Acoustic envelopment (Off, Moderate, Enhanced);
• Acoustical Warmth Settings (Off, Moderate, Enhanced).

The result is an apparent acoustic environment which is not amplified, but rather is an extension of the acoustic capabilities of the theatres and halls that contain these systems. In summary, these systems can make acoustically ordinary theatres, churches or concert halls into extraordinary acoustic facilities.

Systems of this nature have been installed in numerous states in the U.S., and have been proven to be quite an effective tool in the acoustical consultants repertoire. The author’s firm has traveled throughout the U.S. and Asia listening and observing these systems, and embraces the technology as being useful in facilities lacking optimum natural acoustical design because of budgetary restrictions. Typical examples of projects are school auditoriums, churches and university theatres.

An example: the 2300-seat Performing Arts Center at LeTourneau University in Longview, Texas. This hall is an example of a totally natural acoustic environment, and was designed from scratch to serve that mission. Adjustable acoustical curtain systems change reverberation time to support symphony, touring road shows and speaking events.

LeTourneau University Performing Arts Center

LeTourneau Auditorium

The second set of images is of a theatre renovation now (January 2009) under construction at a major University campus in the Southeastern U.S., scheduled for completion in the fall of 2010. Limited available ceiling height, resulting in lower-than-desirable reverberation time for symphonic music performance, made this theatre attractive for electroacoustic architecture; as of this writing, this example is unique in this part of the U.S.

(Rendering credit: HMS)

(Rendering credit: HMS)