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Preferred Acoustics of Performance Spaces and Sanctuaries, Part 2

David Kennedy • May 2021Tech Feature • May 7, 2021

Last month (FOH, April, 2021, page 23) David Kennedy  published text and images extracted from Chapter 10 of Acoustics in Worship by Richard A. Honeycutt (printed by Elektor International Media, London and used by permission). This month, after a summary of last month’s article, he delves deeper into the preferred acoustics of performance spaces and sanctuaries. —ed.

Reverb Time (RT60) is defined as the length of time required for the amplitude of a signal — in this case a steady sound source such as pink noise played at 0 dB — to drop by -60 dB after the sound is turned off. RT60’s can vary widely, from as short as 0.3 seconds in a dry, highly absorptive space such as a recording studio, to 1.4 to 2 seconds in a concert or opera hall, or as much as 10 seconds in a large cathedral.

The preferred acoustical performance of any space depends upon the program material to be used. Performance spaces can be categorized as music halls, drama theaters, lecture halls, or multipurpose auditoria, with several subcategory spaces. Sanctuaries share similar subcategories, depending upon the style of worship music. However, sanctuaries also need to perform well for speech; thus, some compromise is often needed. The classification of worship music styles has involved some effort for generations. Early acoustical texts divided worship music into Catholic styles and Protestant/Synagogue styles. Considerable diversification has occurred, so that now classifying by denomination is not instructive. Neither is classification as “traditional” or “contemporary,” as hymns of the late 19th and early 20th century are considered traditional by some people, while to others, “traditional” means Bach; and to still others, “traditional” means one of the several gospel styles. “Contemporary” can mean the “folk-gospel” styles of the 1960’s and later, while light-pop styles might include many praise choruses or Christian rock styles.

Baroque

Baroque music is typified by the compositions of J. S. Bach, G. F. Handel, and Antonio Vivaldi. These compositions were affected by the environment in which the composers worked. Bach’s church (Thomaskirche in Leipzig Germany), is thought to have had a reverb time (RT60) about 1.6 seconds. The migration of church architecture toward styles having less reverberation came about largely because of the Protestant emphasis on the spoken word in worship services, as opposed to the ritual chants in a foreign language used in Catholic services. This much shorter reverberation time allowed Baroque music to be more highly figured than medieval music, which was written for Gothic cathedrals. Likewise, Handel’s oratorios were often performed in rather small halls (seating about 400-600) having RT60’s of about 1.5 seconds. Therefore, Baroque music and Italian opera sounds best in venues having an RT60 of 1.5-1.6 seconds.

The room dimensions and material choices that lead to an RT60 in this range also lead to good clarity, intimacy and speech intelligibility if proper attention is paid to creating surfaces for early reflection of sound from performers to the audience. Proper shaping of stage houses can provide good stage support as well. Envelopment and spaciousness require diffuse sidewall reflections, which can be provided architecturally or by use of specifically designed diffusing surfaces.

Many performance and worship spaces built since the 19th century make heavy use of gypsum or wood paneling rather than the plaster that was common in older buildings. These materials can have excessive acoustical absorption at low frequencies, even extending into the bass vocal range. The result of this can be an RT60 that is too low and acoustical strength at those frequencies will make the room sound “thin.”

A low RT60 will not mask echoes very well, so Baroque rooms need careful attention to diffusing or absorbing surfaces on the rear and side walls to prevent “slap” and “flutter” echoes. If a Baroque room is built with the correct RT60 and proper attention to clarity, strength and prevention of echoes, even unamplified speech will often be reasonably intelligible, and design of a sound reinforcement system will be straightforward.

Classical

Classical music is the category that encompasses Mozart, Haydn, Beethoven and Schubert. This music tends to be less complex than Baroque music, and often consists of a melody over an accompaniment of chords. Many traditional hymn melodies written before the 20th century are classical in style, so one definition of a “traditional” worship style is that which involves classical-style music. In the development of music, the Classical and the later Romantic eras are not well defined, but have been called a continuum of development. Indeed, although Beethoven’s early music is considered Classical, some of his later music, especially the sixth and ninth symphonies, can be considered Romantic.

Classical and Romantic music encompasses both chamber music, which is usually performed in an intimate setting having an RT60 about 1.4 seconds, and concert repertoire for larger halls, typically in the 1.7second range for Classical and extending to about 2 seconds for Romantic music. In the Romantic period, some of the fine detail in the music became less common, and wide dynamic range and a passionate feel replaced it; hence the decreased need for clarity (due to shorter RT60) and increased need for the emotional charge resulting from a longer RT60. The comments on other acoustical properties made in the section on Baroque spaces also applies to Classical/Romantic spaces, with the reminder that when clear speech is important and a longer RT60 (over 1.6 seconds) is chosen, architectural design needs to incorporate careful provisions to maximize clarity and speech intelligibility, even though a good sound system is used.

Folk/Jazz

Traditional indoor venues for folk music have been cafes and similar small, intimate spaces. Although there are a few auditoria specifically intended for folk music, these are rare. Since folk music requires great intimacy, reverberation time in a venue designed for this music should be very low — perhaps 1.2 seconds. Intimacy, warmth, and clarity are important, as are speech intelligibility and stage support. Acoustical strength is important as well, since folk music does not benefit from sounding “amplified,” where preserving the natural sound of the instruments and voices is important.

The present increasing use of “contemporary” music in worship probably began in the 1960’s “folk era.” Folk Masses appeared in some Catholic churches, and younger ministers of worship and music, and youth pastors, began to employ acoustic instruments other than piano and organ in their services. “Contemporary” worship music has tended to follow the stylistic trends of secular music into pop and rock styles, and today, most contemporary worship music is of a style other than folk.

Rock

Rock music, as well as other musical styles depending heavily upon electronic amplification, is often fast-moving and highly percussive; therefore, it benefits from a very short RT60 — typically less than 1.2 seconds. This type of music is often played at very high sound levels, which command listener attention to the point that spaciousness and envelopment are of little importance. Since either in-ear or floor wedge monitors are usually provided for musicians (and sometimes for talkers as well), stage support is not very important. In fact, in order to avoid echoes from stage walls that can smear the sound of drums and cymbals, absorptive materials are often placed on the stage walls. However, any absorption used on stage walls to prevent percussion smear should be judiciously and sparingly placed. Because of the rapidly-moving nature of the music, clarity and speech intelligibility are very important in rock venues. The high sound levels employed make HVAC noise less likely to be noticed than in other types of venues. The exception is any noise that has a steady-tone component, as these are annoying and distracting even with loud music.

Rock-style worship venues include Nashville Gospel and contemporary African-American Gospel. Rock-style worship spaces are distinguished from rockmusic venues by the fact that the programming includes speech and often drama as well. The requirements for good speech intelligibility are naturally met by the acoustical requirements of rock music. Achieving good strength and low RT60 demands that acoustical absorption not be placed on the ceiling (a good rule, in general), and usually requires that pews or chairs have medium to heavy upholstery on both seats and backs. Usually, the wall at the back of the congregation will need to be quite absorptive to prevent echoes from the drums, and this will help to lower the RT60. If necessary, side walls near the back of the congregation may need to be absorptively treated as well.

Note: Readers untrained in acoustics may wish review Part 1 of this article (FRONT of HOUSE, April, 2021, page 23) and note that attaining the desired acoustics in a performance or worship space involves balancing many conflicting parameters. Many building owners have been the victims of designs that failed to appreciate the complexity of the acoustical design problem, and created a room in which, the RT60 was ideal, but the clarity and speech intelligibility were inadequate. So, the addition of an acoustical consultant to the venue and/or system design team is highly recommended. 

David K. Kennedy operates David Kennedy Associates, consulting on the design of architectural acoustics and live-sound systems, along with contract applications engineering and market research for loudspeaker manufacturers. He has designed hundreds of auditorium sound systems. Visit his website at immersive-pa.com.

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