Note: This text is extracted from Acoustics in Worship (© 2015 Elektor International Media, London) by noted author / consultant / designer / electroacoustics expert Richard A. Honeycutt. Used by permission.
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. Within the category of music halls, there are opera houses, chamber music halls, symphony halls, and jazz/rock/pop music spaces. Sanctuaries share similar subcategories, depending largely 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. The early acoustical texts divided worship music into Catholic styles (organ and choral music) and protestant/synagogue styles (much like general-purpose concert halls).
Classifying Worship Music Styles
In the last three decades, considerable diversification has occurred, so that now classifying by denomination is not instructive. Neither is the 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 gospel styles. Even within gospel styles, there are “Nashville gospel”, using electrical instruments and percussion; “old-time gospel”, using mainly piano and/or guitar, banjo, mandolin, etc.; and “African-American gospel”, which probably includes Hammond organ accompaniment and percussion, along with any of a plethora of other electrical, acoustical and percussion instruments. “Contemporary” can mean the “folk gospel” styles of the 1960’s and later, light-pop styles including many praise choruses or Christian rock.
In order to avoid excessive wordiness, we shall adopt category names that correspond to the musical roots of the various styles, as follows:
Medieval — Slow-moving music such as Gregorian chant or certain pipe organ styles.
Baroque — Bach, Handel, Haydn, and similar musical styles (faster motion than medieval)
Classical — Mozart, Telemann, and similar musical styles (faster motion than baroque). Acoustically, this style includes the requirements for most 19th- and 20th-century hymns.
Folk/Jazz — Music similar in style to British, Irish, Scottish, and American folk music. Acoustically, this style includes “old-time gospel”, “folk gospel”, and light‑pop sacred styles.
Rock — Electronically amplified music with strong percussive elements. Acoustically, this also includes “African-American gospel,” “Nashville gospel” and “Latino” style music.
Speech — Rooms used only for speech.
Multipurpose Venues — Spaces used for a broad spectrum of musical styles, and nonmusical events.
Categorizing worship music styles in this manner also facilitates comparison between the acoustical behavior of worship spaces and that of performance spaces.
RT60 and Musical Styles
The above category listing is in order of decreasing RT60 (Reverb Time), from 5-7 seconds for Medieval to well under one second for Speech. The preferred RT60 also depends upon the room volume, with a longer RT60 needed to make a large room sound right to the listeners.
A requirement for good speech intelligibility in performance and worship spaces is somewhat eased by the ubiquity of sound reinforcement systems. However, since a long reverberation time is detrimental to speech intelligibility, the cost of the sound reinforcement system is also affected by the RT60, especially for values above 1.5 seconds (Classical style). Values over 2 seconds may require heroic measures in order to obtain good intelligibility.
Occupancy and RT60
Since the occupancy of most venues varies widely from one use to another, it is very beneficial for the RT60 to remain reasonably constant in spite of these changes. An excellent chamber ensemble performing on a snowy night in a very good room having an RT60 of 1.3 seconds when fully occupied may be charged with a less-than-adequate performance if the scanty audience results in the RT60 increasing to 1.9 seconds. The sanctuary that sounds wonderful on a high holy day (with full occupancy) may be cave like — exhibiting poor clarity and speech intelligibility — when almost empty.
The stability of RT60 in spite of occupancy changes is also important to musicians who must practice in an empty room and perform in a full one. As people are acoustically very absorptive, the only way to stabilize the RT60 against occupancy variations is to prevent the people’s absorption from dominating the response of the room. In most concert halls, this is accomplished by the use of cushioned seats. A medium- or heavily-upholstered concert chair has nearly the same absorption whether occupied or unoccupied. In a worship space, pew seat cushions can be used, but the use of pew back cushions tends to reduce the helpful reflections needed for strong congregational singing and liturgy, so most consultants recommend pew seat cushions only, knowing that this compromise between stable RT60 and strong hymn singing is necessary.
The stability of RT60 is less problematic in rooms with shorter RT60, since the listeners do not contribute as high a proportion of the total acoustical absorption in such a room. (Short RT60 means that the room is more absorptive empty than a same-size room with long RT60.) Planning for good acoustics cannot wait until the architectural work is more-or-less finalized; it needs to be done early in the process.
In order to promote strength, clarity, definition, and speech intelligibility, ceilings of most performance and worship spaces should be acoustically reflective. Acoustical absorption, when necessary, should be added at other places. Stage support is important in both performance spaces and worship spaces, since musicians and vocalists need to be able to hear themselves and each other no matter what the venue.
Intimacy and warmth are also important in both performance and worship spaces, but envelopment and spaciousness pertain more to a good concert experience than to worship. In fact, too much envelopment is sometimes distracting, especially in the folk/jazz or rock style sanctuary. It should go without saying that control of ambient noise is essential to a good listening or worship experience.
The careful reader will have noticed 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 by architects and/or contractors who failed to appreciate the complexity of the acoustical design problem, and created a room in which, for example, the RT60 was ideal, but the clarity and speech intelligibility were at best inadequate. For this reason, owners should choose their acoustical consultant with at least as much care as they apply to the choice of an architect or builder. It is always a good practice to engage an acoustical consultant in any project in which the venue will be used for listening.
The Medieval Style
Medieval-style venues (sometimes referred to as “Gothic Cathedrals”) — such as the Duke University Chapel in Fig. 1 or the First United Methodist Church in Lexington, NC in Fig. 2 — comprise very large spaces primarily used for performance of pipe organ and choral music. These spaces may have RT60’s of 5 to 7 seconds, and as such, they are suitable for slow-moving music such as Gregorian Chant. Even pipe organ music of the Classical and Baroque periods, and especially more modern or contemporary organ repertoire containing rapid passages are not well supported by such a long RT60. Speech intelligibility needed for announcements or liturgy typically requires heroic efforts on the part of a very competent/specialized sound system designer, and may involve measures such as pew-back loudspeakers or a distributed directional system. Note that there is usually a slight decrease in RT60 at high frequencies. We are accustomed to the sound of this phenomenon, so it sounds fine to us for music.
Since Medieval-style venues are uncommon in the US, and rarely serviced by typical FRONT of HOUSE readers, we have shortened coverage of the Medieval-style category.
Next month, in Part 2, we will explore the other musical styles: Baroque, Classical, Folk/Jazz and Rock, and the diverse-preferred acoustical performance of a space for each of these varied music styles.
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 www.immersive-pa.com.
