The Nature of Sound

by Dennis Fleisher, appearing in Volume 20

Worship space acoustics is a branch of architectural acoustics which deals with the audible effects imparted to sounds produced within architectural spaces. These effects—the most familiar being reverberation and echo—are brought about by the size, shape, and finish materials of enclosed spaces and are physical consequences of these architectural elements. These audible phenomena have, therefore, existed for as long as we have had buildings.

Architectural acoustics as an engineering discipline is, by comparison, a relatively new field, emerging in the early twentieth century when Wallace Clement Sabine, a Harvard physics professor, was called upon to correct speech intelligibility problems in a lecture hall in the Fogg Museum on Harvard’s campus. Considered the father of architectural acoustics, Sabine was the first to develop a scientific basis to quantify and predict acoustical characteristics; because of this he was hired as the acoustical consultant for Boston’s Symphony Hall, the first concert hall designed using quantitative acoustics. Given these historical beginnings and the importance of sound quality in music performance halls, architectural acoustics has focused primarily on concert halls, where most of the research and scientific design developments have occurred.

In concert halls, acoustics is usually the top priority, and the best concert halls are often cited to evoke images of acoustical excellence, such as Carnegie Hall. Although acoustics is also a major priority in worship spaces, it is often compromised by liturgical and architectural imperatives, budgets, and aesthetics.

It is significant that the authors of Worship Space Acoustics state, on the first page, a key motivating factor: “Although concert halls have been a primary subject of room-acoustics research, worship spaces are used more frequently and by more people, thus calling for a book of this nature.”

The authors possess exceptional levels of education, experience, and interdisciplinary perspectives in acoustics, architecture, engineering, music, and liturgy. Their past and present endeavors have extraordinary breadth and diversity: beyond their strong technical credentials, one author is a priest, another a rabbinical student. This interdisciplinary foundation is significant because in practice, worship space acoustics involves a multiplicity of perspectives and priorities. Most, perhaps all, of these priorities are brought to the table in this book.

The introduction lists prospective readers as “architects and students of architectural acoustics, building consultants, contractors and suppliers, administrators, clergy, organists and organ builders, students and faculty of religious educational institutions, and laypersons with interests in religion and architecture.” The authors are comfortable with terminology from all these areas. (Given the roots of architectural acoustics in the concert arena, the use of “stage” and “audience” is almost unavoidable, but the authors generally put such terms in proper context and perspective.)

The book is divided into two parts. Part I is a textbook-like survey of the basic elements of architectural acoustics:

1. Fundamentals: Nature of Sound
2. Hearing
3. Room Acoustics Fundamentals
4. Sound-Absorbing Materials
5. Metrics for Room Acoustics
6. Simulation and Prediction
7. Planning for Good Room Acoustics
8. Quiet
9. Sound Isolation and Other Noise Issues
10. Sound Systems for Clarity and Reverberation

Photos and sketches of churches and synagogues illustrate particular subjects, clearly relating these standard acoustical topics to worship spaces.

In a significant departure from other books on acoustics, Part II includes three separate chapters on Jewish synagogues, Christian churches, and Muslim mosques. In addition to this ecumenical perspective, the authors’ interdisciplinary backgrounds allow them to write knowledgeably about music (citing specific compositions and styles), church documents on liturgy, and a broad range of worship styles such as “liturgical,” “evangelical,” “blended,” etc. This suggests that “optimal” acoustics is not strictly a matter of objective criteria, but rather highly dependent on specific styles of worship and the nature of the sound sources involved. For speech, this means making allowances for trained orators and lay readers; for music, it includes everything from a cappella chant to amplified instrumental and vocal ensembles.

Graphs, tables, and equations supplement and support the principles discussed, together with useful references ranging from acoustics textbooks and engineering journals to publications of the United State Conference of Catholic Bishops. I was fortunate to contribute to the book as well by providing photos, commentary, and an editorial review of drafts for this publication. The authors’ personal experience and interests in the worship spaces they mention make the notes particularly intriguing: the three-and-a-half-page endnote S.15 (“S” for synagogue) about Hearth Israel, the New York City home of North America’s oldest Jewish congregation, offers an invitation to attend a service there, along with explanations of elements of Jewish services likely to be unknown or unfamiliar to visitors of other faith traditions.

The authors’ goal in writing for such a broad range of readers is ambitious. Most readers of Sacred Architecture should find the book a useful reference. The availability of downloadable supplements, errata, and updates from the publisher will keep the book’s material fresh and current, and offer more detailed coverage of areas not included in the original book. Less than a year after its publication date, there are seven downloads (approximately 4MB) including an errata sheet and new topics such as “Choosing an Organ,” a detailed summary of HVAC noise calculations, and case studies. Worship Space Acoustics is a useful resource and should be an ever-renewing source of information.