Acoustics lecture, demonstration defines the indefinable

Physics Professor David T. Bradley gave a lecture on the acoustics of religious spaces. The lecture complemented his class and recently published book, both of which explore acoustics. / Photo courtesy of Vassar College

“Architecture is frozen music,” said Ger­man writer Johann Wolfgang von Goethe. These two entities—architecture and music—have indeed proven inseparable throughout history. Sound, in its many forms, is as crucial to the performance of collective wor­ship as the space in which it takes place.

What one may not immediately consider is the science behind this awe-inspiring synthesis, and it is this intersection between art, religion and sci­ence that Associate Professor of Physics David T. Bradley presented in his lecture “Worship Space Acoustics: The Sound of Space” in the Chapel on Thursday, April 21.

Bradley’s talk was presented in concert with the new course “The Sound of Space: Intersecting Acoustics, Architecture and Music,” cross-listed with the Music, Physics and Art Departments, as well as the Creative Arts Across Disciplines 2015-16 theme of “Sound and Silence.”

Though the science of acoustics is objective by nature, the lecture began with two subjective elements. First, attendees entered the Chapel immersed in the majestic architecture and the stirring sounds of Sarah Johnson ’16 on the or­gan. The lecture then began in the dark, with an auditory montage of various worship practices: the plaintive cry of the shofar, a Spanish Catholic mass, Buddhist monks chanting in unison, a mu­ezzin’s melodic call to prayer.

To connect these spiritual experiences to a basic understanding of the science behind their acoustics, Bradley started, naturally, with a sound: a solitary clap. From this simple clap, a high-pres­sure impulse signal, we can learn a lot about the acoustics within a space. As Bradley put it, “This is the holy grail—no pun intended—of acoustics … From this impulse response, we can learn a lot about the room.”

And the audience did learn a lot, as Bradley went on to walk the audience through the building blocks of acoustical analysis, including the subjec­tive components—reverberance, clarity, loudness and speech intelligibility—and their objective counterparts—reverberation time, the clarity in­dex, strength and the speech intelligibility index. As Bradley’s student Daniel Melody ’19 wrote in an emailed statement, “We are currently analyz­ing spaces of our own around campus, so it was interesting to see how Dr. Bradley went through the process himself and which acoustical/archi­tectural factors he focused his efforts upon.”

In short, the four key parameters that worship space designers must consider are optimizing reverberation time through volume control and sound absorption, eliminating acoustical defects, minimizing ambient noise and maximizing the dynamic range to make the initial impulse sound as loud and clear as possible.

These four elements are true to virtually all worship spaces around the world, despite vast dif­ferences in religious beliefs and practices. For ex­ample, regarding the biblical Tabernacle, the por­table temple of the wandering Israelites, Bradley informed, “…one biblical scholar said, ‘God creat­ed the world in six days, but he used over 40 to instruct Moses about the Tabernacle.’” Such was the importance of the precise construction, both literal and figurative, of the worship experience.

Bradley continued, citing modern examples from the 67 religious buildings featured in the book that he co-edited, “Worship Space Acous­tics: 3 Decades of Design.” He explained the id­iosyncratic challenges of each space, from a wall separating men and women in an orthodox syna­gogue in Massachusetts to acoustical defects from the domes of a mosque in Atlanta.

Bradley then explained a special project, the Tri-Faith Initiative complex in Omaha, NE, which aims to unite the three Abrahamic religions. “I like this idea,” Bradley expressed, “because one of the things I learned in working on the book is that there’s a lot of commonalities across these differ­ent kinds of worship spaces. They have a lot of the same goals.”

Bradley connected this idea to recent strife over BDS at Vassar, saying in reference to the Omaha collective, “This idea of three very differ­ent religions all occupying the same space…I think is really inspirational, and it speaks to some of the things happening on campus with regards to in­terfaith dialogue … You wouldn’t expect that kind of conversation from a physics talk.”

A final component of the lecture came from some of Bradley’s students, who measured the acoustics of the Chapel live. They utilized an om­nidirectional loudspeaker to play chirps from the low- to high-frequency range. This element struck a chord with the collaborative nature of both the course he is co-teaching and of real-world acous­tics itself.

Associate Professor of Music and Director of Choral Activities Christine Howlett, the sec­ond professor involved in the “Sound of Space” course, touched on her specialty relating to acoustics: “Depending on what singers hear (or don’t hear)…[they] may end up having to adjust the way they are singing, or rely on the conductor much more.” Such adjustments may include sing­ing more slowly in reverberant spaces and more quickly in less reverberant spaces.

Associate Professor of Art Andrew Tallon, the other professor teaching the course alongside Bradley and Howlett, shed light on the idea of imbuing religious buildings with the “sacred ge­ometry” of music and acoustics. “Why can’t we include those same [mathematical] relationships in a building in some way?” he posited as the atti­tude of early cathedral designers.

Bradley completes the acoustics course trifec­ta, supplying the science behind the music that Howlett explicates and the historical and artistic developments that Tallon describes.

Ultimately, Bradley’s lecture sought to explain how acousticians quantify the ineffable for a more careful understanding of how all of the el­ements—sound, architecture and religion—come together to create that undeniably magical qual­ity. “These spaces,” Tallon described, “deploy all sorts of tricks to convince the faithful attendee of a liturgy there that he or she really is in a liminal zone between earth and heaven, that there’s some kind of transfer operating in that space, on that day, through the liturgy that’s performed and the space that surrounds, that’s just taking that person a little bit higher.”


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