Notes on architectural acoustics from a talk by Kathleen Stetson

Very interesting talk today at a meeting of the Michigan section of the American Association of Physics Teachers, meeting at Grand Valley State University, by Kathleen Stetson of Trill.  She uniquely has training in both opera and acoustics, and is also a graduate of Interlochen Arts Academy of Michigan.  See here for more biographical information – otherwise, here are some of my notes on her talk (and, below, a photo).  As usual, accuracy of my notes is not guaranteed, but I think they’re pretty good!

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  • Was struck by a reason she gave for her preference of performance art, “performance art happens in time, so it only happens that way once”.
  • Trained to be an opera singer, but loved science, and found the problem was if you wanted to be an opera singer, “you had to only sing”, things were simply that competitive.
  • So, she did purely architectural acoustics for a few years, but the problem with that is that “experiments take seven years” – you design a structure, you think it’s good but you have to wait for construction to finish until you know for sure, and that can take a long time.
  • (And this eventually led to surprisingly popular Hacking-Arts and related projects.)
  • She said acoustics is not a cut-and-dried science, there are a lot of assumptions, a lot of uncertainty, “nobody knows why some halls turn out really great and others don’t”.
  • Therefore acoustics is “The Art of practicing the Science”.
  • Designing a building is difficult because you aren’t just doing what you think is best – you have a client, but also all the engineers, builders.  She said it’s like watching movie credits, there are so many people involved.
  • She gave the example of one performance hall where, after construction was basically done, mechanical engineers realized there wasn’t enough air flow, so they had to add some vents – brand new places for sound to escape, significantly deadened the space acoustically.
  • Computationally, when modeling building design, ideally you would just “solve the wave equation for the space”, but that would require an enormous amount of computational power.  So, the simulations use geometric modeling, treat the sound as rays with a finite travel speed, model reflections and diffraction to some extent and approximate the reverberent tail.  The power comes in comparisons to real structures.
  • Talked about “auralization”, process of putting clients in a room filled with 18 or so speakers to give them a sense of the timing and strength of sound in the space that is being designed for them.
  • Just an amusing comment she made about one space, “way too dry, like singing into a sock”.
  • The most sound-absorbing objects in most rooms – the people.
  • Talked about the difficulties of multi-use spaces.  In one project they wanted to improve reverberations for opera, maybe remove some sound absorbers, but then the ballet was worried they would sound like a herd of elephants.  Ended up removing some absorbers, adding in others near the stage.
  • Struck me that ray-tracing was a pretty good way to analyze the performance of the reflectors you might see above a stage.
  • Talked about an “anechoic chamber”, a space surrounded by six feet of sound insulation on every side, you walk out onto a platform.  You cannot even hear someone right behind you because there are no reflections off the walls.
  • Talked about the importance of having a people-free space near the front in opera houses to allow that first reflection to happen.
  • Scale models 1/50 in size are now constructed at the very end of a design process, with lots of spaces to stick in microphones and a spark to serve as an omnidirectional sound source.
  • Her dissertation was on the preference of *singers* for the acoustics in a concert hall.  Some discussion about the use of overhead reflectors in some spaces so orchestras can hear themselves.

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