Orchestral Acoustics 101: Hearing Troubles?

Christopher Blair –  full time acoustician, part-time conductor, 1st time blogger. First of all, I need to thank Drew for this temporary opportunity to use his blog while he’s away on vacation this week. If I had to come up with something to share every day as he does, I fear that I would not get much else done.

The additional good news, Dear Reader, is that I am not carrying this stand-in responsibility alone. For those that find discussions of how we hear music somewhat arcane: wait a day…and you will learn something completely different from someone completely different. So…for the acoustically curious…we begin…

Chapter 1: Hearing Troubles? –things to try before calling the acoustician.

A substantial percentage of requests for acoustic advice comes not from the glamorous opportunities to build new civic monuments to and for the performing arts, but, rather, to fixing old nagging problems.  These conditions manifest in increasingly irritated conductors and musicians who are having difficulty hearing themselves and/or their comrades onstage.

In 90% of complaints, on-stage hearing difficulties can be traced back to what acousticians refer to as “forward masking”.  (You might want to commit this term to memory as it will pop up in future chapters.) Put simply, forward masking describes the phenomenon in which the first bundle of energy heard by a musician on stage from direct path and early reflections effectively shuts down the hearing mechanism for a period of time. The louder the early energy, the longer the ear takes to recover its full hearing capabilities.

To this concept of forward masking, I would like to add the corollary concept of “two streams” of auditory feedback actually heard by the performer. The first early stream, contains information helpful to coordination of rhythm and attack. The second (post shut down) stream of energy arriving much, much, later provides the performer  all information concerning ensemble balance, intonation, timbre, as well as a sense of connectedness with the audience. The art of designing good on-stage acoustics boils down to providing just enough early energy to help with coordination, but not so much as to mask audibility of the late-energy room response.

The world is filled with concert shells with low ceilings and tight walls that purport to contain an orchestra’s sonic energy and send it out efficiently to the audience in a theater.  This they do, but in the process they create an acoustically “hot” environment onstage.  The loudness onstage masks the late response from the room.  (An analogy: Visualize standing on a stage under very bright lights…you can see your immediate surroundings but not the audience seated in the relative dark).

I can’t even recount the number of times that a conductor has asked me for concert shell ceiling panels suspended from stagehouse rigging  to be lowered to improve hearing.  I usually tell them that they are unlikely to get the improvement they are looking for, but lower the ceiling anyway (It is usually an easy adjustment, and why not be cooperative?). The result is invariably worse.  Then I raise the ceiling from its original setting by 3-4 feet.  You don’t even have to ask if there is an improvement. You can hear it and see it on the faces of the musicians.

So, my long suffering colleagues:  before you toss that orchestra shell into the dumpster, you might try raising the ceiling and opening it up to release some early energy.

Stay tuned for future chapters in Orchestral Acoustics 101

    Chapter 2: Vineyard vs. Shoebox – are visual intimacy and sonic-envelopment mutually exclusive?
    Chapter 3: Avery Fisher Hall –what went wrong and how to fix it
    Chapter 4: Beware The Seductive Model
    Chapter 5: Lies, Damn Lies, and Statistics

About Christopher Blair

As Senior Scientist and Principal Consultant, he collaborates on all the firm’s major projects, focusing in particular on room acoustic design. Chris’ contributions can be heard in the widely praised Schermerhorn Symphony Center for the Nashville Symphony, the Rosch Recital Hall at SUNY-Fredonia (photo, top right), Mixon Hall at the Cleveland Institute of Music, and in renovations to the Eastman Theatre and the new Hatch Recital Hall for the Eastman School of Music, among others.Chris earned dual Bachelors degrees in Mechanical Engineering and Music from the University of Vermont and Masters degrees in Orchestral Conducting from the New England Conservatory, and in Acoustics from the Massachusetts Institute of Technology. He has been a member of the faculties of M.I.T., UMASS/Lowell, Brown University, and Yale University, and currently serves on the Strategic Planning Committee of the New Haven Symphony and the Board of Directors of the Conductors Guild.

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4 thoughts on “Orchestral Acoustics 101: Hearing Troubles?”

    • In Davies Hall, you bring up an interesting case of certain design decisions that were made based on the best scientific understanding of the time. Ted Schultz of BBN was the lead acoustician for this room and its conceptual “sisters”, Roy Thomson Hall in Toronto and Meyerhoff Concert Hall in Baltimore. Of these only the last, because of its smaller seating capacity, had any initial acoustical success.

      The acoustical problems for Davies Hall and Roy Thomson Hall followed the very large seating capacities proposed by their respective clients. Leo Beranek’s studies of many successful concert halls in the 50’s and early 60’s revealed that the optimal reverberation time for a concert hall should be approximately 2.0 seconds.
      Since reverberation is directly proportional to cubic volume and inversely proportional to seating area, very large volumes were required to create a reverberation decay of this duration.

      What was not well understood at the time was that strength of reverberation is as important as length of the decay. The measured reverberation was 2.0 seconds as predicted, but it was weak, and the result was early and late sound fields that were poorly matched in energy.

      Both Davies and Thomson have undergone substantial renovations which reduced their cubic volumes and reshaped the upper part of the rooms to better promote slow decaying resonant energy there. The result is rooms that are substantially better than they were, but still not among the top echelon.

      As I will be writing about the development of Philharmonic Hall (now Avery Fisher) later this week I will leave the topic of BBN and its role in such projects until later. The only commentI will make now is that the blame for acoustical disappointment may not always lie where you think. Stay tuned…

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