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[an error occurred while processing this directive] Report from the Acoustical Society of America's 151st Meeting

By Jacob Skubal, SPS Reporter, Rollins College, Winter Park, FL

The 151st Meeting of the Acoustical Society of American was held in Providence, Rhode Island.  

The 151st meeting of the Acoustical Society of America, Session 3aMU – Musical Acoustics and Structural Acoustics and Vibration: Finite Element and Finite Difference Methods in Musical Acoustics…for the first time, I was scheduled to present in a session where I was less likely to be joined by other undergraduate presenters and more likely to be joined by some ‘big names’ in the field of acoustics. Before arriving at the conference, I even began to wonder whether someone in my audience might know more about the fairly exotic subject of my presentation, the Nigerian Slit Log Gong, than me. Fortunately, in chatting with some fellow physicists and acousticians on our first night, the puzzled and/or interested expressions given in response to my mention of the ‘slit gong’ strengthened my confidence. I was rather excited by the prospect of teaching my audience a thing or two about an African percussion instrument.

Despite the usual delays and hassles associated with air travel, we arrived at the conference in time to attend presentations of three invited papers in the first of two Finite Element and Finite Difference sessions, the second of which I was scheduled to present in the next morning. First, we heard about Finite-element transient calculation of a bell struck by a clapper from Lau Bjrn-Andre from the University of Hannover. His presentation focused on the difficulties of developing an accurate model of the bell/clapper system and ended with what I thought was an impressive animation of the clapper striking the bell and the resulting vibrations of the bell walls along with a synthesized sample of the bell sounding (as predicted by the model).

Next, representing Purdue University, Nick Giordano (a name I had heard numerous times before) presented his research on Finite-difference modeling of the piano. His presentation was less visually stimulating than the first, considering he never showed an image of his model, but his work was remarkable. As a rough translation of the numerous differential equations and boundary conditions he talked through, he constructed a model of a piano soundboard that accounts for the bridges, ribs, hammers, strings, and even the air contained in a theoretical room in which the instrument might be played. He showed a few graphs that (if you were squinting at a distance) demonstrated a good agreement between the acoustical properties of the model and the actual piano. The synthesized sound sample generated using his model is what really convinced me that his model was right on the money.

Gregoire P. Derveaux of Le Chesnay Cedex, France gave the final talk of the session, Finite-element simulation of the acoustic guitar. As he talked about the various features of the guitar model (soundboard, strings, bridge, air, etc.) and their effects on the resonant frequencies and energy transfer mechanisms of the guitar, it was evident that his research was very well funded. The talk ended with a DVD video, narrated by a woman with an unidentifiable accent, which showed numerous animations of the sound radiation and surface vibrations of the guitar. After the talk, an individual in the audience expressed some skepticism concerning the results obtained from the presenter’s model. This resulted in more scoffing and arm folding than intelligent discussion, but apparently that’s too often a real part of science. Soon, Rolf Bader of the University of Hamburg, co-chair of the session, gave the word and the session was officially concluded.

A few members of the audience including myself, Thomas Moore (my advisor), and Nick Giordano hung around to chat about the challenge of designing accurate models of strings and whether the crown found in most soundboards was worthy of adding to Giordanno’s model. The three of us made plans to discuss the mode shapes of piano soundboards over lunch on the next day.

That evening was spent attending a dinner reception (during which I learned quite a bit about ultrasound research at Washington University), perusing the 5 or 6 story mall that was conveniently connected to our hotel, and shopping for a cheap razor since mine was still in Florida.
It would be a lie to say that I was not nervous from the moment I woke up at 7 a.m. the next morning until I presented my research three and a half hours later. In the mean time though, breakfast and the other talks in my session were sufficient distractions (although I say ‘distractions,’ I managed to pay attention to the talks preceding mine).

The Finite Element and Finite Difference session part II opened with Joel Bensoam of the Acoustical Instrumental Team at IRCAM presenting an invited paper about Contact problems with friction applied to musical sound synthesis. Unlike most of the other talks I had heard in the session on the previous day, this research was not aimed at understanding the acoustics of a specific instrument but rather at developing techniques to more accurately model contact or collisions of multiple bodies (like in the bell/clapper model that I heard about on the first day). Upholding the apparent custom of the finite element and finite difference presentations, Joel closed by showing a movie of an arbitrary ring-shaped model bouncing off of an arbitrary surface model, a situation that was presumably used to test their research.

Rolf Bader, representing the University of Hamburg, presented his research on Whole-body finite-difference formulation of the violin. In this talk, focus was placed heavily on a sticking/slipping effect that describes the behavior of the bow and strings when playing a violin. Animated models of the violin body and the violin strings were shown to demonstrate the results of different ‘playing attacks.’

Next, Jan Richter of Hamburg presented a 3D finite-element method (FEM) of the body of a classical guitar. This was the first student talk of the session (the second being mine). In their research, various finite element models of the guitar were used to test the effects of varying certain features of the guitar’s body, including the ribs or braces, the thickness of the bottom wall, and the shape of the block. These effects were evaluated by comparing the mode shapes and resonant frequencies predicted by the original model of the guitar with those predicted by models in which designated features had been varied.

Modeling of steeldrum sounds using finite element and finite difference methods was presented by Michael Steppart of the Institut fur Musikwissenschaft. Michael briefly described the instrument and presented pictures of his steeldrum model, which, as in a few other projects, was constructed using a homemade finite element analysis program. The model demonstrated coupling between notes in ratios of an octave and a fifth, which corresponds to the behavior of the actual instrument. A simulation of the steeldrum’s sound was played as well.

The 151st Meeting of the Acoustical Society of American was held in Providence, Rhode Island.  

Finally, my big moment had come. Remembering my advisor’s comforting words (something along the lines of ‘I wouldn’t have taken you to this conference if I thought you would embarrass the college’), I presented research concerning the Tuning parameters of a Nigerian slit gong. Following a description of the instrument itself, I talked about how we used a finite element model of the instrument to study the effects that varying the gong’s dimensions had on its resonant frequencies. I also reviewed our attempts to describe the oscillations of the gong with some simple theories including beam theory and plate theory.

I could breathe easy again just in time to hear Malte Muenster from Hamburg talk about A three-dimensional, time-dependent simulation of a Turkish cymbal using the finite element method. This presentation consisted of an overview of several modeling experiments to study the effects of strike position, hammering, and alloy type in terms of a cymbal’s transient spectrum.

Stefan Bilbao of the University of Edinburgh presented the final talk of the session, Conservative numerical methods for sound synthesis. Stefan began by playing a few samples of synthesized bell and/or gong sounds to demonstrate the quality of current simulation techniques. The remainder of the presentation consisted of describing an alternate method of producing such simulations using energy conservation laws instead of a ‘frequency domain analysis.’

Afterwards, as planned, I had lunch with my advisor and Nick Giordanno. We pored over the problems of predicting the deflection shapes of piano soundboards using finite element models and shared some ideas. We also discussed the value of undergraduate research (it’s actually a lot of fun). The afternoon conference schedule was filled with talks on various topics in underwater acoustics and noise control, both of which are apparently hot topics in the world of acoustics. Later that evening, I attended a student reception and was reminded of the popularity of noise control and underwater acoustics when almost every graduate student that I met was in one of those two sub-fields of acoustics. Despite the attempts to instantly win me over to their respective fields, I expressed my interest in engineering and they offered a bit of advice: electrical engineering is the way to go.

The next morning, before departing for the airport, I was able to attend three presentations in the Topics in Musical Acoustics session, two of which were presented by students. First up, Gary P. Scavone of McGill University presented Real-time measurement/viewing of vocal-tract influence during wind instrument performance. In his presentation, Gary described the debate of whether a musician’s vocal tract actually affects the sound produced when playing a wind instrument and presented experimental results suggesting that the vocal tract does have an effect when playing wind instruments. He also proposed that the experiments used to confirm these effects (like real time spectrum analysis) could be used as learning tools when training musicians to take advantage of techniques involving vocal tract manipulation.

Benjamin A. Franta presented his undergraduate research on the Acoustical effects of reed cells in the American reed organ. The study was conducted on two different reed organs with two distinct types of reed cells. He showed that the instrument’s spectrum depends greatly on the dimensions and type of the reed cell and less so on the dimensions of the actual reed. However, the reed was shown to provide some enhancement of high frequency harmonics.

In the last talk I was able to attend, Eric A. Dieckman of Truman State University and in collaboration with Coe College presented student research concerning Experimental and calculated frequencies of the Southeast Asian naw. To me, this instrument was as exotic as I’m sure the slit gong is to everyone else. The best way I can describe its appearance is to say that it looks like a squash that has been stabbed by a handful of straws. Anyway, Eric discussed how he measured the instrument’s input impedance to determine its resonant frequencies. Theoretical predictions of the naw’s resonant frequencies, predicted using transmission matrices, were shown to be in good agreement with those found experimentally.

Closing remarks and my overall impressions of the conference: First of all, I think that presenting original research at a professional conference is a great opportunity as an undergraduate (even considering the work involved in preparation). Anyone that has such an opportunity should jump on it. Besides that, the many finite-element models of various instruments that I was able to observe impressed me; models that included time-series synthesis capabilities (so that you could ‘hear’ the model) were especially impressive. In addition to seeing all of the flashy and detailed finite element models, presenting my research at this conference granted me the unique opportunity of gathering advice from a fairly large pool of other acousticians that are actively involved in the research of musical instruments. In receiving some advice from a few members of my session’s audience, I was reminded that it’s always nice to see a problem from a fresh perspective.

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