David C. Copley

A stroboscopic study of lip vibrations in a trombone

The purpose of the present study was to obtain detailed photographic sequences and lip motion data on which lip models for brass instruments may be more accurately based. The study expands upon an earlier study by Martin [J. Acoust. Soc. Am. 13, 305–307 (1942)] by using advanced fiber‐optic stroboscopy, a real instrument mouthpiece, and by studying two dynamic levels. The trombone was selected as representative of the brass family because its relatively large mouthpiece permitted the use of an optic probe. Lip motion was observed from the front and side for six notes (Bflat2, F3, Bflat3, D4, F4, Aflat4) played at loud and soft dynamic levels. The video sequences were used to obtain information on lip opening area, lip motion perpendicular to airflow, and lip motion parallel to airflow. The data are tabulated and represented in graphic form.

Obtaining Structure-Borne Input Power for a SEA Model of an Earthmoving Machine Cab

Properly characterizing input forces is an important part of simulating structure-borne noise problems. The purpose of this work was to apply a known force reconstruction technique to an earthmoving machinery cab to obtain input functions for modeling purposes. The technique was performed on a cab under controlled laboratory conditions to gain confidence in the method prior to use on actual machines. Forces were measured directly using force transducers and compared to results from the force reconstruction technique. The measured forces and vibrations were used as input power to an SEA model with favorable results.

Modeling acoustic resonators: An application to resonator-enclosure coupling

Acoustic resonators, such as the Helmholtz resonator, provide a stable, cost effective passive noise control solution, and have been widely used to attenuate unwanted sound in enclosures and ducts. Classical formulations predicting the input impedance of such resonators often have significant error, creating a need for repeated prototyping or tuning during fabrication to achieve the desired response. Previous work found that higher-order calculations, including impedance translation and equivalent circuit modelling, produce much more accurate predictions [Calton and Sommerfeldt, J. Acoust. Soc. Am. 139, 2205 (2016)], allowing prototyping to be done quickly on a computer before fabrication of the resonators. This talk will continue the discussion in the work referenced above. In addition to resonator impedance predictions, resonator-enclosure coupling predictions will be discussed. It will be shown through comparison of predicted and experimental results that the impedance and coupling predictions can remove the need for repeated prototyping and tuning. We will also show the incorporation of these predictions into a user interface allowing engineers without acoustics background the ability to design resonators for passive noise control.Acoustic resonators, such as the Helmholtz resonator, provide a stable, cost effective passive noise control solution, and have been widely used to attenuate unwanted sound in enclosures and ducts. Classical formulations predicting the input impedance of such resonators often have significant error, creating a need for repeated prototyping or tuning during fabrication to achieve the desired response. Previous work found that higher-order calculations, including impedance translation and equivalent circuit modelling, produce much more accurate predictions [Calton and Sommerfeldt, J. Acoust. Soc. Am. 139, 2205 (2016)], allowing prototyping to be done quickly on a computer before fabrication of the resonators. This talk will continue the discussion in the work referenced above. In addition to resonator impedance predictions, resonator-enclosure coupling predictions will be discussed. It will be shown through comparison of predicted and experimental results that the impedance and coupling predictions can remo...

From musical acoustics to noise control

This presentation is a personal reflection of the influence Bill Strong had on the author’s career in noise control. From first encounters with the decibel to experimental and numerical research in trombone acoustics, from simple textbook quizzes to demanding 20-page single-problem essays, the author shows the influence Bill Strong had on his education in acoustics which became the bedrock for a career in machinery noise control. The presentation will cite specific example of concepts, analyses and techniques found in musical acoustics—first encountered by the author in his studies with Bill Strong—and similarities to industrial noise control situations. The examples will demonstrate how an education in musical acoustic translates to practical applications in noise control engineering.

Vibro‐acoustic model of an enclosed electric power generator.

A vibro‐acoustic model of an enclosed diesel‐powered electric generator was built using commercial vibro‐acoustics software (primarily SEA) and empirical methods. The vibro‐acoustic sources, including the engine, generator, cooling fan, and exhaust were characterized experimentally for several different operating conditions. The vibro‐acoustic performance of the enclosure and sound suppression features were modeled and experimentally validated. Good agreement was achieved between experimental and simulated results.

Energy density active noise control in an earthmoving machine cab

Conventional active noise control (ANC) systems attempt to minimize squared pressure at an error sensor (or sensors) to achieve control, and often result in a relatively small zone of control. Considering a practical application in a vehicle, this approach is acceptable provided the operator’s head remains within the control zone. In the case of an earthmoving machine, an operator’s head regularly moves about the cab, either because of the motion of the machine during operation or as the operator moves about to perform various tasks. By minimizing energy density (ED), instead of squared‐pressure, a potentially larger control zone may be achieved. Active control of the sound field within an earthmoving machine cab was attempted using the ED technique. The scope was limited to controlling the engine firing frequency tonal within the cab with the machine running, but in a static condition (engine idle). Frequency response and spatial results show the method achieved nearly global control within the cab and e...

Reverberant sound in one‐, two‐, and three‐dimensional spaces

The method of images was used to calculate impulse responses for a large (30 m×23 m×18 m) three‐dimensional space, a large (30 m×23 m) two‐dimensional space, and a large (30 m) one‐dimensional space. The reverberation time for these spaces was set to approximately 1.5 s and all sound absorption took place at the walls. Similar impulse responses were calculated for small rooms whose dimensions were one‐tenth those of the large rooms and whose reverberation times were smaller. A short (10‐s) sample of singing was recorded in an anechoic chamber and then convolved with the various impulse responses. The resulting six reverberated samples of singing were recorded binaurally on audio tape. Graphs of the impulse responses and the taped examples will be presented. (Although the taped examples will be presented via loudspeakers, they are best heard via earphones.)

A study of lip vibrations in a trombone

More than 50 years ago, Martin investigated lip vibrations in a coronet mouthpiece using stroboscopic photography [D. Martin, J. Acoust. Soc. Am. 13, 305–307 (1942)]. Since then, several researchers have based lip models on Martin’s data. Unfortunately, due to the quality of the photographs, it is difficult to obtain anything more than a limited quantitative description of the lip motion. The purpose of this study is to obtain more detailed photographic sequences and lip motion data on which new models may be based. The trombone was selected as representative of the lip reed family. A computer‐controlled fiber optic stroboscope was used to capture the motion of a player’s lips on video. By inserting the optic bundle through small holes drilled in the mouthpiece, lip motion was observed from the front and side for six notes (Bflat2, F3, Bflat3, D4, F4, G4) played at loud and soft dynamic levels. Video sequences and resulting lip motion data will be presented and discussed.