Acoustics Research Projects at Kettering University

Dr. Russell's Research Projects
(student names in red italics)

Ongoing Research
Vibrational Analysis of Baseball and Softball Bats Research Summary As a result of some previous work Dr. Russell had done on Little League baseball bats, a company in Canada (CE-Composites Baseball Inc.) that makes baseball and softball bats from composite materials contacted him about doing some consulting work for them. During the last year Dr. Russell has been doing modal analysis experiments on a wide variety of good and bad performing softball and baseball bats to gain an understanding of the vibrational and acoustic characteristics which are exhibited by good and not so good bats. Armed with this data he is currently testing several prototype composite baseball and softball bats, suggesting design improvements in the hopes that for the 2004 season CE-Composites will have the best performing bats on the market. At the same time Dr. Russell is also working on a physical/mathematical model of the ball-bat collision, with a focus on understanding how the "trampoline" effect of a hollow metal or composite bat is able to significantly increase the post-impact ball speed. For more information on this research topic: Physics and Acoustics of Baseball and Softball Bats
Physics of Guitar Pickups Research Summary Electric guitars produce sound not because the instrument's vibration results in acoustic radiation, but because the vibration of the strings is converted to an electrical signal which is amplified and sent to a loudspeaker. The transducers which convert the string vibration to electrical signals in most electric guitars are magnetic pickups which measure the string velocity according to Faraday's Law of electromagnetic induction. While magnetic pickups are the norm, there are other methods of detecting the string motion. Optical pickups use a small beam of infrared light to detect the position of the string and thus measure the string's displacement as a function of time. Piezoelectric pickups in the bridge of the guitar measure the force the strings exert on the bridge. This research project is investigating the differences in the signals measured by each of these three pickups (magnetic=velocity, optical=displacement, piezoelectric=force) with application to variance in the resulting sound output. Since the time signals are very different, the frequency content is also noticeably distinct for the various pickups.	Comparing the time signals obtained by using an optical pickup (top); magnetic pickup (middle); and piezoelectric force pickup (bottom).

Vibrational Analysis of Baseball and Softball Bats

Research Summary
As a result of some previous work Dr. Russell had done on Little League baseball bats, a company in Canada (CE-Composites Baseball Inc.) that makes baseball and softball bats from composite materials contacted him about doing some consulting work for them. During the last year Dr. Russell has been doing modal analysis experiments on a wide variety of good and bad performing softball and baseball bats to gain an understanding of the vibrational and acoustic characteristics which are exhibited by good and not so good bats. Armed with this data he is currently testing several prototype composite baseball and softball bats, suggesting design improvements in the hopes that for the 2004 season CE-Composites will have the best performing bats on the market.

At the same time Dr. Russell is also working on a physical/mathematical model of the ball-bat collision, with a focus on understanding how the "trampoline" effect of a hollow metal or composite bat is able to significantly increase the post-impact ball speed.

For more information on this research topic: Physics and Acoustics of Baseball and Softball Bats

Physics of Guitar Pickups

Research Summary
Electric guitars produce sound not because the instrument's vibration results in acoustic radiation, but because the vibration of the strings is converted to an electrical signal which is amplified and sent to a loudspeaker. The transducers which convert the string vibration to electrical signals in most electric guitars are magnetic pickups which measure the string velocity according to Faraday's Law of electromagnetic induction. While magnetic pickups are the norm, there are other methods of detecting the string motion. Optical pickups use a small beam of infrared light to detect the position of the string and thus measure the string's displacement as a function of time. Piezoelectric pickups in the bridge of the guitar measure the force the strings exert on the bridge. This research project is investigating the differences in the signals measured by each of these three pickups (magnetic=velocity, optical=displacement, piezoelectric=force) with application to variance in the resulting sound output. Since the time signals are very different, the frequency content is also noticeably distinct for the various pickups.

Comparing the time signals obtained by using an optical pickup (top); magnetic pickup (middle); and piezoelectric force pickup (bottom).

Published/presented Research

"Acoustic and modal analysis of an African djembe drum," D. Russell and W. Havemann, presented at: 140th meeting of the Acoustical Society of America, Newport Beach, CA, December 1-5, 2000. Abstract published in: J. Acoust. Soc. Am., 108(5), 2591 (2000)
Abstract of the paper:
The African djebme drum consists of a goat skin stretched over a hand carved shell with a large cavity, open at the bottom. The shape of the shell cavity acts as a Helmholtz resonator providing a strong bass component around 75 Hz. The shell exibits several bell, or wineglass modes, some of which have frequencies close to membrane modes. This talk will present results from acoustic and modal analysis tests of the drum with and without the skin membrane intact. Mode shapes and frequency spectra will be presented as well as a discussion of how the shell, cavity and membrane couple together to provide the djembe's unique sound.
More Information about the Djembe research

"On the sound field radiated by a tuning fork," D. Russell, published in: American Journal of Physics, 68(12), 1139-1145 (2000). [Link to a PDF version of the paper.]
Abstract of the paper:
When a sounding tuning fork is brought close to the ear, and rotated about its long axis, four distinct maxima and minima are heard. However, when the same tuning fork is rotated while being held at arm's length from the ear only two maxima and minima are heard. Misconceptions concerning this phenomena are addressed and the fundamental mode of the fork is described in terms of a linear quadrupole source. Measured directivity patterns in the near-field and far-field of several forks agree very well with theoretical predictions for a linear quadrupole. Other modes of vibration are shown to radiate as dipole and lateral quadrupole sources.
Animations to accompany the published paper.

"Acoustic monopoles, dipoles, and quadrupoles: An experiment revisited," D. Russell, J. Titlow, and Y.J. Bemmen, published in: American Journal of Physics, 67(8), 660-664 (1999). [Link to a PDF version of the paper.]
Sound radiation directivity patterns were measured for monopole, dipole, and quadrupole sources. Four small loudspeakers were mounted in a cloverleaf pattern on a rotating stool and driven at a frequency of 250 Hz. Sound pressure levels were measured with a sound level meter at a distance of 1 m from the speakers. The speaker system was rotated 360^o and pressure measurements were taken every 5^o. By switching the polarity of each speaker it was possible to drive all four speakers together (monopole) or in pairs to form a dipole or quadupole type source. As is shown in the plots at right, the measured data agrees very well with theoretical predictions.
One of the figures from this paper was selected to appear as a figure and background image in the 1999 Annual Report of the American Institute of Physics.

Published/presented Research
"Acoustic and modal analysis of an African djembe drum," D. Russell and W. Havemann, presented at: 140th meeting of the Acoustical Society of America, Newport Beach, CA, December 1-5, 2000. Abstract published in: J. Acoust. Soc. Am., 108(5), 2591 (2000) Abstract of the paper: The African djebme drum consists of a goat skin stretched over a hand carved shell with a large cavity, open at the bottom. The shape of the shell cavity acts as a Helmholtz resonator providing a strong bass component around 75 Hz. The shell exibits several bell, or wineglass modes, some of which have frequencies close to membrane modes. This talk will present results from acoustic and modal analysis tests of the drum with and without the skin membrane intact. Mode shapes and frequency spectra will be presented as well as a discussion of how the shell, cavity and membrane couple together to provide the djembe's unique sound. More Information about the Djembe research
"On the sound field radiated by a tuning fork," D. Russell, published in: American Journal of Physics, 68(12), 1139-1145 (2000). [Link to a PDF version of the paper.] Abstract of the paper: When a sounding tuning fork is brought close to the ear, and rotated about its long axis, four distinct maxima and minima are heard. However, when the same tuning fork is rotated while being held at arm's length from the ear only two maxima and minima are heard. Misconceptions concerning this phenomena are addressed and the fundamental mode of the fork is described in terms of a linear quadrupole source. Measured directivity patterns in the near-field and far-field of several forks agree very well with theoretical predictions for a linear quadrupole. Other modes of vibration are shown to radiate as dipole and lateral quadrupole sources. Animations to accompany the published paper.
"Acoustic monopoles, dipoles, and quadrupoles: An experiment revisited," D. Russell, J. Titlow, and Y.J. Bemmen, published in: American Journal of Physics, 67(8), 660-664 (1999). [Link to a PDF version of the paper.] Sound radiation directivity patterns were measured for monopole, dipole, and quadrupole sources. Four small loudspeakers were mounted in a cloverleaf pattern on a rotating stool and driven at a frequency of 250 Hz. Sound pressure levels were measured with a sound level meter at a distance of 1 m from the speakers. The speaker system was rotated 360^o and pressure measurements were taken every 5^o. By switching the polarity of each speaker it was possible to drive all four speakers together (monopole) or in pairs to form a dipole or quadupole type source. As is shown in the plots at right, the measured data agrees very well with theoretical predictions. One of the figures from this paper was selected to appear as a figure and background image in the 1999 Annual Report of the American Institute of Physics.

Unpublished Research

"Modal Analysis of an Acoustic Folk Guitar" D. Russell, P. Pedersen and Zach Hastings
"Modal Analysis of an Electric Guitar" D. Russell and P. Pedersen