Dr. Ludwigsen's Research in Acoustics
(student names in red italics)
Ongoing Research
Physics and Acoustics of the Mbira - with William Rein

Research Summary
The traditional instrument of the Shona people of Africa, the mbira has metal keys attached to a wooden soundboard.  There are many varieties and variations, especially in handmade instruments; one version that is more standardized and adapted for western tunings was developed by Hugh Tracey, called the Kalimba.  The keys are plucked mainly with the thumbs, and the music is used for both recreation and spiritual functions.  The similarities of the mbira with both guitar and xylophone make this an appealing instrument for study.  Models to better understand this instruments stem from our study of the vibration of bars and plates in Acoustics II. 


Physics and Acoustics of the Trombone - with Dan Neill

Research Summary
Dr. Ludwigsen is currently refining a finite element model of the lip reed in order to understand how the lips drive the trombone. Experiments (most involving students) will involve measuring the radiation characteristics of the trombone, using an inexpensive piezoelectric device to measure the input acoustic impedance as seen by the lips, and developing a state-of-the-art input impedance head with a new type of microelectric particle velocity sensor.  An additional project will develop a set of artificial latex lips to achieve fairly constant and reproducible tone generation.

General Acoustics of Air Columns - with Brandon Dilworth, Tim Swieter, and Chidi Uhiara

Research Summary
Air columns are found in applications from musical instruments to automotive exhaust systems.   The projects growing from this interest include measurements of input impedance, radiation impedance, particle velocity, end correction coefficients for open pipes, and models of similar acoustic phenomena.
Binaural Localization - with Kimberley Pregitzer

Research Summary
In localizing a sound source, the brain uses the signals from the two ears, along with physical structures of the head and torso.  In this work, the processing done by the brain is performed by computer.  The transfer functions of a binaural head have been characterized for positions on the horizontal circle around the head.  Using a clap from wood blocks, the impulse response was recorded for locations at ear level every 10 azimuthal degrees.  The impulse responses were transformed into transfer functions.  Sound samples can then be located at these positions in one of two ways: the input sound file can be convoluted with the impulse in the time domain, or can be filtered with the transfer functions in the frequency domain.  The output sound file can be auditioned through headphones. 

Binaural head in our pseudo-anechoic room

Published/presented Research

  • D. O. Ludwigsen, "Physical modeling of the trombone player's lips," Proceedings of the Stockholm Music Acoustics Conference (SMAC03) , Roberto Bresin, Ed., p. 209 (2003).

  • D. O. Ludwigsen and W. J. Strong, "Normal modes of a finite element lip reed model," J. Acoust. Soc. Am., 109(5), Pt. 2, 2483(A) (2001)

  • J. R. Moffit and D. O. Ludwigsen, "Self-sustained oscillation as a function of blowing pressure in a one mass lip reed model," J. Acoust. Soc. Am., 108, 2591 (2000)

  • D. O. Ludwigsen and W. J. Strong, "Physical modeling of a trombone player's lips," J. Acoust. Soc. Am., 104, 1768 (1998)

Unpublished Research

D. O. Ludwigsen and B. Dilworth, "End correction of the length of an open pipe from measured resonance frequencies," for the Acoustical Society of America meeting in San Diego, November 2004.

D. O. Ludwigsen, "Measurements of the acoustics of the kalimba,"  for the Acoustical Society of America meeting in San Diego, November 2004.

D. O. Ludwigsen, "An imedance head for brass instruments using the Microflown sensor," for the Acoustical Society of America meeting in Vancouver, May 2005.