that if pedagogically correct legato and staccato strokes are played with .... 3pMU8. Synthesis of the sound pressure radiated by a guitar using a mixed time- and ...
vibratory fringe patterns in real time, but also allow direct conversion of fringes into numerical data. This paper will outline the current state of this technology and how it can impact on the study of musical instruments.
Contributed Papers 1:15
2:00
3pMU2. A study on radiation pattern and radiation efficiency of an upright piano soundboard. Philippe Derogis and Rene Causse (I.R.C.A.M., 1 place Igor Stravinsky, 75004-Paris, France)
3pMU5. Time-domain simulation of sound production in brass instruments. Seiji Adachi (ATR Human Information Processing Res. Labs., 2-2 Hikaridai, Seika-cho, Soraku-gun, Kyoto, 619-02 Japan)
In this study, a modal analysis of the soundboard of an upright piano with strings mounted was performed. The measurements of the frequency response functions and the use of modal testing software have allowed us to find the eigenfrequencies and the mode shapes. The results agree for the most part with earlier measurements [I. Nakamura, "The vibrational character of the piano soundboard," Proc. 11th ICA Paris, 385-388 (1983)]. Indeed, below 300 Hz the mode shapes are almost the same for an isotropic rectangular plate. However above 300 Hz, they become more complicated. These results were used to compute the acoustic field resulting from the vibrations of the soundboard by calculating numerically the Helmholtz Huygens integral. Then the radiation pattern curves obtained were compared with measurements and with two simple models (isotropic baffle plate and isotropic plate radiating on one side). The integration of the calculated acoustic field was performed in order to determine the radiation efficiency of the soundboard. Finally, the radiation efficiency as a function of the plate characteristics (size, stiffness) was computed using the models above.
Sound production in brass instruments has been formulated physically, including two different models of lip vibration; the perpendicular model, where lips strike laterally to the direction of the air flow, and the "swinging door" model, where lips execute outwardly rolling motion. The above formulation was used to carry out time-domain simulation. As a result, self-excitation of the brass instrument was found to be possible with both of these lip models. By changing the lip eigenfrequency, sustained oscillations near at least the first through the eighth resonant impedance peaks of the instrument were realized. The simulated sound was shown to have variety in the harmonic structure accompanied with pitch and loudness variations as is seen in sound the natural brass instruments produce. Unusual regimes of oscillation were also obtained; the pedal tone, whose fundamental does not participate in its sound production, a tone octave below the third impedance peak, whose odd harmonics do not contribute to the regime of oscillation, and a multiphonic, which is an oscillation perceived having two fundamentals simultaneously.
1:30
2:15
3pMU3. Analysis of contrast in marimba stroke articulation. Ronald A. Roberts (Aerosp. Eng. and Eng. Mech., Iowa State Univ., Ames, IA 50010) and Barry Larkin (Iowa State Univ., Ames, IA 50510)
3pMU6. Acoustical characteristics of a conch shell trumpet. Lisa R. Taylor, M. G. Prasad (Dept. of Mech. Eng., Stevens Inst, of Technol., Hoboken, NJ 07030), and R. B. Bhat (Dept. of Mech. Eng., Concordia Univ., Montreal, PQ H3G 1M8, Canada)
A current issue in marimba performance is the role of legato and staccato stroke techniques in controlling note articulation characteristics. Pedagogical tradition teaches that an arrested stroke produces a staccato (choppy) sound as compared to a nonarrested stroke that is used to produce a legato (smoother) sound. It has recently been suggested, however, that perceived differences in the mallet stroke attacks are purely contextual, that is, a note is perceived as staccato if it is significantly louder than its neighbors in time. It has also been suggested that if pedagogically correct legato and staccato strokes are played with equal loudness (equal mallet velocity) outside of a musical context, no differences are perceived. This paper presents a time frequency analysis of equal loudness legato and staccato strokes that indicates that there is indeed a physical difference in the sound pressurefieldsgenerated by the two strokes. In the staccato stroke, the broadband third overtone generated by the marimba bar is noticeably greater in amplitude relative to other spectral components, particularly when played with a softer mallet. However, it has yet to be determined if these differences are perceived. Procedures and results of ongoing experiments will be presented and discussed.
1:45 3pMU4. Holographic studies of normal modes in bass handbells. Deepak Gangadharana> and Thomas D. Rossing (Phys. Dept., Northern Illinois Univ., DeKalb, IL 60115) Holographic interferometry has been used to compare the modes of vibration in two Gi handbells, one of bronze and one of aluminum [Rossing and Mansell, J. Acoust. Soc. Am. 93, 2382 (A) (1993)]. Except for the (2,0) and the (3,0) modes, tuned to have a 3:1 frequency ratio, all the other modes in the bronze and aluminum bells occur at different frequencies. In the bronze bell, we observed an unusual family of (m,3*) modes, not found in other bells. a)Present address: Phys. Dept., South Florida Univ., Tampa, FL 336202912
J. Acoust. Soc. Am., Vol. 95, No. 5, Pt. 2, May 1994
The sound spectrum and duct geometry of a conch shell trumpet is examined in this study. The fundamental frequency of a Turbinella Pyrum was sounded and its spectrum recorded in an anechoic chamber. Spectral analysis shows a strong fundamental frequency and five overtones at integer multiples that form a smoothly decreasing envelope. The placement of the harmonics and their relative amplitudes suggest the conch shell duct has an exponential flare similar to a french horn. It was also found that the fundamental frequency of the conch shell could be lowered by insertion of fingers into the shell opening. X-ray tomography pictures reveal the shape and size of the duct cross section at every half-turn, as well as its corresponding location with respect to the longitudinal axis. This information was used to approximate the duct profile as it would appear if the conch were unwrapped. As expected, the duct profile has an exponential flare that gives the conch a characteristic timbre and allows its sound to project over long distances. 2:30 3pMU7. The modern baroque trumpet. Robert W. Pyle, Jr. (11 Holworthy PL, Cambridge, MA 02138) and Robinson Pyle (Osmun Brass, Belmont, MA 02178) Recent years have seen a great increase in the frequency of historically informed performances of early music. While the phrase "modern Baroque trumpet" appears to be an oxymoron, most of the trumpets used professionally in such performances have not been copied from historic specimens. To aid the player in achieving the accuracy and intonation expected by the audience (and conductor!), the design of the modern Baroque trumpet departs from that of its forebears, typically by adding from one to four side holes to be opened and closed by the player's fingers. Another nontraditional feature present on some modern instruments is a tapered mouthpipe just downstream of the mouthpiece. The changes in the input impedance of the instrument produced by the sideholes and tapered mouthpipe will be shown and the relationship between these changes and the playing qualities of the instrument 127th Meeting: Acoustical Society of America
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A. Chaigne [J. Acoust. 5(2), 181-211 (1992)]. This model is used for investigating the influence of various plate parameters on timbre and sound quality of the instrument.
will be discussed. The talk will include demonstrations on at least one instrument. 2:45
3:00
3pMU8. Synthesis of the sound pressure radiated by a guitar using a mixed time- and frequency-domain modeling technique. Thomas Carter, Jean-Louis Guyader (Lab. Acoust. Vib., Batiment 303, Inst. Natl, des Sci. Appl., 69621 Villeurbanne, France), and Antoine Chaigne (Telecom Paris, 75634 Paris Cedex 13, France)
3pMU9. A measurable result of bi-tri octave plate tuning. Carleen M. Hutchins (112 Essex Ave., Montclair, NJ 07042) Many of the finest violins and violas exhibit a special quality, namely that the four quadrants of both top and back, when tapped lightly, can be heard to have approximately the same pitch. In an experiment with three violas made on the same pattern and with very similar wood, the one with bi-tri octave tuning (modes 2 and 5 at matching octaves in both top and back plates and mode 1 in the top an octave below mode 2) was found to have the above condition. The other two, with different conditions of their free plate resonances, did not. An electronic measurement of the eight quadrants in these violas, four in the top and four in the back where one would ordinarily tap, showed that the lowest two resonance peaks in each of the eight quadrants were very similar, for the bi-tri octave plate tuned viola. This was not the case in the other two which were judged by expert players to have considerably less good tone and playing qualities. These findings will be charted and their implications discussed.
A general method has been previously developed by O. Beslin et al. [J. Acoust. Soc. Am. 89, 1868 (A) (1991)], using a variational method to describe the motion of a perforated plate, and a integral formulation for the modeling of the consecutive radiated sound pressure. This model is now adapted to the particular case of a guitar, whose top plate is represented by a rectangular orthotropic plate with hole and back cavity. The sound pressure computation is carried out in the frequency domain, for a point force acting at the bridge. This yields the pressure versus force transfer function H(ta), from which the corresponding impulse response h(t) can be derived by means of inverse Fourier transforms. Finally, the guitar tones are obtained by convolving h(t) with a time-domain formulation of the force F(t) imparted to the bridge by a guitar string, using a finite difference method previously developed by
WEDNESDAY AFTERNOON, 8 JUNE 1994
STUDENT CENTER, ROOM 407, 12:45 TO 3:00 P.M.
Session 3pNS Noise: History of Noise Control: Hearing Protectors Robert D. Bruce, Chair Collaboration in Science and Technology, Inc., 15835 Park Ten Place, Suite 105, Houston, Texas 77084-5131 Chair's Introduction—12:45
Invited Papers 12:50 3pNSl. A history of hearing protection in the United States. C. T. Moritz and R. D. Bruce (Collaboration in Sci. and Technol., Inc., 15835 Park Ten PI., Ste. 105, Houston, TX 77084-5131) During the late 1800s it was known that exposure to high sound levels could lead to permanent hearing loss. Although several U.S. patents were awarded for hearing protective devices in the 1800s, hearing protectors were not generally available until the 1920s. These devices were marketed to help people cope with the high sound levels of the "big city," not to protect against hearing loss. It was not until World War II that hearing-protective devices became generally available for industrial workers. This paper will present an overview of the major developments in hearing protection in the United States from the 1920s to the present and discuss the forces behind their development. Emphasis will be placed on the availability of different types of hearing-protective products to industrial workers and consumers. 1:10 3pNS2. Highlights of hearing protection. Paul S. Veneklasen (Western Electro Acoust. Lab., 1711 Sixteenth St., Santa Monica, CA 90404) Before WWII Dr. Vern Knudsen began the development of ear defenders. In December 1941 this project suddenly took on great urgency; models were developed through V29. Performance was measured by threshold shift. Extreme industrial and military exposures were measured and tentative limit suggested. Development continued at Harvard Psycho-Acoustic Laboratory, resulting in V51. This device was produced in huge quantities for military and industry by MSA. At Harvard two other devices were developed: a comfortable dual-seal circum-aural headphone cushion and an insert device, called the Harveltip, derived from the V51 for coupling a miniature receiver. Both of these were in response to interference of increasing noise with military communication. At Harvard Bob Wallace conceived and tested the possibility of "active" noise suppression. Substantial improvement in direct person-to-person speech communication occurred with a good ear defender. After the war, research progressed with improvement over the Harvintip. The limit of achievable protection with exposed head was due to bone conduction. A method was developed for measurement of attenuation at much higher exposure. All this experience yielded clarification for necessary design parameters. 2913
J. Acoust. Soc. Am., Vol. 95, No. 5, Pt. 2, May 1994
127th Meeting: Acoustical Society of America
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