ASA 127th Meeting M.I.T. 1994 June 6-10

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

R. B. Bhat

Dept. of Mech. Eng., Concordia Univ., Montreal, PQ H3G 1M8, Canada

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.