Acoustics demonstration extravaganza
Authors: Russell Daniel A. 
Published: April 2023

The Education in Acoustics and Physical Acoustics committees are pleased to present an Acoustics Demonstration Extravaganza - a showcase of demonstrations and apparatus to inspire and challenge your understanding of acoustics and vibration phenomena. In the spirit of the “Circus of Acoustics” demonstration show from the June 2002 ASA 143 Pittsburgh meeting [J. Acoust. Soc., Am., 111, 5, Pt2, p. 2451, (2002) session 4pPAb] this session will consist of several short demonstrations covering a wide variety of acoustics and vibration topics. Among the demonstrations intended to be shown are the following (there may be some last-minute additions or substitutions depending on equipment and presenter availability):

Simple Sound Sources: Directory patterns and frequency spectrum characteristics of monopole, dipole, and quadrupole sources, the pressure doubling effect of a baffle, and a beam-forming array.

Radiation of Sound from Plates: Demonstration of the radiated intensity from various vibrational modes of a simply supported thin plate.

Strings of Pearls: Modes of vibration for a N-DOF mass-spring system and standing waves on a compound string comprised of a two string segments with different densities.

Burning Wire of Death: Standing waves on a nichrome wire carrying a high current so it glows red at nodes.

The Song of the Singing Rod: The singing rod demonstration is commonly used to describe longitudinal waves in a free-free rod. However, if the length of the rod is adjusted just right, a nonlinear pulsating effect is observed resulting from modal coupling of transverse bending modes and either subharmonic longitudinal modes or torsional modes.

Nonlinear Oscillations in a Membrane: A membrane is driven with a large amplitude, so the vibration becomes nonlinear. As the frequency sweeps up and then down, the amplitude jumps and follows a hysteresis loop characteristic of a stiffening nonlinear spring.

Demonstration apparatus of the Cochlea (designed by Robert Keolian): A mechanical hydrodynamic analog model of the basilar membrane in the cochlea illustrating von Békésy's classical passive tonotopic traveling wave as an explanation of how the ear responds to different frequencies.

Acoustic Resonator Rockets: A pair of lightweight Helmholtz Resonators, balanced on a pivot, will rotate when exposed to a loud amplitude sound at their resonance frequency.

Acoustic Filters: An audible and visual demonstration of low-pass, high-pass, and band-stop acoustic filters using PVC pipes.

Vocal Tract Models: A collection of short pipes with varying cross-sectional areas (designed by Takayuki Arai) that produce vowel sounds and may be used to model the acoustics of speech.

Speed of Sound: A series of short demonstrations that illustrate the effect of temperature on the speed of sound in air, sound speed dependence on gas composition, and the effect of bubbles on the speed of sound in water.

Fluid Loading of a Plate: A comparison of the vibration response of a vibrating plate, and the audibly radiated sound, when the plate is in air versus submerged in water.

Rectangular Waveguide: Plane waves will propagate down a waveguide without decay at all frequencies, but non-plane wave modes will propagate only if driven above the cut-on frequency. When driven below the cut-on frequency, non-plane modes become evanescent and decay exponentially.

Baseball Bat Piano: The hollow cylindrical barrels of metal and composite softball bats exhibit cylindrical shell vibrational modes. A collection of softball bats with hoop-mode frequencies corresponding to a musical scale may be played like a xylophone.