Vibrational behavior of a soundbox in an atmosphere with a variable speed of sound.

This paper describes a semi-quantitative method, suitable for a student laboratory exercise that shows that the acoustic properties of the soundbox of a musical instrument depend on the sound speed of the atmosphere surrounding and filling the instrument. A gas tent was constructed and used to enclose instruments in helium, carbon dioxide and mixtures thereof, allowing the sound speed to be varied from 250 to 1000 m/s. Soundboard admittance data were taken using a guitar and a violin as examples. The data, expressed as contour plots, show clearly the qualitative relationship between air and wood modes, and the guitar data are compared with a simple mechanical model. Experimental details of the construction and operation of gas tent are given, with attention paid to safety issues.

Vibroacoustic characteristics of a gothic harp.

The "gothic" style of harp was popular across most of Europe from the late medieval period to the Renaissance. These harps have a one-piece, longitudinally oriented hardwood soundboard, as opposed to the transverse-oriented bonded softwood structure on a modern instrument. In addition, the one-piece back is flexible, whereas the back of a modern instrument is a rigid molded shell. To study the gothic harp, one was constructed from plans created by the Boston Museum of Fine Arts from a late German model in their collection. The vibrational behaviors of the soundboard and soundbox were measured at various stages of construction. The completed instrument was subjected to modal analysis and radiativity measurements. The sound radiation is dominated by two breathing modes at 188 and 273 Hz, each with strong motion of the back, and modes around 350 Hz. Taken together, these modes function like the A0/T1 resonance pairs seen in the soundboxes of other instruments, and a comparison is made with the guitar. Also observed is that as the frequency increases, radiation is emitted from higher up the soundboard, and from higher soundholes. This feature has been observed in other harps, and is a consequence of the harp family's unique geometry.

Vibro-acoustic characteristics of an Aoyama Amphion concert harp.

The mechanical admittance of the soundboards of four full-size concert harps from three manufacturers was measured, and the results show that there is little variation between them. More detailed vibro-acoustic data were then obtained for an Aoyama Amphion harp. Analysis of these data show that the individual soundholes amplify the radiated sound in successive frequency bands associated with the modal frequencies of the soundboard. The lower holes tend to contribute at the lower end of the frequency scale, and the higher holes at the higher end of the scale.

Vibrational characteristics of harp soundboards.

Harps exist in different forms, from large factory-made concert harps to small hand-made folk harps. This variety presents both a challenge and an opportunity for acousticians. The musical quality of a harp depends on many factors, but key among these is the soundboard. This work sets out to define some general desirable qualities of a harp soundboard. First, in order to understand the relationship between the vibrational behavior of a bare soundboard and that of a completed instrument, a 36-string harp was built from scratch. Measurements were made at each stage of construction, and the results showed how the bare soundboard properties affect those of the finished harp. Second, the soundboards of several harps of different sizes were assessed by measuring the admittances along the string bar. These data showed that one relationship crucial to the quality of the soundboard is that between the modal shapes and modal frequencies of the soundboard, and the position and fundamental frequencies of the strings attached to it. A general statement is made about this relationship, one which should be of use to harp makers.

A new model of protein adsorption kinetics derived from simultaneous measurement of mass loading and changes in surface energy.

We describe a novel technology based on changes in the resonant frequency of an acoustically actuated surface and use it to measure temporal changes in the surface energy gamma (N m(-1)) of an elastomeric polymer membrane due to the adsorption of macromolecules from aqueous solution. The resonant elastomeric surface-tension (REST) sensor permits simultaneous determination of mass loading kinetics and gamma(t) for a given adsorption process, thereby providing a multivariable data set from which to build and test models of the kinetics of adsorption at solid-liquid interfaces. The technique is used to measure gamma(t) during the adsorption of either sodium dodecyl sulfate (SDS) or hen egg-white lysozyme (HEWL) onto an acrylic polymer membrane. The adsorption of SDS is reversible and is characterized by a decrease in gamma over a time period that coincides with that required for the mass loading of the membrane. For the adsorption of HEWL labeled with Alexa Fluor 532 dye, gamma continues to change long after the surface concentration of labeled HEWL, measured by using the elastomeric polymer membrane as an optical waveguide, reaches steady state. Gradual but significant changes in gamma(t) are observed as long as the concentration of protein in the bulk solution, c(b), remains nonzero. HEWL remains adsorbed to the membrane when c(b) = 0, but changes in gamma(t) are not observed under this condition, indicating that the interaction of bound protein molecules with those free in solution contribute to the prolonged change in the surface energy. This observation has been used to define a new model for the kinetics of globular protein adsorption to a solid-liquid interface that includes a mechanism by which the molecules in the bulk can facilitate the desorption of a sorbate molecule or change the energetic states of adsorbed molecules and, thus, the overall surface energy. The model is shown to capture the unique features of protein adsorption kinetics, including the relatively fast mass loading, the much more gradual change in surface energy that does not cease until the protein is removed from the bulk, the rapid desorption of an incubation-time-dependent fraction of bound protein when the protein is removed from the bulk, and the fixing of the residual surface concentration and surface energy at constant values once the removal of reversibly bound protein and free protein is complete.

Modulation of retroreflection by controlled frustration of total internal reflection.

Retroreflective images are useful in outdoor application for which high legibility is required both during the day and in response to vehicular illumination. To date, all variable message retroreflective images have employed mechanical shutters as the switching mechanism. As an alternative, we propose a method for switching the total internal reflection effect used in retroreflectors by means of pneumatic actuation of surface treated polydimethylsiloxane gel. This approach is both effective and compatible with current large-scale manufacturing methods.