Bracing Pattern Research Articles

On the structural‐acoustic design of guitars

A structural‐acoustic model of a guitar top plate backed by a rigid cavity has been built. Acoustic coupling between the interior and exterior acoustic fields is accomplished with a simple model of the soundhole. Acoustic power spectra are calculated in 1/12 octave intervals from 55 to 440 Hz. The soundboard is modeled as an orthotropic damped plate with reinforcing beams and a circular cutout forced by harmonic point loads representing the strings. The model requires the plate outline to be axisymmetric. There are no limitations on the number or orientation of the reinforcing beams. Material property variations, brace cross section, brace pattern layouts, individual brace tapers, plate thickness, and varnish and glue line effects can be studied with this model. A suitable database of material properties and guitar geometry parameters, string lengths, bridge placements, etc. has been built to support the model.

The physiology of wandering behaviour in Manduca sexta. III. Organization of wandering behaviour in the larval nervous system.

The locomotor patterns typical of wandering behaviour were studied electromyographically in abdominal segments of freely moving larvae of Manduca sexta. Crawling locomotion consisted of stereotyped, anteriorly-directed, peristaltic waves of intersegmental muscle contraction. During burrowing the intersegmental muscles of all abdominal segments contracted simultaneously for several consecutive cycles and then performed a single bout of the crawling pattern. Sensory inputs determined which motor patterns were used and how they were modified. Local sensory inputs could modify patterns in the specific segments affected. The neural circuitry that was required to generate the peristaltic and bracing patterns was repeated among the thoracic and abdominal ganglia, and normally wa activated by the suboesophageal ganglion (SEG) and brain. In the absence of connections with the SEG and brain the segmental motor pattern generators could be activated by strong sensory stimuli. When the thoracic and abdominal segments lacked connections with the SEG, spontaneous movements were infrequent prior to wandering, but increased markedly at wandering or following 20-hydroxyecdysone (20-HE) infusion. Prior to wandering the SEG drives spontaneous locomotion in debrained larvae, but this function disappears in wandering larvae, or following 20-HE infusion. Prior to wandering the brain exerted a net inhibitory influence on locomotion. Removal of the medial region of the brain abolished this inhibition, resulting in strong, continuous locomotion which was driven by the lateral region of the brain. This lateral excitatory function of the brain was not altered by 20-HE infusion prior to wandering, nor did it change with the appearance of wandering behaviour. We conclude that the locomotor patterns used during wandering are produced by pattern generators in the segmental ganglia and are modified by sensory information. The circuitry responsible for activating these motor pattern generators is associated with the SEG, and is under the control of the brain. The brain exerts a net inhibitory influence prior to wandering, which becomes excitatory during wandering. Ecdysteroids appear to alter locomotor function by acting at various levels including the segmental ganglia, the SEG and the brain. A model is advanced describing this effect.

Modes of vibration of guitar plates with and without bracing

An earlier study [R. E. Ross and T. D. Rossing, J. Acoust. Soc. Am. Suppl. 1 65, S72 (1979)] indicates that the bracing pattern of the top plate, through its influence on the modes of vibration of the top plate, has a substantial influence on the acoustical properties of a guitar. We therefore tested six guitar top plates of identical shape (but varying in thickness and type of wood) in the raw state and again after various patterns of bracing had been applied and a sound hole cut. The modes of vibration were observed with both free and clamped edges. The vibrational modes of the unbraced plates resemble those of a rectangular plate, but the modes of the braced plates are considerably less predictable. Special thanks are due to luthiers Jim Williams, Gerard Gilet, and Robin Moyes, who supplied the plates used in these studies. [Work supported in part by the U.S.‐Australia Cooperative Science Program while the author was at the University of New England.]