2017 GAL Convention

Science and Technology Seminar – Wednesday, July 19, 2:30pm
The Science and technology Seminar will feature a number of short (approx. 30 minute) presentations on topics of science and technology in lutherie. These include reports on recent research by the researchers as well as descriptions of practical technical approaches to lutherie design and construction.

Barlike Bending Modes and What They Do (or Don't) to the Rest of the Modes
Dave Cohen
Synopsis: Whole-body + neck bending motions were imaged using electronic speckle pattern interferometry (aka TV holography) for both a mandolin and a guitar. The body motions were imaged both with a neck in place and without a neck. It was expected that bending motions close in frequency to body modes would perturb the body modes. It was found that there is a significant interaction between the second bending mode and the upper main body mode for both instruments. Resonance plots were done to examine the strength of the interaction. A simple four-oscillator model was derived Calculations are pending to compare the model to the experimental results.

A Crossover-Blend Dual-Source Pickup System
Mike Doolin
Synopsis: Mike Doolin reveals his design for a dual-source, crossover-blend acoustic instrument pickup system. His preamp circuit mixes the best characteristics of under-saddle and contact pickups, while filtering out the "quack" and the "woof" for which each is respectively reviled.

Beyond the Three Sisters – Spectral and Time Domain Investigations of the Sound Produced by Three Radically Different Guitar Top Bracing Designs
Oscar Azaret
Synopsis: In American Lutherie #122, summer 2015, the author documented the construction, Chladni testing, and player perceptions of three guitars built to the designs of Fleta, Romanillos, and Kasha. This presentation will summarize those results, plus demonstrate real-time analysis of the spectrum and time domain waveforms using PC and smart phone apps. Correlation between these results, Chladni testing, and listener/player perceptions will be discussed. At least two of the three sisters will be present.

Experimental Guitars: a Program for Investigation
Greg Byers
Synopsis: A few years ago Finnish luthier Keijo Korelin and the author constructed a set of four guitars with interchangeable parts that can easily be disassembled and reassembled in different configurations. More recently Swedish luthier Johannes Larsson and the author ran some experiments with them to help understand classical guitar sound. Here the author will describe the system and share some preliminary results.

Measuring Young’s Moduli of Guitar Top Panels Using Bar Modes
Howard Stephens
Synopsis: Young’s modulus is a key property used to select high quality tone wood for guitar top panels. Conventional methods for accurately determining the longitudinal (EL) and radial (ER) Young’s moduli use the resonant frequencies of the flexural “bar” modes of narrow, thin beams, cut along and across the wood grain. But, what about measuring these moduli without cutting the panels into narrow beams? Can the resonant frequencies of bar modes of wide wood panels be used to accurately determine EL and ER? To answer this question the author compares the results of Chladni mode and frequency measurements on narrow beams and wide panels.

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