Guitars are made in a variety of tonewoods, with the properties of each highly debated among guitarists. Even in electric guitars – where the output sound is heavily dependent on electrical circuitry and amplification, and often subjected to various effects - manufacturers may have custom shops where a customer can specify a neck and body from a range of options at great expense. This paper establishes the physical properties of a range of tonewoods and relates them to sounds such as “dark,” “warm” and “bright.” This is part of a wider body of work to establish which properties and features of electric guitars are quantifiable, to what extent they are genuinely perceivable, and whether they can be recreated using alternative budget or sustainable materials. A set of tonewood samples were subjected to impact testing using laboratory equipment. Impact testing is usually used to identify structural vibrational properties in the form of a transfer function, over a frequency range of around 5-100Hz. However, the equipment can cover a frequency range of up to 2kHz which is in the audible range. Furthermore, the frequencies identified in the upper frequency range are often harmonics of those in the lower range. Our hypothesis was therefore that vibrational modes identified in the tonewood sample at relatively low frequencies (<1kHz) are related to tone (which is normally associated with a much higher frequency range). A preliminary observation was that wood samples generally had similar natural frequencies (50Hz and its harmonics) but exhibited different amplitudes and damping ratios. Analysing a range of tonewood samples – Ash, Maple, Mahogany and Walnut – revealed a particular mode in the ~200Hz range which appears to correlate to ‘brightness.’ In Maple (the ‘brightest’ wood tested) this is a clear peak at 206Hz. In Ash (which is also fairly ‘bright’) this mode has a slightly lower amplitude and frequency at 182Hz, and in Mahogany and Walnut (both ‘warm’ woods) this mode appears to couple with a 150Hz mode. There are some other modes (250Hz. 350Hz and 450Hz) which also vary slightly in frequency and amplitude across samples and may indicate tonal properties. Analysis is ongoing at the time of writing, with a wider range of tonewood samples to be tested.
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