Speaker
Description
The tuning of guitar soundboards is traditionally anirreversible subtractive process, relying on the removal of bracingmaterial. This study proposes a reversible, additive approach utilizingtop plate mounted Locally Resonant Metamaterials (LRMs) to suppresspathological resonances arising from strong string-body coupling,commonly referred to as wolf tones, which cause uneven note decay. UsingScanning Laser Doppler Vibrometry (SLDV), we mapped the operationaldeflection shapes of the guitar's top plate under controlled excitationto identify its eigenmodes. We then experimentally simulated wolf toneconditions by tuning strings to couple directly with a specificstructural resonance. To counteract this effect, custom metamaterialresonators were designed and manufactured to act as subwavelengthmechanical band-stop filters. To distinguish the local resonance effectfrom simple mass-loading, the system’s response was compared against acontrol using equivalent masses. The efficacy of the treatment wasevaluated through comparative vibrometry and audio signal analysis ofthe decay envelope and timbre of a plucked note. Results demonstratethat LRMs can clearly reduce note decay irregularities and achievesuperior suppression and frequency-specific targeting compared to massaddition alone, providing a non-invasive solution for instrument voicingapplicable both during manufacturing and for post-production adjustment.