Sailboat Acoustics / Resonances Research

By Alan B. Richmond Jr.

Initial observations on phase, frequency, and other such relationships at stereo contact microphones (L/R) on the bow fiberglass deck (approximately 1-2 feet from foremost bow point / seam), with stereo width separation of approximately 3-4 feet)

Wind drag can be heard on the windward side / and the leeward side, on both the sail sheets heard through the deck mounted blocks resonating on deck (leeward), as well as on the surface of the fiberglass hull itself (windward). Upon this initial phase of examination and investigation, I am finding some difficulty in deciphering windward / leeward directions, as there is so much sonic activity from the hull, water wave surface, and sail sheets / blocks on deck. From observation, it sounds as though there is contrast of similar lower resonances of ‘drag’ coming from opposing sides, one from the sail, sheets, and blocks taking wind on the leeward, the other from the windward hull side, which exhibit similarities in frequency range, character, and sustain / decay. To add, there is also some subtle drag coming from the leeward side, from the hull that is heeled deeper into the water surface, where impacted waves and heel activity have a constancy of subsequent surface grazing activity. Interesting anomalies at this time have been discovered as opposing frequency ranges, seemingly with the windward facing hull sonics exhibiting deeper, more broad frequency ranges, as well as narrower higher frequency range hyper activity of wave impacts, splashes, and the like, where as the opposing leeward side that is heeled into the water surface is a higher frequency range due to less surface area resonating (much like pipe organ sizes that resonate at lower pitches in larger length, and higher pitches in shorter lengths, or kalimba and other instruments with tines at longer lengths having deeper frequencies, and those of shorter length having higher).

Also, there are some interesting phase relationships identified thus far, as would be expected similarly in any architectural acoustic setting, whereby waves, in this case hydro, are reaching hull sides off the bow at very slightly different timeframes (milliseconds) before taking on the aforementioned noticeably different characteristics. By slowing down the speed of audio playback, it creates longer timeframes and slightly better differentiation, some of which can be detected audibly and by seeing the L/R dB meters spike at very slightly different times for the same impact event, indicating the impact side, and the drag side (most often corresponding to windward / leeward sides). Slowing playback too much creates exaggerated artifacts and makes such differentiation difficult, so finding a proper speed / balance here is important. Confirming such activity and characteristics at normal playback speed can aid in this process, and reinforce ability to decipher such activity at normal speed, pace, and event timelines, as well as present accurate frequency pitches and ranges recorded and their structural and material relationships . Through further examination and investigation, it could be discovered that this analysis is incorrect and perhaps opposite these origin findings, but identifying such differentiation in this stage is helpful in such overall and correct determination and findings.

samples of such phenomena from the investigation archive file will be added to this published written analysis at a future time for reference.

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Alan B. Richmond Jr. / www.audioeins.com

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