I’m currently doing R&D on a physical instrument/sound generator, and my go-to practical reference book has always been this one:
Another book I found recently, ‘rented’ for free as an ebook via Archive.org
Vibrations : Making unorthodox musical instruments
by Sawyer, David
This one looks interesting:
Acoustics of Wood
by Voichita Bucur
but the purchase price is rather prohibitive at $379.99 for a paperback copy….
Another free to rent ebook from Archive.org
Tone : a study in musical acoustics
by Levarie, Siegmund, 1914-2010
Please comment if you know of any other books or resources?
Sound Designs: a handbook of musical instrument building
by Reinhold Banek & Jon Scoville
Sound Sculpture, ed. John Grayson
Download [PDF, 24mb] at ubuweb
A collection of essays by artists surveying the techniques; applications; and future directions of sound sculpture.
UPDATE via comments, thanks Dan:
There are a couple of other, smaller, Bart Hopkin books I’ve also found helpful. Built a few things over the years. Not sure which book I found it in, but the last one I built and sampled was this waterfall: https://barthopkin.com/instrumentarium/waterfall/
Back issues of his magazine “Experimental Musical Instruments” are brilliant too:
Table of Contents PDF of all issues is text searchable