I've seen two koa basses here in Hawaii. Both had spruce tops and. koa back, sides, & neck. While both were beautiful, neither had a sound worth a fraction of the asking/selling price. This may simply reflect the skills of the luthiers that made them
My experience with koa as an instrument wood** as used in basses, electric guitars, and acoustic guitars has been similarly disappointing: pretty to look at, "meh" in the tone dept. Koa has no advantages over maple other than looks. It also wants to crack & split over time, as evidenced by the many beautiful,
repaired antique Koa calabashes to be found all over Hawaii
**A bit off topic:
The obvious exception here of course being the use of koa in ukuleles. Even here, the best recording instruments are usually all mahogany (IZ, Lyle Ritz, Moe Keale), or koa with a spruce top (Jake Shimakbukuro, Troy Fernandez). One notably incredible sounding all koa uke is Troy Fernandez' "On Fire" uke. This instrument if it still exists, is an insanely good sounding uke.
This is only my experience. Yours certainly may vary, and I could just be full of it.


