by stevemac » 22 Jul 2008, 00:41
We've never tried that combination before; the nearest, at least in terms of using a hardwood soundboard, would be a mahogany top on a rosewood guitar or koa top on an all koa guitar. My recollection of the mahogany top was that it had a lot less tonal complexity than spruce or cedar (but it was on a super jumbo guitar and that may have had something to do with it).
Since the aim in soundboard design is 'controlled resonance', softwoods like spruce or cedar provide more latitude in shaping the voice of the instrument. As for walnut in particular, I'd be interested to hear if anyone has ever come across that.