MIMF

I'm fairly new at building music instruments. I'm currently building my third acoustic guitar and I'm building a hammered dulcimer. For the dulcimer, I'm using the 17/16 plans from harpkit.com. It seems a lot of folks think baltic birch ply would make a decent soundboard. Harpkit.com says plywood isn't strong enough, yet spruce, cedar, and redwood is strong enough. Really?! Btw their kit, which is based on the same plans comes with 3/8 " mahogany. I can buy a mahogany soundboard from them for Us$150. I bought 3/8 baltic birch ply to use for the soundboard. Btw, this dulcimer has a fixed soundboard. I almost forgot, i have a spruce soundboard i salvaged from an old piano, but it's only 1/4" thick. Probably too thin.

At this point, I'm not sure what to do. Also, i plan to start learning to play the HD, and an entry level HD will be fine. Should i use the birch ply, or use something else. Oh, and so far i have not found a source of wood for a soundboard other than the one from harpkit.

Thanks for any advice,
Kevin

How thick is the ply?

I've used 1/4" mahogany on a 13/13 (fixed soundboard) and 1/4" redwood on a 14/15 (floating soundboard).

If the soundboard covers the tuning and hitch pin holes, softwoods (like spruce) will be a little harder to drill clean holes in. On my first one,

If you have a local wood shop, you might see if they can glue up and thickness a soundboard for you.

Thanks Charlie. I can glue up and thickness the soundboard in my shop. My big problem with doing my own is getting quarter sawn soundboard wood locally. If i order it, it's going to be expensive. My only source in town only has flat sawn lumber, except for oak. I guess i could get a 6x6 cedar or redwood post and resaw it.

Often the issue with strings instruments is not strength per se, but stiffness, particularly along the grain. Most common hardwoods are not much stiffer along the grain at a given thickness than a piece of softwood with about half the density. That's why we use softwoods for soundboards; to keep the weight down. Plywood suffers in the long-grain stiffness department due to the cross plies. The outer plies do contribute more stiffness than the inner ones, but it still tends to be less stiff 'along' the grain than the equivalent solid wood would be.

We use quartered wood for three reasons: it has higher cross grain stiffness than other cuts, it has less of a tendency to cup across the grain, and it's less likely to split from shrinkage. Cross grain stiffness is hardly an issue in hammered dulcimers. Cupping mostly happens when there's a lot of curvature in the annual ring lines on the end grain. Splitting is more of an issue with really flat cut wood. You can often find skew cut softwoods fairly easily; with the annual ring lines at 45* to the end grain surface. Wood cut like this will not be notably more prone to cupping than dead on vertical wood, and actually has the highest resistance to splitting. It will be floppy as all get out across the grain, but, again, in this application, that hardly matters.

Thank you for fantastic explanation! What you said about plywood makes sense. I got my hands on some quarter sawn European spruce. I had to resaw it, glue it up and thickness it. As soon as I figure out how, I'll post some photos.