Bill Croffut at Grizzly was having trouble getting it because the guitar makers and piano makers keep snapping it up. Someone explain why this stuff is so great.
Michael Dresdner: Ok, I’ll be glad to. I spent some 25 years as a guitarmaker before moving on to other woodworking pastures. For the tops of guitars, guitarmakers look for woods that have a very high stiffness to mass ratio (very stiff and lightweight), have significant working strength even when very thin, flex repeatedly without weakening or cracking, have specific directional strength (one directional flex) and transmit sound well. Spruce fits the bill all the way around better than any other wood, at least as far as guitar tops and piano soundboards are concerned. Cedar and redwood are close seconds, and it is not unusual to find guitars, especially classical (nylon string) guitars with cedar or redwood tops.
Just to give you a sense of what we ask of it, a guitar top is typically around 0.110″ (one hundred and ten thousandths of an inch) or just under an eighth of an inch, and is “loaded” with over 120 pounds of string tension. That’s a lot to ask, but spruce delivers.
Of the various spruces, Sitka is one of the stiffest (and brightest sounding), while Engleman spruce is favored for a slightly warmer sound and its whiter appearance. Other types sold in guitar circles include Adirondack and European spruces. Curiously, most of the Sitka spruce being sold these days comes not from the Sitka region of Alaska (where it got its name) but from Canada.
In guitars, (both flat top and arch top) both the top and the braces that reinforce the top are made from straight grain spruce with no “run out” that is cut absolutely dead on the quarter (perfectly quarter sawn.) Guitarmakers pay a premium for this, because it means the wood must be processed a certain way from the moment the tree is cut down. Considering how difficult it is to get appropriate soundboard spruce, I think it is in all our best interests to leave that to the instrument makers. There are plenty of other fine woods for us to use in woodworking without depriving those who help fill the world with music.
Rob Johnstone: Sitka spruce is great for sound boards on musical instruments because … it just sounds great. Now that my bout with wisecracking has passed, let me say that spruce, in general is a very nice softwood with a wide variety of uses, but the Sitka sub-group is the cream of the crop. But there is nothing magical about it. Quarter sawn Sitka spruce simply displays qualities Luthiers have been looking for in sound boards for hundreds of years: tight (but not too tight) annual ring growth and the proper specific density to help amplify the vibrations of musical strings. It is also great for any number of other applications (the door of the outhouse up at my cabin is made of spruce ?too much information?). Bill Croffut’s desire to use it on his handmade airplanes is perhaps a better example.
Simon Watts: Sitka Spruce was in great demand whenever the highest possible strength/weight ratio was required?aircraft, sailplanes, masts for yachts, etc. This greatly depleted the supply and has made it one of the more costly softwoods.