Friday, January 6, 2017

"Ability to Resonate"

I've just received a technical paper from a Canadian supplier (one prepared particularly by a research scientist working for a Canadian organization which carries out scientific research for the Canadian forest industry) which compares, among other factors, a variable called the wood's ATR or Ability To Resonate. Interested?

"In the musical-instrument building industry, researchers have established the importance of Modulus of Elasticity (MOE) and wood density (Krzysik 1967, Ono 1983). They have developed the following equation for selecting suitable woods, by calculating the acoustical coefficient; also known as the ability to resonate (ATR):
ATR = Square root of (MOE/ wood density3)"

Furthermore, "The Ability to Resonate is calculated as the square-root of MOE/relative density cubed. The higher the value, the greater the ability to resonate." Essentially it is a function of the wood's elasticity relative to its density. Allow me to share the paper's findings, listing in order the ATR of common instrument soundboard conifers. In order of the species' ability to resonate:

Englemann Spruce picea englemannii    373
Western White Pine pinus monticola      400
White Spruce picea glauca                     404
Sitka Spruce picea sitchensis                  428
Western Red Cedar thuja plicata            463

These were all well above the rest of the tested species, including larches, pines, and cypress. But all were below one species: Rocky Mountain Fir abies lasiocarpa that topped all the rest and came in at a ringing 470. Curious, I looked and found Rocky Mountain Fir to be plentiful and available in log sizes that compared favorably to the other spruces. The list confirms my preference for WR Cedar for classic soundboards but makes me interested in finding out about sources of this plentiful material (prominent across Western US and Canada) that seems at present to be used essentially only for general construction, paper pulp and ...Christmas trees.

Another interesting finding was that samples with middling annual ring width (not too small or too wide) i.e. about 11 per inch showed the greatest ATR among the test samples. Also that wide ring width actually was no more resonant than the very narrow. The paper concludes with "The tonewood industry could benefit from trying other British Canadian species with relatively high ATR values."

I was privileged to have befriended an expert woodcutter in British Columbia that supplied coniferous softwood to musical instrument makers. I asked him if he had abies lasiocarpa in his area. He responded that it was "all over the place" but it was considered "junk wood" because it had a skunk smell and much of it displayed patches of green color. I asked him to send me several split soundboards from the material. He selected the little of it that was perfectly white. I dried it and used it. It was beautiful! It had fine, silky medullary rays and a splendid, whiter-than-white color. The several guitars I made from it were outstanding! I've been using the material ever since, but tragically, my friend died from a stroke, ending both my friendship and my supply of these tops. Anyone who can connect me to a future supply of abies lasiocarpa will receive my undying gratitude.