Selection of Wood Used for Piano Soundboards

Abstract

In order to improve the yield rate of wood used for piano soundboards, measurements were made of the dynamic mechanical properties for Sitka spruce (Picea sitchensis) wood pieces containing reaction wood, sapwood, indented rings, knot, resin streak, and resin pocket, which have been accepted to be defects according to the maker's own selection measure. In the present study the suitability of wood for soundboards was evaluated by using both the values of internal friction and specific Young's modulus in longitudinal direction; low internal friction and high specific Young's modulus were considered to be favorable for soundboards. The pieces containing intense reaction wood had higher value of internal friction and lower value of specific Young's modulus compared with those of slight reaction wood. The one with extremely low value of specific Young's modulus had large average microfibril angle in the cell wall. About half of the pieces containing slight reaction wood showed the acoustical properties comparable to those of defect-free high grade ones. Sapwood pieces had high value of internal friction and high specific Young's modulus. The high friction of sapwood was considered to result from their high moisture content. The acoustical properties of the pieces containing intense indented rings and resin streak were inferior to high grade ones. However, the acoustical properties of the pieces containing slight indented rings, knot, and resin pocket were almost comparable to those of high grade ones; probably these pieces are regarded as being inferior not because of their acoustical properties but because of their appearance. It was suggested that the selection based on the dynamic mechanical measurement is necessary to improve the yield rate of wood for piano soundboards.