Relationship Between Speed of Sound and Moisture Content of Red Oak and Hard Maple During Drying

The transit time for sound was measured both perpendicular and parallel to the grain of red oak and hard maple during drying under constant temperature (27°C (80°F)) and varying relative humidity conditions. Transit time perpendicular to the grain increased slightly with decreasing moisture content initially during drying but then decreased with decreasing moisture content. Transit time parallel to the grain remained nearly constant with moisture content initially during drying but then decreased. Transit time became sensitive to moisture content change at average moisture contents well above 30%. The relationship between relative transit time and moisture content showed three linear regions that could be characterized by a three-component regression equation. These results suggest that speed of sound measurements have good potential for control of hardwood kiln schedules in which changes in kiln conditions are made at moisture contents above 30%