Acoustic log sorting of western hemlock gang logs



Although logs of the same grade may look similar, they can have different characteristics that can lead to different product values. FPInnovations and the Canadian Wood Fibre Centre used a Hitman “log thumper” to separate a batch of second-growth hemlock logs into three acoustic velocity classes that were then cut into boards. When they were tested at FPInnovations’ Vancouver laboratory, boards from the different acoustic classes had different stiffness values, which could result in different sales prices. Acoustic testing has been used in other jurisdictions around the world to sort logs by their strength properties to increase their overall value.


Using information from the mill test, FPInnovations looked at eight second-growth hemlock sites on the Vancouver Island to determine if the Hitman acoustic testing could distinguish between logs from the different sites. The logs had different acoustic responses, which could lead to different marketing strategies if the logs were sorted by acoustic class. The greatest benefit of sorting would occur where the high-value grades comprise 40-60% of the stand. Stands with higher or lower percentages of the high value grades would not benefit as much, suggesting that measuring the acoustic velocity on a sample of logs would be beneficial before committing to measuring the whole cutblock. For more information, please contact Jack MacDonald.



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