This study investigates the relation of fibre length and ray dimensions to the sound propagation velocity in four commercial tropical hardwoods. The species used in the study were Doussié (Afzelia bipindensis Harms), Merbau (Intsia bijuga (Colebr.) Kuntze), Muiracatiara (Astronium graveolens Jacq.) and Wengé (Millettia laurentii De Wild.). The sound propagation velocity was established by the frequency-resonance method. A positive correlation was obtained between fibre length and sound velocity within species. The correlation was stronger in species with a higher proportion of libriform fibres. A trend analogous to fibre length within species was observed for ray ratio but, in contrast to fibre length, the correlation was strong also between species. The samples with higher and at the same time narrower rays (higher ray ratio) showed a higher velocity of sound propagation along the grain.
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