Sound speed in solids depends only on density and elastic modulus

Evidence

For longitudinal waves in solids, the speed of propagation is only affected by the density and Young’s modulus of the material … However, although the density of a solid is independent of the direction of propagation in a solid, the Young’s modulus may not be. For example, brass will have a Young’s modulus that is independent of direction because it is homogeneous, whereas wood will have a different Young’s modulus depending on whether it is measured across the grain or with the grain. Thus brass will propagate a disturbance with a velocity that is independent of direction, but in wood the velocity will depend on whether the disturbance is traveling with the grain or across it. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 64

However, although the density of a solid is independent of the direction of propagation in a solid, the Young’s modulus may not be. For example, brass will have a Young’s modulus which is independent of direction because it is homogeneous, whereas wood will have a different Young’s modulus depending on whether it is measured across the grain or with the grain. Thus brass will propagate a disturbance with a velocity which is indepen­ dent of direction, but in wood the velocity will depend on whether the dis­ turbance is traveling with the grain or across it. — David Howard, Jamie Angus, coustics and Psychoacoustics, 41

Categorization

• XREF: Wood’s directional sound speed means instruments and loudspeaker cabinets behave differently along the grain — connects to my interest in how material choice shapes the timbre of wooden instruments. — connects to: A medium’s intrinsic acoustic impedance equals density times sound speed — Eric J. Heller, Why You Hear What You Hear- An…, 102; Shape-dependent spring constants make vibration speeds complex in solid objects; Medium density and elasticity shape the pressure-velocity amplitude relation — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 165 (+5 more)
• SHARE: A cabinet maker or guitar builder would appreciate why wood grain direction matters for acoustic propagation.
• corroborated: 3 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 64; David Howard, Jamie Angus, coustics and Psychoacoustics, 41

Broader Connections

• Higher material density slows sound propagation speed #contradicts (0.95)
• Sound propagation depends on interactions with objects and the medium #qualifies (0.72) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 322