Shape-dependent spring constants make vibration speeds complex in solid objects

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 (#contradicts, via linked claim)

Consider the simple mechanical model of the propagation of sound through some physical medium, shown in Figure 1.1. This shows a simple one-dimensional model of a physical medium, such as air, which we call the golf ball and spring model because it consists of a series of masses, e.g., golf balls, connected together by springs. The golf balls represent the point masses of the molecules in a real material, and the springs represent the intermolecu­ lar forces between them. If the golf ball at the end is pushed toward the others then the spring linking it to the next golf ball will be compressed and will push at the next golf ball in the line, which will compress the next spring, and so on. — David Howard, Jamie Angus, coustics and Psychoacoustics, 25 (#expands, via linked claim)

Categorization

• XREF: connects to: Trapped compressible air and moving air form a mass-spring acoustic resonator; Sound speed in solids depends only on density and elastic modulus — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 64; Sound propagation can be modeled as coupled masses and springs — David Howard, Jamie Angus, coustics and Psychoacoustics, 25 (+1 more)

Broader Connections

• Complex shapes make transverse wave propagation velocity extremely complicated, affecting percussion design #corroborates (0.95)
• Sound speed in solids depends only on density and elastic modulus #contradicts (0.90) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 64
• Sound propagation can be modeled as coupled masses and springs #expands (0.75) — David Howard, Jamie Angus, coustics and Psychoacoustics, 25