Wood’s anisotropy makes sound radiation direction- and frequency-dependent

Evidence

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. … This variation of the speed of sound in materials such as wood can affect the acoustics of musical instruments made of wood and has partic­ ular implications for the design of loudspeaker cabinets, which are often made of wood. In general, loudspeaker manufacturers choose processed woods, such as plywood or MDF (medium density fiberboard), which have a Young’s modulus that is independent of direction. — David Howard, Jamie Angus, coustics and Psychoacoustics, 41 (#corroborates, via linked claim)

There is an additional effect on the reverberation field, and that is the directivity of the source of sound in the room. Most hi-fi loudspeakers and musical instruments are omnidirectional at low frequencies but are not necessarily so at higher ones. As the level of the reverberant field is a function of both the average absorption and the directivity of the source, the variation in directivity of real musical sources will also have an effect on the reverberant sound field and hence the perception of the timbre of the sound. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1796 (#expands, via linked claim)

Categorization

• XREF: connects to: Wood grain direction drastically changes the speed of sound through the material — David Howard, Jamie Angus, coustics and Psychoacoustics, 41; Stringed instruments radiate low frequencies omnidirectionally but high frequencies directionally; Sound propagation depends on interactions with objects and the medium — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 322 (+5 more)

Broader Connections

• Wood grain direction drastically changes the speed of sound through the material #corroborates (0.90) — David Howard, Jamie Angus, coustics and Psychoacoustics, 41
• Stringed instruments radiate low frequencies omnidirectionally but high frequencies directionally #exemplifies (0.85)
• A source’s changing directionality with frequency alters perceived timbre via the reverberant field #expands (0.85) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1796
• Sound propagation depends on interactions with objects and the medium #expands (0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 322
• Room acoustical behavior changes across a broad transition region, not at one frequency #exemplifies (0.75)