Tree branches, not leaves or twigs, resonate as forced acoustic oscillators near 275-450 cps.

Evidence

Experiments were conducted in the laboratory using branches cut from the lower parts of various trees—all the types mentioned above and also some other varieties. These branches were 4 to 6 ft long and were held either in a vise or by hand. It was quickly shown that it was the branch itself, not the twigs nor the needles or leaves, that was capable of acoustic response in this frequency range. All the branches had one well-defined resonance lying between about 275 and 450 cps and having a “Q” of between 5 and 12. — T. F. W. Embleton, Sound Propagation in Homogeneous…, 49

Categorization

• XREF: Directly supports the reader’s INTD 3970 soundscape-ethnography thread on acoustic ecology — the physical substrate of how forests shape (not just attenuate) sound. — connects to: Spruce and pine differ physically in needle length, stiffness, and flex. — T. F. W. Embleton, Sound Propagation in Homogeneous…, 29; Woods sound attenuation stays near constant regardless of optical visibility through the canopy. — T. F. W. Embleton, Sound Propagation in Homogeneous…, 46; Branch transverse vibrations are the active oscillators in tree sound absorption. — T. F. W. Embleton, Sound Propagation in Homogeneous…, 2 (+3 more)
• SEED: An essay angle on how a ‘quiet forest’ is not silent but filtering — the forest as a bank of tuned oscillators rather than a passive absorber.

Related

• Branch transverse vibrations are the active oscillators in tree sound absorption. (similarity 0.92)
• Trunk scatter cannot alone explain forest high-frequency sound attenuation (similarity 0.86)
• Woods sound attenuation stays near constant regardless of optical visibility through the canopy. (similarity 0.85)
• Open and dense forest canopies create distinct sound atmospheres (similarity 0.84)
• A source at a wood’s edge creates large boundary effects on forest sound attenuation. (similarity 0.83)
• T. F. W. Embleton — Sound Propagation in Homogeneous Deciduous and Evergreen Woods (similarity 0.81)
• Individual trees each sing distinct sonic textures a patient listener can analyze (similarity 0.81)
• Spruce and pine differ physically in needle length, stiffness, and flex. (similarity 0.80)
• Rayleigh attributed a forest echo’s octave rise to size-dependent scattering of high frequencies (similarity 0.79)
• Forest birds favor pure tones around 2,200 Hz where attenuation is lowest (similarity 0.79)
• Leaf width and canopy leaf area drive sound scattering in dense vegetation (similarity 0.79)
• Vegetation substrate type shapes the spectral character of wind noise (similarity 0.79)
• Wind instruments resonantly amplify only frequencies that reflect back at the drive period (similarity 0.79)
• Forest edges are sonic discontinuities segregating wind noise from animal sounds. (similarity 0.79)
• Woodland attenuation shows a characteristic peak-dip-rise spectral shape (similarity 0.79)

Broader Connections

• Trunk scatter cannot alone explain forest high-frequency sound attenuation #complicates (0.75) — Margaret A. Price, Keith Attenborough, and Nicholas W. Heap, Sound Attenuation through Trees, 87
• Wind instruments resonantly amplify only frequencies that reflect back at the drive period #expands (0.72) — Eric J. Heller, Why You Hear What You Hear- An…, 1548
• Wood’s anisotropy makes sound radiation direction- and frequency-dependent #expands (0.70)