Adjacent opposite-phase regions on a vibrating surface cancel their radiated sound

Evidence

Suppose a thin rectangular metal plate is singing at 1600 Hz, with 6 cm between nodes, which may be a set of parallel lines for a particular mode. These are reasonable numbers for thin aluminum plates. What is the speed of bending waves on the surface of the metal plate? There are two nodes per wavelength; therefore, λ = 0.12 m and the speed of the deformation wave is cs = 1600/s × 0.12 m = 192 m/s, less than two-thirds of the speed of sound in air. In one half period—1/3200 s, sound can travel 343/1600 = 11 cm, much farther than the 6 cm distance between adjacent and oppositely phased antinodes on the surface. Sound from such a surface wave will be attenuated by acoustic short-circuiting, which is why baffling thin Chladni plates with a specially made mask is so effective at making them louder (see figure 7.37). — Eric J. Heller, Why You Hear What You Hear- An…, 676

Categorization

Category: Causal Relationships

• DEFINE: Concretely defines acoustic short-circuiting: opposite-phase surface regions on a thin plate radiate sound that cancels out.
• XREF: Connects to the dipole-source lesson in section 7.7 where two close out-of-phase monopoles radiate far less total power.

Related

• Adjacent compression and rarefaction regions can short-circuit and kill radiated sound (similarity 0.86)
• Adjacent surface compressions and rarefactions can cancel sound before it radiates. (similarity 0.81)
• Oppositely phased paired resonators short-circuit radiation and raise Q to 70 (similarity 0.80)
• Edge diffraction sources can be canceled by out-of-phase speakers (similarity 0.79)
• Superposed sounds cancel or amplify locally without changing each other (similarity 0.78)

Broader Connections

• Nearby reflecting surfaces constructively pile up wave reflections to amplify sound #contradicts (0.80) — Eric J. Heller, Why You Hear What You Hear- An…, 886
• Linear superposition lets separate vibrations coexist independently while interfering in shared space #expands (0.75) — Eric J. Heller, Why You Hear What You Hear- An…, 838
• Edge diffraction sources can be canceled by out-of-phase speakers #expands (0.72) — Eric J. Heller, Why You Hear What You Hear- An…, 193