Confinement or wave return, not mere amplitude, is essential to resonance

Evidence

Not every constructive addition of amplitude corresponds to a resonance. For example, the focal point of a lens has high wave amplitude, but there is no confinement to the focal point—waves are just passing through—and no echo back to a source. Confinement or return is essential to resonance. — Eric J. Heller, Why You Hear What You Hear- An…, 896

Categorization

• DEFINE: Sharpens the definition of resonance by contrasting it with mere constructive interference like a lens focus.
• corroborated: 2 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 896
• XREF: connects to: Resonance requires confinement of previously emitted amplitude; Resonance requires confined old amplitude returning in phase with fresh drive amplitude; Supported standing-wave frequencies in bounded systems occur at odd multiples of the lowest (+3 more)

Broader Connections

• Resonance requires confinement of previously emitted amplitude #expands (0.95)
• Resonance requires confined old amplitude returning in phase with fresh drive amplitude #expands (0.95)
• Supported standing-wave frequencies in bounded systems occur at odd multiples of the lowest #qualifies (0.80)
• Standing waves can form without two bounding reflectors #qualifies (0.75)