An open pipe end only reflects sound when an impedance mismatch exists there

Evidence

As an interesting test of our understanding, suppose we send a pulse through a tube heading toward an open end, but this time the pulse exists outside the pipe as well. What will happen when the pulse reaches the end of the tube? The air inside the pipe has no idea that the pressure pulse exists outside until it reaches the end; as the pressure exits the pipe, instead of finding lower pressure laterally as it did before, it now finds matched higher pressure outside. There is no sudden pressure release laterally, no impedance change. The entire pulse proceeds as if nothing happened; there is no back reflection inside the pipe at all. — Eric J. Heller, Why You Hear What You Hear- An…, 117

Categorization

Category: Causal Relationships

• XREF: Connects to the broader impedance-mismatch principle in acoustics that underlies why horns, woodwinds, and organ pipes behave as they do — and conversely why a flanged or baffled open end behaves differently.

Related

• A sound pulse passes an open pipe end unreflected when matching pressure exists outside (similarity 0.91)
• Pipe walls raise air impedance by reflecting pressure pulses back in phase (similarity 0.90)
• An open pipe end inverts a sound pulse’s sign via a reflected rarefaction (similarity 0.86)
• Any pipe diameter change causes partial sound reflection at the junction (similarity 0.86)
• Impedance discontinuities split an arriving wave into reflected and transmitted parts (similarity 0.85)
• Open tube ends preferentially transmit high frequencies and reflect low ones, smearing echoes. (similarity 0.85)
• Open and closed pipe ends reflect pressure pulses with inverted phase (similarity 0.83)
• Waves split into reflected and refracted parts at impedance-mismatched interfaces (similarity 0.83)
• Open-tube end reflection arises from air-parcel overshoot into lower impedance beyond the opening. (similarity 0.83)
• Rigid-wall tube terminations fully reflect waves while open ends reflect with phase inversion. (similarity 0.83)
• Narrower pipes raise acoustic impedance through in-phase wall reflections (similarity 0.82)
• Pipe diameter changes reflect pressure pulses with opposite sign (similarity 0.82)
• Open pipe ends invert pulse polarity while closed ends preserve it (similarity 0.82)
• Open pipe ends invert compression pulses while closed ends preserve them (similarity 0.81)
• Wall losses, not radiation, dominate resonance damping in narrow pipes (similarity 0.81)

Broader Connections

• Perfect impedance matching eliminates reflection while mismatch causes it #corroborates (0.95) — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 237
• Acoustic impedance mismatch determines both reflection phase and magnitude #expands (0.90) — David Howard, Jamie Angus, coustics and Psychoacoustics, 353