Acoustic Doppler shift in a medium
Source and observer velocities are measured relative to the medium.
Key knowledge
For collinear subsonic motion in a stationary uniform medium, observed sound frequency is f_o=f_s(c_s−u_o)/(c_s−u_s), where the positive axis points from source toward observer and u_s,u_o are their signed medium-frame velocities. Source motion toward the observer shortens wave spacing; observer motion toward the source increases encounter frequency. This differs from relativistic light Doppler shift.
Values and equations
f_o=f_s(c_s−u_o)/(c_s−u_s)
- f_o,f_s
- Observed and emitted frequencies Hz
- c_s
- Sound speed relative to the medium m s⁻¹
- u_o,u_s
- Observer/source velocity components along the source-to-observer direction in the medium frame m s⁻¹
Conditions and scope
- Constant source/observer velocities, c_s>0 and |u_s|,|u_o|<c_s along a fixed propagation direction.
- Wind requires the actual medium-frame geometry. Curved/accelerating trajectories use emission/observation geometry; supersonic sources and shocks lie outside this formula.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read §17.7 source/observer separate derivations17.18–17.19 and combined17.20. The single signed-axis formula is an explicitly disclosed rewrite of the approach/recession convention.
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Entry details
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- foundation-physics-acoustic-doppler
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions