The first arriving sound wave dominates perceived direction of a source

Evidence

In this context, an effect termed the “law of the first wave front” deserves attention. If a sound is switched on with a click in the left loudspeaker, then it will be perceived as originating from that location, even if the left loudspeaker is later faded out and the sound is radiated only from the right loudspeaker! This effect of the “first wave front” works even if the level of the second loudspeaker is increased by some decibels above the level of the first loudspeaker. The “law of the first wave front” has great importance in room acoustics. The localization of the sound of musical instruments is in the direction of the stage, even if the level of sound reflected e.g. from a balcony is higher than the level of the direct sound wave. However, if the time difference between the direct sound and the reflected sound exceeds a critical value (for speech and music near 50 ms), echos may be perceived which can be highly annoying for values larger than 100 ms. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1724

Categorization

• DEFINE: Defines the precedence effect / “law of the first wave front” and its echo threshold.
• ADDENDUM: The 50 ms echo threshold connects to how reflected sound shapes spatial perception in built environments, relevant to the trees-as-infrastructure piece’s broader sensory-environment theme.
• corroborated: 2 independent passages support this claim — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1724