Haas effect
Hearing lets whichever sound arrives first decide the direction, even when a copy arriving a few milliseconds later is louder.
Helmut Haas described it in his 1949 dissertation at Göttingen; the same year Hans Wallach and colleagues called it the precedence effect. Two identical sounds arriving roughly one to thirty milliseconds apart fuse into one, perceived as coming from the first source. The later copy can be around 10 dB louder before the illusion breaks. It is the bit of psychoacoustics that stops wall reflections from confusing us about where things are.
Engineers use it both ways. PA systems delay the speakers further back in a venue so the sound still seems to come from the stage. In a mix, delaying one channel by 10–20 ms makes a wide stereo image out of a mono source. Summed to mono, the same trick becomes a comb filter, which people tend to discover the first time the song plays from a phone.