Where intelligibility lives
Around 2 kHz the ear canal's natural resonance begins boosting what you hear, ramping toward peak sensitivity near 3-4 kHz. Speech exploits this: the consonant energy that distinguishes "cat" from "hat" from "that" concentrates in the 2-4 kHz band. Telephone systems, hearing aids, and PA intelligibility standards all prioritize this region because losing it means hearing voices without understanding words.
In music production, 2 kHz is "presence": boosting it pushes a vocal or guitar to the front of a mix; too much turns forward into harsh. The classic radio-voice EQ, the bite of a rock guitar, the edge that cuts through a busy arrangement - all of it lives within an octave of this tone.
A fair test tone for everything
Every functioning speaker on earth reproduces 2 kHz - it needs almost no air movement - so problems here are never physics. Distortion, harshness, or level mismatches between left and right at 2 kHz point at damaged drivers or electronics, and the frequency is squarely in every audiogram's pure-tone average, so both your gear and your ears are supposed to handle it perfectly.
It is also right where tweeters typically take over from woofers in two-way speakers (crossovers commonly sit at 1.8-3 kHz), making a slow sweep through 2 kHz a good listen for crossover bumps or dips.