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Its occupied reverberation time is about 1.9 s.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eT₆₀ = 0.161 V \/ A,   A = Σ S α\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003eT₆₀: time for sound to fall by 60 dB (s)\u003c\/li\u003e\n\u003cli\u003eV: room volume (m³)\u003c\/li\u003e\n\u003cli\u003eA: total absorption (m²)\u003c\/li\u003e\n\u003cli\u003eS: area of each surface (m²)\u003c\/li\u003e\n\u003cli\u003eα: absorption coefficient of that surface\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eWallace Clement Sabine, Harvard, late 1890s; Boston Symphony Hall, 1900.\u003c\/p\u003e\u003cp\u003e\u003cem\u003eHonest caveat:\u003c\/em\u003e Sabine's formula is not exact: it fails for very absorbent rooms, where Eyring's version does better. Sabine's own calculation for Symphony Hall gave 2.31 s, as reported in E. Thompson's history The Soundscape of Modernity (2002); historians attribute the overestimate to how he counted audience absorption.\u003c\/p\u003e\u003ch3\u003eOn the shirt\u003c\/h3\u003e\u003cp\u003eFront: Sabina, the pixel-art character, with “THE ECHO HAS A CLOCK”. Back: Sabine's law, the absorption sum, the 60 dB definition and the Symphony Hall figure. 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L. Rijke put a hot metal gauze inside a vertical tube open at both ends and heard it sing loudly. The sound stops when the tube is laid horizontal and the upward air flow stops. Rayleigh gave the reason in 1878: an acoustic oscillation grows if heat is added where and when the pressure is high.\u003c\/p\u003e\u003cp\u003eIn an open–open tube the fundamental has a pressure node at each end. The drive is strongest with the gauze about a quarter of the way up from the bottom; a gauze in the upper half damps the sound instead. The same feedback causes dangerous combustion instability in rocket engines and gas turbines.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003ef ≈ c \/ 2L   (loudest with the gauze at about L\/4 from the bottom)\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003ef: tone frequency (Hz)\u003c\/li\u003e\n\u003cli\u003ec: speed of sound in the warm air (m\/s)\u003c\/li\u003e\n\u003cli\u003eL: tube length (m)\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eRijke, Ann. Phys. 183, 339 (1859); Rayleigh, “The explanation of certain acoustical phenomena”, Nature 18, 319 (1878).\u003c\/p\u003e\u003cp\u003e\u003cem\u003eHonest caveat:\u003c\/em\u003e c is the warm-gas value, so the pitch depends on how hot the air is. Rijke used a hot gauze, not a flame; flame versions are variants.\u003c\/p\u003e\u003ch3\u003eOn the shirt\u003c\/h3\u003e\u003cp\u003eFront: Rijka, the pixel-art character, with “SINGING HEAT”. 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