The reverberation number home theater builders ignore
A 2,000 cubic foot room with bare drywall walls and a hard floor has an RT60 around 1.2 seconds at 500 Hz. Your target for a home theater is 0.3 to 0.4 seconds. Closing that gap takes about 8 to 12 acoustic panels, typically $300 to $500 from GIK Acoustics or ATS Acoustics.
This calculator uses the Sabine equation: RT60 = 0.049 x V / A, where V is room volume in cubic feet and A is total absorption in sabins across six frequency bands from 125 Hz to 4 kHz.
Use this to estimate how many panels you need before ordering treatment.
How the Sabine RT60 Formula Works
The Formula
The Sabine equation for imperial units: RT60 = 0.049 x V / A. Room volume V is in cubic feet. Total absorption A is the sum of each surface's area in square feet multiplied by its absorption coefficient (alpha) at the target frequency, plus sabins contributed by occupants. The 0.049 constant is derived from the speed of sound and the definition of RT60 (60 dB decay).
Worked Example
Room: 15 x 12 x 9 feet (1,620 cu ft). Walls: painted drywall (alpha 0.05 at 500 Hz), total wall area: 486 sq ft, contributing 24.3 sabins. Ceiling: drywall (alpha 0.05), 180 sq ft, 9.0 sabins. Floor: thick carpet on pad (alpha 0.40), 180 sq ft, 72.0 sabins. Two occupants: 8.0 sabins. Total A: 113.3 sabins. RT60: 0.049 x 1620 / 113.3 = 0.70 seconds. Target is 0.4 seconds, so you need A = 0.049 x 1620 / 0.4 = 198.5 sabins. Deficit: 85.2 sabins, or about 11 panels at 8 sabins each.
Standards
The Sabine equation was developed by Wallace Clement Sabine in 1898 and remains the standard for reverberation estimation in architectural acoustics. Absorption coefficients are published per ASTM C423 test methodology. Target RT60 values for home theaters (0.3 to 0.5 seconds at 500 Hz) come from THX, Dolby, and the ITU-R BS.1116 recommendation for critical listening rooms.
Limitations
Sabine's equation overestimates RT60 in rooms with high absorption (alpha above 0.5 on most surfaces), where the Eyring equation is more accurate. It also assumes uniform absorption distribution. A room with all panels on one wall and nothing on the opposite wall will have a different actual RT60 than the formula predicts. For rooms that are heavily treated on some surfaces and bare on others, treat the Sabine result as an upper bound.