Room Reverberation Time (RT60) Calculator

Determine room acoustic decay time in seconds using classic Sabine and Eyring formulas, calculate total room absorption in Sabins, and optimize speech intelligibility.

Length (Ft)

Width (Ft)

Height (Ft)

Wall Surface Material

Ceiling Treatment

Floor Covering

Room Target Application

Reverberation Time (Sabine RT60)

0.48 Sec

Eyring Model: 0.41 Sec (Dead room corrected)

Total Room Absorption

610 Sabins

Avg α: 0.277

Speech Clarity (STI)

Excellent

Target: 0.50 - 0.70s

Total Enclosed Room Volume: 6,000 cu ft (170 m³)

Total Interior Surface Boundary: 2,200 sq ft

Ceiling Absorption Contribution: 390 Sabins (63.9%)

Wall Absorption Contribution: 50 Sabins (8.2%)

Floor Absorption Contribution: 150 Sabins (24.6%)

Evaluated according to ISO 3382 and ANSI/ASA S12.60 classroom acoustic standards.

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Room Acoustics & The Sabine Reverberation Time (RT60) Equation

Reverberation Time (RT60) is the time required for the sound pressure level in an enclosed room to attenuate by 60 decibels after the sound source abruptly ceases. Wallace Clement Sabine, the pioneer of architectural acoustics at Harvard University, established that reverberation time depends directly on the room volume and inversely on the total acoustic absorption present on boundary surfaces.

Acoustic Governing Mathematical Formulas

Sabine Formula (Imperial units):
RT60 (seconds) = (0.049 × V) / A
Where V is room volume in cubic feet, and A is total room absorption in Sabins.
Metric Formulation:
RT60 (seconds) = (0.161 × V_m³) / A_metric
Total Absorption (Sabins):
A = ∑ [ Surface Area (sq ft) × Sound Absorption Coefficient (α) ]
Where an absorption coefficient of α = 1.0 represents a 100% open window or perfect acoustic absorber.
Eyring Formula (Dead / Highly Absorptive Rooms):
When average absorption α_avg exceeds 0.25, the Sabine formula underestimates decay; the Eyring equation is preferred:
RT60 = (0.049 × V) / [ -S_total × ln(1 - α_avg) ]

Frequently Asked Questions

Why is RT60 critical for classroom speech intelligibility?

When RT60 in a classroom exceeds 0.8 seconds, sound reflections from spoken syllables linger and collide with subsequent syllables. This acoustic masking degrades speech recognition, forcing teachers to strain their voices and reducing student comprehension. ANSI/ASA S12.60 mandates RT60 ≤ 0.60 seconds for school classrooms.

What is a Sabin in acoustics?

One Sabin is a unit of sound absorption equal to one square foot of a 100% sound-absorbing surface (such as an open window through which sound escapes completely without reflection).

Why do recording studios need such low RT60 (0.25 - 0.35s)?

Microphones in a studio must capture only the direct sound of the singer or instrument. A "dead" room with low RT60 prevents flutter echoes and room modal coloration from bleeding into the track, allowing audio engineers to add controlled digital reverberation in mixing.

What frequency is standard for single-number RT60 ratings?

When a single RT60 number is quoted, it represents the average decay time across the mid-frequency 500 Hz and 1,000 Hz octave bands, which dominate human speech intelligibility.