RT60 Reverberation Time
RT60 Reverberation Time Measurement and Analysis · Also known as: RT60, reverberation time, decay time
RT60 (reverberation time) is the duration required for sound energy in a room to decay by 60 decibels after the source stops. Pioneered by Wallace Clement Sabine in 1900, RT60 is the most widely used single-number descriptor of room acoustic properties. It reflects how much sound is absorbed versus reflected by room surfaces and directly affects speech intelligibility, music clarity, and acoustic comfort.
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When to use it
Use RT60 analysis when designing or renovating rooms for speech (classrooms, offices, auditoriums), music (studios, concert halls, recording spaces), or noise control. RT60 is essential for meeting acoustic standards and predicting speech intelligibility. Avoid over-reliance on RT60 alone; use it alongside other metrics (early decay time, clarity index, initial time delay gap) for complete acoustic assessment.
Strengths & limitations
- Simple, standardized, and universally understood metric; a single number captures fundamental room acoustic character.
- Well-established optimal values for different room types (speech, music, noise control) enable rapid assessment and design decisions.
- Low cost to measure with industry-standard sound level meters and impulse generation methods.
- Directly related to room absorption through Sabine and Eyring formulas, enabling prediction of acoustic treatment effectiveness.
- Frequency-dependent (RT60 varies by band), providing insight into spectral acoustic behavior of the room.
- RT60 is a late-decay metric; it does not capture early reflections or spatial perception, which significantly affect acoustic quality.
- Dependent on measurement position; a single RT60 measurement may not represent the whole room, especially in non-uniform spaces.
- Assumes exponential decay; many real rooms show non-exponential behavior (multiple decay rates, room modes), making simple exponential fits inaccurate.
- Dominated by late reflections and background noise; reliable RT60 measurement requires adequate SNR and clean late-decay regions.
- Sabine and Eyring formulas are approximations that break down for highly absorptive or low-absorption rooms; empirical data is preferred for design.
Frequently asked
What is the difference between RT60, T20, and T30?
RT60 measures decay from 0 to –60 dB; T20 measures from –5 to –25 dB and is extrapolated by 3; T30 measures from –5 to –35 dB and is extrapolated by 2. In practice, T20 and T30 are often more accurate because they avoid very-low-amplitude noise regions. All three should yield similar values in ideal conditions.
What is a good RT60 for a lecture hall?
For speech, optimal RT60 ranges from 0.4 to 0.8 seconds (depending on room size and acoustic standards). A concert hall requires 1.8–2.5 s for music, while a recording studio may need 0.2–0.5 s. Consult acoustic standards (e.g., ISO 11957) for your specific room type and desired use.
Why does RT60 vary across frequencies?
Different materials absorb different frequencies differently. Soft materials (foam, carpet) absorb high frequencies more than low frequencies, so RT60 is typically longer at low frequencies. Frequency-dependent RT60 measurements (octave or one-third octave bands) reveal this behavior.
How do I measure RT60 accurately?
Use a calibrated sound level meter or audio recorder, emit a broad-spectrum impulse (clap, gunshot, or pink noise burst), and record decay in a quiet environment. Measure in multiple locations and frequency bands, average results, and follow ISO 3382 protocols to ensure consistency and accuracy.
Can RT60 alone predict speech intelligibility?
RT60 is one factor; speech intelligibility also depends on room geometry, initial time delay gap, early-to-late ratio, and background noise. Use RT60 alongside other metrics (clarity index C50, definition D50, early decay time EDT) for a complete assessment.
Sources
- Sabine, W. C. (1900). Collected Papers on Acoustics. Dover Publications. link ↗
- Schroeder, M. R. (1965). New method of measuring reverberation time. Journal of the Acoustical Society of America, 37(6), 409–412. DOI: 10.1121/1.1909343 ↗
- Eyring, C. F. (1930). Reverberation time in dead rooms. Journal of the Acoustical Society of America, 1(2), 217–241. DOI: 10.1121/1.1915175 ↗
How to cite this page
ScholarGate. (2026, June 3). RT60 Reverberation Time Measurement and Analysis. ScholarGate. https://scholargate.app/en/acoustics/rt60-reverberation-time
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
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- BEM AcousticsAcoustics↔ compare
- Psychoacoustic MaskingAcoustics↔ compare
- Room Impulse ResponseAcoustics↔ compare
- Speech IntelligibilityAcoustics↔ compare