RT-60, or Reverberation Time 60, is a fundamental metric used in architectural acoustics to measure the decay of sound within a space.
Based on the provided reference, RT60 is defined as the measure of the time after the sound source ceases that it takes for the sound pressure level to reduce by 60 dB. In simpler terms, it tells you how long it takes for sound to become essentially inaudible after the source stops.
Understanding RT-60
When a sound is made in a room, it doesn't just stop instantly when the source does. The sound waves bounce off surfaces (walls, floor, ceiling, objects), creating reflections. These reflections are called reverberation. If these reflections decay quickly, the space has a short reverberation time. If they continue to bounce around for a while, the space has a long reverberation time.
RT-60 quantifies this decay process. A lower RT-60 value indicates that sound reflections die out quickly, while a higher value means they persist for longer.
The 60 dB Drop
The "60" in RT-60 specifically refers to a 60-decibel (dB) drop in sound pressure level. A 60 dB reduction represents a significant decrease in sound intensity, typically corresponding to the difference between a very loud sound source and the threshold of hearing or the background noise level in many rooms. This specific criterion provides a standardized way to compare the reverberation characteristics of different spaces.
Factors Affecting RT-60
Several elements influence the RT-60 of a room:
- Volume of the Space: Larger rooms generally have longer reverberation times than smaller rooms, assuming similar materials.
- Absorption Properties of Surfaces: The materials used on the surfaces (walls, floor, ceiling), as well as furnishings, absorb sound energy. Highly absorptive materials (like acoustic panels, carpets, soft furnishings) lead to shorter RT-60 times, while reflective materials (like concrete, glass, bare plaster) lead to longer RT-60 times.
- Shape of the Space: The geometry of the room can affect how sound waves reflect and decay.
- Presence of Occupants and Objects: People, furniture, and other objects within a space also absorb sound, reducing the reverberation time.
Why RT-60 Matters
Controlling and optimizing RT-60 is crucial for the intended use of a space:
- Speech Intelligibility: In spaces like classrooms, conference rooms, and lecture halls, a shorter RT-60 is desired to ensure that speech is clear and easy to understand without reflections blurring successive sounds.
- Musical Clarity: For music, the ideal RT-60 varies depending on the genre. Concert halls for orchestral music often benefit from a longer RT-60 to provide richness and fullness, while recording studios or rock music venues typically require shorter RT-60s for tightness and definition.
- Overall Comfort: Excessively long reverberation times can make a space feel noisy and uncomfortable, leading to poor communication and listener fatigue.
Typical RT-60 Values
The optimal RT-60 varies greatly depending on the room's purpose. Here are some approximate target values for different types of spaces:
| Space Type | Typical Target RT-60 (seconds) |
|---|---|
| Small Office/Meeting Room | 0.4 - 0.8 |
| Classroom/Lecture Hall | 0.6 - 1.0 |
| Conference Room | 0.5 - 0.8 |
| Restaurant | 0.8 - 1.2 |
| Concert Hall (Music) | 1.5 - 2.5 (varies by genre) |
| Opera House | 1.2 - 1.6 |
| Theatre (Speech/Drama) | 0.8 - 1.2 |
| Sports Hall | 2.0 - 5.0+ |
Note: These are general guidelines; specific requirements can vary.
Measuring RT-60
While the technical measurement involves specialized equipment (like a calibrated microphone, sound source, and acoustic analysis software), the concept is based on recording the sound decay after an impulsive noise (like a balloon burst) or a controlled signal (like a sine sweep) ceases. The analysis software then calculates the time it takes for the sound pressure level to drop by 60 dB from its initial level. Often, measurements are taken over a smaller dynamic range (e.g., 20 dB or 30 dB) and extrapolated to the full 60 dB range.
In conclusion, RT-60 is a key acoustic parameter that quantifies how long sound lingers in a space, directly impacting its suitability for different activities by affecting clarity, intelligibility, and overall sonic environment.
