Question 1

What is reverberation time (RT60)?

Accepted Answer

Reverberation time RT60 is the time in seconds it takes for a sound signal to decay by 60 dB after the sound source has been switched off. It is the most important parameter of room acoustics and strongly determines speech intelligibility, music quality and acoustic comfort in a room. Requirements for reverberation time are defined in DIN 18041 according to room use.

Question 2

What is the difference between the Sabine and Eyring formulas?

Accepted Answer

The Sabine formula (T = 0.163 × V / A) is suitable for rooms with low to medium absorption (α < 0.3). The Eyring formula (T = 0.163 × V / (−S × ln(1 − ᾱ))) delivers more accurate results with higher absorption and short reverberation times. For acoustically optimized rooms with absorbers the Eyring formula is recommended, since Sabine systematically overestimates reverberation time in that regime.

Question 3

Which reverberation time is optimal for my office?

Accepted Answer

Per DIN 18041, reverberation time in open-plan offices should be between 0.5 and 0.8 seconds, in single offices between 0.4 and 0.6 seconds, and in meeting rooms between 0.5 and 0.7 seconds (each at 500 Hz). Too long reverberation degrades speech intelligibility, too short sounds unnatural. Requirements vary with room volume.

Question 4

What is the weighted sound absorption coefficient αw?

Accepted Answer

The weighted sound absorption coefficient αw is a single-number metric per ISO 11654 that describes how much sound energy a material absorbs. An αw of 1.00 means full absorption, 0.00 full reflection. Materials are classified by αw into absorption classes A (very good, αw ≥ 0.90) down to E (poor, αw 0.15–0.25).

Question 5

How is the sound absorption coefficient measured?

Accepted Answer

The sound absorption coefficient is measured in a reverberation chamber per ISO 354. The reverberation time of the empty chamber is compared with the reverberation time with the test specimen (at least 10 m²) installed. From the reverberation-time difference, the Sabine absorption coefficient αs is calculated for every frequency. For smaller samples the impedance-tube method per ISO 10534-1 is used.

Question 6

Where do the material data in this calculator come from?

Accepted Answer

The calculator uses standard acoustic values for base materials (floor, wall, ceiling) from the literature. For acoustic products you can access the Acoustic Index database, which contains ISO-compliant measurement data directly from manufacturers — including more than 2,500 materials with absorption, scatter and diffusion values.

Reverberation calculator

Reverberation calculator