How long does measuring reverberation time in a gym hall take?

It depends on the size of the hall and the background noise. The engineering method requires at least 6 source–microphone combinations, and each measurement captures all octave bands at once — the hall must be empty and quiet throughout.

Do you need to measure before installation?

It is not mandatory, but it is very useful. From the reverberation time before installation and the room volume, you can calculate how much absorption the hall already has and how much needs to be added — instead of guessing. The Sabine formula is used for this: A = 0.161 × V / T.

Can reverberation be measured with a phone app?

For a rough idea — yes, to see the order of magnitude. For acceptance and to demonstrate compliance with PN-B-02151-4, you need a measurement compliant with PN-EN ISO 3382-2, using calibrated equipment and a report — usually as part of an acoustic design .

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How reverberation time is measured — before and after installation

Measurement per PN-EN ISO 3382-2: at least 6 source–microphone combinations, octave bands from 125 to 4000 Hz, a T20 or T30 result. What that means, and what the report you receive should contain.

Opublikowano 3 November 2025

For clients accepting an acoustic adaptation project, and for designers and contractors who need to demonstrate compliance with the requirements.

Reverberation time T is the time it takes for sound in a room to decay by 60 dB after the source is switched off. It is the basic quantity for which the PN-B-02151-4 standard sets limit values for many types of room — and one that can be verified by measurement once the work is finished.

The most useful approach is to measure twice: before installation, to know the starting point and how much absorption needs to be added, and after installation, to confirm the result. PN-EN ISO 3382-2 describes how to carry this out.

T20 and T30 — why the full 60 dB isn't measured

In a real building, it is rarely possible to achieve a full 60 dB drop above the background noise. So a section of the decay curve is measured instead and extrapolated to 60 dB. T20 is derived from the range 5 to 25 dB below the starting level, T30 from 5 to 35 dB. The standard prefers T20.

Quality condition: the start of the decay must lie at least 35 dB above the background for T20 and 45 dB above the background for T30. That is why measurements are taken in silence — no running machinery, conversations, or windows open onto the street.

Three levels of measurement accuracy

To check whether a building meets the requirements, the standard specifies the engineering method. The survey method stops at 2000 Hz, so it does not cover the 4000 Hz band, for which PN-B-02151-4 also sets a requirement, nor the 125 Hz band, where large halls typically lack absorption.

Minimum number of positions and band range per ISO 3382-2:2008, Table 1 and Section 5.1
Method	Source–microphone combinations	Sources / microphones	Octave bands	Accuracy in octaves
Survey	≥ 2	≥ 1 / ≥ 2	250–2000 Hz	better than 10%
Engineering	≥ 6	≥ 2 / ≥ 2	125–4000 Hz	better than 5%
Precision	≥ 12	≥ 2 / ≥ 3	125–4000 Hz	better than 2.5%

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How the equipment is set up — and what the report should contain

Microphones at least about 2 m apart from each other and about 1 m from walls, ceiling and floor. Positions should not be symmetrical.
The microphone must not stand too close to the loudspeaker. The minimum distance is d = 2 √(V / (c × T)). For a 24 × 12 × 7 m hall (V = 2016 m³), c = 343 m/s and an expected T = 5 s: d = 2 × √(2016 / 1715) ≈ 2.2 m.
The room should be empty — at most two people are permitted. For comparison against PN-B-02151-4, the room should be finished and fitted with its permanent elements.
It is worth requiring the report to state: the method (survey, engineering, precision), the number and plan of positions, T20 or T30 for each octave band, and a comparison of results against the standard's requirement band by band. A single average across bands is not enough to assess compliance.

Najczęściej zadawane pytania

How long does measuring reverberation time in a gym hall take?
It depends on the size of the hall and the background noise. The engineering method requires at least 6 source–microphone combinations, and each measurement captures all octave bands at once — the hall must be empty and quiet throughout.
Do you need to measure before installation?
It is not mandatory, but it is very useful. From the reverberation time before installation and the room volume, you can calculate how much absorption the hall already has and how much needs to be added — instead of guessing. The Sabine formula is used for this: A = 0.161 × V / T.
Can reverberation be measured with a phone app?
For a rough idea — yes, to see the order of magnitude. For acceptance and to demonstrate compliance with PN-B-02151-4, you need a measurement compliant with PN-EN ISO 3382-2, using calibrated equipment and a report — usually as part of an acoustic design.

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