Measuring reverberation time in offices: how to do it in line with the standard
Poor acoustics in offices often lead to fatigue, loss of concentration and stress. The cause? Often a reverberation time that is too long. In this blog you will learn how to measure and calculate reverberation time in line with ISO 3382. With the right equipment, such as the Svantek SVAN 979 sound level meter and a noise source you carry out an RT60 measurement with which you can easily assess whether a space meets the acoustic standards for offices.
What is reverberation time and why does it matter?
The reverberation time, also known as RT60, is the time the sound needs to fall by 60 decibels in a space after the sound source stops. A reverberation time that is too long causes sound to linger, which makes speech less intelligible and makes it harder for people to concentrate. Especially in office environments this can have a negative impact on the productivity and well-being of employees. That is why measuring reverberation time is very important for pleasant acoustics.
How do you measure reverberation time in office spaces?
To measure reverberation time you need a suitable sound level meter that can determine RT60, combined with a reliable noise source. The method according to ISO 3382 consists of emitting a noise or impulse signal in the space, after which the sound level meter measures how quickly the sound dies away.
With a measuring set such as the Svantek SVAN 979 with 128 MEMS microphones and a suitable noise source, you can determine reverberation time accurately and efficiently. The measurement results are then analysed, giving you insight into the acoustic quality of the space.
Calculating and interpreting reverberation time
The RT60 value is calculated on the basis of the decay of the sound over time. In offices a reverberation time of approximately 0.4 to 0.6 seconds is often desirable in order to guarantee good speech intelligibility.
Do you have a longer reverberation time? Then acoustic measures such as adding absorbent material or improving the ceiling may be necessary.
Why choose professional measuring equipment?
Not every sound level meter is suitable for measuring reverberation time. Accurate RT60 measurements require high resolution, multiple microphone channels and a wide frequency range. Svantek models such as the SV971A, SV977D and SVAN 979 offer these advanced capabilities, combined with user-friendly software for reporting and analysis.
Is measuring reverberation time (RT60) mandatory under Dutch legislation?
The answer depends on the application and the type of building.
When is measuring reverberation time mandatory?
1. Educational buildings (schools, classrooms):
Under the Dutch Building Decree and NPR 3438, speech intelligibility (STIPA) must meet minimum values. Reverberation time (RT60) is a crucial parameter for assessing this.
The Fresh Schools programme of requirements also lays down reverberation times per room type (e.g. classroom: max. 0.6 – 0.8 s). Start by measuring reverberation time to assess your own situation.
2. Non-residential buildings with programme-of-requirements demands:
Buildings such as offices, hospitals, theatres or courtrooms often set acoustic requirements in a programme of requirements (PoR). The contractor or consultant must then demonstrate through measurements that these requirements have been met. RT60 measurements are then part of handover or quality control.
When is measuring reverberation time not mandatory?
Legally, measuring reverberation time is not mandatory in homes. But in some cases it is certainly advisable.
1. Reverberation in homes
For homes, the Building Decree sets no direct requirements for reverberation time. But in open-plan kitchens, stairwells or large living spaces with many reflective materials, for example, an acoustically uncomfortable space quickly becomes a complaint. In such cases RT60 measurements are used for advice or improvement (think of absorbent materials or panels). Measuring reverberation time can therefore also be a smart choice in situations where it is not mandatory.
2. Reverberation in office spaces
The Dutch Building Decree sets no direct requirement for reverberation time in offices. The focus is on airborne sound insulation and impact sound, not on the reverberation time within a space.
But please note: it is sometimes mandatory under the programme of requirements, the specifications or certification. In many office projects, acoustic performance requirements apply that are laid down in:
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The client's or architect's programme of requirements
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Specification documents or ISO standards
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Certification systems such as WELL, BREEAM or LEED
These requirements state, for example:
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A maximum of 0.6 – 0.8 s reverberation time in open or enclosed office spaces
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Minimum requirements for speech intelligibility (STIPA) in meeting and consultation areas
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Requirements for quiet zones or concentration areas
In that case measuring reverberation time / RT60 is indeed mandatory as part of quality assurance and handover.
3. Occupational health and safety legislation and reverberation in offices
For office spaces already in use, in most cases there is no legal obligation to measure reverberation times (RT60) or to comply with them. Once a space has been bought or rented and there is no refurbishment or change of function, there are generally no specific acoustic requirements from the Building Decree or other regulations. Yet the absence of obligations does not mean that reverberation plays no role in the quality of the working environment.
Exceptions may arise if:
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The space is refurbished or reorganised → then programme-of-requirements or building-technical requirements sometimes apply.
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There are structural complaints from employees regarding noise → then occupational health and safety legislation may apply indirectly (think of speech intelligibility, stress, reduced concentration).
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You are working towards certifications such as WELL/BREEAM, or you want to meet certain office comfort standards.
In offices a reverberation time that is too long can cause unclear speech, reduced concentration and a tired feeling at the end of the day. Especially in open-plan office concepts or meeting rooms without acoustic measures, the sound experience can quickly be perceived as unpleasant. That is why more and more organisations choose to have measurements carried out on their own initiative, for example during a refurbishment or after complaints about intelligibility.
In addition, measuring reverberation time is often applied as part of certification processes such as WELL or BREEAM, in which the indoor climate – and therefore also the acoustics – plays an important role. From an occupational health and safety perspective too, it is wise to keep an eye on whether spaces meet the guidelines for acoustic comfort, certainly when employees report experiencing nuisance.
Recommended equipment for measuring reverberation time
The SVANTEK SV 971A is a compact yet powerful class 1 sound level meter, perfectly suited to measuring reverberation time (RT60) in offices, classrooms and other indoor spaces. Thanks to full compliance with the IEC 61672 standard, this instrument guarantees accurate and reliable measurement results. With this sound level meter you can:
Measure RT60 (reverberation time) in line with the ISO 3382 standard
Evaluate STIPA (speech intelligibility) for classrooms or meeting rooms
Thanks to the direct integration with the mobile app and pre-programmed measurement protocols, the SV 971A is also suitable for quick baseline measurements, before-and-after measurements and consultancy projects within the construction and installation sector.
To measure reverberation time (RT60) in line with ISO 3382-1 you need not only a class 1 sound level meter such as the SV 971A, but also a suitable sound source. The SVANTEK SV 90/303 is specially designed as an omnidirectional noise source for measurements in building and room acoustics. What makes this noise source suitable?
Omnidirectional character: distributes sound evenly in all directions, as required by the standard
High power (300W RMS): generates the required sound level to achieve measurement levels of +45 dB above background noise, necessary for T20 or T30 measurements
Rechargeable battery: ideal for locations without mains power; one charge is good for hundreds of measurements
Want to know more about acoustics in offices?
Also read our blog about measuring STIPA in office environments and discover how to improve speech intelligibility.
Contact us for advice or measuring equipment
Would you like to measure reverberation time in offices yourself? Our experts will be glad to advise you Request a quote here without obligation or call us directly on 050-5712124, or e-mail info@basystemen.nl.
Would you like to know which measurement solution suits your application best?
Contact our specialists for advice without obligation by using the button below.
The reverberation time, also known as RT60, is an essential acoustic parameter indicating how long it takes for the sound in a space to fall by 60 dB after the sound source stops. It determines the acoustic quality of a space and is crucial for designing and optimising spaces such as offices, classrooms, theatres and concert halls.
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For speech intelligibility: A reverberation time that is too long causes echoes that mask consonants, making speech hard to understand.
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For music: A certain amount of reverberation can make the sound fuller and more pleasant by connecting notes, but too much results in a muddy sound.
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For workspaces: In offices a short reverberation time helps to reduce background noise and promote concentration.
| Type of space | Reverberation time (RT60) |
|---|---|
| Church | 2 – 10 seconds |
| Concert hall | 1 – 2 seconds |
| Office | 0.5 – 1.1 seconds |
| Classroom | 0.4 – 0.7 seconds |
In line with the ISO 3382 standard, RT60 is measured with special equipment: a class 1 sound level meter and an omnidirectional sound source producing pink noise, for example. Two methods are common here:
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Interrupted noise method: Here the sound source is switched on and off and the decay of the sound level is measured.
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Impulse response method: Here an impulse (for example a pistol shot or a noise impulse) is used to determine the reverberation time via the response of the space.
The sound source is usually placed at a height of 1.5 metres and the sound is recorded at several positions in the space in order to obtain a representative picture.
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SV977D: This is an advanced sound level meter that meets all the requirements for accurate RT60 measurements, including the necessary filters and measurement methods in line with ISO.
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SV90/103 noise source: These noise sources produce the uniform, omnidirectional pink noise that is essential for carrying out a reliable and reproducible reverberation time measurement.
The reverberation time depends on the volume of the space and the total absorption of all surfaces (walls, floor, ceiling, furniture). The total absorption is calculated by multiplying the area of each surface by the absorption coefficient of the material.
By first measuring RT60 without acoustic material and then with it, you can calculate how much and which type of absorption material is needed to achieve the desired reverberation time. This helps, for example, when improving office acoustics for better speech intelligibility and concentration.
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Office spaces: Ideally an RT60 between 0.5 and 1.1 seconds for good speech intelligibility.
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Classrooms: Between 0.4 and 0.7 seconds to promote clarity.
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Concert halls and churches: RT60 can rise to 2-10 seconds, depending on the purpose of the space.
In addition to RT60, EDT (Early Decay Time), RT20 and RT30 are also calculated. These parameters are variants that determine the reverberation time on the basis of shorter dynamic ranges and help to assess acoustic quality under different conditions.
Yes, there are apps with which you can get an indication of the reverberation time (RT60). These apps use the microphone of your smartphone to analyse how the sound behaves in a space.
But please note: these measurements are not suitable for reliable or normative assessments.
Apps for measuring reverberation time are of limited accuracy, because:
- Smartphones do not have calibrated microphones
- Frequency range and sensitivity vary per device
- Measurements do not meet the requirements of ISO 3382
- Ambient noise strongly influences the measurement
As a result, results are often unreliable or not reproducible.
An app can be useful for:
- a quick indication of acoustics
- an initial screening of a space
- raising awareness of reverberation problems
But: it is no substitute for professional measurements.
Professional measuring equipment is necessary when:
- you have to comply with standards such as ISO 3382
- measurements form part of handover or certification (BREEAM, WELL)
- you need reliable and reproducible results
- you want to base advice on measurement data
The difference lies in accuracy and reliability:
- An app → indication with a high margin of error
- A class 1 sound level meter → certified measurement
With equipment such as the SVANTEK sound level meters and an omnidirectional noise source you measure in line with the standard and obtain data that really is usable for reporting and decision-making.
| Method | Accuracy | Suitable for |
|---|
| App | Low | Indication |
| Sound level meter | High | Official measurements |
Why?
1. Calibration (this is the biggest deal breaker)
A professional sound level meter is calibrated and complies with standards such as IEC 61672. That means:
- you know exactly how many dB you are measuring
- measurements are reproducible
- you can use them in reports
A smartphone:
- has no fixed calibration
- differs per device
- can easily be 5–10 dB out. Because sound is measured on a logarithmic scale, that means an enormous deviation.
For RT60 (reverberation time) that is disastrous, because you are looking precisely at the decay of sound.
2. Frequency range and accuracy
With reverberation it is not only about “how loud”, but also: how quickly different frequencies die away
A professional microphone:
- measures accurately across the entire frequency spectrum
- can analyse octave or 1/3 octave bands
- complies with ISO 3382 requirements
A smartphone:
- is optimised for speech (not measurements)
- filters sound automatically (noise suppression!)
- lacks accuracy at low and high frequencies
Result: your RT60 is simply wrong.
3. Dynamic range
For a good RT60 measurement you often have to measure from a high level (noise source) to a low level (the sound dying away).
Professional meters:
- have a large dynamic range
- measure that entire “decay curve” properly
Smartphones:
- clip at loud sounds
- miss detail at low levels
So you are not measuring a real reverberation time, but a rough estimate.
4. Measurement method (ISO 3382)
An official RT60 measurement requires:
- a controlled noise source
- a specific measurement procedure (T20 / T30)
- correct positioning
- several measurement points
A sound level meter supports these methods directly. An app often does a simple calculation without correct measurement conditions. So even if the microphone were perfect (which it is not), the method is still wrong.
5. Reliability and repeatability
The microphone of a professional sound level meter is suitable for measuring reverberation time because it:
- is calibrated and standardised
- measures accurately across all frequencies
- has a large dynamic range
- complies with measurement methods such as ISO 3382
A smartphone app, by contrast, only gives an indication and is not suitable for reliable or normative measurements.
