Office acoustics - part 3

Introduction

This guide provides a brief overview of the standards commonly used in office acoustics.

Acoustic standards evaluate a wide range of parameters that influence the perceived acoustic comfort of a space. Some standards apply only to the testing of individual acoustic products, while others define performance requirements for the acoustic environment of the entire office.

We have summarized the most important standards and, wherever possible, included the corresponding reference values to help interpret their practical significance.

ISO 22955

Acoustic Comfort in Open-Plan Offices

ISO 22955 is one of the most important modern standards for the acoustic design of open-plan offices. Its purpose is to create working environments that support concentration, effective communication, and reduced distraction caused by surrounding noise.

The standard provides guidance on workplace planning, workstation layout, and the selection of acoustic solutions that improve overall acoustic comfort.

ISO 22955 places particular emphasis on:

• speech intelligibility,
• speech privacy,
• limiting the propagation of sound,
• dividing office space into functional acoustic zones.

Today, it is one of the key reference documents used in the design of modern office environments.

The standard describes methods for assessing the acoustic quality of office spaces and provides recommendations for the most important parameters affecting user comfort. These include reverberation time, background noise level, speech intelligibility, Distraction Distance (rD), and the effectiveness of speech attenuation between workstations.

Unlike standards that evaluate individual materials or products, ISO 22955 assesses the acoustic performance of the entire working environment. It considers not only the acoustic properties of materials, but also room layout, workstation arrangement, and the overall organization of the office space.

ISO 22955 is a comprehensive document covering the acoustic design of open-plan offices and includes detailed recommendations and target values for numerous acoustic parameters. Owing to its broad scope, a complete discussion is beyond the scope of this guide. Architects, designers, and organizations planning or renovating office spaces should refer to the full standard and work with qualified acoustic consultants during the design process.

The parameters evaluated by this standard include:

• STI (Speech Transmission Index) – a measure of speech intelligibility (0–1),he lower the STI value, the more difficult it is to understand speech,
• rD (Distraction Distance) – the distance over which a conversation is likely to distract other occupants,
• rP (Privacy Distance) – the distance beyond which speech becomes practically unintelligible, providing conversational privacy,
• Lp,A,S,4m – the A-weighted speech level measured 4 m from the speaker, indicating how quickly speech levels decrease within the office,
• LAeq – the equivalent continuous background noise level in the room,
• RT (Reverberation Time) – the time required for sound to decay within the room, reflecting the amount of sound reflection in the space.
  

As the number and complexity of these parameters illustrate, office acoustics is a highly multidisciplinary field that requires a comprehensive approach. No single parameter is sufficient to assess acoustic quality—achieving a comfortable and productive working environment requires considering multiple acoustic factors together.

ISO 3382

Measurement of Room Acoustic Parameters – RT60

ISO 3382 specifies methods for measuring the acoustic performance of completed rooms, primarily focusing on reverberation time (RT60).

The standard is widely used during building commissioning and for evaluating the acoustic quality of conference rooms, auditoriums, offices, and other occupied spaces.

By following ISO 3382, it is possible to objectively compare the acoustic conditions of different rooms.

Although ISO 3382 defines how reverberation time should be measured, it does not prescribe a single target value for all room types. Appropriate RT60 values depend on the size and intended function of the space.

Typical reference ranges are:

• RT < 0.4 s – very short reverberation; suitable for small rooms intended for conversations or recording,
• RT 0.4–0.8 s – typical range for well-designed offices and conference rooms, depending on room volume and intended use,
• RT 0.8–1.2 s – noticeable reverberation that may reduce speech comfort,
• RT > 1.2 s – excessively long reverberation for most office environments.

EN ISO 11654 / 354

Measurement of Sound Absorption and Classification of Sound-Absorbing Materials – αw and NRC

EN ISO 354 specifies the laboratory method for determining the sound absorption coefficient of materials and interior products. Testing is carried out in a reverberation chamber, allowing the proportion of incident sound energy absorbed by the test specimen to be accurately measured.

Based on the results obtained according to EN ISO 354, manufacturers can determine the sound absorption values used for the subsequent classification of acoustic materials.

EN ISO 11654 uses the test results obtained in accordance with EN ISO 354 to classify materials into sound absorption classes A to E.

Class A represents the highest level of sound absorption, while the lower classes indicate progressively reduced acoustic performance.

It is according to EN ISO 11654 that the widely used weighted sound absorption coefficient (αw) is determined.

The classification based on αw is as follows:

• αw 0.90–1.00 – Class A – very high sound absorption, recommended for demanding office environments,
• αw 0.80–0.85 – Class B – high sound absorption, suitable for most office applications,
• αw 0.60–0.75 – Class C – moderate sound absorption; often requires a larger surface area to achieve the desired acoustic effect,
• αw 0.30–0.55 – Class D – limited acoustic performance,
• αw < 0.30 – Class E or below – minimal contribution to improving room acoustics.
  

A similar parameter is the Noise Reduction Coefficient (NRC). This coefficient describes a material's ability to absorb sound and ranges from 0 to 1, where higher values indicate better sound absorption.

NRC is calculated as the average sound absorption at selected frequencies and is used primarily in North America. In Europe, the αw coefficient is considerably more common.

Although both parameters describe the sound-absorbing properties of materials, they are calculated using different methods and should not be compared directly.

Typical reference values for NRC are:

• NRC 0.90–1.00 – very high sound absorption,
• NRC 0.70–0.85 – high sound absorption,
• NRC 0.50–0.65 – moderate sound absorption,
• NRC 0.30–0.45 – limited acoustic performance,
• NRC < 0.30 – minimal sound absorption effect.

ISO 23351-1

Assessment of Acoustic Booths - Ds,a / SLR

ISO 23351-1 specifies the test method for acoustic booths designed for work and speech communication.

The standard measures how effectively a booth limits the transmission of speech to the surrounding environment and provides a consistent framework for manufacturers to present performance results. This makes it easier for users to compare products from different manufacturers.

ISO 23351-1 defines a laboratory method for measuring the ability of acoustic booths to reduce speech transmission outside the enclosure. The test compares the sound level emitted by a reference source in an open environment with the sound level measured outside the booth when the same source is placed inside it. The result is expressed as the Speech Level Reduction (Ds,a) value, measured in decibels (dB).

The higher the Ds,a value, the less speech escapes from the booth and the greater the level of speech privacy for people outside.

Practical interpretation of Ds,a values:

• Ds,a ≥ 30 dB – Class A – very high speech level reduction.
  The booth provides excellent speech privacy and is suitable for confidential phone calls, online meetings, and focused work.
• Ds,a 25–29.9 dB – Class B – high speech reduction performance.
  Suitable for the vast majority of offices and open-plan workspaces.
• Ds,a 20–24.9 dB – Class C – moderate speech reduction.
  Conversations are significantly less audible, although privacy may be insufficient in particularly noisy environments or at very short distances.
• Ds,a 15–19.9 dB – Class D – basic speech reduction.
  The booth improves acoustic comfort but does not provide a high level of speech privacy.
• Ds,a < 15 dB – Unclassified – limited speech reduction.
  Booths in this range cannot generally be considered effective solutions for ensuring speech privacy.

ISO 11957

Sometimes acoustic booths are tested in accordance with ISO 11957. This standard was developed primarily for industrial acoustic enclosures designed to protect against noise.

For modern office acoustic booths (office pods), however, ISO 23351-1 is now more commonly used.

As a result, manufacturers of office acoustic booths typically present their performance data in accordance with ISO 23351-1 rather than ISO 11957, as it more accurately reflects the intended use and real-world performance of these products.

ISO 11957 defines several parameters that may be reported when testing acoustic enclosures. The most important are:

• Sound Pressure Insulation, Dp [dB] – indicates the difference between the sound pressure level outside the enclosure and the sound pressure level inside it for each frequency band,
• Weighted Sound Pressure Insulation, Dp,w [dB] – a single-number rating derived from the frequency-dependent Dp values, making it easier to compare the acoustic performance of different enclosures.
  

In practice, Dp,w values are often interpreted using the following guidance. These ranges are indicative only and are not formally defined by the standard:

• Dp,w > 30 dB – very high sound insulation,
• Dp,w 25–30 dB – very good sound insulation,
• Dp,w 20–25 dB – good sound insulation,
• Dp,w 15–20 dB – moderate sound insulation,
• Dp,w < 15 dB – low sound insulation.

EN ISO 717-1

Assessment of Sound Insulation of Building Partitions – Rw

EN ISO 717-1 specifies how the results of airborne sound insulation tests for walls, doors, and other building partitions should be interpreted.

The standard is used to determine, among other parameters, the weighted sound reduction index (Rw), which indicates how effectively a partition reduces airborne sound transmission between adjacent spaces.

Although practical reference ranges are often used to help interpret Rw values, they should be regarded as general guidelines rather than formal performance classifications. The acoustic performance required always depends on the intended use of the building or room.

Typical guidance for Rw values is as follows:

• Rw < 30 dB – low sound insulation,
• Rw 30–40 dB – basic sound insulation,
• Rw 40–50 dB – good sound insulation for many office applications,
• Rw > 50 dB – very good sound insulation.

IEC 60268-16

Speech Transmission Index (STI)

IEC 60268-16 provides an objective method for measuring and evaluating speech intelligibility.

The Speech Transmission Index (STI) is widely used to assess the acoustic performance of conference rooms, auditoriums, lecture halls, acoustic booths, public address systems, Voice Alarm Systems (VAS), and other spaces intended for spoken communication.

It is also increasingly used in the design of modern office environments, where clear verbal communication is an important aspect of acoustic comfort.

According to IEC 60268-16, STI values are generally interpreted as follows:

• STI 0.75–1.00 – excellent speech intelligibility,
• STI 0.60–0.75 – good speech intelligibility,
• STI 0.45–0.60 – satisfactory speech intelligibility,
• STI 0.30–0.45 – poor speech intelligibility,
• STI < 0.30 – speech is largely unintelligible.

EN ISO 10140

Laboratory Testing of Sound Insulation

EN ISO 10140 specifies laboratory methods for measuring the sound insulation performance of building elements such as walls, doors, windows, partitions, and other systems that separate adjacent spaces. Its purpose is to determine how effectively a building element limits the transmission of sound from one room to another.

The test results obtained in accordance with EN ISO 10140 provide the basis for determining sound insulation ratings, such as the weighted sound reduction index (R_w), which are used to compare the acoustic performance of different construction solutions.

EN ISO 10140 applies to the laboratory testing of permanent building elements that separate spaces, including walls, doors, windows, and partition systems. It is not intended for evaluating the sound absorption performance of acoustic panels or the majority of office furniture.

In the past, this standard was also used to assess the acoustic performance of office acoustic booths. However, since 2020, ISO 23351-1 has become the primary standard for this purpose, as it was developed specifically to evaluate the ability of acoustic booths to reduce speech transmission.

We include EN ISO 10140 because of its importance within the broader field of office acoustics. However, its scope extends beyond the subject matter of this guide.