> Office acoustics - part 2
This guide is intended as a concise reference to the fundamentals of office acoustics. It explains the key concepts, acoustic parameters, and design considerations that play an important role in creating comfortable and effective working environments.
Acoustics is one of the fundamental disciplines of building physics, concerned with the generation, propagation, and behavior of sound within enclosed spaces. In office environments, its significance extends far beyond simply reducing noise levels. In practice, acoustics has a direct impact on speech intelligibility, the ability to concentrate, speech privacy, and the overall comfort and well-being of occupants.
Modern offices are increasingly designed as open, multifunctional environments where individual work, team meetings, phone calls, and video conferences take place simultaneously. This creates a complex acoustic environment that cannot be assessed solely by measuring sound pressure levels. Equally important are factors such as reverberation time, the acoustic properties of finishing materials, workstation layout, and the way sound propagates between different areas of the office.
The purpose of this guide is to provide a structured overview of the most important aspects of office acoustic design. It is not intended to replace a professional acoustic design or the relevant standards. Instead, it explains the principles that influence how office spaces are perceived by their users and supports informed decision-making when designing or renovating office environments.
Sound is a mechanical wave that propagates through an elastic medium, most commonly air. It is generated by vibrations of a sound source, which create local variations in air pressure. These pressure waves travel in all directions at approximately 343 m/s (at 20°C), transferring energy without causing any permanent displacement of the air particles.
In office acoustic design, the most important frequencies are those associated with human speech. It is within this frequency range that sound reflections and reverberation time must be effectively controlled, as they have a direct impact on speech intelligibility and the ability to communicate without disturbing other occupants.
When a sound wave encounters an obstacle, its energy is divided into several components. Part of the energy is reflected, part is absorbed by the material, part is scattered in different directions, and the remainder may be transmitted through the partition. The proportion of each phenomenon depends on the material's properties, its structure, thickness, and the frequency of the sound.
The balance between reflection, absorption, and diffusion determines the acoustic character of a room. Spaces dominated by reflective surfaces tend to have longer reverberation times and a greater number of secondary reflections. By contrast, the use of sound-absorbing materials and sound-diffusing elements helps control acoustic energy and improve occupant comfort.
One of the most important sound sources in office environments is, of course, the human voice.
Office equipment and building components such as doors are generally designed to operate as quietly as possible. Human speech, however, cannot be controlled in the same way. For this reason, acoustic assessments of office environments focus primarily on speech as the dominant source of unwanted noise.
Speech frequencies can be considered in two different ways: the fundamental frequency of the voice (pitch) and the frequency range that carries speech information. In architectural acoustics, the latter is far more important because it defines the frequency range for which acoustic solutions are designed and evaluated.
The following frequency ranges are commonly used:
For example, standards for the acoustic performance of office acoustic booths often do not evaluate the entire audible frequency range (20 Hz–20 kHz). Instead, they focus on the frequency range that is most important for human speech. In practice, speech is influenced primarily by sound attenuation within the 250–5,000 Hz range, with particular emphasis on 500–4,000 Hz.
This explains why two acoustic booths may exhibit similar sound insulation at low frequencies while providing noticeably different levels of speech privacy. If one booth attenuates the 500–4,000 Hz range more effectively, conversations inside the booth will be significantly less intelligible to people outside.
For the acoustic design of offices and telephone booths, the most critical frequency range is generally considered to be 250–4,000 Hz, and especially 500–2,000 Hz, as this range has the greatest influence on the intelligibility of human speech.
This is, of course, also closely linked to speech privacy.
The design of room acoustics is based on international standards that define methods for testing, classifying materials, and evaluating acoustic performance. These standards do not prescribe which solutions should be used in a particular office. Instead, they provide standardized measurement procedures that allow results obtained by different manufacturers and testing laboratories to be compared objectively.
In practice, investors, architects, and designers most often encounter these standards in the technical documentation of acoustic panels, office booths, partitions, and finishing materials. A basic understanding of their scope makes it easier to assess the credibility and significance of the declared acoustic performance.
For a more detailed discussion of the standards used in office acoustics, please refer to our next guide: Office Acoustics – Part 3: Standards and Reference Values.
Among the standards related to office acoustic design, the most important is ISO 22955.
ISO 22955 is an international standard dedicated to the acoustic design of open-plan office environments. Its objective is to create workplaces 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 enhance acoustic comfort.
ISO 22955 places particular emphasis on:
Today, it is regarded as one of the principal reference documents for the acoustic design of modern office environments.
A wide range of acoustic parameters is used when designing room acoustics. Each describes a different physical phenomenon and provides different information about the acoustic conditions within a space. Understanding their meaning makes it easier to interpret measurement results and compare acoustic materials and solutions correctly.
One of the most common mistakes is assessing room acoustics solely on the basis of noise level, expressed in decibels. In reality, this is only one of many parameters that characterize an acoustic environment.
The design of modern office spaces relies on the analysis of several complementary indicators, each describing a different aspect of acoustic performance.
The most important are:
None of these parameters should be considered in isolation. Only by evaluating them together can the acoustic quality of a room be assessed correctly. Although they often appear side by side in product datasheets, they describe different physical phenomena and should never be used interchangeably.
Reverberation Time (RT60) describes how long sound remains audible in a room after the sound source has stopped. It is one of the most important parameters used to evaluate room acoustics.
The longer the reverberation time, the more sound reflections occur from walls, ceilings, and floors. As a result, successive speech sounds begin to overlap, reducing speech intelligibility and making concentration more difficult.
An excessively short reverberation time is not always desirable either, as the room may sound unnaturally "dead." The objective of acoustic design is therefore to achieve a reverberation time appropriate for the intended use of the space.
In office environments, the goal is to strike the right balance between comfortable communication and limiting the spread of unwanted noise.
Common Mistake
Assessing acoustics based solely on noise level. In many offices, the primary issue is not excessive loudness, but excessive reverberation time.
The weighted sound absorption coefficient (αw) describes a material's ability to absorb acoustic energy. It ranges from 0 to 1, where values close to 0 indicate almost complete sound reflection, while values close to 1 indicate very high sound absorption.
This parameter is mainly used to compare materials such as wall coverings, ceiling panels, acoustic partitions, and other products designed to improve room acoustics.
A high αw value does not automatically guarantee good room acoustics. The overall acoustic performance also depends on the total surface area of the material, its placement within the room, and the room's geometry.
The Noise Reduction Coefficient (NRC) is used primarily in North America to assess the sound absorption performance of materials.
Like αw, NRC describes sound absorption, but it is calculated using a different method and should not be regarded as its direct equivalent.
European acoustic projects typically use the αw rating in accordance with EN ISO 11654, whereas international product documentation often includes both values.
Sound insulation describes the ability of a partition to reduce sound transmission between adjacent spaces.
Unlike the sound absorption coefficient, Rw does not describe the behavior of sound inside a room. Instead, it measures how effectively walls, doors, windows, or other partitions prevent sound from passing from one space to another.
Typical examples include partition walls, doors, and acoustic booths. Their primary purpose is not to absorb sound energy but to reduce sound transmission into or out of the enclosed space.
Understanding the distinction between sound absorption and sound insulation is essential, as these concepts are often confused during office design.
Good to Know
An acoustic wall panel can significantly reduce reverberation time, but it cannot replace a wall with adequate sound insulation. These are two different acoustic functions requiring different solutions.
In many modern offices, the primary objective of acoustic design is not to achieve the lowest possible noise level, but to ensure high speech intelligibility where communication is required.
This is evaluated using the Speech Transmission Index (STI), which measures how clearly speech can be understood within a given space.
STI is particularly important in conference rooms, video conferencing rooms, acoustic booths, and any environment where spoken communication is essential.
A well-designed office should provide high speech intelligibility within collaboration areas while limiting the transmission of speech into surrounding workspaces.
Key Takeaway
No single parameter is sufficient to evaluate the acoustic quality of a room. Only the combined assessment of reverberation time, sound absorption, sound insulation, and speech intelligibility provides a complete understanding of acoustic performance and enables the design of comfortable, productive workplaces.
Acoustic design begins long before selecting specific materials or products. The most important stage is analyzing how the space will be used and defining the acoustic requirements for each area of the office. Workstations requiring concentration have different needs from conference rooms, while collaborative spaces and informal meeting areas require yet another acoustic approach.
One of the most common mistakes is attempting to solve every acoustic issue using a single type of product, most often wall-mounted acoustic panels. In reality, acoustic comfort results from the combined performance of many elements and from the careful design of the entire interior.
The principles of office acoustic design are covered by ISO 22955, the international standard dedicated to open-plan office acoustics. This standard is discussed in greater detail in the next part of this guide.
The first step is to assess the existing conditions or review the architectural design. The analysis typically includes:
At this stage, it is often possible to identify the factors that will have the greatest influence on the final acoustic performance of the space.
There is no single acoustic solution suitable for every office.
The designer should first answer questions such as:
Only after the intended use of each area has been established can appropriate acoustic solutions be selected.
Good to Know
Two offices with exactly the same floor area may require completely different acoustic solutions. The way the space is used is far more important than its size.
In most modern offices, the greatest acoustic challenge is not external noise but the excessive number of sound reflections from hard surfaces.
For this reason, one of the primary objectives of acoustic design is to reduce reverberation time by increasing the amount of sound-absorbing surfaces.
Common solutions include:
However, installing more acoustic panels does not automatically produce better acoustics. Their location and distribution within the room are equally important.
In large open-plan offices, one of the most effective ways to improve acoustic comfort is to limit the unrestricted propagation of sound.
This can be achieved by:
These measures not only improve acoustic conditions but also enhance privacy and support concentration.
One of the greatest challenges in acoustic design is achieving the right balance between reducing reverberation and providing adequate sound insulation.
Sound-absorbing materials reduce reflections within a room, while high-performance partitions prevent sound from traveling between different areas of the office.
Only by combining these two approaches can a workplace achieve a high level of acoustic comfort.
Several design mistakes occur repeatedly in office projects, including:
Most of these problems can be avoided by considering acoustics from the earliest stages of the design process.
Common Mistake
Treating acoustic panels as a universal solution. Good acoustics always result from the interaction of multiple factors, including materials, room geometry, furniture, and the overall organization of the workspace.
Key Takeaway
Well-designed acoustics are not the result of a single product. They are achieved through the thoughtful integration of appropriate materials, spatial planning, and the intended function of each area within the office. The earlier acoustics are considered during the design process, the easier it is to create a comfortable working environment while avoiding costly modifications later in the project.
Acoustic booths are now evaluated using standards that differ from those applied to the acoustic assessment of general office environments.
Modern acoustic booths are assessed based on several parameters that describe both their acoustic performance and user comfort. The most important of these is DS,A (Speech Level Reduction), determined in accordance with ISO 23351-1.
DS,A is the primary indicator of a booth's ability to reduce the transmission of speech to the surrounding environment. It is expressed in decibels (dB). The higher the DS,A value, the greater the level of speech privacy provided inside the booth.
For easier interpretation, booth performance is also classified into performance classes, ranging from Class A (the highest level of speech reduction) to Class D (the lowest).
Acoustic comfort is the result of multiple factors working together. It does not depend solely on the number of acoustic panels installed or on the noise level measured in decibels. The quality of the acoustic environment is influenced by factors such as reverberation time, the acoustic properties of materials, the way sound propagates throughout the space, and the overall organization of the workplace.
Improving acoustics effectively begins with an analysis of the room's intended function and the needs of its users. Only then can appropriate materials, sound-absorbing elements, and sound-insulating solutions be selected and positioned to achieve the desired acoustic performance.
The goal of modern office acoustic design is not to create complete silence. Instead, it is to provide an environment that supports clear communication while minimizing distractions that interfere with concentration and day-to-day work.
The knowledge presented in this guide provides a solid foundation for the informed design of comfortable workspaces. It helps readers better understand the technical parameters of acoustic materials, interpret acoustic test results, and make more informed decisions when planning new office environments or renovating existing ones.
In the next guide, we will present the most common solutions used to improve office acoustics. Topics will include acoustic panels, desk-mounted screens, acoustic booths, and other products designed to enhance workplace comfort, explaining not only how they are constructed but, more importantly, the situations in which they deliver the greatest benefits.
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Chairs and armchairs
Introduction