Quiet zones in open-plan offices: a guide to effective office acoustics

Modern offices, with their open spaces and flexibility, pose a challenge for effective acoustic management. Open-plan offices, although designed to promote interaction and flexibility in layout, often become a source of functional and sensory problems. The main factors that undermine their advantages are excessive noise, chronic lack of privacy and sensory overload, leading to reduced productivity and comfort for employees.

In response to these challenges, the need for zoning has emerged, the key premise of which is to transform open space into a controlled mosaic. Dividing the office into functional zones not only organises the space, but also defines and optimises how it is used, ensuring that each part has its own precise meaning and purpose.

The principle of ‘Separate, but don't divide!’ is at the core of modern acoustic design for hybrid offices. It focuses on achieving sensory and functional separation – key to concentration and privacy – using acoustic measures and flexible barriers, while eliminating the need for permanent, rigid physical walls. Separation is therefore achieved at the sound level, not just at the structural level.

Effective acoustic management requires precise definition of work environments and assigning specific acoustic requirements to them:

• Focus Zone: areas designed for work requiring high concentration, such as programming, report writing or analytical tasks. These zones are characterised by the lowest permissible background noise level (35-40 dB);
• Collaboration Zone: open or semi-open spaces designed for brainstorming and discussion. Although they accept higher sound levels, it is critical to use intensive absorption to prevent noise from radiating into adjacent, sensitive zones;
• Hub Zone: main desk-based work areas characterised by moderate noise and constant movement (e.g. customer service, administration). In this zone, the priority is effective speech intelligibility management (40-55 dB);
• Privacy/Phone Booth Zone: small, enclosed units, such as acoustic booths, designed for confidential phone calls, video conferencing and difficult tasks requiring almost complete silence (30-35 dB).

The discrepancy between legal standards and cognitive needs necessitates zonal separation. Although the acceptable equivalent sound level for standard administrative work may be ≤ 55 dB, ergonomic requirements for complex and difficult tasks range from 35 to 55 dB. Since open-plan offices are unable to naturally maintain such low background noise levels, designers are forced to introduce physical or sensory separation.

Zonal acoustics design must be embedded in a rigorous legal and technical framework that defines acceptable sound levels and room characteristics.

Polish standards define maximum equivalent sound levels (L_Aeq,T) during working hours:

• PN-N-01307:1994: Sets permissible values at ≤ 55 dB for administrative and office buildings intended for conceptual work and ≤ 65 dB for secretariats and customer service offices.
• PN-EN ISO 9241-6:2002: Emphasises ergonomic requirements for computer workstations, where the sound level should not exceed 55 dB when performing difficult and complex tasks, with recommended lower limits reaching 35 dB.
• PN-B-02151-2:2018 (for open-plan offices): The reference equivalent A-weighted sound level is 40 dB. This value is often adjusted to account for the reverberation time of the room. Studies show that for typical open-plan offices, the acceptable sound level is in the range of 35-39 dB.

The PN-EN ISO 3382-3:2012 standard is crucial for assessing open space acoustic environments, as it focuses not only on the overall noise level, but above all on the propagation and distracting nature of speech.

The key parameters of this standard are:

• Speech Diffusion Radius (r_D): This is the distance from the speaker beyond which speech intelligibility decreases rapidly. Reducing r_D is the direct goal of zonal acoustics design, as it shortens the area of distraction,
• Speech Sound Level at 4 metres (L_p,A,S,4m): The standard imposes a limit on the A-weighted speech sound level at a distance of 4 m to a maximum of 48 dB. This parameter indicates how far speech from a given position can be heard and is distracting,
• Minimum Sound Absorption: Requirements for acceptable reverberation noise specify the minimum unit sound absorption of a room in the range of 1.1-1.3 m².

In the case of offices, regardless of the type of building, the sound insulation requirements are the same as for office buildings. According to PN-B-02151-3:2015-10, the minimum sound insulation index (R'_A,1) for partitions between office rooms, meeting rooms and conference rooms should be ≥ 40 dB, with the possibility of reducing it to ≥ 35 dB under certain conditions. This is a basic requirement that must be met, even when using mobile or glass partitions.

Table 1: Summary of Normative Requirements for Office Acoustics

Passive acoustic solutions are the foundation of effective zonal design, as they are designed to reduce reverberation (i.e. the time it takes for acoustic energy to decay in a room) and shorten the propagation time of sound waves. This mechanism directly improves speech propagation indices as defined by ISO 3382-3.

In order to increase the acoustic absorption of a room to the required level, materials that actively prevent the reflection of sound waves must be used consistently. Soft floor coverings are key here: carpets and rugs work much better than hard tiles because they significantly reduce noise transmission and reflection.

In terms of architectural finishes, it is essential to use wall and ceiling panels with a high absorption coefficient (class A). Aesthetic solutions, such as perforated wooden acoustic panels, effectively combine natural beauty with acoustic requirements. These panels not only reduce unwanted noise, but also add elegance, being particularly recommended for collaboration areas and conference rooms.

Office furniture plays a dual role – functional and acoustic – enabling passive separation in line with the principle of ‘Separate, but don't divide!’. Upholstered furniture, including sofas, armchairs and seats made of soft materials, are natural sound absorbers, helping to reduce background noise.

Furniture with high acoustic walls (so-called soft seating), such as the Kaiva and Agora series of acoustic booths, allows you to create micro-environments. They act as passive separation, dampening ambient noise and offering the user visual protection, which is essential for maintaining a high level of concentration in the Concentration Zone.

This is complemented by partition walls and screens placed between desks. Their use helps to dampen sounds from the immediate environment, effectively creating a more focused workspace without the need to completely enclose the workstation.

Current acoustic design is evolving in a holistic direction. Solutions such as greenery in the office and space branding elements are deliberately combined with sound-absorbing materials. The introduction of these elements suggests that contemporary office design aims to improve not only technical parameters (dB reduction) but also visual and sensory comfort.

While passive absorption controls reverberation in a room, active insulation aims to block sound transfer between zones, implementing the idea of flexible, temporary separation.

Mobile acoustic partitions are invaluable in managing the dynamics of office space. Their lightweight and mobile design allows for the quick creation of quiet zones for individual or group work. This is key to the flexible management of a hybrid office, allowing for easy rearrangement of space according to current needs, for example during workshops, meetings, or to temporarily create a quiet zone. These partitions can be either transparent or fabric-based, but their effectiveness depends on their absorption and insulation parameters.

Multifunctional acoustic booths and cubicles are the most effective way to create a quiet, private space in an open working environment. They provide maximum sound insulation, which is essential for conducting confidential meetings and video conferences without interference. The critical insulation performance of modern booths reaches 35 dB, which allows for effective isolation from the environment.

Achieving high insulation in booths requires the elimination of so-called flanking paths. The most important technological solutions in this area are:

• Triplex Glass of Variable Thickness: The use of three-layer, safety triplex glass with varying layer thicknesses is fundamental. The varying thickness of the layers prevents resonance at specific sound frequencies, enabling effective blocking of a wide spectrum of sound waves.
• Ventilation Silencers: The ventilation system is a potential weak point in insulation. Air must enter the cabin through special acoustic silencers that actively block noise from escaping outside and inside. At the same time, a quiet fan must ensure effective air exchange, renewing up to 30 m³ of air per hour, eliminating CO₂ stagnation.
• Elimination of Internal Echo: To ensure a comfortable environment inside the cabin, its interior must be lined with sound-absorbing materials that effectively dampen echo and reverberation.
• Smart Automation: Modern cabins are equipped with presence detection systems that automatically turn lighting and ventilation on and off (e.g. after 6-8 minutes), optimising energy consumption and increasing user comfort.

Sound masking systems represent the most advanced method of implementing the principle of ‘Separate, but do not divide!’, as they manage acoustic information (speech) without introducing physical barriers. These solutions are ideal for administrative areas and open ‘Hub Zones’ where complete silence is impossible or undesirable.

The operation of masking systems is based on two natural phenomena of hearing physiology:

• Acoustic masking: this phenomenon consists in the fact that a sound with a higher intensity level (controlled noise emitted by the system) effectively drowns out other sounds with a similar bandwidth (e.g. human speech), making them incomprehensible.
• Auditory adaptation: the human brain is able to ignore monotonous and constant sounds, such as uniform noise. The system emits controlled noise with specially shaped characteristics, tailored to the environment. The brain adapts to this background noise, minimising the distracting effect of ambient noise, such as conversations or ringing telephones.

Controlled noise effectively reduces the intelligibility of speech and other distracting sounds. As a result, the privacy of conversations in open spaces is increased, which is crucial, for example, in customer service offices or in situations where the content of conversations should not be heard by bystanders.

In a normative context, a sound masking system allows for a controlled increase in background noise, which leads to a faster decrease in speech sound levels at a distance. This improves key acoustic indicators defined by PN-EN ISO 3382-3 (e.g. r_D) without the need for additional physical barriers.

In offices where very high absorption (minimum reverberation) has been achieved, the so-called ‘library effect’ often occurs; every sound, even quiet ones, is immediately distracting. The masking system prevents this by introducing a constant, comfortable level of background noise that simultaneously suppresses distractions, increasing concentration and work efficiency.

These systems are available in flexible configurations, from single-zone (e.g. CMS-II-1Ch) to dual-zone (e.g. CMS-II-2Ch), allowing for precise zoning of the masking level and adaptation to the local acoustic requirements of individual office areas. In addition, the masking system can act as a public address system, allowing the playback of background music, announcements, or other audio content.

Effective zoning requires strategic alignment of acoustic technologies with the function of each zone. The matrix integrates normative objectives with available solutions, creating an action plan for managing the sound environment.

Table 2: Acoustic optimisation matrix for a zonal office

The introduction of zonal acoustics requires rigorous verification. The technical design must take into account all mandatory elements and requirements in accordance with applicable regulations.

The acoustic properties of an office should be assessed in accordance with PN-EN ISO 3382-3:2012. This standard allows for a more reliable assessment by taking into account the grouping of workstations, which makes it possible to ignore the impact on the assessment of areas where work is not actually performed.

Table 3: Critical Characteristics of Insulation Elements

The principle of ‘Separate, but do not divide!’ in acoustic design for hybrid offices is achieved through the synthesis of three complementary pillars: passive absorption, flexible insulation and active sound management.

Key recommendations:

• Maximise reverberation control: It is necessary to strive for high unit sound absorption (in accordance with PN-B-02151-4) by using floor coverings, ceiling and wall panels, and acoustic furniture. This is a prerequisite for achieving an effective reduction in speech sound levels.
• Use of flexible infrastructure: Providing micro-environments with high acoustic insulation (e.g. soundproof booths up to 35 dB) and mobile partitions allows for dynamic adaptation of space to changing work needs and management of zone division without permanent interference with the office layout.
• Active distraction management: The introduction of sound masking systems is the most modern method of reducing speech intelligibility in open work areas, which directly improves ISO 3382-3 parameters and increases the subjective comfort of employees. This system eliminates the risk of the ‘library effect’ by creating an acceptable, constant background noise.

The implementation of advanced acoustic systems is a strategic investment in human capital efficiency. It is recommended to use analytical tools to quantitatively determine the cost-effectiveness of implementing sound masking systems by measuring the potential increase in work efficiency.

It should be emphasised that acoustic design should not be limited to meeting minimum legal requirements. Although achieving a level of 55 dB may comply with PN-N-01307, it is insufficient to protect employees performing complex cognitive tasks. Continuous exposure to noise, even within acceptable limits, contributes to stress and sensory overload. Striving for the rigorous targets of 35-40 dB in Concentration Zones (in accordance with PN-EN ISO 9241-6) is therefore crucial not only for optimising efficiency, but above all for ensuring an ergonomic and healthy working environment.

Strategic implementation planning requires:

1. acoustic audit: conducting professional noise level measurements in different areas of the office;
2. needs analysis: identifying priority areas (focus on Concentration Zones);
3. selection of solutions: choosing the right combination of passive, insulating and active solutions;
4. pilot implementation: testing solutions in one section before full implementation;
5. ROI evaluation: measuring improvements in productivity and employee satisfaction after implementation.

Proper zonal acoustic design transforms an open-plan office from a distracting environment into a diversified, acoustically optimised space that supports both focused work and flexible collaboration.