Harmonizing Sound and Style in Open-Plan Offices

Workplace conversations and calls are generally a distraction in open-plan offices. To improve the acoustical conditions of a workplace, Swiss consultancy Zeugin Bauberatungen models how sound propagates through office building designs and analyzes specific design modifications to find the right fit.

By Alan Petrillo
August 2023

Acoustical engineers, like composers, can help shape the effect that sound has on human ears. And while the sounds that surround everyday life may not be as moving as a symphony, the acoustics of a room can have a profound impact on the people inside. Many modern offices are open-plan designs, meaning there is minimal physical separation between workspaces. Silencing every open-office conversation is neither possible nor necessary, but attention to workplace acoustical conditions can make other people's conversations less distracting.

To help fine-tune the composition of workday soundscapes, Swiss consultancy Zeugin Bauberatungen uses the COMSOL Multiphysics® software to predict how sound will propagate through a proposed room design. Zeugin's precise models of acoustical effects enable the team to suggest practical improvements that are pleasing to the ear as well as the eye.

"Large sound-absorbing barriers may contradict the interior design concept by visually cluttering the space," said Thomas Zeugin, founder and managing director of Zeugin. "Our simulations help us propose optimization methods that harmonize with the architects' vision, along with improving employees' acoustical work environment."

Figure 1. An open-office design that was modeled by Zeugin Bauberatungen using the COMSOL® software. The modeled space includes a series of workstations (shown in tan at left) in a large carpeted room with a suspended ceiling and windows along the entire back wall. Sound-absorbing panels and curtains (shown at right) reduce the noise level and improve acoustical working conditions.

Simulation-Guided Design to Make Speech Less Distracting

Thoughtful interior design decisions can significantly improve the sound quality of a room. When optimizing workplace acoustics, improving sound quality actually involves making speech less intelligible. A muffled murmur of voices is simply less distracting than a clear, crisp conversation among other people.

The sound waves of comprehensible human speech occupy a particular set of frequencies. Zeugin produced a case study on building acoustics that explains that the fundamental frequency of voices during a conversation typically ranges between 100 Hz and 250 Hz. When we form words, certain movements of our throats and mouths cause changes in frequency; for example, consonants have their own frequency range of 250 Hz–8 kHz. Modifying sound waves in these ranges can help make speech less intelligible — and thereby less distracting.

The table in Figure 2 presents three indicators related to speech intelligibility, along with ranges that correspond (from left to right) with better overall acoustic conditions. The Zeugin team constructs models of possible room designs using the COMSOL® software, which enables them to predict values for these and other relevant metrics.

Poor Acoustic Conditions Moderate Acoustic Conditions Good Acoustic Conditions
Deflection Distance rD rD > 10 m 10 ≥ rD > 5 m rD ≤ 5 m
Spatial Decay Rate D2,S D2,S < 5 dB 5 dB ≤ D2,S < 7 dB D2,S ≥ 7 dB
A-Weighted Sound Pressure Level of Speech at 4 m LP,A,S,4m LP,A,S,4m > 50 dB(A) 50 ≥ LP,A,S,4m > 48 dB(A) LP,A,S,4m ≤ 48 dB(A)
Figure 2. A table presenting poor, moderate, and good ranges of acoustical performance according to the three metrics listed in the left-hand column. Source: EN ISO 3382-3:2012.

Calculating Sound Paths and Insulation Values

Considering his professional role of orchestrating aural effects, it is no surprise that Thomas Zeugin is also a trained musician. "I completed a music degree in guitar at the Swiss Jazz School in Bern before founding an engineering consultancy with my father," he explains. "Due to my musical education, I have been strongly interested in acoustic and sound optimization of rooms and buildings from the very beginning."

Of course, Thomas' analyses are based on much more than his well-tuned hearing. "The first step is a rough statistical calculation, based on Eyring's reverberation time equation, for the room that is being examined. After we receive more detailed architectural plans of interior design, we can construct a 3D model in COMSOL," he said.

"Once we have a model of the room, we can perform calculations using ray acoustics to obtain those important room acoustics metrics. We also use the Acoustic Diffusion Equation interface in the add-on Acoustics Module," continues Thomas. "This enables us to calculate secondary sound path transmissions and the sound insulation values of room partitioning components. We can then simulate how those factors influence acoustic conditions across the modeled space."

Comparing the Effects of Sound Mitigation Measures

The case study mentioned previously provides instructive examples of how Zeugin uses simulation to address real-world design problems. This particular project, which focused on an office building in the Swiss city of Ostermundigen, included analysis of sound propagation in a large open room. The initial design of the space (Figure 3) featured multiple shared work tables, a wide wall of windows, a double-layer floor, and a concrete ceiling with suspended acoustical panels. Other materials and furnishings had yet to be selected.

Figure 3. An overhead view of the office design modeled by Zeugin. The red dot indicates the source of simulated sound waves, and the blue dots indicate measurement points.

"Our simulation shows that if no sound mitigation measures are taken, the low-frequency sound waves generated by speech can spread unhindered throughout the room," Thomas said. "We can derive a deflection distance value from our simulation, and it shows that distracting levels of speech can spread as far as 12 meters from the source." These and other metrics decisively place this room's acoustics in the poor–moderate categories, as defined in Figure 2.

Fortunately, this performance can be improved through strategic placement of architectural elements. Figure 4 shows the impact of two specific design changes: the installation of sound-absorbing curtains over the windows and the placement of two suspended foam panels with an inserted sheet of steel near the center of the room.

Figure 4. Images from Zeugin's model showing the volume distribution of 1000-Hz sound waves in the office with no mitigation measures present (left) and the distribution of 1000-Hz sound waves with suspended panels and acoustical curtains installed (right).
Figure 5. A close-up of the leftmost suspended panel and how it affects the volume distribution.

The curtains bring the entire room into Zeugin's "moderate" range, and the hanging panels significantly expand the area encompassed by "good" acoustical working conditions. "Absorbent materials can help," said Thomas, "but we see the largest benefit from placing high-mounted barriers that directly interrupt the paths of sound waves."

Note that the beneficial barriers he describes are large panels near the center of the room, rather than cubicle walls around individual desks. Such dividers may provide workers with a visual sense of privacy, but acoustically, "walls between the workstations only reduce sound levels by 2–3 dB," Thomas said. By providing data-driven analyses to counteract popular misconceptions about sound, simulation can help guide Zeugin's clients toward more acoustically effective interior designs.

Composing Indoor and Outdoor Soundscapes with Simulation

Just as a composer's work should resonate with audiences of any size, the value of the Zeugin team's acoustical analyses extends far beyond the individual office worker's ears. For example, the team is currently working on a redesign of a company's dining halls and conference rooms, which host gatherings that place high demands on acoustics both within and between rooms. Other projects call for noise abatement on an even grander scale. In the city of Bern, Zeugin has been engaged to improve the acoustics of an entire neighborhood that is located next to a busy highway.

"Due to the functionality and flexibility of the COMSOL software, we can construct models and perform comparable calculations for many different types of projects," said Thomas. "Based on our follow-up measurements, we've found that our simulated results closely match real-world conditions. This gives us confidence in our findings and reassures our customers as well."