Acoustics experts: Open-plan offices can be too quiet

It doesn’t take much noise before your concentration starts to wane in open-plan offices – and often it’s chatting colleagues who are to blame.

However, creating noise-free offices is not the solution, according to two Swedish acoustics experts we have spoken to. 

We have both some good news and some bad news when it comes to the acoustics in open-plan offices. First, the good news: Architects have succeeded in designing some very modern offices with a very low level of background noise, and which keep out the noise of traffic, for example.

The bad news is that the low level of background noise is actually a problem. At least if you ask the two acoustics experts Philip Zalya and Timmy Kristofferson from Tyréns Sverige AB.

“Our measurements in office environments show that the level of background noise, for example from ventilation or traffic, is usually 25-28 decibels. And that is very low,” says Philip Zalya, an acoustician with an MSc in Engineering.

By comparison, a bedroom or a quiet forest has about the same decibel level.

On the face of it, you might think that quiet office environments would be preferable. But there is more to good office environment acoustics than meets the eye, and this can largely be ascribed to human hearing:

“The main problem is that, as an office worker, you hear what people are saying nearby, and this upsets your focus and concentration,” says Timmy Kristofferson, who is also an acoustician with an MSc in Engineering at Tyréns Sverige AB.

Our hearing tunes into conversation

Philip Zalya makes the point that office acoustics are very important for employees:

“Many studies have shown that poor acoustics, especially in open-plan offices, can affect people’s health and productivity. So, it’s very important that we address the problem,” he says, adding:

“What’s most disturbing is colleagues talking. Our brains are designed to pick up speech and to try to decode the information. This happens automatically and subconsciously, and the urge is very hard to resist,” he says. And this is why office environments with a very low level of background noise can actually be a problem, because even normal conversations between colleagues can suddenly be heard even more clearly.   

For the same reason, the two acousticians believe you have to work with the level of background noise if you want to create optimum working conditions in offices. However, we’ll return to this later.

From reverberation time to quieter talking

According to Philip Zalya and Timmy Kristofferson, the building industry has been focusing for years on reverberation time alone as the key to understanding and creating good acoustics.

“It’s a very one-dimensional approach to only look at the reverberation time in office buildings. You can easily have 20 different rooms with the same reverberation time, yet the acoustics may be completely different in each of them. The shape of the room, its dimensions, how the employees are placed and what people are working with are all important factors too. In some offices, people just sit in front of their screens working in AutoCAD and don’t talk to each other all day,” says Philip Zalya.

Instead, he recommends using the ISO standard 3382-2:2008, which aims to reduce speech levels in rooms. However, there is still a long way to go before the standard becomes incorporated into Swedish legislation, but it might be included as a recommendation when the related guidelines are revised in the near future.

From ceiling to walls and partitions

According to Philip Zalya and Timmy Kristofferson, the poor acoustics in many office environments are also down to the basic fact that no single person or body is responsible for the acoustics.

“One party will usually be in charge of constructing the actual building and be responsible for all the walls, ceilings and surfaces. And then you have the users – i.e. the companies that will be occupying the building. They decide the interior design, where the workstations are going to be, where the employees will be sitting, and what furniture to buy. In other words, there’s no single party who is responsible for the acoustics,” says Philip Zalya.

However, he and Timmy Kristofferson do recommend that you start with the ceilings when it comes to acoustics regulation.

“In most cases, we start with the ceiling and choose a highly absorbent ceiling material. If your ceiling material is not good at absorbing the sound effectively, you don’t gain anything by erecting partitions to try to control the sound in an office, because the sound will simply bounce off the ceiling,” says Philip Zayla, while Timmy Kristofferson adds:

“The ceiling is such an important surface because it’s often the surface which is closest to the sound source. In other words, it’s the first surface to be hit by the sound as it travels from its source,” he says. After that, you can think about sound-absorbing materials on the walls:

“A common mistake that many people make is having lots of glass surfaces, such as around meeting rooms, for example.  If you place sheets of glass opposite each other, sound is reflected between them. Therefore, it’s a good place to install sound-absorbent material,” says Timmy Kristofferson, who adds, however, that because wall absorbers are not required by law in Sweden, it’s not usually a priority.

Finally, Timmy Kristofferson and Philip Zalya point out that designing and furnishing an office which supports the right culture for good acoustics is a huge responsibility:

“Of course, the workplace culture matters, and people not making and taking phone calls in the middle of an open-plan office environment. But it’s also important to have small meeting rooms for telephone calls or informal meetings,” says Philip Zalya.

Office environment infused with background noise

Because low levels of background noise can exacerbate concentration problems for office workers, more and more offices in Sweden are starting to experiment with adding background noise, explains Philip Zalya:

“It might be the noise of ventilation, but noise can also be added via special sound-masking systems. That is, loudspeakers which are used to add a very neutral sound – not music – which is basically just noise. Usually, the sound is in the same frequency range as human speech, so it masks conversation in the office,” he says. 

“I’m involved with a project at the moment where background noise is added, and it has been installed in several offices. I’ve been to see them and conducted measurements, and it looks very promising indeed. They can simply control the level of the background noise,” says Philip Zalya.