9 Acoustical Considerations For Open Offices

This article, written by Nicole Cuff, originally appeared Building Operating Management’s FacilitiesNet. Click here to see the original piece.

Today, companies — and their employees — are seeking healthier workspaces that embrace good acoustics, natural light, and other aspects of good indoor environmental quality as part of open plan offices that foster collaboration and communication. With open plan offices, good acoustics is one of the more critical aspects of a productive and comfortable workplace.

Here’s a look at the top ten design features considered critical for open plan office design.

1. Sound masking: Not Just White Noise

Sound masking is the most important determinant of privacy in open plan office designs. Sound masking introduces a background sound spectrum designed to closely match speech. The idea is that a continuous, pleasant sound masks, or covers up, speech sounds so that co-workers who are not part of the conversation cannot make out the words. Sound masking will not make a noticeable difference with a colleague whose desk is immediately next to your desk — communication and collaboration are preserved — but it will reduce the intrusion from the voice of a colleague down the hall.

What we call white noise has a different frequency spectrum than the best sound masking systems; the technical definition of white noise is an equal level of sound energy per frequency, while sound masking systems have a frequency spectrum designed to be particularly effective at masking speech.

2. Reduce HVAC Noise Levels

Even with a continuous background sound from an electronic soundmasking system, the noise generated by HVAC equipment cannot be ignored. If the HVAC noise is louder than the soundmasking, you will hear HVAC noise over the masking; not only that, you will hear more low-frequency noise — at worst a rumble. HVAC noise is also transient because HVAC operation is transient, and the low-frequency noise would turn on and off, which is more distracting than constant noise.
A better solution is to locate variable air volume (VAV) boxes above mineral fiber ceilings to reduce radiated box noise emitting to offices below, as well as below packaged rooftop units supply and return ductwork penetrations. Otherwise, air-turbulence noise from the airflow striking the elbow transitions to the ductwork main can emit noise throughout the ductwork run. Additionally, include a sound attenuator from the VAV box manufacturer downstream of the VAV box to reduce the discharge noise from the unit.

3. Provide Collaboration Spaces

Even with soundmasking and controlled HVAC systems, there is only so much noise that can be tolerated by your office neighbor. If someone needs to conduct a three-hour conference call, soundmasking may not be sufficient. A major part of one recent office renovation included more meeting space so that colleagues could feel comfortable holding lengthy video conference calls and in-person meetings. Previously, the office had only three conference rooms; with the new renovation, six meeting rooms of various sizes and videoconferencing technology are available.

4. Maintain A Noise Barrier Between Workspaces

Even with the expectation to find a conference room for long phone calls, employees need to be able to conduct short phone conversations at their desks and not disturb their neighbors in the process. Completely open workspaces allow a direct speech path to people nearby, which is why some level of noise barrier is still needed to block speech transmission. One way to do that is to maintain relatively high partitions between offices by using glass for the top 13 inches of the office wall partition, blocking sound but allowing light through.

5. Reduce Noise Build-Up In Gathering Spaces

The renovated office mentioned earlier also includes a bright and colorful café area with comfortable seating. Adjacent to the workspace but separate enough to keep noise in check, the café is a perfect spot for colleagues to gather casually for lunch or impromptu meetings throughout the day. The café is the largest gathering space in the office. A key design goal was to reduce the overall noise build-up from the centrally located café so it would be acoustically comfortable and not transfer too much noise to surrounding working areas. The café includes highly-absorptive fiberglass ceiling panels directly over the eating area to reduce noise build-up.

6. Provide Sound Isolation Around Conference Spaces

Conference spaces that workers use for meetings and conference calls need to be well isolated from one another and from the open office areas so that activity noise does not bother others nearby. One approach is to use double or staggered-stud walls with batt-insulation in the stud cavity for partitions between conference rooms. In addition, conference room doors can be fully gasketed.

7. Use The Right Sound-Absorbing Products

Different ceiling tiles should be used for different purposes: highly absorptive fiberglass ceiling tiles above areas where groups congregate, and less absorbing but denser mineral fiber ceiling tiles above spaces that have mechanical equipment above. Glass fiber absorbs more sound than mineral fiber, but mineral fiber blocks more sound from passing through it than does glass fiber.

Some conference rooms are modest in size with flat parallel walls. This is a recipe for a phenomenon called flutter echo, where sound quickly reflects between the two walls, leaving an unpleasant pinging sound if you speak in the direction of one of the walls. This can be addressed by installing fabric wrapped panels on one of the parallel walls so that sound reflections in the horizontal plane are absorbed.

8. Address Sound Isolation In Private Offices

Consider giving employees who prefer a high-degree of acoustical privacy the option of working in a private office. Those offices should have a high degree of sound isolation as well — for example, drop bottom seals on the doors, and demising walls that extend to the deck with batt-insulation in the cavity.

9. To Have An Open Office, Have An Open Mind

When an organization has had the same office layout for many years, there can be trepidation by some people to change the office environment from both a workspace and acoustical standpoint. Acknowledging that acoustics do sound different in an open plan office, the key point that should be communicated to employees is that there is much to be gained with the new layout and it can still be acoustically successful with the right design.