A little less conversation
Perhaps the most obvious distraction to employees is the noise coming from the conversations of others. In a space with no acoustical control, sound waves from discussions ricochet and bounce back and forth between the ceiling and floor, allowing them to spread out farther and farther around the office. Even conversations taking place 3 or 6 m (10 or 20 ft) away can be distracting.
On the other side of that, it is important for employees to be able to have private conversations in certain situations. Just as much as one employee at his or her workstation does not want to overhear the conversation of a colleague, that colleague most likely does not want his or her words to be broadcast around the office.
While it is impossible to eliminate that sound in an open plan, the goal should be to make conversations unintelligible to someone working nearby. If the sound is deadened, blocked, or masked, it morphs into innocuous background noise and helps achieve a level of both focus and privacy.
The most effective method for minimizing the spread of those sound waves and reduce noise is to use sound-absorbing materials in the ceiling and floor. This prevents the sound from bouncing around the space. Using high-density fiberglass panels on the ceiling and floor assemblies with carpeting or sound-absorbing tiles can help limit the spread of sound.
The more absorptive the materials on the ceiling and floor, the greater amount of sound is controlled. As mentioned, design professionals can look for products with a high NRC—a rating of 0.70 is considered minimum performance in an office application.
Another important technique used in many offices is sound masking—the introduction of highly engineered sound at specific frequencies into the office environment. Such systems employ very specifically tuned devices that emit engineered sound in strategic places in the space. This has the effect of interrupting the spread of other sound without becoming a disruption itself. Used in conjunction with passive design strategies like an absorptive ceiling, sound masking can be very effective to manage sound.
Air up there
Another common complaint in office spaces comes from noise emanating from HVAC assemblies. The mechanical system has an extremely important role in the workings of a building, but seldom is much thought given to the disruptive sounds it can make.
Quiet air-handling unit (AHU) madels are available, so it is possible to design a less sonically invasive HVAC system for an office. It is something to consider with the entire building team upfront if an owner or designer wants to try to prevent an HVAC noise issue before it starts. In most cases, however, heating and cooling systems are designed to meet parameters that have nothing to do with sound, so owners and designers are left with managing the noise after the fact.
One very effective technique is to strategically place high-performing ceiling panels directly underneath the AHUs. The fiberglass panels discussed earlier are excellent at absorbing sound waves that collide with them, but actually have little ability to block sound going through them.
Insulated panels can achieve that sound blocking and stop excessive air-handling noise. One can look for products with a high CAC rating. Generally, above 35 is considered ‘above-average’ performance, but above 40 should be sought when possible.
Contain and control
Another acoustic challenge that must be dealt with in an office environment is the transmission of sound between rooms. Sound, much like water, will find any tiny passage through which to move. This means a theoretically ‘soundproof’ ceiling with a small gap of 0.1 per cent in a ceiling space can reduce sound performance by as much as 25 percent. For context, within a 100-m2 (1075-sf) ceiling, a vent of 0.1 m2 (1 sf) has this capacity.
Most offices use an open-plenum air system, which means the air is being pumped into the space and needs to return to the air-handling system to be heated or cooled. The penetrations needed to accomplish that in most cases would create an opening much larger than 0.1 per cent of the ceiling and likely compromise the room’s privacy. However, even in this case, there are things that can be done to help bring the sound performance back up to a more acceptable level.
For example, chimneys can be built over the air returns to deny sound an easy pathway. Insulation and products with high sound transmission class (STC) ratings can also be added around perimeter walls, and gaskets and thresholds can be applied to doorframes. While no single product or technique may be perfect on its own, a combination of components and strategies can deliver the desired results.
I am really interested in the sound masking techniques that you mention here. It is something that I never considered as a possibility. I would think that adding more sound would just add to the general noisiness of the office. So, when you say that these masking sounds are specially engineered, do you mean that they are engineered to both disrupt sound and to be at frequencies that people can’t hear?
I loved reading about your rule of three and how office acoustics should absorb, block, and cover sound. I can see how this would be important, especially in a call-center setting where there is lots of phone conversation. I would imagine that an acoustic consulting company could help you make good design choices in this area.