- By Steven Thorburn
- May 1st, 2013
The acoustical environment inside our buildings has gotten worse over the last few years, according to the 2009 International Facility Management Association (IFMA) workplace satisfaction study. Unlike the 1991, 1997 and 2004 studies, that had noise as number 10 in the list of top 10 complaints (behind other complaints like temperature and cleanliness), noise has risen to number 5 on the list — still behind 4 air quality items. The 2009 list is as follows:
- It’s too cool
- It’s too hot
- Bad air quality
- Too drafty
- Noise level/too noisy
The only change in the last few years is the growth of LEED and its design requirements, which, in part, promote daylighting and green materials. Further, the General Services Administration has reported that absenteeism is up in buildings that are designed to LEED standards. It seems that the greening of our work places, schools included, is not having the positive impact on our buildings we hoped it would. So why is this and what can we do to turn around the negative acoustical reviews coming from the newly developed work/learning environments?
The big three
To make improvements, three key elements in the acoustical design of any space must be reviewed.
First, and some say the most important, is room acoustics. This refers to how the space sounds — an analogy would be interior design for the ear. Reverberation, echoes, diffusion and the effect of room finishes on sound all fall under the umbrella of room acoustics.
Sound isolation, or how sound or noise is contained in a room, closely follows room acoustics. Sometimes we may be working to contain noise in an equipment room so it does not impact the adjacent space. At other times, we may be keeping exterior noise out of a quiet space like a reading room. Sound isolation has been referred to as the “bones” of the building. Once these bones are in place, they are very hard and usually costly to modify.
The third aspect of the acoustical environment is the noise generated by the building systems. Mechanical noise control includes the heating and cooling systems (i.e. items 1 through 4 of the IFMA Workplace complaint study), as well as the pumping systems and any other systems that circulate items within the lungs and arteries of the building.
So, what besides the adoption of the formal process of sustainable design (LEED) has changed in the last few years, and what can we do about it in the future? The biggest impact we have seen is in the introduction of truly “open work spaces” and “collaborative learning areas.” Yes, group think is great; we love it. However, the activity of one group creates a distraction for others, which is not helpful.
For schools it could feel like the difference between the cafeteria at noon, with the cliques around the tables, and the library where scholarly learning was expected. In our offices, we have moved from cubes to clusters of tables. In the cube environment, the short walls did provide some protection from the person’s voice on the other side of the cube wall when they were on the phone.
To provide some level of speech privacy between work spaces, we need to break the “your mouth to my ear” path. When there is a direct path for sound, with nothing interfering with it, there is no privacy. If we add a 60-inch partition between us, it really helps. Without some type of barrier, there is no chance for any type of speech privacy.
The same is true for our classrooms; we need the walls or alcoves to provide some privacy to the group at work. Open cluster spaces, where two or three classes share a larger common gathering space for presentations or assemblies, need easy and effective ways for teachers to close those spaces off when the students retreat to their home rooms.
Walls have been removed from many of the designs to promote better daylighting into spaces. This is great, but if daylighting is really required on all four sides of a personal work space, what about glass in the partitions? While it is not soft and absorptive, it still helps get daylight into the interior spaces while blocking some of the sound. It is all about the speech privacy — without barriers, speech privacy will not exist.
Dealing with background sound
While barriers are one part of the speech privacy equation, the other is background noise. While we do not want too much background noise, it does need to be in place. When natural ventilation and thermal masses are used to heat and cool our buildings, the noise associated with the building’s circulating systems are much quieter. Natural ventilation, plus no partitions makes for some very intimate work groups where everybody overhears the phone call or conversation about family issues and weekend plans.
One solution to the quiet background noise levels in a space could be sound masking. Sound masking is a great tool for the acoustical design of a space. While it uses loudspeakers, it is not a sound system and should not be thought of as such. You do not want a sound masking system unless it has been carefully designed and coordinated with the rest of the building systems, including walls, ductwork, light fixtures, anything in or above the ceiling.
There are many predesigned systems on the market right now. Some work better than others. We have yet to be satisfied with the installation from one from a “turnkey” vendor, but that is another article. The key to a successful sound masking system is to have enough loudspeakers whose sound can be adjusted to blend in with the natural sounds of the building heating and cooling systems. The systems must also provide nonintrusive uniform background sound level throughout the space, which helps cover sound or noises that were once audible because of the quiet background noise levels associated with natural ventilation.
On the other extreme, we have seen mechanical systems become too noisy. This is due to one of two things. The first, is the desire to remove acoustical liner from the ductwork. Acoustical duct liner is a form of insulation that is installed inside the duct. The acoustical duct liner is treated so it will not flake or disintegrate as the air blows over it; the surface treatment allows it to reduce the noise from the fan. Without this material, noise from duct systems is much louder and can be distracting in its own right.
The concern with the duct liner is the buildup of mold. Here is where “the rest of the story” is helpful. Acoustical duct liner does not and cannot support the growth of mold. It is the dust inside the duct system (that is there with or without the liner) that supports the growth of mold. So, it is back to the “it’s dirty” issue — one of those original top 10 complaints.
The last “it is too loud” issue is heat pump air conditioners. These are becoming common in many schools. They are standalone units, so each room is individually controlled. But each of them have a compressor. If you have an air conditioner for your home that has an outside unit, you know the noisy part is the compressor.
How do you think your workspace or classroom would sound with that unit in the room? These units are becoming popular because they work well with geothermal energy. They would work even better, acoustically, with a central boiler and chiller system that provides hot and cold water to the unit as needed.
This brings us back, full circle, to room acoustics. In most spaces, we are looking to minimize the buildup of occupant noise, either work or play, so the room you are in does not sound too harsh or reverberant. In the past, this was done with acoustical treatments on the walls, some form of acoustical ceiling system, office partitions, etc.
LEED design requirements for green materials and daylighting have placed a number of compromises on the acoustical design. Historically, fiberglass batting compressed into a semi-ridged board was one of the most cost-efficient acoustical treatments in our acoustical finish pallet. The problem with fiberglass, which comes from sand (a very sustainable material), is that the process of turning sand into fiberglass is not sustainable.
Early in the LEED process there were not a lot of acoustically green finishes that could be used. This is changing as recycled content and new substrates for acoustical finishes are being introduced daily. By treating the walls and ceilings with these newer components, we can create environments that are not as fatiguing and acoustically hard and stark as those spaces that were forced upon us by the early adoption of “green” finishes.
So what is the solution to IEQ factors, acoustics, daylighting, thermal control, air quality and the effect each of these places on the other? The short answer is proper planning and coordination. When we are part of a team who truly designs a project with sustainability, instead of a checklist, in mind, then the project can be a success. When a project is designed only for points, or the full impact of the design goals are not coordinated, we have a newly built environment that is noisy and potentially creates problems like absenteeism.
Steve Thorburn, PE, LEED-AP, is the engineering/design principal at Thorburn Associates Inc., which has offices in San Francisco, Burbank, Orlando, Charlotte and Raleigh-Durham. He can be reached at firstname.lastname@example.org.