THE ABC RULE

The traditional message is that creating an effective acoustic environment relies on three strategies: A, B and C, which stand for absorb, block, and cover. However, there are a few letters missing from this alphabet.

‘R’ is for Reduce

Reduction is a key element of acoustical design. It addresses the noises in your space that simply do not need to be there. Think of loud and endless ringtones, speaker phones, office or other equipment out in the open, improperly designed or balanced ventilation, squeaky filing cabinets, and so on. Sometimes these sounds can be reduced or even eliminated by the simplest interventions.

‘E’ is for Etiquette

Etiquette is a subset of the reduction strategy that involves our ability to behave in an ‘acoustically sensitive’ manner. There are habits we all fall into at one point or another that we should be more conscious of because they disturb others: tapping your pen, having an impromptu meeting over someone’s workstation, talking to someone across the hall through your open doorways, leaving your phone at an emergency evacuation volume and giving yourself a dozen rings to answer it.

‘D’ is for Density

Density has a critical impact on acoustics and our ability to control them, but it is rarely included in the ABC discussion. The fact is, the tighter we space people, the tougher it is to design spaces that work well acoustically. In open plans, the average number of square feet per person has dropped dramatically in recent years. There’s not only less distance between people—meaning any noises they generate reach more listeners at higher volume—but many more people within the same area, producing more noise overall. Organizations placing more people into a smaller space need to take greater care with acoustical design, but the trend seems to be not only to increase density, but to systematically eliminate most methods of acoustical control. Given that people usually cost 10 times more than the building and its maintenance combined, it is worth questioning if this is really the right course of action.

‘A’ is for Absorb

Absorptive materials reduce echo and overall noise levels by decreasing the energy of sounds that would otherwise bounce off hard surfaces and back into your space. Because they only work on sounds that reflect off their surface, they typically have greater influence on noises created farther away from you. In other words, absorption requires some distance to take effect and cannot control noises directly transmitted between nearby occupants.

‘B’ is for Block

Blocking works at shorter distances because its effect is immediate. However, walls, windows and doors will not completely stop noise transferring from one side to the other. Rather, they will lower their volume as they pass through them. Though primarily used in the construction of closed rooms, blocking is also a relevant technique for open plans, unless partitions are below seated head height, nullifying their acoustical value. Layout can also be used to isolate noise. For example, the originators of the open-plan concept, the Quickborner Team, used break zones that were separated from workgroups, offering an inviting space in which to come together for ad hoc meetings, fostering interaction while not disturbing those in surrounding areas.

‘C’ is for Cover

Because many believe that noise is only truly under control when a space is as silent as possible, they tend to try to enlist the above strategies in pursuit of the old adage ‘silence is golden.’ However, just as with light and temperature, there is actually a comfort zone for sound—and it is not zero. If a facility’s background sound level is too low, conversations can easily be heard from a distance and occupants are even disturbed by lower-level noises.

To ensure the space has an appropriate minimum background level and spectrum conducive to speech privacy at all times, use a sound masking system. This technology uses a system of loudspeakers to distribute a comfortable sound similar to softly blowing air, covering up conversations and noises occurring at a distance and reducing the intelligibility and disruptive effect of those happening closer to you, making them less distracting. Sound masking is the only acoustical technology that can accurately control the background sound by adjusting both the volume and frequency within your space. When properly implemented, it is highly effective at covering speech and noise and, in the case of loud noises, diminishing their impact on occupants by reducing the amount of change between baseline and peak volumes.

Many assume that providing effective acoustics is a single design requirement. Unfortunately, this notion leads to the misconception that any acoustical element can yield the desired results on its own. For example, one might install an acoustical ceiling and believe their job is done. But a well-performing space uses all of the described strategies—reducing, absorbing, blocking, and covering—because each one performs a unique role in the final result.

In fact, it is even more effective if you turn the traditional ‘ABC Rule’ on its head and start with ‘C.’ By using sound masking to define and, therefore, know exactly what the background sound level and spectrum will be anywhere in the facility, you can more accurately specify the remaining materials, such as the walls’ STC rating. That can also reduce costs by lowering STC requirements and allowing walls to be built to the suspended ceiling rather than to the deck. Once the space is complete, if the walls’ real-world performance doesn’t live up to their lab-tested results, you can increase the masking level (within comfortable limits) to make up for that deficiency—a flexibility uniquely afforded by this technology.