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Sound is Golden

Unlocking the secret to effective workplace soundscaping

BY NIKLAS MOELLER

Sound greatly affects our experience of the built environment, including how we feel and behave within it. As appreciation of this fact grows, so does interest in actively managing the workplace soundscape to promote health, well-being and productivity.

As someone who has spent decades in the field of acoustics and often witnessed this key indoor environmental quality (IEQ) parameter pushed to the sidelines in favor of a particular visual aesthetic or kicked to the curb by budgetary constraints, I am relieved to see occupants’ auditory needs finally getting the attention they deserve. But rather than talking about the types of sounds generating all the buzz, I need to address the topic of noise, as well as an acoustical quality many people assume is its opposite, but is often its partner in crime: silence.

DECIBELS

Decibels (dB) are used to measure sound levels and intensity. Because the dB scale is logarithmic, every +10dB represents a 10-fold increase in sound energy. The human brain interprets this as twice as loud. A +20 dB would be a 100-fold increase of loudness.

QUIETEST SOUND EVER RECORDED

Microsoft's anechoic chamber, quieter than the thermal noise of air molecules colliding

FAINT

Threshold of hearing — the quietest sound an average human can hear

Normal breathing

SOFT

A quiet whisper or rustling leaves

PARTNERS IN CRIME

While the decibel levels known to cause hearing damage are not typically a concern within an office, evidence of the non-auditory health (e.g., increased stress hormones, heartrate and blood pressure) and productivity impacts of the lower-level noises routinely encountered within these environments is mounting. Many studies identify intermittent and impulsive noises as the main culprits; basically, relatively silent periods punctuated by random, unpredictable noises that rapidly increase and decrease in level.

Whether occupants are trying to concentrate or taking a moment to relax, noise that starts and stops causes more physiological and psychological distress than either steady-state sound at the same A-weighted, equivalent continuous level or quieter sounds closer to the low ambient levels characteristic of the built environment. Humans are hardwired to respond to such acoustical disruptions because they represent a potential source of danger. However, in this case, it is not a twig snapping as a predator approaches, but people talking, walking, typing, a door closing, HVAC turning on, a truck driving by and so on.

In between such noises, occupants experience moments of relative silence. Although many people consider noise and silence opposite ends of an acoustical spectrum, when it comes to disturbing occupants, they are, in fact, related. We perceive both the noises and the silences as changes in our acoustic conditions. The greater the difference between them, the more we notice it. And the more frequently such changes occur, the more often we are startled, interrupted, annoyed… the list goes on.

Typically ignored during acoustical planning — or even placed on a pedestal — there are more reasons why silence deserves attention when talking about acoustic problems. For example, the longer it continues, the more uncomfortable it can become. Studies reveal occupants are concerned about their level of acoustical privacy in too quiet spaces. Due to feelings of exposure, they tend to whisper and rely more heavily on electronic communication. These are just a few of the reasons why researchers conclude that an environment that seems too quiet is just as tension inducing as one perceived as too loud.

Supporting focus is critical to workplace experience, but facility effectiveness in this regard has plunged to the lowest level since 2008. Occupant-generated noise is the most significant source of disruption and because of its complex nature, building professionals are not easily able to account for it during design, unless they implement masking sound.

As one can surmise from the above, both noise and silence have serious implications for three goals occupants consistently identify as top workplace priorities: speech privacy, focus and collaboration. Studies show that higher levels of perceived office noise are also linked to more negative moods, which can, in turn, be tied to greater employee withdrawal and task conflict, as well as to people trying to mark their physical territories.

So, when talking about strategically adding sound to the built environment to support occupants, it is clear the first step is to address these extremes. However, there is a tendency to target only the first part of this equation — the noise — and particularly its ‘loudness,’ which is usually approached in terms of its decibel level. After taking steps to reduce it using absorptive treatments and blocking strategies, organizations are frequently surprised when noise remains a problem. The typical conclusion is the offending sounds must be unusually loud or the materials used are somehow insufficient or deficient. But the key is human perception.

A quiet library

MODERATE

Moderate rainfall

Normal conversation in an office or background music

LOUD

Loud talking across a room or a vacuum cleaner

Alarm clocks

VERY LOUD

PERCEPTION IS KEY

Although offices are not plagued by rock-concert-level noises followed by anechoic-chamber-level silences, their minimum background sound level is typically similar to that of a library. Within such an environment, occupants experience many sounds as loud and impulsive, even when their decibel level is quite low. Noises can easily and often be heard and, therefore, people are easily and often disrupted. The lack of background sound makes any noise, including conversation, seem that much louder.

Fortunately, the flipside of this coin is that human beings can perceive a space with a higher continuous background sound level as quieter.

credit: KR Moeller Associates Ltd.

A facility’s unmasked ambient level (in green, left-hand side) is typically too low to cover noises (in red). When a masking sound provides an effective, comfortable level (in green, right-hand side), it either completely covers noises or reduces their disruptive impact by minimizing the difference between the noise floor (i.e. the lowest level of sound in the space, which is now provided by the masking sound) and the loudest noises in the space.

The question then becomes: what type of sound is best equipped to provide this background level? While the ability of sound to move, sooth and motivate us has many talking about the role music, birdsong and binaural beats can play within the workplace, striking the right balance between noise and silence involves establishing a comfortable and effective sonic base using a particular type of sound we rarely remark upon: random, non-informational sound spread over a broad frequency range.

Because we are not typically conscious of this type of sound unless it reaches a level that interferes with sounds we want to hear (e.g., a conversational partner within the hum of a busy restaurant), many members of the general public and even the facility management community are not aware of the essential role it plays in creating effective indoor acoustics — an oversight compounded by the belief buildings can be constructed in a way that reduces noise and conversation to the point we will not hear them.

Of course, introducing this type of sound to the built environment presents both the need and opportunity to perfect it as much as possible; in other words, to ensure it meets our specific requirements as human beings.

Studies show the ideal level for a comfortable and functional open workplace is 45 to 50 dBA. Levels higher than 55 dBA are irritating and raise stress levels, while levels below 45 dBA also cause stress because it is simply too quiet to prevent distraction. However, many other factors also influence whether we experience sounds positively or negatively, including their spectral (e.g., rumbly, hissy), temporal (e.g., constant, fluctuating) and spatial (e.g., adjacent, throughout a space) characteristics.

So, although distributing a noninformational background sound might not seem like a complex task, to be successful, it actually has to tick a lot of boxes.

A lawnmower, hair dryer, power tools or a passing motorcycle

MP3 players at full volume

Car horns, sporting events or concerts

UNCOMFORTABLE

Jet planes during takeoff

PAINFUL & DANGEROUS

Jackhammers and emergency sirens

Fireworks and gunshots

GETTING IT RIGHT

Because it is meant to improve comfort and minimize the amount of change occupants experience in their acoustical conditions — not add to them — the masking sound cannot fluctuate in volume or spectrum, contain certain frequencies at too high or low a level, or include perceptible patterns.

The electronics generating the masking sound as well as the physical positioning and capabilities of the loudspeakers distributing it bear some of the burden of ‘getting it right,’ but just like any other sound produced within the space, it is subject to physical forces exerted by facility’s interior, including the materials used and items placed within it.

To ensure the masking sound that ultimately exists in the space actually hits all the right notes, a trained technician should use a professional-grade (i.e., Class 1) sound level meter to measure its level and frequencies post-installation and adjust each zone’s settings as needed. Each zone should only cover a small area, maximizing the technician’s ability to finely adjust the sound to consistently meet the target masking level and spectrum across all treated spaces.

The above-noted requirements are the reasons why incidental, unpredictable sounds (e.g., the noise generated by HVAC equipment) and informational, variable sounds (e.g., lapping waves, chirping birds, any genre of music) cannot be relied on to provide the sonic base for a facility, even if they may — erratically, temporarily and to some unmeasurable degree — cover up noise and speech. The former are merely byproducts of a process completely unrelated to acoustics, and the latter not only exhibit volatile levels and frequencies, but are subject to personal preference and also trigger (potentially negative) thoughts, feelings and emotions.

A sound masking system consists of a series of loudspeakers installed in the ceiling, as well as electronics to control their output. However, the product is not the equipment, but the sound itself. For that sound to reliably provide the desired masking effect, it must be expertly tuned to meet a specific spectrum within all treated areas.

credit: Vincent Lions

LOUDEST SOUND EVER RECORDED

the 1883 eruption of Krakatoa, clearly heard 3,000 miles (4,800 km) away

credit: KR Moeller Associates Ltd.

Many people assume a facility’s acoustic conditions are fairly uniform throughout; however, they actually vary considerably, as shown by these ambient measurements (inset graph) taken within 26 locations in an unmasked, mostly open-plan office space, versus the same area (main graph) when treated with properly tuned masking sound.

This last quality makes writing about masking sound in an article about soundscaping challenging. On the one hand, its inclusion makes sense; after all, it is a designed sound introduced to influence occupants’ auditory experience within the built environment. On the other hand, there is a tendency to get caught up in — or rather, captivated and inspired by — the ability of sound to affect our emotions. To be clear, this is not the role of masking.

In fact, in order to do its job properly, the sound must essentially disappear from occupants’ consciousness. However, few people are aware of what such an implementation involves — specifics further obscured by indiscriminate use of terms like “white noise,” social media posts touting the virtues of various sonic hues (e.g., pink, violet) and studies that do not provide details regarding the masking spectrum, levels and/or type of system tested, leading readers (and even some researchers) to flawed conclusions. Omitting specifics also reinforces the erroneous notion that all sound masking systems produce roughly the same sound and results.

THE “C” IN ABC

When formulating a soundscaping plan, it is also crucial not to lose sight of the fact that masking sound is one of the three pillars of effective acoustical design: the “C” (cover) in the “ABC Rule.”

As such, this sound is not only a subjective parameter (i.e., occupants will perceive treated areas as quieter), but a critical objective (i.e., measurable) feature of the acoustical environment. When expertly tuned to a specific level and spectrum (e.g., the NRC Optimum Masking Spectrum), it not only provides a reliable sonic foundation for key occupant needs and workplace activities, but for speech privacy calculation and, hence, improved specification and more cost-efficient selection of the materials used for “A” (absorb) and “B” (block).

credit: KR Moeller Associates Ltd.

The masking spectrum or ‘curve’ should be specified by an acoustician or supplied by an independent third party such as the National Research Council (shown here to 5000 Hz). Delivery can only be considered complete upon reporting measured conformity within specified tolerances, preferably using testing procedures that meet or exceed ASTM E1573-22, Standard Test Method for Measurement and Reporting of Masking Sound Levels Using A-Weighted and One-Third-Octave-Band Sound Pressure Levels.

Once this strong acoustical foundation is laid, one can strategically add sound and music in smaller, select areas—such as reception, social and wellness spaces — to achieve specific aims. Use of masking does not negate their addition. In fact, a professional-grade system can simultaneously distribute other sounds over the same loudspeakers. Together with “A” and “B,” masking also helps prevent those other sounds from being heard in areas where their effect is not required or desired.

FOCUS ON FOCUS

Of course, the majority of a facility should be acoustically supportive of the majority of the work done within it. Office occupants spend most of their time on focus work, which they also identify as the most strategically important aspect of their jobs. They also frequently shift between concentrating on a task and collaborating with others, which typically involves just a quick, spontaneous discussion with someone at their workspace, online or on the phone. With an acoustically well-designed space, those tasks are supported and most of a person’s day can be spent in one location, without feeling the need to escape elsewhere. Moving is a choice; they are seeking a change when actually needed, not fleeing a poor environment.

IN CONCLUSION

It is great to see increasing interest in crafting occupants’ aural experience within the built environment — one that facilitates concentration, socialization, tranquility, and aesthetic pleasure rather than (albeit inadvertently) causing anxiety, isolation and frustration. When formulating an acoustical plan, it is key to consider how the objective and subjective parameters inform one another and contribute to occupants’ experience. As Eduardo Souza points out in What Is Soundscape and What Does It Have to Do with Architecture (2021), environmental noise control and soundscape are not incompatible approaches. On the contrary, they are complementary, because occupants’ holistic assessment of the acoustical environment is influenced by both. Because masking sound straddles both domains, it requires particularly careful specification and implementation.

DECIBELS

QUIETEST SOUND EVER RECORDED

Microsoft's anechoic chamber, quieter than the thermal noise of air molecules colliding

FAINT

Threshold of hearing — the quietest sound an average human can hear

Normal breathing

SOFT

A quiet whisper or rustling leaves

A quiet library

MODERATE

Moderate rainfall

Normal conversation in an office, or background music

LOUD

Loud talking across a room, or a vacuum cleaner

Alarm clocks

VERY LOUD

A lawnmower, hair dryer, power tools, or a passing motorcycle

MP3 players at full volume

Car horns, sporting events, or concerts

UNCOMFORTABLE

Jet planes during takeoff

PAINFUL & DANGEROUS

Jackhammers and emergency sirens

A lawnmower, hair dryer, power toolFireworks and gunshotss, or a passing motorcycle

LOUDEST SOUND EVER RECORDED

the 1883 eruption of Krakatoa, clearly heard 3,000 miles (4,800 km) away