{"id":118721,"date":"2020-08-28T10:22:52","date_gmt":"2020-08-28T14:22:52","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=118721"},"modified":"2020-08-26T19:30:22","modified_gmt":"2020-08-26T23:30:22","slug":"rethinking-acoustics-understanding-silence-and-quiet-in-the-built-environment","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/rethinking-acoustics-understanding-silence-and-quiet-in-the-built-environment\/","title":{"rendered":"Rethinking acoustics: Understanding silence and quiet in the built environment"},"content":{"rendered":"<p><strong>by Viken Koukounian, PhD, P.Eng., and Niklas Moeller<\/strong><\/p>\n<figure id=\"attachment_118730\" aria-describedby=\"caption-attachment-118730\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Opener_Masking.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-118730\" src=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Opener_Masking-300x221.jpg\" alt=\"Photo \u00a9 Adrien Williams\" width=\"300\" height=\"221\" srcset=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Opener_Masking-300x221.jpg 300w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Opener_Masking-500x368.jpg 500w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Opener_Masking-768x565.jpg 768w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Opener_Masking.jpg 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-118730\" class=\"wp-caption-text\"><em><span style=\"font-size: 10pt; font-family: arial, helvetica, sans-serif;\">Photo \u00a9 Adrien Williams<\/span><\/em><\/figcaption><\/figure>\n<p>Background sound is an intrinsic part of our daily experiences, yet its fundamental role within the built environment can often be overlooked. This omission is most apparent in noise mitigation projects where the building professionals exclusively rely on the absorptive materials and partition assemblies and, hence, performance indicators such as the noise reduction coefficient (NRC), sound transmission class (STC), and the noise isolation class (NIC)\u2014none of which provide insight into occupant experience of sound in that space.<\/p>\n<p>In other words, this singular focus on objective physical acoustics fails to consider the human (psychological and physiological) component\u2014specifically, that occupants can perceive a space with a higher controlled level and spectrum of background sound as \u2018quiet.\u2019 As a result, organizations forgo opportunities to significantly improve acoustical privacy and satisfaction and realize labor and material savings engendered by a more holistic approach to design.<\/p>\n<p>Revisiting the acoustical lexicon and refining use of terms such as \u2018noise,\u2019 \u2018sound,\u2019 \u2018silence,\u2019 and \u2018quiet\u2019 allows for a more nuanced discussion of occupants\u2019 needs and expectations, and fosters opportunities to improve the design of the built environment through a proportional exchange between the measure of attenuation and the control of background sound.<\/p>\n<p><strong>Architectural acoustics<\/strong><\/p>\n<figure id=\"attachment_118722\" aria-describedby=\"caption-attachment-118722\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_1_Masking.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-118722\" src=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_1_Masking-300x209.jpg\" alt=\"The ABCs of architectural acoustical design involve the use of a variety of methods and materials to absorb, block, and cover noise, with the intention of creating an environment that is more comfortable for building occupants and supportive of their tasks. Images courtesy KR Moeller Associates Ltd.\" width=\"300\" height=\"209\" srcset=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_1_Masking-300x209.jpg 300w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_1_Masking-500x348.jpg 500w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_1_Masking-768x534.jpg 768w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_1_Masking.jpg 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-118722\" class=\"wp-caption-text\"><span style=\"font-size: 10pt; font-family: arial, helvetica, sans-serif;\">The ABCs of architectural acoustical design involve the use of a variety of methods and materials to absorb, block, and cover noise, with the intention of creating an environment that is more comfortable for building occupants and supportive of their tasks.<\/span><br \/><em><span style=\"font-size: 10pt; font-family: arial, helvetica, sans-serif;\">Images courtesy KR Moeller Associates Ltd.<\/span><\/em><\/figcaption><\/figure>\n<p>The study of acoustics dates back thousands of years. Given its roots are deeply entangled with those of mathematics and physics, it is unsurprising that the typical approach to acoustic investigation is quantitative. Consideration of \u2018soft\u2019 parameters (<em>i.e.<\/em> subjective and descriptive) is relatively scarce until the last century.<\/p>\n<p>Interest in evaluating human response to acoustics gained momentum in the 1900s, with the rise of architectural acoustics, also known as building or room acoustics. Notably, contributions from Bell Telephone Laboratories, Bolt Beranek &amp; Newman Inc., and others have formed the foundation for psychoacoustics, a branch of psychology focusing on the perception of sound and its physiological effects. Research examined occupants\u2019 assessment of the intruding noise (<em>e.g.<\/em> annoyance, distraction, inadequate acoustical privacy) in their environment.<\/p>\n<p>Motivated by the need to develop an objective approach to effective architectural acoustical design, renowned acoustician William Cavanaugh et al. published <em>Speech Privacy in Buildings<\/em> (1962), asserting neither acoustical privacy nor acoustical satisfaction could be guaranteed by any single design parameter. This work was instrumental in what later became to be understood as the \u2018ABCs\u2019 of architectural acoustical design:<\/p>\n<ul>\n<li>\u2018A\u2019 is for \u2018absorb,\u2019 which involves providing sufficient, but not excessive, absorptive materials, in order to reduce the amount of sound energy within the space;<\/li>\n<li>\u2018B\u2019 is for \u2018block,\u2019 which involves providing sufficient isolation within the space; and<\/li>\n<li>\u2018C\u2019 is for \u2018cover\u2019\u2014or one might say \u2018control\u2019\u2014which involves management of the spectral distribution and overall level of background sound within the space, with the intention of masking speech and noise (rather than, for example, adding biophilic sounds, with the intention of increasing the building occupant\u2019s connectivity with the natural environment).<\/li>\n<\/ul>\n<p>Although the authors of <em>Speech Privacy in Buildings<\/em> appreciated the importance of background sound, they tended to use the words \u2018noise\u2019 and \u2018sound\u2019 interchangeably\u2014a practice deeply rooted in historical habits, and continues today.<!--nextpage--><\/p>\n<figure id=\"attachment_118724\" aria-describedby=\"caption-attachment-118724\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_3_Masking.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-118724\" src=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_3_Masking-300x162.jpg\" alt=\"Figure 1: Many people assume acoustic conditions are uniform throughout a facility, but without the use of a properly designed and commissioned sound masking system, it is never the case. In this example of an unmasked space\u2014one floor, primarily consisting of open plan\u2014the \u2018natural\u2019 background levels of the unoccupied space vary considerably between the 26 zones in which ambient measurements were taken.\" width=\"300\" height=\"162\" srcset=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_3_Masking-300x162.jpg 300w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_3_Masking-500x270.jpg 500w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_3_Masking-768x415.jpg 768w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_3_Masking.jpg 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-118724\" class=\"wp-caption-text\"><span style=\"font-size: 10pt; font-family: arial, helvetica, sans-serif;\"><strong>Figure 1:<\/strong> Many people assume acoustic conditions are uniform throughout a facility, but without the use of a properly designed and commissioned sound masking system, it is never the case. In this example of an unmasked space\u2014one floor, primarily consisting of open plan\u2014the \u2018natural\u2019 background levels of the unoccupied space vary considerably between the 26 zones in which ambient measurements were taken.<\/span><\/figcaption><\/figure>\n<p><em>Signal-to-noise ratio<\/em><\/p>\n<p>Initially, acousticians were primarily interested in evaluating the conditions needed to clearly hear sounds. They determined the critical factor was the level of the desired sound\u2014called the \u2018signal\u2019\u2014relative to the background sound present in the listener\u2019s location. In most cases, the background sound used during testing was broadband and did not contain information (<em>i.e.<\/em> noticeable patterns, such as running speech, nature sounds, traffic noise). However, it was termed \u2018noise\u2019 because it could potentially interfere with the intelligibility of the desired sound. The ratio of the desired sound to background sound was termed the signal-to-noise ratio.<\/p>\n<p>In the above case, the \u2018signal\u2019 is the sound one wants to hear because it conveys useful information, while the \u2018noise\u2019 is an unwanted input challenging one\u2019s ability to clearly hear the desired sound. As acousticians developed an understanding of background sound as a fundamental component of speech privacy, the methodology\u2014and the terminology\u2014remained the same. Hence, the word \u2018noise\u2019 continued to be used to describe the background\u2014or, in this case, the masking\u2014sound, despite the fact it was now being viewed in a positive light.<\/p>\n<p>Understandably, the term \u2018noise\u2019 can cause confusion when the \u2018signal\u2019 is the unwanted sound and the \u2018noise\u2019 is actually the desired background sound. Meanwhile, the general public tends to use \u2018noise\u2019 as a non-technical descriptive word, typically when relating negative acoustical experiences\u2014ones that are uncomfortable, annoying, disturbing, or even painful.<\/p>\n<p>To highlight the difference in the way in which \u2018noise\u2019 is used, consider an individual working in an office, who complains about \u2018noise\u2019 to a colleague. There are several sources of sound within the space (exterior traffic, fan, and a radio playing music), but the source bothering the individual is a heated debate taking place in the meeting room adjacent to their workspace. In this scenario, the terms are defined in this way:<\/p>\n<ul>\n<li><strong>sound<\/strong> \u2013 there are four sound sources identified in the workplace.<\/li>\n<li><strong>signal<\/strong> \u2013 the noise capturing the individual\u2019s attention<br \/>\n(<em>i.e.<\/em> the debate) and, hence, the cause of their complaint.<\/li>\n<li><strong>noise<\/strong> \u2013 the individual uses the word \u2018noise\u2019 to describe the debate. However, if the term is used in a technical assessment of this environment, the \u2018noise\u2019 is actually the combination of all other sound sources (<em>i.e.<\/em> the traffic, fan, and radio), excluding the signal (<em>i.e.<\/em> the debate).<\/li>\n<\/ul>\n<p>Technical use of the word \u2018noise\u2019 requires a \u2018signal.\u2019 In this scenario, noise accounts for the combination of sounds (<em>i.e.<\/em> it considers everything that is not the signal), while the signal only considers the source of the sound that is of interest.<\/p>\n<p><strong>The human factor<\/strong><\/p>\n<p>What turns a \u2018sound\u2019 into a \u2018noise\u2019 in the common vernacular? Humans demonstrate remarkable tolerance to sound and are only susceptible to its disruptions when they become aware of it\u2014typically when the level of sound is too high, its qualities are unbalanced (<em>e.g.<\/em> it is too \u2018hissy\u2019 or \u2018rumbly\u2019), or it presents with temporal instability of its dynamic range (<em>i.e.<\/em> the change and\/or rate of change in sound level over time).<\/p>\n<p><em>Context<\/em><\/p>\n<p>A person\u2019s assessment of sound generally depends on personal preferences and expectations for the occupied environment, as well as the activity in which they are engaged. For instance, consider a conversation at \u2018normal level\u2019 in two environments: a library and a busy restaurant. In the former, the nearby occupants engrossed in a task requiring concentration are likely to find the conversation too loud, annoying, and disruptive. In the latter, the level of conversation may not be sufficiently loud to allow for clear communication. Expectations are based on an understanding of the purpose of the space and the task at hand.<\/p>\n<p><em>Content<\/em><\/p>\n<p>One\u2019s description of sound tends to focus on two main properties: level (often referred to as volume) and spectral distribution. A \u2018hissy\u2019 or \u2018screechy\u2019 sound is one that has a lot of high frequency information (<em>e.g.<\/em> a young child screaming). A \u2018bassy\u2019 or \u2018rumbly\u2019 sound is one with a lot of low frequency information (<em>e.g.<\/em> a lion roaring). A space without a balanced sound spectrum can sound worse than one with a higher sound level, but with a balanced spectrum.<\/p>\n<p><em>Cover<\/em><\/p>\n<p>The human experience is also determined by the space\u2019s background sound level, which is considered to be the collection of all (ambient) sounds within it. Often, a room is too \u2018silent\u2019 (<em>i.e.<\/em> its ambient level is too low) and a source of sound becomes uncomfortable (<em>e.g.<\/em> a clock ticking, cars driving by, people talking, lights humming). In these cases, the \u2018signal\u2019 is disturbing because its level is higher than the background sound. The disruptive impact of these annoying noises can be lessened by reducing the signal-to-noise ratio, which is achieved by raising the background sound level. In some cases, it is possible to raise the background sound level sufficiently to completely cover up these unwanted sounds.<!--nextpage--><\/p>\n<figure id=\"attachment_118725\" aria-describedby=\"caption-attachment-118725\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_4_Masking.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-118725\" src=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_4_Masking-300x162.jpg\" alt=\"Figure 2: These inconsistencies can be addressed using a sound masking system\u2014the only acoustical treatment that can accurately control the background sound level within a facility. Here, one can see the difference when masking sound is applied and tuned so that it consistently meets the noise reduction coefficient (NRC) curve within each zone to ensure uniformity of acoustic conditions throughout the space. The acoustically consistent environment is more comfortable\u2014or \u2018quiet\u2019\u2014for occupants.\" width=\"300\" height=\"162\" srcset=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_4_Masking-300x162.jpg 300w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_4_Masking-500x270.jpg 500w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_4_Masking-768x415.jpg 768w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_4_Masking.jpg 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-118725\" class=\"wp-caption-text\"><span style=\"font-size: 10pt; font-family: arial, helvetica, sans-serif;\"><strong>Figure 2:<\/strong> These inconsistencies can be addressed using a sound masking system\u2014the only acoustical treatment that can accurately control the background sound level within a facility. Here, one can see the difference when masking sound is applied and tuned so that it consistently meets the noise reduction coefficient (NRC) curve within each zone to ensure uniformity of acoustic conditions throughout the space. The acoustically consistent environment is more comfortable\u2014or \u2018quiet\u2019\u2014for occupants.<\/span><\/figcaption><\/figure>\n<p><strong>The need for control<\/strong><\/p>\n<p>Given both the scientific and human factors, one can readily see there are advantages to controlling background sound, rather than accepting large variations in its level and spectra.<\/p>\n<p>The consequences of neglecting this principal parameter of architectural acoustical design is an environment that is perceived to be \u2018noisy,\u2019 as presented in Figure 1. The alternative\u2014to add sound to reduce the perception of a noisy environment\u2014might seem counterintuitive, but consider Figure 2. By precisely controlling the spectrum and level of sound (in this case, to a target overall sound pressure level of 47 dBA), one can make the space sound more comfortable.<\/p>\n<p>The difference between one\u2019s experience in a space with a very low ambient level and one with a higher ambient level suggests just as there is a need to differentiate between \u2018sound\u2019 and \u2018noise,\u2019 there is value in distinguishing between a \u2018silent\u2019 space and a \u2018quiet\u2019 one. Whereas \u2018silent\u2019 infers the absence of sound, a \u2018quiet\u2019 space can be characterized by a constant ambient sound that is comfortable and not readily noticeable by its occupants. Spaces such as these are perceived to be less \u2018noisy\u2019 and more comfortable\u2014or \u2018quiet.\u2019<\/p>\n<p><strong>Evolution of sound masking<\/strong><\/p>\n<p>Advanced technologies\u2014called sound masking systems\u2014have been developed to control the level and properties of ambient sound within commercial spaces. These systems consist of a series of loudspeakers installed in a grid-like pattern in an open ceiling or above the ceiling treatment. The loudspeakers\u2019 output is controlled using additional equipment. The first instances of their installation followed the publication of Cavanaugh\u2019s book. However, at the time, there were several obstacles to the adoption of sound masking as an effective acoustical design strategy.<\/p>\n<p>Firstly, these early systems were considered failures due to technological limitations and a lack of understanding and application of acoustical theory, which affected both their design and commissioning (<em>e.g.<\/em> large zones, limited control over volume and frequency settings). Ultimately, they failed to deliver a consistent, comfortable sound.<\/p>\n<p>Secondly, their deployment coincided with the sudden awareness and aggressive regulation of \u2018noise exposure.\u2019 Although earlier efforts were made in other countries, the most comprehensive attempt to combat noise nuisance came in the form of the United States of America\u2019s <em>Noise Control Act <\/em>of 1972. Many other governments and organizations have since used this document as the basis for their own regulations regarding occupational health and safety, environmental noise, transportation noise, and built environments (<em>e.g.<\/em> HVAC, building services), the primary focus of which is to limit the sudden or prolonged exposure to high \u2018noise\u2019 levels that would cause hearing loss (in the current discussion of appropriate noise exposure limits for activity-based spaces [<em>e.g.<\/em> for learning, recovery, sleep]\u2014such as those set by the World Health Organization [WHO]\u2014the focus continues to be on sound level, with little consideration of the other factors playing into human evaluations of acoustics. There is little appreciation of psychoacoustical parameters, which would consider the existing level and spectrum of background sound in review of the intruding sound from the noise source. By way of example, lacking understanding of the existing level and spectrum of sound in space, it is impossible to conclude sleep disruption can occur as a result of intruding traffic noise at any defined value [<em>e.g.<\/em> 30 dBA]).<\/p>\n<p>However, research shows the definition of \u2018noise\u2019 should also include \u2018unwanted sound\u2019 (<em>e.g.<\/em> that which interferes with one\u2019s ability to concentrate on the task at hand or get a good night\u2019s rest). These noises do not meet the same criteria as those damaging physical structures, but their impact is nonetheless undesirable. Background sound can have a positive and mitigating effect here and, hence, the need to make the distinction. Rather than trying to create a silent, library-like space in which there is little to no sound at all (<em>i.e.<\/em> a \u2018silent\u2019 space), the goal is to create a \u2018quiet\u2019 space\u2014one in which there is little to no unwanted sound.<\/p>\n<p>Lastly, developing the masking spectrum was an iterative process spanning several decades. With the development of methodology to assess the acoustical privacy of spaces\u2014namely, the articulation index (AI)\u2014discussion turned toward specification of reasonable targets for acoustical privacy and renewed interest in determining what type of background sound would work best and how it could be delivered. After all, if the intention is to improve privacy, one not only needs to control the level of background sound, but also ensure the sound has specific qualities. In the 2000s, the National Research Council Canada (NRC) refined the spectrum, based on tests measuring both comfort and effectiveness, resulting in the cost-effective open-plan environment (COPE) masking spectrum (Figure 3).<\/p>\n<p>It is important to note delivery of effective \u2018masking\u2019 is not a product of the sound generating and control equipment (<em>i.e.<\/em> the electrical signal), but rather the ability of the sound masking system to adapt the generated sound that is actually delivered to the space and which is dependent on the space\u2019s architecture\u2014its layout, furnishings, and finishings. To achieve the desired effect, the sound produced within the space must be adjusted to a specific spectrum through a post-installation process known as tuning.<\/p>\n<p>Ensuring effective performance also requires verification. ASTM E1573-18, <em>Standard Test Method for Evaluating Masking Sound in Open Offices Using A-Weighted and One-Third Octave Band Sound Pressure Levels<\/em>, offers guidance and instruction on the measurement procedure to evaluate the performance of a commissioned masking system. Measurements are performed in every 93 m<sup>2<\/sup> (1000 sf) of open space and a representative number of closed rooms to review effectiveness of the tuning process against performance targets and tolerances, and to provide an indication of the spatial uniformity of the masking sound.<!--nextpage--><\/p>\n<figure id=\"attachment_118727\" aria-describedby=\"caption-attachment-118727\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_6_Masking.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-118727\" src=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_6_Masking-300x162.jpg\" alt=\"Figure 3: The graph illustrates the National Research Council Canada\u2019s (NRC\u2019s) cost-effective open-plan environment (COPE) masking spectrum. The slope is approximated by 4.90 dB\/oct. between 125 and 5000 Hz. While the low frequencies do not contribute as greatly to speech privacy as the frequencies in the middle to high range, they are necessary for comfort. Without those, occupants would perceive the sound as \u2018hissy.\u2019\" width=\"300\" height=\"162\" srcset=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_6_Masking-300x162.jpg 300w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_6_Masking-500x270.jpg 500w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_6_Masking-768x415.jpg 768w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_6_Masking.jpg 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-118727\" class=\"wp-caption-text\"><span style=\"font-size: 10pt; font-family: arial, helvetica, sans-serif;\"><strong>Figure 3:<\/strong> The graph illustrates the National Research Council Canada\u2019s (NRC\u2019s) cost-effective open-plan environment (COPE) masking spectrum. The slope is approximated by 4.90 dB\/oct. between 125 and 5000 Hz. While the low frequencies do not contribute as greatly to speech privacy as the frequencies in the middle to high range, they are necessary for comfort. Without those, occupants would perceive the sound as \u2018hissy.\u2019<\/span><\/figcaption><\/figure>\n<p>In the last decade or so, great advancements have been made with regards to masking technology\u2019s ability to accurately and consistently achieve a comfortable and effective masking sound across treated spaces. When designed with small zones no larger than 21 to 63 m<sup>2<\/sup> (225 to 625 sf) offering fine volume (<em>i.e.<\/em> 0.5 dBA) and frequency (<em>i.e.<\/em> <sup>1<\/sup>\/<sub>3<\/sub> octave) control, a networked-decentralized architecture can provide consistency in the overall masking volume not exceeding \u00b10.5 dBA, as well as highly consistent masking spectrums, yielding much better tuning results than possible with previous architectures. Some systems can also be automatically tuned using software, which first measures the sound within a zone and then rapidly adjusts the volume and frequency settings to achieve the specified curve.<\/p>\n<p><strong>Standardizing sound masking<\/strong><\/p>\n<p>The importance of managing background sound levels using sound masking technology is now recognized in many standards, guidelines, and building codes, including:<\/p>\n<ul>\n<li>Standards Australia\/New Zealand (AS\/NZS) 2107:2016, <em>Acoustics, Recommended design sound levels and reverberation times for building interiors<\/em>;<\/li>\n<li>Canadian Standards Association (CSA) Z412-17, <em>Office Ergonomics<\/em>, an application standard for workplace ergonomics;<\/li>\n<li>Facilities Guidelines Institute (FGI) documents such as <em>Sound &amp; Vibration<\/em> (2010), <em>FGI Guidelines for Design and Construction of Hospitals<\/em> (2018), and <em>FGI Guidelines for Design and Construction of Outpatient Facilities<\/em> (2018);<\/li>\n<li>General Services Administration\u2019s (GSA\u2019s) PBS-P100, <em>Facilities Standards for the Public Buildings Service<\/em> (2017);<\/li>\n<li>Green Building Initiative\u2019s (GBI\u2019s) Green Globes for New Construction 2019;<\/li>\n<li>The U.S. Green Building Council\u2019s (USGBC\u2019s) Leadership in Energy and Environmental Design (LEED) v4.1 Building Design &amp; Construction (BD+C) and Interior Design &amp; Construction (ID+C);<\/li>\n<li>International WELL Building Institute\u2019s (IWBI\u2019s) 2014 WELLv1 and 2018 WELLv2;<\/li>\n<li>ASTM 1374-18e1, <em>Standard Guide for Office Acoustics<\/em>, and Applicable ASTM Standards;<\/li>\n<li>American National Standards Institute\/Acoustical Society of America (ANSI\/ASA) S12.70-2016, <em>Criteria for Evaluating Speech Privacy in Healthcare Facilities<\/em>; and<\/li>\n<li>The International Organization for Standardization (ISO) 3382-3, <em>Acoustics \u2013 Measurement of room acoustic parameters \u2013 Part 3: open plan offices<\/em>, and ISO 22955, <em>Acoustics \u2013 Acoustic quality of open office spaces<\/em>.<\/li>\n<\/ul>\n<p>However, many have yet to capitalize on the ways in which masking systems can be used as a tool in architectural design. For that reason, the strategies employed by two of these documents are worth further discussion.<\/p>\n<p><strong>Ensuring minimum background sound level<\/strong><\/p>\n<p>In closed rooms, speech privacy depends on the background sound at the listener\u2019s position being higher than the residual voice level penetrating the wall (for more information, read Niklas Moeller\u2019s \u201cMind the Gap: Using Sound Masking in Closed Spaces\u201d in the October 2012 issue of <em>Construction Canada<\/em>). This point is highlighted in ASTM E2638, <em>Standard Test Method for Objective Measurement of the Speech Privacy Provided by a Closed Room<\/em>. Background noise is presumed to be due to building systems (<em>i.e.<\/em> HVAC) and is, therefore, highly variable. In the absence of continuous masking sound, the measurement\u2014and, hence, any conclusion based on it\u2014is valid only at the time it is done (in any case, the dBA levels produced by traditional HVAC varies and this equipment cannot generate a spectrum conducive to speech privacy).<\/p>\n<p>To promote a more well-rounded design approach, AS\/NZS 2107:2016 specifies criteria acknowledging several benefits of minimum background sound levels, including the \u2018insurance policy\u2019 it provides against loss of acoustic isolation and speech privacy. The document introduces guidance with regards to adequate level and spectrum for the built environment. While this standard specifically excludes setting performance guidelines for masking sound, it promotes sound masking systems as a possible solution building professionals may consider to ensure acoustical privacy and satisfaction.<\/p>\n<p><strong>Using a point-for-point exchange<\/strong><\/p>\n<p>An even more beneficial approach was proposed by Cavanaugh, when he said, \u201can increase in the background sound level has the same effect on intelligibility as an increase in the transmission loss,\u201d (referenced from <em>Speech Privacy in Buildings<\/em> [1962]). It is on this basis that <em>Sound &amp; Vibration 2.0: Design Guidelines for Health Care Facilities<\/em>\u2014the companion document to the FGI\u2019s <em>2018 Guidelines for Design and Construction of Hospitals<\/em> and <em>2018 Guidelines for Design and Construction of Outpatient Facilities<\/em>\u2014allows for a point-for-point exchange in kind between the measure of isolation\u2014the sound transmission class (STC)\u2014and the background level (dBA) (for more information, read Niklas Moeller\u2019s \u201cPlacing Sound Masking on the Front Line of Acoustic Design\u201d in the July 2017 issue of <em>Construction Canada<\/em>).<\/p>\n<table border=\"0\">\n<tbody>\n<tr>\n<td style=\"padding: 5px;\" bgcolor=\"#67be49\">\n<p class=\"Sidebar-Heading\"><span style=\"color: #ffffff;\"><strong><span style=\"text-transform: none;\">THE LOMBARD EFFECT AND MASKING SOUND<\/span><\/strong><\/span><\/p>\n<\/td>\n<\/tr>\n<tr>\n<td style=\"padding: 5px;\" bgcolor=\"#eef6dd\">Subconsciously raising one\u2019s voice level in order to be more clearly heard within a noisy environment is known as the \u2018Lombard effect\u2019\u2014or, colloquially, the \u2018cocktail-party effect.\u2019 Sometimes, people express concern it will be triggered by the increased ambient level provided by a sound masking system.<\/p>\n<p>In brief, this concern is unwarranted. For reference, masking is usually set to 45 to 48 dBA in open areas and 40 to 45 dBA in closed rooms. Research shows the Lombard Effect begins when \u201cdisturbing noises exceed 45 dBA\u201d\u2014a value near the typical limit of masking. The literature also shows the impact of raising background noise levels to 48 dBA is negligible\u2014prompting less than 1 dBA increase in speech levels.*<\/p>\n<p>Moreover, there is a distinct difference between \u2018disturbing noises\u2019 and masking sound. The latter is designed to be as comfortable as possible. In fact, when the masking system is properly engineered, installed, and tuned, the sound is unobtrusive to occupants.<\/p>\n<p>In closed offices, there is even less concern due to the lower masking levels that is typically specified for these environments. Not only would the person speaking not feel \u2018triggered\u2019 to raise their voice, but the intelligibility of speech at normal levels would be unaffected. Rather, masking would perform its intended function: bolstering speech privacy (transmission of sound out of the room) and the perception of privacy (intrusion of noise into the room).<\/p>\n<p>* Read H. Lazarus\u2019 article, \u201cPrediction of Verbal Communication in Noise\u2013A Review: Part 1,\u201d from the 19<sup>th<\/sup> volume of <em>Applied Acoustics<\/em> (1986) and J. H. Rindel and C. L. Christensen\u2019s article, \u201cDynamic sound source for simulating the Lombard effect in room acoustic modeling software,\u201d from the proceedings of InterNoise 2012 in New York.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><!--nextpage--><\/p>\n<figure id=\"attachment_118726\" aria-describedby=\"caption-attachment-118726\" style=\"width: 216px\" class=\"wp-caption alignright\"><a href=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_5_Masking.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-118726\" src=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_5_Masking-216x300.jpg\" alt=\"A sound masking system uses a series of loudspeakers installed in a grid-like pattern in an open ceiling or above the ceiling treatment to control the level and properties of background sound within commercial spaces. Photo \u00a9 Jon Evans Photography\" width=\"216\" height=\"300\" srcset=\"https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_5_Masking-216x300.jpg 216w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_5_Masking-360x500.jpg 360w, https:\/\/www.constructionspecifier.com\/wp-content\/uploads\/2020\/08\/Image_5_Masking.jpg 576w\" sizes=\"auto, (max-width: 216px) 100vw, 216px\" \/><\/a><figcaption id=\"caption-attachment-118726\" class=\"wp-caption-text\"><span style=\"font-size: 10pt; font-family: arial, helvetica, sans-serif;\">A sound masking system uses a series of loudspeakers installed in a grid-like pattern in an open ceiling or above the ceiling treatment to control the level and properties of background sound within commercial spaces.<\/span><br \/><em><span style=\"font-size: 10pt; font-family: arial, helvetica, sans-serif;\">Photo \u00a9 Jon Evans Photography<\/span><\/em><\/figcaption><\/figure>\n<p>Historically, background sound levels were (and continue to be) non-uniform in level and spectra, and highly variable over time and throughout the built environment. As a result, partition walls were often overbuilt in an effort to reduce the transmission of sound from source to receiver. Rather than employing effective controls for background sound, designers and engineers heavily overcompensated by using additional materials to provide greater isolation and absorption. This hyper-focused approach on objective components of acoustics consistently failed to appreciate the importance of human factors\u2014namely, that a space can be perceived as quiet.<\/p>\n<p>It is in the consideration of the pseudo-subjective evaluation of acoustical privacy\u2014estimating acoustical privacy of a space using a combination of objective metrics (<em>i.e.<\/em> measure of isolation and background sound)\u2014that we have the opportunities to realize cost savings at the design stage of a project.<\/p>\n<p>Consider the following simplified scenario, which is intended to quickly illustrate the approach:<\/p>\n<ul>\n<li>an enclosed room conforming to a field-tested STC-45 rating requires a 30 dBA background sound level for speech privacy; and<\/li>\n<li>alternatively, if the background sound level is raised to a constant level of 35 dBA, the composite performance of the construction of the environment (walls, ceiling, floor) can be reduced to STC-40 rating.<\/li>\n<\/ul>\n<p>A mere five STC points may not seem significant; however, the cost savings in terms of materials, labor, and time can be. Also, if one reduces the STC rating of the partition by five points and raises the controlled background sound levels by 10 dBA to a level of 40 dBA, acoustical privacy is more assured and the psychoacoustics of the space are improved.<\/p>\n<p>A more assertive effort could pursue the reduction of the STC rating of the partitions from STC-45, which relies on 30 dBA of background sound, to an STC-35 with 40 dBA of background sound (this considers field-tested STC values reflecting composite acoustic performance of all sound transmission paths). Providing the background sound is precisely generated and consistently delivered by the masking system, this enhanced design process affords the opportunity to explore new options including:<\/p>\n<ul>\n<li>greater selection of materials (performance, cost);<\/li>\n<li>cost of labor associated with installation (difficulty, and the time required);<\/li>\n<li>building to the ceiling instead of to the deck, with appropriate selection of acoustical tile with isolation properties (ceiling attenuation class [CAC] criteria);<\/li>\n<li>reduction in quantity of materials and labor (installation time, difficulty, and complexity);<\/li>\n<li>ease of reconfiguration of a space due to demising walls;<\/li>\n<li>layout consideration and post-building adjustments (facility flexibility);<\/li>\n<li>the cost of continuing the partition above the ceiling to the deck is more significant and the difficulty in installation (height of plenum, penetrations, interferences); and<\/li>\n<li>reduction in material waste and environmental repercussions.<\/li>\n<\/ul>\n<p>As mentioned earlier, using masking to control background sound levels also acts as an \u2018insurance policy.\u2019 Should the space underperform\u2014which can occur for any number of reasons\u2014there still remains the opportunity to raise the background sound level upward to 45 dBA for enclosed spaces and 48 dBA for open areas to improve the psychoacoustical measures<br \/>\nof the space.<\/p>\n<p><strong>Conclusion<\/strong><\/p>\n<p>Although sound is ubiquitous\u2014a constant and inescapable experience\u2014its positive role within the built environment is underappreciated, leading to ongoing debate about the control (or lack thereof) of background sound levels within various types of facilities. Reviewing the technical and popular use of various words allows one to gain appreciation of how they can lead to misunderstandings of what it takes to achieve an effective acoustic environment and, more specifically, the role played by background sound set to a controlled level and spectrum. The distinction between \u2018noise\u2019 and \u2018sound\u2019 is expansive and the implications are significant in terms of subjective and objective attributes of the built environment. It is by refining the definitions of those terms, as well as that of \u2018silence\u2019 and \u2018quiet,\u2019 that appreciable opportunities can be fostered to improve the design of the built environment and promote occupant well-being.<\/p>\n<p class=\"Sidebar-BodyTextsidebar\"><em><img loading=\"lazy\" decoding=\"async\" class=\"alignleft\" src=\"https:\/\/www.constructioncanada.net\/wp-content\/uploads\/2020\/07\/Viken_Koukounian-300x215.jpg\" width=\"59\" height=\"42\" \/>Viken Koukounian, PhD, P.Eng., is an acoustical engineer at K.R. Moeller Associates Ltd. He is an active member of many international standardization organizations, such as the American National Standards Institute\/Acoustical Society of America (ANSI\/ASA), the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), ASTM, the Green Building Initiative (GBI), and the International WELL Building Institute (IWBI). He completed his doctorate at Queen\u2019s University (Kingston, Ontario, Canada) with foci in experimental and computational acoustics and vibration. Koukounian can be reached via e-mail at <a href=\"mailto:viken@logison.com\" target=\"_blank\" rel=\"noopener noreferrer\">viken@logison.com<\/a>.<\/em><\/p>\n<p class=\"Sidebar-BodyTextsidebar\"><em><span style=\"letter-spacing: -.1pt;\"><img loading=\"lazy\" decoding=\"async\" class=\"alignleft\" src=\"https:\/\/www.constructioncanada.net\/wp-content\/uploads\/2020\/07\/Niklas_Moeller-300x200.jpg\" width=\"54\" height=\"36\" \/>Niklas Moeller is the vice-president of K.R. Moeller Associates Ltd., manufacturer of the LogiSon Acoustic Network and MODIO Guestroom Acoustic Control. He has over 25 years\u2019 experience in the sound masking industry. Moeller can be reached via e-mail at <a href=\"mailto:nmoeller@logison.com\" target=\"_blank\" rel=\"noopener noreferrer\">nmoeller@logison.com<\/a>.<\/span><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Background sound is an intrinsic part of our daily experiences, yet its fundamental role within the built environment is often overlooked. This omission is most apparent in noise mitigation projects where building professionals exclusively rely on absorptive materials and partition assemblies. This singular focus on objective physical acoustics fails to consider the human (psychological and physiological) component\u2014specifically, that occupants can perceive a space with a higher controlled level and spectrum of background sound as \u2018quiet.\u2019<\/p>\n","protected":false},"author":13542,"featured_media":118730,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[520,179,449,200,355,1253],"tags":[53,1215,627],"class_list":["post-118721","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-features","category-masterformat","category-uniformat","category-27-00-00-communications","category-27-50-00-distributed-communications-and-monitoring-systems","category-d6060-distributed-communications-and-monitoring","tag-acoustics","tag-division-27","tag-sound-masking","entry"],"acf":[],"yoast_head":"<!-- This site is optimized with the 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