July 23, 2020
By Sean D. Browne
As sensitivity to confidentiality continues to heighten, specifiers need to become more aware of the need to control sound within a space and isolate sound between spaces. Whether the spaces are closed and private or open and collaborative, speech privacy is now more important than ever.
Speech privacy refers to how well a conversation is overheard and understood by an unintended listener in an adjacent space. It is a concern in a variety of buildings, ranging from health-care facilities where physician-patient confidentiality is critical and commercial office buildings where privacy is required in meeting rooms and private offices to educational facilities where it is important to reduce the level of speech intrusion from adjacent spaces.
In health-care settings, patients can be exposed to situations in which they overhear conversations about other patients or have their own private information communicated in an environment where it can be heard by others. Examples include examination rooms, consultation rooms, treatment rooms, patient rooms, meeting rooms, and physicians’ private offices.
Research shows such scenarios are likely to impact patients’ trust and their ability to discuss their health problems freely with their physicians, which can then have serious implications on their care. As a result, it is critical private conversations with or about a patient are not overheard. Rules pertaining to patient privacy can be found in Canada’s Personal Information Protection and Electronic Documents Act (PIPEDA).
According to the Acoustical Society of America (ASA), students, on average, only hear 75 per cent of spoken words in a classroom with poor acoustics. One reason is the level of activity noise intruding the classroom from adjacent spaces.
High levels of intruding noise can mask speech, reducing the students’ ability to not only hear, but also to understand their teacher. Moreover, teachers must speak louder to overcome the noise, causing vocal fatigue over time.
Sound-absorptive materials can reduce some of the noise from mechanical systems and intruding activities. However, the best way to reduce it is to keep sound from intruding into the classroom in the first place. Targets for background noise level and sound isolation can be found in the American National Standards Institute (ANSI) S12.60, Acoustical Performance Criteria, Design Requirements, And Guidelines For Schools, Part 1: Permanent Schools.
Office employees have long considered the intrusion of unwanted noise as one of the leading sources of workplace dissatisfaction. Over the years, study after study by the Center for the Built Environment (CBE), the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), and many others points to poor acoustics as a major cause of reduced effectiveness, higher stress, and declining job satisfaction.
The studies also indicate the majority of acoustical complaints relate to speech privacy—hearing an unwanted conversation or feeling one is overheard. Such conversations can lead to unintentional breaches of confidentiality in sensitive work areas. Keeping private interactions confidential is thus a key concern in conference rooms, executive offices, and other similar spaces in an office environment.
Additionally, a workplace survey conducted by design firm Gensler indicates organizations offering mostly open environments with on-demand private spaces consistently prove best, enabling collaboration in open spaces without sacrificing the ability to focus in concentration areas. The challenge in areas such as these is to balance the need for privacy with the need for energetic teaming.
Speech privacy – open plan
The degree of speech privacy attained in an open plan space is indicated by its privacy index (PI). It takes into account the acoustical performance of everything in the space, including ceiling, walls, floorcovering, furniture, and background noise and voice levels. It is expressed as an integer value between zero and 100.
The recognized levels of speech privacy as defined by ASTM E1130, Standard Test Method for Objective Measurement of Speech Privacy in Open Plan Spaces Using Articulation Index, are as follows.
Represents a PI rating of 95 to 100. Nearby occupants may hear muffled sounds but the meaning of spoken words is unintelligible, and occupants are not distracted from what they are doing.
Normal or non-intrusive
Represents a PI rating between 80 and 95. Nearby occupants may hear some of the conversation but the loudness of speech is not distracting, and occupants can generally continue what they are doing. Non-intrusive speech privacy is a common goal for open-plan environments, especially where ‘knowledge worker’ productivity is a key issue.
Marginal or poor
Represents a PI rating of 60 to 80. Nearby occupants can understand most words and sentences, and the loudness of speech can be distracting to them.
Represents a PI rating of 60 or less. Nearby occupants can understand all words and sentences and the loudness of speech can be a constant distraction.
Speech privacy – closed plan
The degree of speech privacy attained in a closed plan space is indicated by the following.
Speech privacy class (SPC)
It is calculated as the sum of factors related to the sound isolation provided by the room construction and furnishings and the ambient background sound. It is determined by a test procedure conducted in an existing space according to ASTM E2638, Standard Test Method for Objective Measurement of the Speech Privacy Provided by a Closed Room. SPC values normally range from 70, which represents ‘minimal speech privacy,’ to 90, which is speech security.
Noise isolation class (NIC)
It is a single-number rating indicating how much sound is blocked between adjoining closed spaces, taking into account all transmission paths and acoustic properties of the source and receiving rooms. This includes walls, door, windows, ceiling, lights, etc. It is a field test to assess actual installed conditions. It is conducted according to ASTM E336, Standard Test Method for Measurement of Airborne Sound Attenuation between Rooms in Buildings. The higher the number, the better the sound isolation.
Speech privacy potential (SPP)
It is a single-number rating serving as a rule-of-thumb prediction of speech privacy between two spaces. It is a function of two factors: the designed ambient background sound level in the receiving space and the designed sound isolation performance of the total construction between the two spaces.
SPP is simply the sum of the two factors (sound isolation and background sound). An SPP rating of 75 is minimally acceptable speech privacy and greater than 80 is high speech privacy.
To attain a specific level of speech privacy for a space, it is important to be familiar with several acoustical performance parameters influencing it.
Noise reduction coefficient
The noise reduction coefficient (NRC) indicates the ability of a material to absorb sound from all angles. It is expressed as a number between 0.00 and 1.00, and indicates the average percentage of sound the material absorbs. An NRC of 0.60 means the material absorbs 60 per cent of the sound striking it. The higher the number, the more sound the surface absorbs. A ceiling with an NRC less than 0.50 is considered low performance, and one with an NRC that is greater than 0.70, high performance.
Ceiling attenuation class
Ceiling attenuation class (CAC) is the acoustical ceiling performance parameter most associated with speech privacy. It indicates the ability of a ceiling to block sound in one area from passing up into the plenum and transmitting back down into an adjacent area sharing the same plenum. CAC is an important consideration between adjacent closed spaces as well as between nearby closed and open areas.
It is measured according to ASTM E1414, Standard Test Method for Airborne Sound Attenuation Between Rooms Sharing a Common Ceiling Plenum. The higher the CAC, the better the ceiling acts as a barrier to sound intrusion between the spaces and the better the sound isolation and speech privacy performance.
A ceiling with a CAC less than 25 is considered low performance, one with a CAC that is greater than 35, high performance. A CAC that is greater than 35 should be the minimum for closed plan spaces.
The right combination of NRC and CAC values represents the best approach to ceiling selection tailored to the needs of the space. To make selection easier, there are acoustical ceiling systems today offering both sound absorption and blocking in the same panel. By providing an ideal combination of a high CAC and a high NRC, these panels deliver the best solution for both keeping noise levels down and conversations private in either closed or open plan spaces.
When examining NRC and CAC values, base ceiling selection on Underwriters Laboratories (UL)-classified acoustical performance parameters. A UL label on a carton certifies the ceiling panels have been tested by an independent third party on a continuing basis to ensure the panels’ performance meets or exceeds published values.
Sound transmission class
Sound transmission class (STC) indicates the ability of a wall to block the transmission of sound through it into an adjacent space. The higher the number, the better the construction acts as a barrier to sound transmission. A wall system with an STC less than 35 is considered low performance, one with an STC greater than 45, high performance. It is measured according to ASTM E90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions
Balanced acoustical design
Attaining speech privacy is dependent on good acoustical design and the proper selection of interior systems and materials. The proper choice of ceiling is vital because a ceiling’s ability to block sound can both affect the quality of sound within a space and limit the sound intrusion between spaces. It is a key element not only in creating an acoustical environment that can maintain speech privacy, but also in providing greater overall acoustic comfort and a reduction in noise-related annoyance.
One of the most effective and often least costly methods for achieving speech privacy is the balanced acoustical design approach. It consists of three components:
Speech privacy in closed spaces can be achieved, even at raised voice levels, using balanced acoustical design with attention to the right combination of acoustical values.
Absorb sound with an acoustical ceiling. For speech privacy, it is recommended to use a mineral fibre acoustical ceiling installed wall-to-wall that combines high ceiling attenuation (CAC 35 or higher) with good sound absorption (NRC 0.60 or higher).
Block sound with an effective combination of ceiling and wall construction. To obtain high levels of speech privacy, care must be taken at the penetration points in walls and ceilings. All components of the wall system should be engineered to preserve STC performance and for the removal of problematic sound leaks around doors, wall joints, and seals at the ceiling and floor interface. Wall, window, and door details are critical since joints, cracks, and other penetrations allow sound to intrude into the adjoining space.
It is also critical to choose light fixtures and HVAC elements that do not compromise the sound-blocking capability of a ceiling design. This might involve ducting return air, using common accessories, or specifying acoustical fixtures to maintain the sound isolation of the room design.
An acoustical ceiling with a CAC of 35 or higher is best in closed spaces to block sound from transmitting into an adjoining office, corridor, or open plan area. It will also block sound from adjacent spaces from intruding into the closed area, thereby improving the acoustic environment.
Balanced acoustical design requires the CAC value of the ceiling match the STC value of the wall, especially in partial-height wall construction to ensure speech privacy. When equal CAC and STC values are paired, optimized performance is achieved. Today there are ceiling panels offering CAC 45 and 50 options to match partial-height walls with high STC values.
Cover intruding noise with sound masking. Blocking sound through the wall and ceiling is one half of the speech privacy equation. The ambient background sound is the other. Achieving the full privacy potential of spaces may require the use of tuned and designed electronic sound masking. Co-ordinating the performance between the sound masking and ceiling/wall system is essential. Each component must be engineered to ensure the design of the sound masking system complements the architectural performance over the key speech frequency range.
Acoustics plus aesthetics
Finally, it is important to note regardless of the space, aesthetics do not have to be compromised when using a high performance acoustical ceiling. Many of today’s highest performing acoustical ceiling panels feature a popular smooth, fine textured surface visual. Today there are even ceiling systems offering the seamless appearance of a drywall but perform like an acoustical ceiling.
Additional esthetic options range from large panels more in scale with bigger spaces to panels with a unique edge detail that produces a 6-mm (¼-in.) reveal minimizing visible grid creating a ceiling plane that is more monolithic in appearance than ordinary suspended ceilings. Panels are also available with a tegular or reveal edge to create a shadow line to help camouflage the suspension system.
Added acoustic value
The ability to isolate sound through balanced acoustical design not only helps achieve speech privacy, but also increases speech intelligibility throughout the spaces by controlling reverberation. Adequate sound isolation also results in increased overall acoustic comfort and productivity as distraction is reduced.
Sean D. Browne is senior principal scientist for Armstrong Ceiling & Wall Solutions in Lancaster, PA, where he leads the Armstrong Acoustics Program. He is a member of the Acoustical Society of America (ASA) and ASTM International. He holds engineering degrees from Florida State University and the University of Miami and has been published in the journals of the International Symposium on Room Acoustics and Acoustical Society of America. He can be reached at firstname.lastname@example.org.
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