In most business settings, it’s critical to have office spaces and conference rooms with sufficient speech privacy to protect confidential information. This is especially true in healthcare, education, government, and for executive leadership and HR professionals in corporate settings. Architects and acousticians have traditionally had few to design these spaces to achieve privacy. The purpose of this article is to provide an overview of the existing methods including newer low-cost, easy to implement approach many architects and designers may not be familiar with.

How is soundproofing measured?

First, let’s review the different rating systems used to measure aspects of the amount of sound leaving a private office space. These standards are all set by ASTM International, an organization that produces over 12,000 standards for many different types of products worldwide.

CAC—Ceiling Attenuation Class (ASTM Designations E 1414, E 1414 M-16, E413-16)

CAC indicates a suspended acoustic ceiling’s ability to block sound traveling through a plenum when the wall does not extend full height. High CAC values indicate higher levels of sound insulation between rooms. Suspended acoustic ceilings typically have CAC ratings between 20 and 35. A higher number indicates a better capability to block sound from entering the plenum space above a suspended ceiling grid.

STC—Sound Transmission Class (ASTM Designations E90-09 and E413-10)

STC measures the sound blocking and noise-blocking capacity of the wall construction between rooms and to other assemblies such as doors or windows as well. Blocking sound between rooms can be categorized as best (STC 50 or higher), better (STC 45 or higher), or good (STC 40 or higher). Wall assemblies with an STC below 40 do not provide adequate sound privacy.

SPC—Speech Privacy Coefficient (ASTM Designation ASTM E2638)

Speech Privacy Class or SPC is an ASTM standard of measurement designed to measure and precisely calculate how hard it would be to eavesdrop and understand speech from outside of a room. SPC is much more useful at determining speech privacy or speech security than Sound Transmission Class (STC) or Noise Reduction (NR) because it is intended to measure intentional as opposed to casual eavesdropping. However, it is a difficult standard for architects to design around because there are no standard wall and flooring assemblies available to specify like there are with STC rated wall and flooring assemblies.

Table 1: Above is a classification table describing various SPC values. The table displays the category of speech privacy or security and the corresponding SPC value needed to achieve the desired level. Attribution: ATSM International, and shared by State of the Art Acoustik, Inc.
Category SPC Description
None < 60 Speech expected to be frequently intelligible (more than once a minute) and almost always audible.
Standard Speech Privacy 60–65 Brief phrases expected to be occasionally intelligible (at most once every minute); speech sounds usually audible.
Enhanced Speech Privacy 65–70 Brief phrases expected to be rarely intelligible (at most once every 3.5 minutes); speech sounds frequently audible.
Standard Speech Security 70–75 Speech expected to be essentially unintelligible (brief phrases intelligible at most once 15 minutes); speech sounds occasionally audible (at most once every minute).
Enhanced Speech Security 75–80 Speech unintelligible (brief phrases intelligible at most once every hour); speech sounds rarely audible (at most once every 3.5 minutes).
High Speech Security 80–85 Speech unintelligible (brief phrases intelligible at most once every 4.5 hours); speech sounds essentially inaudible (audible at most once every 15 minutes).
Top Speech Security > 85 Speech unintelligible (brief phrases expected to be intelligible at most once every 20 hours); speech sounds inaudible (audible at most once every hour).

Industry standards define a “private” meeting space as having a speech privacy coefficient of 60 to 65. This means that only brief phrases are occasionally intelligible in an adjacent room, perhaps one phrase per minute. 

Sound isolation in spaces with full-height walls

The traditional method for designing private office space starts with isolation from external noise. To accomplish this, demising walls, ceilings and floor construction designs are copied from one of the catalogued STC55/IIC55 or better sound rated assemblies. For these assemblies, walls do not stop at a suspended ceiling; they extend and are sealed watertight from floor to structural deck. All penetrations are specially designed to maintain the sound isolation rating of the room. All leakage paths are sealed including potential leakage around doors and ceilings.

Full-height walls mean extending all the lower wall construction up past the ceiling level so that it completely blocks off the plenum and seals up against the floor or roof decking above.

The advantage of this approach:

  • It achieves a high level of sound blocking (STC 45, 50+) depending upon wall construction design.

The disadvantages of this approach:

  • It eliminates the open plenum HVAC design and requires adding return air ducting between rooms to get adequate return air flow. The challenge is sealing this ducting to eliminate noise leakage between adjacent rooms.
  • Compared to other approaches, it is costly to raise the wall height to full height and add the required ducting.

Using plenum barriers in spaces with suspended ceilings

An alternative to building full height walls is to add plenum barriers on top of standard height walls to achieve a desired STC rating of 40 to 50. Plenum barriers are lightweight and removable and are fastened and sealed to the wall and the roof decking. They include mass-loaded vinyl (MLV), stone wool insulation, gypsum wall board, or a combination of these materials. Standard height walls are built to a height just above the suspended ceiling as is standard industry practice. To ensure success, all leakage paths must be properly sealed.

The advantages of this approach:

  • Achieves the STC rating goal but is lightweight and lower cost compared to building full height walls.
  • Plenum barriers walls can be removed so changing office lay-out in the future is easier than building full height walls.

The disadvantage of this approach:

  • It eliminates the open plenum HVAC design and requires adding return air ducting between rooms to get adequate return air flow. The challenge is sealing this ducting to eliminate noise leakage between adjacent rooms.

Speech privacy for existing spaces with minimal construction

Silkworm Cocoon

Image by butterflyarc from Pixabay

An alternative approach to building full height walls or adding plenum barriers to standard height walls is to seal the room up in a “privacy cocoon”. In nature silkworms spin a cocoon around their larvae to protect them from the environment. A similar concept can be used to create speech privacy in existing office spaces by building a cocoon of privacy around the room. The key tenet of this design approach is to stop the sound from the entering the ceiling plenum in the first place.

This can be done in any space using demising walls with a suspended ceiling (with a high CAC rating) and an open plenum. The wall detail can include Green Glue between a second layer of drywall for improved sound blocking. Next the suspended ceiling, including light fixtures and return air louvers, need to be sealed using the PrivacyShield® Ceiling Overlay System.

The PrivacyShield® Ceiling Overlay System is a modular system pre-sized to fit squarely on top of the suspended ceiling tiles, light fixtures, and return air louvers. It prevents speech from entering the ceiling plenum. The PrivacyShield® system drops right in and installs as easily as the ceiling tile. It does not require penetrations for communication wires and special air ducts.

The advantages of this approach:

  • The easiest installation, requiring only a six-foot-high ladder and minimal disruption in the workspace.
  • The most cost-effective approach by eliminating the need to build full height walls, adding plenum barriers to standard height walls, or creating ducting between adjacent spaces.
  • It provides maximum flexibility if redesigning the workspace is needed in the future.
  • Provides the Architect with a predictable and measurable Ceiling Attenuation Rating of 38 minimum for the entire ceiling assembly. According to CISCA, the Ceilings and Interior Systems Construction Association, “Ceilings with a CAC of 35 or greater are considered very good barriers of sound intrusion.”
  • Can be installed on existing ceilings that have plenum-mounted sound masking systems.
  • In offices where a sound masking system is mounted in the plenum, the sound masking decibel level is typically between 45-50 decibels. The PrivacyShield® Ceiling Overlay System significantly reduces the amount of white noise entering the private office, therefore it is easier for occupants to hear each other with or without face masks. A quiet private office is more comfortable for everyone.

Sealing up the plenum area from sound leakage is the first and most important step in building a “privacy cocoon” around a private office. For more details, you can also review AIA specification for PrivacyShield® Ceiling Overlay System.

Addressing sound leakage through doors

All sound leakage areas need to be tackled including paths through, around, and under the office door. Ensure that the door chosen for the room matches the STC level of the wall and floor assembly. It makes no sense to choose a high STC rated wall and floor assembly and then not consider the same requirements for the door. Standard solid wood or hollow metal doors are typically rated STC 30 or 35, so look for high STC rated (STC 43–64) door options.

If a standard solid wood door or hollow metal door is chosen for the room, a door seal kit is recommended to eliminate leakage around and under the office door.

The good news is that architects and designers have many options to create private office spaces. We hope this article helps describe some of the design considerations and their advantages and disadvantages. If you have further questions about the PrivacyShield® Overlay System, high STC rated doors, or other design-related soundproofing questions, please contact an Acoustical Solutions sales associate at 800-782-5742.

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