The impact of poor acoustics

Post-occupancy building surveys show that the number one dissatisfaction with buildings is their acoustics – and more specifically, sound privacy. Those low scores relate to the use of open spaces, but they relate to poorly designed, private rooms, too.

People don’t expect speech privacy when they are in a large open area full of people. But, when they enter a private room and close the door, their expectations for sound privacy change a lot. The problem is that whether or not they will have their expected privacy is completely out of sight. It depends on if you decided to compromise the architecture – inside the walls and above the ceiling.

Before you do that, think about the weight of a wall compared to that of an acoustic ceiling panel. Think about how solid and massive that wall is compared to a lightweight acoustic ceiling full of holes for lights and air devices. The ceiling is no match. That’s why building standards, guidelines, and rating systems require full-height walls with high Sound Transmission Class (STC) ratings.

What is sound insulation?

Sound insulation, also referred to as sound isolation, occurs when a massive and nonporous architectural surface or assembly, such as a concrete slab or multi-layer gypsum board wall, reflects sound energy.

Because the sound reflects off the surface, very little sound transmission into adjacent rooms occurs. Sound insulation helps to provide sound privacy and speech privacy.

Rockfon’s Optimized Acoustics™ design process utilizes full-height walls with the appropriate noise blocking sound capabilities or lightweight acoustic plenum barriers combined with our stone wool ceilings to ensure speech privacy.

Sound insulation in building standards, guidelines and rating systems

 More and more building types and room types must now comply with more stringent sound insulation criteria in standards, guidelines and rating systems.

• Guidelines for the design and construction of healthcare facilities, published by the Facilities Guidelines Institute (FGI) , require that "sound insulation shall be considered for all demising construction separating occupied spaces."
• The WELL Building Standard typically used for commercial office buildings states that “noise from adjacent spaces can be disturbing to building occupants” (feature 81) and can negatively impact the human immune and nervous systems.
• The Collaborative for High Performance Schools (CHPS) emphasizes that "student learning suffers in acoustically poor environments" where "excessive noise negatively affects speech communication" (EQ14.0). Minimum sound insulation performance for all learning spaces is required.

Understanding the reality of sound insulation inside buildings and how to block sound between rooms

Sound insulation between rooms on the same floor mostly relates to the walls and doors. In the past, some interior designs had walls that stopped at the height of a suspended ceiling, leaving the plenum above the ceiling open. The designers did not realize that the sound insulation between rooms would only be as good as the weakest link – the acoustic ceiling. They did not realize that the sound insulation of the ceiling (meaning a CAC 20-35) should be the same as the sound insulation of the wall (meaning an STC 40, 45 or 50). In fact, the ceiling system typically performs 10-20 points below the wall’s performance. To learn more about this topic, read Acoustic Myth: Ceiling and wall blocking performance does not need to be equal.

While this practice is no longer permitted by most building standards, guidelines and rating systems, open plenums can still be found in some existing and new buildings.

Stopping the walls at the height of a suspended ceiling and relying on the acoustic ceiling alone to provide adequate sound insulation is a risky and unadvised design practice. This design approach still lingers because some ceiling manufacturers still claim that acoustic ceilings alone are adequate for blocking noise or sound between rooms. As you navigate the ceiling panel options available, you may notice products in the market that claim to absorb and block noise. The reality is that modular acoustic ceilings by themselves do not have the mass needed to block enough noise. To learn more about this topic, read Acoustic Myth: Ceilings are Effective at Blocking Sound and an original Rockfon article titled All-in-one acoustic ceiling solutions are not the answer.

Additionally, when acoustic sound reducing ceiling tiles or panels are placed into a standard suspension grid, along with other building system components, such as supply-air diffuser (left) light fixtures (center) and return-air grille (right), substantial flanking paths – or noise leaks – are created. Rockfon used a high-definition acoustic camera linked to a sound intensity probe to help designers actually see noise leaking through the ceiling system (red and yellow colors). These noise-flanking paths degrade the ceiling system’s acoustic performance substantially. In fact, these leaks can cut perceived noise or sound blocking performance in half, making speech from adjoining spaces intelligible.

By attempting to address both blocking sound and absorbing sound, those dual-purpose panels in the market actually compromise both. Designers mistakenly sacrifice Noise Reduction Coefficient (NRC) for Ceiling Attenuation Class (CAC), and the ceiling sound insulation or blocking is simply not good enough. To learn more about this topic, read Acoustic Myth: It’s OK to sacrifice absorption for blocking. Look to your ceiling panels to meet the high sound absorption requirements and look to your walls for blocking, when it is needed. The CAC approach is no longer compliant with most acoustic standards, guidelines and rating systems.

Plenum ceiling

Ceiling plenum design includes a growing number of standards, guidelines and rating systems that are encouraging designers to use lightweight plenum walls to block off the ceiling plenum when the partition between the rooms stops at the ceiling. This requirement is necessary due to the ceiling noise insulation properties, by themselves, being inadequate to achieve speech privacy. The combination of the acoustic ceiling and return-air plenum barrier working together matches the STC performance of the partition below the ceiling level.

Sound-blocking plenum barriers are an excellent sound barrier solution, beginning at the top of the wall and extending to the underside of the floor or the roof above. Rockfon^® Plenum Barrier Board is made of pliable stone wool insulation to conform without gaps into tight spaces and around structural members and mechanical, electrical and plumbing elements that may be located in the plenum. The fiber-reinforced aluminum foil facing that is applied to one side increases its sound-insulating performance. When positioned above interior partitions that stop at the height of the suspended, acoustic ceiling, our Plenum Barrier Board stops noise and speech from traveling between rooms through the plenum above the ceiling.

If the adjacent room has a lot of people or equipment, and transmitted noise would interfere with sensitive activities being performed in the room being designed, use the Best STC category of 50. An example is classrooms. Also use the Best STC category of 50 if there needs to be a high level of confidentiality for example, in executive offices.

If one person usually occupies the adjacent room, and the main function of the room being designed is not sound sensitive, use the Better STC category of 45. Some examples of the Better STC category are standard, private offices and patient rooms in healthcare facilities.

See the difference: Why plenum barriers combined with ceilings work better than ceilings alone

Rockfon used a high-definition acoustic camera linked to a sound intensity probe to show visually the difference between using a ceiling alone for sound insulation between rooms and boosting the performance of the ceiling with an acoustic plenum barrier. This visualization method shows noise leaking through a high CAC mineral fiber ceiling (CAC 37) in red and yellow colors. The worst leaks are the return-air grille on the right side and recessed light fixtures in the center. Other noise leaks include the supply-air diffuser on the left and the intersection of the wall and ceiling along the bottom of the images. Altogether, these leaks decrease the ceiling system rating to just CAC 27, a 10 CAC point drop.

When our stone wool ceiling panels and Plenum Barrier Board is used (bottom image), the noise leaks disappear. This Rockfon Optimized Acoustics^TM approach performs at STC/CAC 40, 45 or 50 (STC/CAC 50 pictured) depending on the panel and plenum barrier combination. The low noise levels shown in purple are over 25 decibels lower than when the mineral fiber ceiling panels alone (top image) was being used for ceiling sound insulation.

Final words on sound insulation

Made of naturally-absorptive stone wool, Rockfon acoustic ceiling panels combined with Rockfon^® Plenum Barrier Board or full-height walls can be used as part of an overall sound insulation strategy to achieve Optimized Acoustics™ and for compliance with standards.

Did you also learn about these other parts of Rockfon’s Optimized Acoustics™?

Learn about the 1^st part: Acoustic absorption of the ceiling

Learn about the 3^rd Part: Background sound level

Check out our tools to help you design your next acoustics project