Seeing your way through the noise

All over the world on April 25, International Noise Awareness Day encourages people to do something about bothersome noise where they work, live and play.

This annual event was founded by the Center for Hearing and Communication, which reminds us: “Continuous exposure to noise above 85 decibels can cause hearing loss, but research shows that even below that threshold, noise instigates physiological changes. Blood pressure elevation, sleep and digestion problems, and other stress-related disorders are linked to environmental noise. Studies on children’s learning and behavior document find that noise poses great risks.”

Helping assess and mitigate these risks involves understanding the complex, three-dimensional, acoustical experience within and between rooms. This can feel like an overwhelming challenge – especially for visual learners and communicators.

The message can be lost during translation from quantitative acoustics metrics and their acronyms to the design and intersection of actual building elements, such as walls and ceilings.

Using color-mapping technology, we now can see a clearer picture of a ceiling system’s ability to absorb noise and its inability to block noise.

Show Me, Don’t Tell Me

Two years ago, Rockfon introduced this simple approach to Optimized Acoustics:

• Due to their light weight and many penetrations, acoustic ceilings cannot be used to block sound. Walls and plenum barriers are for blocking sound.
• Acoustic ceilings are for sound absorption. A Noise Reduction Coefficient (NRC) of 0.70 is good, 0.80 is better and ratings above 0.90 are best.
• A wall Sound Transmission Class (STC) rating of 40 is good, 45 is better and ratings at 50 or above are best.
• Acoustic standards require these performance levels.

Because many of us learn better by seeing and hearing, Rockfon recently created a video showing the basics of Optimized Acoustics in a real-world application. The video’s background audio works with the narrated storyline and visual graphics for an immersive experience. This approach is clearly understood in 90 seconds, instead of reading pages of acoustic terms, acronyms and ratings.

See What I’m Hearing

Building on our success, Rockfon has taken acoustic visualization to the next level.

Collaborating with A3 Acoustics, a consultancy in Seattle, and NGC Testing Services, a NVLAP-certified laboratory in Buffalo, New York, Rockfon used a high-definition acoustic camera to show you what others hear inside their buildings.

Much like a thermal imaging camera shows differences in surface temperatures, a sound intensity probe can be used to produce high-definition color, sound mapping.

Noise Leaking In

Figure 1 shows how noise from an adjacent room leaks through ceiling systems when the wall is not full height or a plenum barrier is not used.

During the laboratory testing, there were two identical rooms adjacent to each other. The ceiling shown in figure 1a was installed in both rooms, representing two offices. The common partition, which stops at the underside of the ceiling leaving the plenum above the ceiling open between the rooms, is along the bottom of the image.

Figure 1b shows how the noise being generated in the adjacent room leaks easily into this room via the many gaps and penetrations in the ceiling. The dark red color to the right shows the loudest noise leak, the return air grille. Lighter red and yellow around the light fixtures and supply air diffuser show other significant noise leaks. Noise also can be seen leaking through the wall-ceiling intersection along the bottom of the image. The ceiling panel is a typical, wet-felted, mineral fiber panel with a Ceiling Attenuation Class rating of CAC-37. The CAC rating of the ceiling system decreased 10 CAC points to CAC 27 when the light and air distribution devices were installed. The acoustic performance of this design approach does not comply with minimum standards for many types of facilities.

When lightweight Rockfon Plenum Barrier Board made of foil-faced, stone wool is installed above the partition, blocking off the plenum above the ceiling, the noise leaks essentially disappear below background sound levels. Refer to the blue and purple colors in figure 1c. Even though the stone wool ceiling panels in this test have a lower CAC rating of 22, when they are combined with the plenum barrier, the system performs at CAC 49. This is 22 CAC points higher than the mineral-fiber ceiling panels alone and complies with most acoustic standards for offices, schools and healthcare facilities. Extending the partition to full height instead of using a plenum barrier would produce similar results, albeit at a potentially higher cost.

Noise Bouncing Around

This visualization technique also can be used to show the room acoustics differences inside a room. Figure 2 shows how more noise reflects off certain acoustic ceiling panels with low Noise Reduction Coefficient (NRC) ratings compared to those with high-performing sound absorption properties.

Noise reflecting off a mineral fiber ceiling panel with a low NRC rating of 0.60 continues to bounce around the room and is only attenuated several decibels relative to the noise reflecting off the metal light fixtures and supply air diffuser. Compare the red-colored reflections around the fixtures in figure 2b to the yellow-colored reflections off the ceiling panels. Because noise passes through the open return air grille into the plenum and does not return into the room, the light blue color represents complete noise “absorption.”

Figure 2c shows how high-NRC Rockfon acoustic stone wool ceiling panels perform as near-perfect absorbers. Compare the light blue color of the noise disappearing through the open return air grille to the light blue color of the noise not reflecting off the ceiling panels. The red and yellow colors show that there are still loud noise reflections off the light fixtures’ and the supply-air diffuser, but the ceiling is doing its primary job – to absorb noise.

This color-mapping method helps to bridge the gap between the technical, quantitative side of acoustics and the visual side of design in an impactful and memorable way.