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Choosing the right ceiling panel material, or materials, for a project makes a huge difference in managing the acoustical response of a room. An acoustical design strategy needs to include an adequate balance of both sound absorbency and sound attenuation.

In this article, we will look at the different ways fibreglass and mineral fibre—the two most common ceiling panel materials— react to sound and how the two materials can work together to create exceptional acoustic control. We will begin by going over the two main criteria used to rate acoustic ceiling panels—noise reduction coefficient (NRC) and ceiling attenuation class (CAC).

Rating Acoustic Ceiling Panels

NRC

Specified by ASTM C 423, the predominant standard for sound absorption, NRC is a scalar representation of the amount of sound energy absorbed by a particular test sample. It is calculated as an arithmetic average to the nearest 0.05 over a limited frequency range (250 Hz, 500 Hz, 1,000 Hz and 2,000 Hz). In a simplification of the concept, an NRC of 0 indicates total reflection, while an NRC of 1.00 indicates total absorption.

CAC

CAC is the measurement of the ceiling’s ability to block sound in a closed space from passing up into the plenum and transmitting back down into a neighbouring closed space under the same plenum. It is derived from the normalized ceiling attenuation values in accordance with standard ASTM E 413. Ceilings with a CAC less than 25 are rated as lower performance, while those with a CAC greater than or equal to 35 are considered high-performance.

Ceiling panels usually post a high rating in either NRC or CAC, but not typically in both areas. Such is the difference between fibreglass and mineral fibre ceiling panels.

Fibreglass Ceiling Panels

If ceilings are of standard height [less than 3 metres (≈ 9 feet 6 inches)], it is best to choose a quality fibreglass ceiling panel for acoustic control because of its superior sound absorption properties across a wide range of frequencies (NRC). Fibreglass is considerably more effective at quieting a room than is mineral fibre, as it performs well in both high and low frequencies. At the same time, the low density of fibreglass ceiling panels, which makes them resistant to moisture and sagging, limits their ability to contain sound. So, fibreglass ceiling panels typically have a very high NRC, but a CAC that is on the low end.

Mineral Fibre Ceiling Panels

Mineral fiber ceiling panels are denser and heavier than fibreglass ceiling panels, and as such are reasonably effective sound attenuators (meaning they impede the transmission of sound from room to room). With good sound attenuation and average sound absorption, mineral fibre ceiling panels tend to have a higher CAC and lower NRC than their fiberglass counterparts. Often, architects, who might not be aware of all their options, will accept the significantly lower NRC ratings of mineral fibre ceiling panels as a trade-off for their higher CAC. Unfortunately, this compromise may result in a design with substandard acoustic control. It may also leave the end user with a ceiling panel more prone to moisture absorption and sagging over time.

Building and design professionals can maximize acoustic control, however, by combining a sound-absorbent ceiling panel with one that halts the transmission of sound waves.

Sandwich/Composite Ceiling Panels

In years past, acoustic contractors have utilized a “sandwich panel concept”—an in-the-field fabrication that first places a sound-absorbent fibreglass panel in the grid and then places a mineral fibre ceiling panel on top of it—for increased sound containment. Though this can work well, two-piece sandwich panel solutions often lose their effectiveness if maintenance workers improperly return them both to their original placement in the grid system after completing work above the plenum. More often than not, only the fiberglass panel is replaced thus compromising the entire acoustic assembly. The answer to this problem is a one-piece, composite sandwich panel, in which fibreglass and mineral fibre components are fused together.

With a composite panel, manufacturers laminate the sound-absorbent layer to a sound-attenuating layer, and the resulting product is sold and installed as a single ceiling panel. This greatly simplifies operations for the architect and contractor and provides the end user with the best of both worlds in acoustic control for many years to come.

In Closing

Individually, fibreglass and mineral fibre ceiling panels have their own ways of controlling excess noise. However, it is as a team that they produce top-notch acoustical results in a space. Whenever acoustics is a design requirement, allowing fibreglass and mineral fibre to work together in the form of a composite panel is an excellent choice. â– 

Robert L. Marshall is the manager of marketing technical services for CertainTeed Ceilings Corp., manufacturer of Adagio ™ composite panels. Marshall has more than 30 years of experience in contracting, distribution, and manufacturing of acoustic ceilings, and can be contacted at <robert.l.marshall@saint-gobain.com>.