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Sound Advice from Ask The Pro!

Quick question. What is the NRC rating (Noise Reduction Coefficient) of your couch at home? Donít know? I didnít know mine either! But with a brief search on the internet you can find that an upholstered piece of furniture has an NRC of about 0.60; thatís better than leather furniture, which has a rating of about 0.40. So why donít we see that type of information when we shop for furniture? Because we buy based on the comfort and style of a piece - not on itís acoustical attributes.

For those of you researching ceiling systems, you may see the terms NRC, CAC, STC, SAA and many other 3 letter acronyms. What do they mean and how important are they for your project? Learning all of the acronyms can be confusing; so letís break through all the sound barriers and understand 3 basic characteristics of sound in your room... it can be reflected, absorbed, or it can pass through:

NRC (Noise Reduction Coefficient): The Mystery Revealed

The NRC rating focuses specifically on absorption... how well a specific material will absorb sound, particularly speech, as it passes through an object. The industry standard ranges from zero to 1, with zero being completely reflective and 1 being completely absorptive. The closer you are to a 1 rating, the quieter your room. The NRC is most commonly used to rate the acoustic properties of ceiling tiles, wall panels, baffles, as well as floor coverings and construction materials.But the list could stretch much further because everything in your room affects the overall acoustics: the curtains, carpet, furniture, and people in the room all absorb sound. Thatís why, when standing in an empty room with hardwood floors, you have an echo effect - thereís very little surface material to absorb the sound. Add some furniture, your wall dťcor and some carpeting, and all of a sudden you completely change the dynamics of the sound in that room.

CAC (Ceiling Attenuation Class): Keeping Sound Where it Belongs

Ceiling attenuation describes how much sound is able to pass through the ceiling and into another room. Letís imagine that your teenager has started a band with his friends and they have launched their career in the basement of your home. No matter how good they sound (chuckle), you probably want those guitar riffs and drum solos to stay in the basement and not reverberate throughout the house. A business environment is another good example, where you want to make sure that sound doesnít pass from one office to the next.

So the ceiling attenuation rating isnít based on how quiet the originating room is, but how well it keeps sound from affecting other rooms.Thatís why ceiling tiles may have a low NRC value, but still provide great privacy. An example of this is a tin tile, which only has an NRC of .10 but has a higher ceiling attenuation class than most materials; it simply doesnít allow much sound to pass through its surface.

When considering ceiling attenuation there are several factors other than the tile that affect the passage of sound. When it passes through the tile it encounters other materials above the ceiling system that will once again reflect, absorb, or filter the sound. To improve the ceiling attenuation of a ceiling system it is wise to add elements like polyester batting to absorb most of the sound as it filters through the ceiling tile.

How Important Is Sound Absorption in Ceilings?

By now youíve probably figured out that when shopping for ceiling tiles, it is important to consider how they will affect the sound in your room - but no more so than considering the effect that your flooring will have, or your furniture for that matter. In an empty room you would probably hear a considerable difference when installing a tin ceiling tile (which only has an NRC of about .10) compared to a mineral fiber tile (which has an NRC of about .70). But once you factor in furniture, decor, etc., that sound difference will be considerably less; in fact it may not be noticeable at all.

Here is a quick look at some common ceiling tile materials and what applications they work well in:

Tin Ceiling Tiles:

With a low NRC and high CAC, tin ceiling tiles are best suited for rooms that include other objects that will absorb sound well (carpet, furniture, drapes). Tin tiles are suitable for almost all home applications (perhaps with the exception of a home theater) and do well in businesses that arenít overly noisy.

PVC Ceiling Tiles:

With a better NRC rating than tin, PVC ceiling tiles are good for almost all residential and business applications. For louder rooms like home theaters or in offices where privacy is an issue, use polyester batting to help absorb any sound that passes through the tile.

Mineral Fiber / Acoustic Ceiling Tiles

Mineral fiber ceiling tiles have good acoustical properties and can be used in most residential and commercial applications. Due to the porous qualities of the material, avoid using Mineral Fiber tiles in any environment that has high humidity or potential for water damage.