Light Acoustic Panels Suitable for Offices

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NRC number 1.0 is the best a wall can be whereas .85 is very good and .15 does little but is better than a concrete wall.

What is NRC?

Average sound absorption coefficient measured at four frequencies: 250, 500, 1,000, and 2,000 Hz expressed to the nearest integral multiple of 0.05. Rates the ability of a ceiling or wall panel or other construction to absorb sound. NRC is the fraction of sound energy, averaged over all angles of direction and from low to high sound frequencies, that is absorbed and not reflected. NRC ranges from 0 (concrete floor) to 1.00 (high performance acoustical products).

What does STC mean?

STC stands for Sound Transmission Class. It is a one-number measurement of the overall efficiency of a sound barrier. It summarizes the sound transmission loss at 16 different frequencies. The Building Code has established a minimum STC for the dividing walls running between dwellings; in Ontario this minimum is 50 STC (a higher STC rating, of course, will give improved results). The code lists specific acceptable systems or permits the use of systems measured under ASTM E90 or ASTM E336.

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Acoustical Terms -- What Are They/What Do They Mean?

Recently we were asked "What is the difference between STC, NRC, and NC and are they interrelated?"

STC or Sound Transmission Class, describes how much sound a wall or a floor/ceiling construction will block from one room to the next. A good analogy to an STC rating is the fire rating of a partition. A two hour fire-rated assembly will keep the fire on the opposite side of the partition longer than a 20 minute assembly. Just like fire ratings, the higher the STC rating, the better the isolation. Therefore, an STC 50 partition will block more sound than an STC 30 partition.

NRC or Noise Reduction Coefficient, defines how much sound specific materials absorb. This is analogous to a room's finishes. Just as various colors of paint, or textures, visually alter a room, various materials with different NRC ratings, such as carpet or tile, audibly alter a room. A material with a low NRC rating (tile) absorbs little sound and a material with a higher NRC rating (carpet) absorbs more sound.

Finally, NC or Noise Criteria measures how much mechanical noise can be heard in a room. This type of measurement can be compared to the amount of light in a room. A foot candle describes how much illumination a lighting fixture provides on a surface, NC describes how much mechanical system noise is heard in a room. The brighter the light on a surface the higher the foot candles, and the higher the NC rating, the more noise that is heard.

Are STC, NRC and NC related? Not really. They do interact in the total design of a room, just as the building structure, room finishes and lighting interacts on the visual design of a space. However, individually they all play separate roles. Room finishes are independent of the fire rating of the partition, just as the amount of sound a material absorbs is independent of its ability to block sound from one room to the next.

Hopefully these analogies of Sound Transmission Class to fire ratings; Noise Reduction Criteria to a room finish; and Noise Criteria to foot candles helps define and explain these acoustical terms.