NRC measures how well something absorbs sound, how well materials stop sound waves from reflecting). The NRC of different materials vary significantly. Understanding these, differences can go a long way in knowing what materials to use to achieve a specific result.
A Basic diagram that shows the difference between NRC & STC Ratings
STC - is short for sound transmission class. Sound Transmission Class is more complicated calculation than NRC, involving the graphing of "contour curves", transmission loss curves, and identifying a number on the contours where the two graphs are closest together. In regular terms, however, it measures how well an item blocks sound from passing through it.NRC is a measurement of how well a product makes the room you are in quieter, while STC measures how well a product keeps sound from escaping the room.
A simple diagram showing the difference between NRC & STC acoustic ratings
When to use NRC
When you are in a noisy room like a gymnasium, you want a product with a higher NRC on the walls or ceiling to make the room less noisy.
When to use STC
If you are in a conference room where you are talking about sensitive topics that you don’t want people on the other side of the wall to hear. You need a product on the wall with a high STC. The image below features panels mounted to a gym wall to help reduce the echo.
NRC Units of Measurement
NRC usually ranges from zero to 1.0. A reasonable rule of thumb is that the NRC of a product is the percentage of sound a product will absorb. A painted drywall wall has NRC of about .05, so it absorbs only about 5% of the sound that hits it and reflects back 95% of the sound. A deep-pile carpeted floor may have an NRC as high as .35. 1” thick fabric covered acoustical panels designed specifically to absorb sound have an NRC closer to .80, making them very sound absorptive, reflecting back only 20% of the sound that hits them.
STC Measurement is a little More Complicated
Unfortunately, the STC value is not something one can explain simply. It may be easier to explain using a real life situation. A metal stud wall with ½” thick drywall on both sides has an STC of 34. While that is certainly better than nothing, it’s not very good. A metal stud wall with sound attenuating batt insulation in between the studs and 5/8” thick drywall on both sides has an STC of 47. That is much better and probably the most common construction in commercial buildings. breezeblock walls typically have an STC in the upper 40’s to low 50’s. There are ways to increase the STC of a wall even further – adding another layer of drywall to the wall, staggering the studs, using resilient channels – but that can be discussed elsewhere. Unless you are building movie theatres or some other application where blocking every bit of sound penetration is critical, you should not have to go to those extremes. STC ratings in the upper 40’s are good. STC ratings in the 50’s are excellent. When selecting the right Working Walls Solutions product for your noise problem, you need to first identify what the problem is. If you have a space with too much echo, you need a product with a good NRC. On the other hand, if the problem is sound going through a wall, you need one of our products with a decent STC.
Live Acoustics provide a comprehensive service to help you refurbish or develop your auditorium, multipurpose room or performance space.
Live Acoustics have a proven track record in providing effective Acoustic Solutions
High Sound Absorption is very important in open office spaces, lobbies, passages, boardrooms and theatres where people need to talk normally without affecting others in the rest in the space.
High Sound Absorption distributed throughout the space also significantly reduces flanking noise between rooms, so people can easily talk to each other without disturbing people in the room next door.
Sound absorption is the measure of the energy removed or energy reduction of the sound wave as the wave passes through a given thickness or type of material. Sound absorption is necessary for soundproofing.
While distributing the sound wave into an absorbable material, the sound wave in addition to absorption could also experience sound wave reflection, as energy dissipate and displaces. Dampening or vibration or energy loss results as the energy-dissipated is converted into heat.
Soundproofing makes (a room or building) resistant to the passage of sound or prevents sound from traveling. Soundproofing products block sound from leaving or entering a room, and consist of dense layers inside walls, between floors and above basement ceiling drywall.
Soundproofing ideally occurs in early construction, as it can be a challenge to soundproof a room once the construction is completed.
Sound absorption involves the absorption of sound. Sound absorption happens when the sound waves is absorbed by a material Sound absorption enhances the space’s sound quality as it reduces unwanted noise and dampens sounds, like echoes and reverberation vibration. Sound absorption products can be temporary and non-permanent, unlike soundproofing products (and layers). Acoustic fabric wall panels are one such sound absorption product, and this is our focus in this feature.
Sound is created by the vibration of substance and is spread by sound wave produced through the sympathetic vibration of the medium. When sound is spreading, part of it is gradually diffused and part of it is weakened due to the absorption of air molecules, which are more apparent in the open air; but in indoors sound is much less diffused or weakened, instead it is mainly absorbed by the surface of materials.
When a sound wave meets the surface of a material, part of it is reflected, part of it passes through the material, and the rest of it is transferred to the material. The part of sound wave transferred to the material enters the pores of the material and causes the friction and viscosity resistance between the air molecules and the wall of pores, thus certain part of sound energy is converted into heat energy and is absorbed in this way.
The sound absorption coefficient is used to evaluate the sound absorption efficiency of materials. It is the ratio of absorbed energy to incident energy and is represented by α. If the acoustic energy can be absorbed entirely, then α = 1
NB: The air gap between the acoustic layer and the space behind increases the sound absorption coefficient value in the mid and higher frequency ranges
The density of the acoustic material is also important. Less dense and more open structures absorb the sound of low frequencies (500Hz) while the denser structures perform better for frequencies above than 2000 Hz range
A NRC is an average rating of how much sound an acoustic product can absorb. An NRC of zero means that the product absorbs no sound. An NRC of 1 means that the product absorbs all the sound. The higher the NRC, the better the product is at absorbing the sound.
A .90 or .95 NRC rating. A Noise Reduction Coefficient of .90 or .95 means our panels are big sound absorbing sponges, absorbing 90% or 95% of the noise, creating a more pleasantly sounding environment.
Formaldehyde is a colourless, strong-smelling gas. It is widely used in the manufacture of building materials and many other household products.
Some unfortunately are still using it in homes as an adhesive resin in some compressed wood products. Building materials made with formaldehyde resins can radiate formaldehyde gas.
Formaldehyde exposure has various bad side effects Formaldehyde has a link to some forms of cancer in animals and humans.
When present in the air at levels at or above 0.1 ppm, acute health effects can occur including watery eyes; burning sensations in the eyes, nose and throat; nausea; coughing; chest tightness; wheezing; skin rashes; and other irritating effects. The World Health Organization recommends that exposure should not exceed 0.05 ppm.
Volatile organic compounds (VOCs) are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short - and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. VOCs are emitted by a wide array of products numbering in the thousands.
Organic chemicals are widely used as ingredients in household products. Paints, varnishes and wax all contain organic solvents, as do many cleaning, disinfecting, cosmetic, degreasing and hobby products. Fuels are made up of organic chemicals. All of these products can release organic compounds while you are using them, and, to some degree, when they are stored.
The method used to calculate how much sound is reflected in a room by using a metric called the absorption coefficient. The Absorption Coefficient measures of how much sound is absorbed, and is not reflected.
The absorption coefficient ranges between zero and one, one meaning no sound energy is reflected and the sound is either absorbed or transmitted. For example, an opened exterior window has the absorption coefficient of one because no sound returns to the room. An effective absorber will have a sound absorption coefficient greater than .75.