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What is STC Rating?

//What is STC Rating?
What is STC Rating?2019-07-25T21:17:58+00:00

STC rating (Sound Transmission Class rating) is a way to rate how well an assembly of materials reduces sound. Assemblies of material reduce sound through absorption or reflecting sound waves.

The higher the rating, the less noise penetration. STC rating goes from 20 – 65, 25 and lower being low or no soundproofing and 65 and above being soundproof or where no noise can penetrate. A standard single-pane window would have an STC rating of 25 where most “soundproof” products have an STC rating in the range of 35-55. Industry average for windows is STC rating of 38. 

 
heavy traffic on a highway through a city at night
 

STC rating is a way to compare products for their ability to stop the transition of sound. Using this number you are comparing apples to apples. This isn’t just within one product type. You can compare window to window, but also window to door for their ability to stop outside noise from coming into your space.

 

STC Rating Chart

This STC rating chart shows a variety of building materials, their average STC rating and what noise can and cannot be heard at that STC rating. Specific products for these building materials will vary, so talk to the manufacturer to get the exact STC rating before purchasing.

 
STC Rating chart with material assembly, STC rating, & relative noise level
 

Things to note: STC rating of 25 is what can be easily heard. STC rating of 38-42 is considered good soundproofing for residential. STC rating of 50-65 is professional, commercial soundproofing for recording studios, etc.

 
Other Sound Transmission Definitions
 

These terms and definitions are related to Sound Transmission Class and will help provide the full picture of how sound is measured.

dBa – A-weighted decibels. Measurement of sound as perceived by the human ear. Decibels relate to all sound possible (that can be perceived by say, a dog). A-weighted decibels are a scale of measurement for all sound that can be heard by humans, starting with zero as the lowest threshold of human hearing and going up to 110 dBA for jet fly-over/indoor rock band.

 
STC noise reduction soundproofing infographic
infographic of dBa levels and examples of relatives noises
 

Transmission Loss – How much sound is lost going through a material. When sound reaches an object, some of the noise vibrations are reflected by it, some are absorbed, and some travel through it. The amount of sound that does not travel through it, is considered loss. It is the difference between the sound going into the object and the sound coming out the other side.

Frequency (Hz) – Sound is vibrations that travel through the air. Frequency is the speed of the vibrations. Frequency is measured in units of Hertz (Hz). Hertz measure the number of wave cycles per second. Low frequency sounds, like thunder or a train, would have a lower Hz. High frequency sounds, like a whistle or a bird chirping, would have a higher Hz.

For more definitions see our glossary of acoustic terms.

While STC rating can provide a good indication of how a material or product will perform against sound in general, it isn’t the whole picture. That’s why it’s good to keep these other definitions in mind. Certain sounds or noises will affect different people differently. STC rating is one number that shows general sound resistance, but does not take into account Hz.

 

STC Rating Limitations

STC is a single number used to describe the ability of an assembly (how a product is put together) to reduce noise against a wide range of frequencies. An STC rating alone won’t show what Hz will be blocked. STC rating only gives you an overall average of noise blocking.

Different products work differently to block different noise so you must compare exact product assemblies to each other (e.g.: a double-pane window with the same air gap). Talk to the manufacturer about what their product can block if you are having issues with a particular noise (e.g.: dog barking, a train horn).

 
woman installing Indow insert to block noise
 

STC Rating Windows

Without the addition of soundproofing materials, STC rating for regular windows not optimized for noise range from 25-38. Factors that can affect the STC rating of windows are: whether they are single or double-pane, the size of the gap between the panes, if gas is inserted between the panes, the thickness of the glass, and how airtight they are.

With the addition of window inserts such as Indow inserts, the STC rating for windows can increase to 39-45. Indow inserts are made of acrylic, which absorbs more sound and resists sound better than glass. Adding another layer to your window via a window insert also creates an air pocket that insulates against sound. STC rating windows at 42-45 usually only happens when Indow window inserts are added to double-pane windows.

 

STC Rating Chart For Windows

This STC rating chart for windows goes down for the higher STC values to represent the quieter environment you will experience.

 
stc rating chart
 

Is Complete Soundproofing Possible?

Our STC rating chart above only goes to 50 where STC rating goes up to 65. Most products don’t promise anything above 55 and even at a rating of 60, it still doesn’t guarantee complete soundproofing. Nothing is completely soundproof. You cannot stop outside noise completely from entering your space. Anywhere air can get in, noise can get in.

*We want to ensure our inserts help solve your noise problem. Overall noise reduction depends on the amount of noise coming through your walls, ceilings, floors, doors, and existing windows. Noise reduction will be less when placed over double-pane windows. Read our full Noise Reduction Sheet to learn more.

 
Let Us Help You
 

If you’d like to know more about STC rating or evaluating your space for soundproofing, get a free assessment today.

bedroom with window with indow inserts installed for noise blocking