When it comes to evaluating the acoustic performance of materials, two common metrics are often discussed: Noise Reduction Coefficient (NRC) and Sound Transmission Class (STC). While both are essential for assessing how materials can impact sound within a space, they measure different aspects of acoustic behavior.
Noise Reduction Coefficient (NRC)
What is NRC?
The Noise Reduction Coefficient (NRC) is a measure of a material's ability to absorb sound. It is expressed as a number between 0 and 1, with higher values indicating greater sound absorption. NRC is an average rating across four specific frequencies: 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz.
How is NRC used?
NRC is commonly used to evaluate the acoustic performance of materials such as fibreglass wall and ceilings panels, wood wall and ceilings panels, and even acoustic curtains. A higher NRC value indicates that the material is more effective at absorbing sound, which can help reduce reverberation and improve speech intelligibility in a room.
What does it mean?
A material with an NRC of 0.80 means that it absorbs 80% of the sound that contacts it.
Sound Transmission Class (STC)
What is STC?
Sound Transmission Class (STC) is a measure of how well a building partition reduces airborne sound. It is a single-number rating (0-100) that indicates the effectiveness of a material or assembly at blocking sound across a range of frequencies. A higher STC rating indicates better sound isolation.
How is STC used?
STC ratings are used to compare the sound-blocking performance of walls, floors, doors, and windows. The higher the STC rating, the more effective the material is at reducing the transmission of sound from one space to another.
What does it mean?
An STC rating of 50 means that the material reduces the sound level by 50 decibels, with higher numbers indicating better sound isolation.
Reminder!
Flanking occurs when sound waves travel through paths that bypass the primary sound-blocking barrier, such as through gaps, cracks, mullions, doors, or other openings in walls, floors, or ceilings. Flanking transmission can significantly reduce the effectiveness of soundproofing measures and result in sound leakage into or out of a room or space.
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