Acoustics 101: Understanding STC Ratings

What is an STC Rating? The Sound Transmission Class rating and how it applies to acoustical materials and reducing sound heard between two rooms. The Key to Choosing Sound-Absorbing Materials.

When designing room acoustics, there are many different ratings that may be applied to a product to identify how it will shape the sound of a space or between spaces. You may come across ratings for NRC (Noise Reduction Coefficient), SAA (Sound Absorption Average), STC (Sound Transmission Class), IIC (Impact Insulation Class) or CAC (Ceiling Attenuation Class).

A Sound Transmission Class (STC) Rating is determined by how well a complete wall, ceiling, floor, window, or door assembly’s reduces sound transmission in decibels (dB). The higher the STC number, the better the sound blocking capabilities. The Ratings are presented from 0 to 60+.

Lower STC, such as 25, would allow normal volume voices to still be understood. Higher STC, 35+, would increase likelihood that sounds are not intelligible or potentially not audible at all.

It is important when designing or constructing a wall or ceiling assembly, to consider the material’s ability to block transmission. Rubber clips are often utilized in wall assemblies to limit sound transfer between hard building materials, which can be quite good at transferring sound vibration.

Keep STC ratings in mind to ensure an effective barrier against sound transmission.

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