STC, IIC, DELTA IIC…What’s this all about?

As a home owner, or if you’re new to the industry and acoustics, the acronyms STC, IIC and DELTA IIC may not mean a lot to you. These acronyms are industry standards that identify sound ratings and are very useful in determining not only the severity of the noise in the space or the noise generated from a source, but it is also key to determining the effectiveness of acoustic solutions.

STC – Sound Transmission Class

STC is used to determine airborne sound transmission loss for frequencies between 125 and 4,000 Hz. These frequencies cover most of the typical noises we would hear such as televisions, radios, animals, speech, cars, etc… The higher the STC rating the greater the effectiveness of a material or construction to reduce the transmission of airborne sound. In essence, the objective is to achieve noise reduction, by using materials with a high STC rating in order to block some of the sound energy.

For example, the STC rating of a basic wall with a single layer of drywall on each side is 35-38, once treated with acoustic materials the wall could achieve an STC of 60 or more, virtually eliminating the airborne noise transmitted through the wall.

Acoustic treatments to improve STC ratings include sound isolation clips, noise barriers such mass-loaded vinyl, acoustic underlayments, acoustic panels and many more depending on the space and application.

IIC – Impact Insulation Class

IIC is used to determine the amount of impact noise isolation. As the STC rating, IIC tests measure sounds between 125 to 4,000 Hz but in this case it measures the amount of vibrations that travel through the floor/ceiling assembly. The higher the IIC rating, the more effective the floor or ceiling assembly is at isolating vibrations and at absorbing impact sound, such as steps from someone walking on the floor above.

For example, the IIC of a basic wood sub-floor with no resilient underlayment is between 40-45 IIC. Once treated with a sound impact underlayment the construction could achieve an IIC of 70. This results in a very significant reduction of the vibrations being transferred through the structure, with a corresponding reduction in noise.

Acoustic solutions to increase IIC ratings include sound isolation clips, impact sound underlayments, and other anti-vibration materials.


Delta IIC rating shows what the product adds to the assembly in terms of impact sound isolation. It is the difference between the total IIC achieved once the construction is acoustically treated and the IIC the material has prior to being acoustically treated. For example, If the floor construction has an IIC of 40 and once an impact sound underlayment is added the construction achieved an IIC of 70, then the Delta (change) IIC is 30.

This rating isn’t used very often; reason being is that most company’s use IIC to demonstrate a higher reduction rating. Delta IIC is the best rating to consider when comparing the impact sound performance of different materials as it doesn’t allow for misleading results; it provides the IIC rating of the product rather than of the entire assembly.

ARCACOUSTICS provides an extensive line on acoustic materials with exceptional noise reduction capabilities. Our experts in acoustics and noise control offer complete architectural and interior building noise control products and systems. We continuously serve acoustic solutions to a number of markets providing added visual and acoustic aesthetics to environments. Our objective is to improve individual comfort levels and increase productivity, through the improvement of STC and IIC ratings.

As the responsible company ARCACOUSTICS™ strives to be, we work with the best manufacturers in order to provide our clients with the foremost acoustic products for a variety of applications. In conjunction with our manufacturers we work hard to ensure we not only meet our clients requirements but we exceed their expectations through excellent customer service, design, and acoustic results.

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