Acoustics 101: Understanding CAC Ratings

What is a CAC Rating? The Ceiling Attenuation Class and how it applies to acoustical materials and inter-room sound transmission. 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 Ceiling Attenuation Class (CAC) Rating of a product measures how well a ceiling can block sound from traveling through into the ceiling plenum in spaces where the wall does not extend to the deck.

CAC is essentially an STC (Sound Transmission Class) rating for sound attenuation of a suspended ceiling system over two adjacent rooms sharing a plenum. This rating class was created for drop-in acoustical ceiling tile manufacturers to more clearly represent this type of Sound Transmission Loss. However, it does not differ from the STC rating.

First, it is important to understand what a CAC rating measures. CAC ratings range from CAC 25 to CAC 50, with CAC 50 being the best rating a ceiling can have. Ceilings with a CAC 25 are considered to have poor sound blocking capabilities, while those with a CAC 50 provide excellent sound blocking. A rating of 35+ is considered very good.

A good CAC rating is important for minimizing inter-room noise pollution and ensuring a comfortable environment for employees or tenants. A higher CAC rating can lead to improved acoustic comfort for those in the space, particularly in offices or other spaces where sound privacy is important.

It is also important to note that CAC ratings are not permanent. The rating can change over time as some less-durable ceiling material wears, if new ceiling penetrations are made for air ducts, or if modifications are made to the plenum above the ceiling.

Overall, understanding CAC ratings can help you make informed decisions when it comes to choosing a ceiling for your space. It is just one aspect to consider in creating an acoustic plan, but an important one nonetheless.

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