Explaining STC: Sound Transmission Classification

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What is STC rating? Just as NRC is the standard rating for how well a material absorbs sound, the sound transmission class  (STC) is a single-number rating that gives a rough idea of how much sound a specific type of material might stop.

An industry standard when it comes to calculating sound transmission through barriers, STC is the most common sound reduction measurement currently in use. An STC rating can help you determine how much sound is being reduced and the frequencies of sound being affected.

An STC rating of 20 is considered very poor (low speech audible) while a rating of 60 is considered excellent (loud sounds barely heard). Nowadays, many building codes require condos and townhouses to meet an STC of 50, while luxury hotels and condos should reach a rating of 60 or higher. For example, a standard 2×4 wood stud wall with ½” drywall has an STC of 32.

An important point to keep in mind is that the STC only tests on frequency ranges from 125 to 4000 Hz and one common problem with this type of classification is that a lot of common noise issues can be attributed to sounds that often falling below or above this range. Examples of this include bass drums, deep male voice and trucks—all of these can potentially start at 50 Hz; high-pitched female voices,  the shrill ringing of phone and car horns are good examples of sounds that reach above the 4000 Hz range.

This will explain why many big projects—even after having paid tens of thousands of dollars on expert acoustical engineers and getting thousands of pages of tested soundproofing materials with lab testing of STC of 50 and above—still receive complaints for poor acoustical performance.

Fortunately, there are several different ways to soundproof your living space!
At Residential Acoustics, we pride ourselves on helping you reduce the sound in your bedroom, living room and office with quality, state-of-the-art products such as the AcousticCurtain™ and AcoustiDoor™—an easy and affordable way to soundproof your home!

To ensure you get the absolute best results, call TODAY for a FREE over-the-phone consultation! One of our soundproofing experts will assist you in diagnosing your issues and offer a solution—the best approach to fix them.