Decoding STC Ratings: What They Mean and Why They Matter

Soundproofing isn’t just a luxury. In today’s bustling and high-volume world, it’s an essential aspect of design. As homeowners and business owners, understanding STC ratings, what they mean, and why they matter could mean the difference between creating a quiet space and a space with lots of noise and distractions.

Sound Transmission Coefficient (STC)—otherwise known as “Sound Transmission Class”—is the golden standard that evaluates how well a barrier, be it a wall, ceiling, door, or window, reduces airborne sound. Essentially, it’s the report card of a structure’s ability to reduce noise.

Higher ratings mean a greater resistance to sound penetration. So, when you consult an STC rating chart, you’re essentially seeing the effectiveness scoreboard of various materials against intrusive noise. This is super important when soundproofing your home or business because it helps you establish the perfect options.

Imagine you’ve created the perfect, cozy reading nook in your home, but you can still clearly hear every car that drives by, the chatter from the apartment next door, and stomping from upstairs. What if there was a way to reduce all that noise so you could have the tranquil space you want?

That’s the difference a high STC rating can make. Whether it’s a child’s bedroom shielded from living room sounds, a quiet and serene basement, or a home office insulated from street noise, knowing the STC rating for your space is pivotal to crafting acoustical solutions that work.

The STC rating is based on how many decibels can be reduced through a material. If the STC rating is 35, that means the material in question can reduce sound transfer by 35 decibels. Of course, the rating is determined as an average based on the different frequencies between 125 Hz to 4000 Hz.

The lower the frequency, the more difficult it is to reduce the decibels that pass through the material. The higher the frequency, the easier it is to reduce. The STC rating is an average of all those numbers.

A “good” STC rating is probably about 50 and can usually be accomplished with a standard wall assembly with insulation and Green Glue. That’s enough to reduce your sound bleed to a point where normal activities won’t disturb the other people in your home. If you need something a little more serious or professional, you’re going to want to aim for an STC rating of 55 or higher. For commercial-grade STC ratings, you could aim as high as 60, which is more than enough to reduce the sound in a firing range.

Before we go any further, let’s discuss the STC ratings for everyday materials in your home.

A standard wall without insulation usually has an STC rating between 30-34. However, if you integrate specialized materials and effective insulation, you can get those numbers as high as 60.

If an STC rating is the measurement of how much sound is reduced, then NRC (Noise Reduction Coefficient) is the measurement of how much sound is absorbed. Both are vital when creating acoustical solutions. It’s important to understand the distinction.

Sound absorption (NRC) is necessary when you’re trying to create a pristine sound environment. It enables you to control the sound within the room. Sound reduction (STC), however, is necessary when you’re trying to reduce sound from exiting or entering the room. An STC rating makes the room sound quiet. An NRC rating makes the room sound better.

Determining how this applies to creating acoustical solutions is pretty simple. I’ll give you an example. I recently worked with a client who wanted acoustic solutions for a drum set. Drums are incredibly loud, so they (understandably) wanted to create a room where they could play their drums without disturbing everyone in the home and their neighbors.

My recommendation was to use the STC rating for the materials that were already present and add new materials to raise the STC rating to an acceptable level (between 50 and 60). The biggest challenge was that we had to tackle the low frequencies of the bass drum. Here’s what we did:

Sound can define your space, and by harnessing the power of STC ratings, you can turn your home or business into the perfect sound environment.

Contact us today to learn more about how we can transform your home or business with the power of STC ratings!