What is STC?

Technically speaking, STC stands for Sound Transmission Class, which is the measurement used to calculate the effectiveness of soundproofing materials in reducing sound transmission between rooms. STC is measured roughly by the decibel reduction in noise a material/partition can provide, abbreviated 'dB'. Simply put, it measures how much sound a wall, for instance, will block from getting through to the other side.

STC ratings were introduced in 1961 as a way to compare different types of walls, ceilings, floors, doors, and windows. By taking the transmission loss values and testing them at 18 of the most common frequencies (between 125 Hz-4000Hz), a curve is created, which is then compared to the standard STC curves of reference. Whichever curve of reference your curve most closely matches is the STC rating for your specific fixture. For example, if the curve created by one of your walls most closely matches the standard STC 40 curve, your wall will be said to have an STC of 40. Generally speaking, the higher the STC rating, the more effective a material is at blocking sound at the most common frequencies.

What Are Decibels?

Decibels noted as dB, are a simple measurement of how loud something is. On a Sound Pressure Scale, with 0dB being the threshold of audibility and 130dB causing physical pain when listening, most quiet homes register at 40dB.

What is Frequency?

Frequency, by definition, is the measurement of the tone or musical note of the sound. A really high sound, like a flute, registers at 2000Hz whereas a really low sound, like a tuba, registers under 30Hz. It’s important to note that humans can only hear sounds between 20Hz and 20,000Hz- a range that shrinks as people get older.

What is Transmission Loss?

Transmission loss is the measurement of the volume (dB) difference on either side of a wall. Let’s say there is a loud sound on one side of your wall (maybe your son playing the drums) that registers at 100dB. We go to the other side of your wall and measure the volume there, and that only registers at 75dB. The difference between the two walls is 25dB, so we could say there is a 25dB transmission loss, meaning 25dB less sound made it to the other side of the wall.

The interesting thing about this type of measurement is that the same wall may have a different level of transmission loss if the pitch changes. So even though there might be 25dB less sound when your kid is playing the drums, there may only be 4dB of sound loss when someone is vacuuming in the same room.

Peacemaker® And STC

To reduce the transmission of sound between rooms, the STC of a room’s wall needs to be increased. This can be done using many soundproofing materials such as Peacemaker Sound Insulation, which is a flexible rubber soundproofing noise insulation easily installed in walls, floors, and ceilings. Peacemaker noise insulation is ideal for apartments, multi-family residences, condos, commercial installations, studios, theaters and more.

Peacemaker's impact extends beyond the area you are soundproofing. Peacemaker rubber soundproofing puts old and recycled tires to sound use, keeping them out of already-overflowing landfills. When you purchase this cost-effective and high-performance rubber soundproofing material, you are making a difference not only in your immediate environment but in the greater one as well.

Peacemaker acoustical barrier is available in two densities. These product variations allow us to offer our customers an affordable and versatile product that is both healthy for the environment and you.

1. Peacemaker Soundproofing Underlayment - the thickest of the two is ideal for floors and recommended more for impact and vibration control.
2. Peacemaker Sound Barrier - the thinner, high-density version of the product blocks mid- to high-range frequencies, and is perfect for wall and ceiling applications.

Additional STC Information

• When soundproofing rooms, the STC of your doors & windows need to be equal to or greater than the STC of your walls in order to maximize the rating.
• Structurally decoupling drywall panels from each other (using steel studs, a staggered-stud wall, double wall stud, or resilient channels) can produce an STC rating as high as 63 (for a double stud wall) and will result in an effective low-frequency loss. This figure, when compared to a normal wall with an STC of 33, will make most frequencies inaudible, making the room sound 88 percent quieter.
• Music-related sounds may require the highest STC ratings. In practical terms, a 55 STC rating will prevent a resident living in a multi-family home from being bothered at all by their neighbor’s loud music.
• Homes usually require 50-80 STC for sensitive areas, including home theater walls.
• It’s not always practical to test the entire wall configuration of an assembly to determine the true STC.
• Higher STC ratings generally are better. However, don’t forget that STC ratings only take into account sounds over 125Hz. This means that extremely low frequencies don’t register on the STC rating scale, thus when a sound on one side of a wall is below 125Hz, the ability of the wall to block sound cannot be calculated.
• STC is not a direct measure of how many decibels of sound a wall can stop. If a wall has a rating of 35, it does not mean that the wall stops 35dB of sound.
• You can’t add STC ratings together. For instance, if you have an STC of 40 on one wall and decide to add another wall with an STC of 20, the STC of both walls combined will not be 60. Instead, the STC will be calculated using logarithms, and will probably produce a rating of about 45. When soundproofing rooms, adding materials with higher STC ratings will considerably reduce the sound being transmitted through walls, windows, floors, etc.

Need more help understanding acoustics? Call one of our Acoustic Specialists at 1.866.505.MUTE to receive free acoustic advice specifically for your space or fill out a Free Room Analysis Form.