STC (Sound Transmission Class) – Definition & Detailed Explanation – Acoustic Treatment Glossary

What is STC (Sound Transmission Class)?

STC, or Sound Transmission Class, is a rating system used to measure how well a building material or assembly reduces the transmission of airborne sound. It is a standardized measurement that provides a numerical value to indicate the soundproofing capabilities of a particular material or structure. The higher the STC rating, the better the material is at blocking sound.

How is STC measured?

STC is measured in accordance with ASTM E413, which outlines the procedures for conducting sound transmission tests in a laboratory setting. During testing, a sound source is placed on one side of the material or assembly being tested, and a microphone is placed on the other side to measure the sound levels. The difference in sound levels between the two sides is used to calculate the STC rating.

What are the typical STC ratings for common building materials?

Different building materials have different STC ratings based on their composition and thickness. Here are some typical STC ratings for common building materials:

– Single layer of drywall: STC 33-38
– Double layer of drywall: STC 45-50
– Solid wood door: STC 25-30
– Hollow metal door: STC 20-25
– Concrete block wall: STC 45-50
– Fiberglass insulation: STC 30-35

It is important to note that these ratings can vary depending on the specific product and installation method used.

How can STC be improved in a building?

There are several ways to improve the STC rating of a building or structure. Some common methods include:

– Adding additional layers of drywall or other soundproofing materials
– Using soundproofing sealants and gaskets to fill gaps and cracks
– Installing soundproofing curtains or panels
– Using resilient channels or sound isolation clips to decouple walls and ceilings
– Adding mass-loaded vinyl or other soundproofing barriers

It is important to consult with a professional acoustical engineer or contractor to determine the best approach for improving the STC rating of a specific building.

What are the limitations of STC as a measure of soundproofing effectiveness?

While STC is a useful tool for comparing the soundproofing capabilities of different materials, it does have some limitations. One of the main limitations is that STC only measures the transmission of airborne sound and does not account for impact noise or low-frequency sound. Additionally, STC ratings are based on laboratory tests and may not always accurately reflect real-world conditions.

Another limitation is that STC ratings do not take into account flanking paths, which are indirect paths that sound can travel through in a building. These paths can significantly reduce the effectiveness of soundproofing measures and may not be reflected in the STC rating.

How does STC relate to other acoustic measurement standards?

STC is just one of several acoustic measurement standards used to evaluate the soundproofing capabilities of building materials and structures. Other commonly used standards include Impact Insulation Class (IIC), Noise Reduction Coefficient (NRC), and Outdoor-Indoor Transmission Class (OITC).

IIC is used to measure the impact sound insulation of floors, while NRC is used to measure the sound absorption capabilities of materials. OITC is similar to STC but is specifically designed to measure the sound transmission loss of exterior building elements.

Each of these standards provides valuable information about the acoustic properties of a material or structure and can be used in conjunction with STC to create a comprehensive soundproofing plan.