Industrial noise control is essential for enclosure design, operator cabins, and recreational vehicles.. When noise levels get too high, it can be disruptive, frustrating, and dangerous. Manufacturers and installers facing major issues may need to further soundproof structures.

STC ratings, or Sound Transmission Class ratings, create a relatively standardizing rating system that measures sound transmission (as opposed to sound attenuation or decibels). STC ratings help designers confirm the degree of soundproofing they can provide in a given space.

Learn more about how STC works, what ratings to aim for, and how to decrease unwanted sound transmission across your structures.

What Is STC?

Sound Transmission Class (STC) is a single rating number system that evaluates how effective different materials are at blocking sound. When more sound is being blocked, the material scores higher. It’s a generalized scale, meaning that loud sounds may be faintly audible (high scores) or normal conversational volumes are audible (low scores).

Most enclosures will have different materials for their floors, ceilings, walls, and doors, as the materials within each area uniquely contribute to overall soundproofing.

While STC measures vocal noise and relatively high-frequency noises, it is less accurate when measuring low-frequency noises such as machinery or music.

What Is a Good STC Rating?

As a general rule, the higher the STC rating is, the better. Walls, floors, and ceilings may each warrant different levels of soundproofing. An operator cabin may require more soundproofing for walls, headliner, and floors while a generator would require a more basic treatment.

If you want to construct environments with very little external sound interference, you will need to achieve a higher STC rating with your soundproofing. For instance, an apartment should generally rate on the higher end of the scale so residents can perform daily functions with adequate privacy.

How Is STC Measured?

While STC ratings provide a generalized, rough understanding of how soundproof a structural surface is, they don’t directly measure decibel reduction. The STC ratings follow specific laboratory testing procedures that adhere to ASTM standards.

Laboratories can determine the STC rating of materials (or combinations of materials) by measuring transmission loss and plotting it against the frequency of the sounds.

What Is a Good STC Rating for Windows?

Windows are harder to soundproof than other surfaces like floors and walls because it’s much harder to layer effective materials.

Single-pane windows typically have a rating of 26-28, and it’s hard to significantly raise it. However, builders can install double-pane windows and add more insulation around the windows to mitigate sound overall.

STC Rating Chart

Use this STC rating chart as a rough guide to the different STC ratings for soundproofing materials:

  • 25: There is no functional soundproofing, and quiet conversations can easily be overheard
  • 30: Quiet speech is muffled, but conversations at normal volumes are audible
  • 35: Loud speech is clearly audible
  • 40: You can hear loud conversations next door but not clearly understand them.
  • 45: Conversations can be private
  • 50: Loud conversations and sounds are muffled but faintly audible
  • 60+: Soundproofing is very good, and even loud conversations will be hard to overhear

STC Rating vs. Decibels

STC ratings measure how much sound is being blocked, while decibels (dB) measure the volume of the sound. The two concepts are related but not identical; acoustic absorbers can both have a high STC rating and reduce decibels.

Consider these common sound thresholds:

  • 10 dB: Sound is now audible
  • 35 dB: Whisper volume
  • 55 dB: The volume of a large transformer at 200 feet
  • 70 dB: Normal speech from one foot away
  • 85 dB: Pneumatic drill 50 feet away
  • 95 dB: Subway train 20 feet away
  • 105 dB: Operator’s experience of a pneumatic hammer’s volume
  • 120 dB: Jet taking off from 200 feet away

Learn More About STC Ratings From Technicon Acoustics

Technicon Acoustics specializes in industrial noise control and vibration-damping solutions. We provide solutions for construction equipment, marine applications, power generation equipment, and trucks.

Contact us today to learn more about our products and their applications or to request a quote.