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Understanding Sound Transmission and the Principles of Soundproofing

Understanding Sound Transmission and the Principles of Soundproofing


Soundproofing is critical in both residential and commercial settings for creating comfortable and productive environments. By understanding the principles of sound transmission and soundproofing, you can optimize the effectiveness of soundproofing products like Green Glue and Resilient Sound Isolation Clips. This comprehensive guide will give you an overview of these principles and show you how they can help you with your soundproofing projects.

Basics of Sound Transmission

Types of Sound

There are two primary types of sound:

  1. Airborne noise: This type of noise travels through the air and includes sounds like conversations, music, or barking dogs.
  2. Structure-borne noise: This type of sound, also known as impact noise, is transmitted through the structure of a building as a result of vibrations caused by footsteps, machinery, or other impacts.

Sound Transmission Class (STC)

The Sound Transmission Class (STC) is a rating system that quantifies a material or construction assembly's ability to reduce airborne sound transmission. The higher the STC rating, the more effective the material or assembly is at blocking sound.

The following factors influence STC ratings:

  • Material composition
  • Thickness
  • Density
  • Construction methods

Noise Criteria (NC) and Room Criteria (RC) Levels

The Noise Criteria (NC) and Room Criteria (RC) rating systems are used to describe acceptable background noise levels in various spaces.

  • Noise Criteria (NC): A single-number rating system that describes the overall noise level in a space by taking both the level and frequency of the sound into account.
  • Room Criteria (RC): This system also considers the overall noise level in a space but includes additional factors such as room size, shape, and function.

Understanding STC Ratings: What Makes a Good Rating?

Sound Transmission Class (STC) ratings are critical in determining the efficacy of soundproofing materials and assemblies. To make informed decisions about the materials to use in your soundproofing projects, you must first understand what constitutes a good STC rating and what different STC ratings mean.

What is a Good STC Rating?

STC ratings range from 20 to 80, with higher numbers indicating better sound insulation. A general rule of thumb for interpreting STC ratings is as follows:

  • 20-30: Poor soundproofing, minimal noise reduction. Conversations can be easily heard and understood through the barrier.
  • 30-40: Moderate soundproofing. Normal speech can be heard but is difficult to understand. Suitable for people who only need a little privacy.
  • 40-50: Good soundproofing. Loud speech may be audible but not understandable. Ideal for living rooms and private offices.
  • 50-60: Very good soundproofing. Most loud sounds, including music and noisy appliances, will be significantly reduced. Suitable for home theaters and music studios.
  • 60-80: Excellent soundproofing. Offers near-complete sound isolation. Ideal for specialized environments, such as recording studios and concert halls.

Aim for a soundproofing construction assembly that achieves an STC rating of at least 50-60 for a home theatre.

Remember that these are only estimates, and actual sound insulation performance may vary depending on factors such as construction methods, material quality, and the specific frequency of sounds being blocked.

Examples of STC Ratings

To better understand STC ratings, consider the following examples of common building materials and assemblies:

  • Single-pane window (3mm glass): STC 26-28
  • Standard interior wall (1/2" drywall on each side, wood studs, no insulation): STC 30-34
  • Double-pane window (3mm glass with 6mm air gap): STC 35-38
  • Interior wall with insulation (1/2" drywall on each side, wood studs, fiberglass insulation): STC 40-44
  • Interior wall with Green Glue and additional drywall layer (two layers of 1/2" drywall on each side, wood studs, fiberglass insulation, Green Glue between drywall layers): STC 50-55
  • Specialized soundproof wall assembly (decoupled construction, multiple layers of drywall, Green Glue, resilient channels, and insulation): STC 60-70

Remember that these examples are only meant to be general guidelines. Consult a soundproofing expert for the best results, and select materials and assemblies that best meet your specific noise reduction requirements.

Principles of Soundproofing


Mass plays an essential role in soundproofing. Increasing the mass of a material or construction assembly makes it more difficult for sound waves to pass through. Examples of mass-based soundproofing materials include drywall, mass loaded vinyl, and concrete.


Absorptive materials reduce sound by converting sound energy into heat. Acoustic foam, fiberglass insulation, and mineral wool are examples of absorbent materials.


Decoupling is the separation of structural elements in order to reduce the transfer of sound vibrations. Decoupling techniques include the use of resilient channels or Resilient Sound Isolation Clips (e.g., GenieClip RST).


Damping materials reduce sound transmission by dissipating vibrational energy. Examples of damping materials include Green Glue Noiseproofing Compound and viscoelastic materials.

Green Glue and Soundproofing Principles

When applied between layers of drywall or other rigid construction materials, Green Glue effectively reduces both airborne and structure-borne noise. Understanding soundproofing principles allows you to combine Green Glue with other soundproofing methods to achieve the best results.

Resilient Sound Isolation Clips

GenieClip RST is a Resilient Sound Isolation Clip that decouples walls, ceilings, and floors from the structure of a building in order to reduce sound transmission.

These clips provide the following benefits:

  • Improved soundproofing performance
  • Simple installation process
  • Compatibility with various construction materials and methods

When used in conjunction with Green Glue and other soundproofing materials, GenieClip RST and other sound isolation clips can significantly enhance your soundproofing projects.

Resilmount A237R Installation. Notice the Resilient Sound Isolation Clip is installed on the stud and then the furring channel is installed onto the clip. 


Understanding sound transmission and soundproofing principles is critical for effective noise reduction. You can create comfortable, quiet spaces that promote well-being and productivity by applying these principles to your projects and using products like Green Glue and GenieClip RST. To achieve the best results, always consider the specific needs of your space and select the most appropriate combination of soundproofing techniques.

Remember to:

  1. Evaluate the type of noise you need to mitigate – airborne or structure-borne – and select the appropriate materials and methods accordingly.
  2. Combine soundproofing principles such as mass, absorption, decoupling, and damping to create a comprehensive soundproofing solution.
  3. Optimize the effectiveness of Green Glue by understanding its role as a damping material and how it can be used in conjunction with other soundproofing products like GenieClip RST.

By taking these steps and applying the principles outlined in this guide, you can create a more comfortable and enjoyable living or working environment, free from unwanted noise and distractions.

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