What STC Ratings Mean (Sound Transmission Class Definition)

Understanding soundproofing requires understanding Sound Transmission Class (STC) ratings, a measure for assessing how well a material or partition blocks airborne sound.

Whether you’re working on a home studio, office space, or residential project, knowing what these ratings mean can help you make informed decisions. 

What is STC?

STC stands for Sound Transmission Class, a standardized system used to measure the effectiveness of a material in blocking sound. Essentially, the higher the STC rating, the better a wall, floor, or ceiling is at isolating sound.

STC Rating Chart And Definition - SoundAssured

Typical STC Ratings for Common Materials

Adding Mass Loaded Vinyl helps reduce noise transmission through walls, enhancing overall sound insulation performance.

STC For Wall Assemblies

Common wall assemblies typically include drywall and insulation, and their STC ratings vary based on material combinations and construction techniques.

Below are some example wall construction techniques for soundproofing. 1 lb Mass Loaded Vinyl is shown in addition to simple walls with insulation and without insulation. 

Soundproof Wall Assemblies Construction - Simple Walls - SoundAssured - graphic displaying walls from the top with studs, drywall, insulation, and mass loaded vinyl layers
This next graphic illustrates how adding an air gap between wall layers can significantly increase the STC rating of a wall structure. This method is known as creating adjacent walls for better soundproofing.
Soundproof Wall Assemblies Construction - Adjacent Walls with air gaps - SoundAssured - graphic displaying walls from the top with studs, drywall, insulation, and mass loaded vinyl layers
Wall Type STC Rating Description
Simple Wall STC 33
Basic wall construction with no insulation or added material
Simple Wall + MLV STC 43
Simple wall with Mass Loaded Vinyl layer for soundproofing
Simple Wall with Insulation STC 36
Basic wall with added insulation for improved sound control
Simple Wall with Insulation + MLV STC 48
Insulated wall with MLV for enhanced noise reduction
Adjacent Walls STC 57
Two walls with an air gap in between to absorb sound
Adjacent Walls + MLV STC 63
Adjacent walls with MLV for maximum sound blocking

How STC is Calculated

STC is calculated by measuring how well a material reduces sound levels across various frequencies. The process involves testing from low bass to higher treble sounds, and calculating the average noise reduction. The final STC rating is a weighted average of how much sound is blocked over the entire frequency range.

Application of STC

In everyday environments, STC ratings are used to evaluate walls, floors, and ceilings, but they can also be helpful in choosing soundproofing products like Mass Loaded Vinyl (MLV). Here’s what different STC ratings mean for your soundproofing needs:

  • STC 25-30: Normal speech can be heard clearly through the barrier.
  • STC 30-40: Loud speech can be heard, but not entirely clear.
  • STC 40-50: You can hear some muffled sounds, but not specific words.
  • STC 50-60: Sound is barely heard, providing solid privacy.
  • STC 60+: Excellent sound isolation; very little can be heard.

The Science Of Soundproofing Materials

Soundproofing is about controlling the way sound waves interact with materials, primarily through absorption, reflection, and damping. The effectiveness of a material in soundproofing depends a lot on its cell structure.

A lot of people think that acoustic foam panels are used for soundproofing, but this is not true.

Porous materials like acoustic foam or fiberglass have open-cell structures that allow sound waves to enter and dissipate as heat, reducing sound energy. Porous absorbers like these work by trapping air in their complex matrix of interconnected pores.

Dense materials like Mass Loaded Vinyl (MLV) use their high mass to block sound transmission. The layered structure in some materials also helps by creating barriers that absorb and deflect sound, effectively reducing noise transfer.

Sound Blocking
Sound Absorbing
Material Type Dense, Mass-Loaded Materials
Porous, Fibrous Materials
Primary Purpose Preventing sound from passing through walls, floors, or ceilings
Absorbing and dissipating sound waves within a space
Best for Blocking external noise from entering a room
Reducing echo and reverb within a room
Example Materials Mass Loaded Vinyl (MLV), Concrete, Drywall
Acoustic Foam, Fiberglass Panels, Fabric
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