How Are STC Ratings Calculated?

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 foryour 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.  The higher the STC rating, the more effective that material is at reducing sound transmission of the most common frequencies.  To see how past Audimute customers used Peacemaker Sound Insulation to increase the STCs of their walls, floors and ceilings, check out the following video showcasing photos and reviews.  To learn more about STC, continue reading below.

STC is roughly the decibel reduction in noise a material/partition can provide, abbreviated 'dB'. The human ear perceives a 10dB reduction in sound as roughly reducing the volume by half. For example, a sound reduction from 50dB to 40dB seems half as loud. This is an important fact to keep in mind when considering a sound solution that ‘fits’ the problem. Don’t over purchase soundproofing material. Consider your budget and your desired acoustic result.

To understand how to soundproof a wall to create a higher STC rating, consider the example of Peacemaker Sound Insulation.

Table of Common STC Ratings
 STCBuilding Material/Partition without PeacemakerWhat Can be Heard Through Barrier
26-30Single Pane Glass Window
Sentences spoken in a normal
voice can be understood clearly
30-35Double pane window, hollow core wood door,
typical interior wall with single layer of
½’ drywall on each side, no insulation
Sentences spoken in a normal tone of
voice can still be heard with some straining
35-40Solid core wood door
Loud talk can be heard, but
not clearly understood
42-45Double layer of ½" drywall on each side,
single batt insulation in wall
Loud talk is somewhat audible, but only occasional words can be understood
47-50Single layer of 1/2" drywall, glued to 6" lightweight concrete block wall, both sides paintedLoud talk is audible only by straining
to hear it; music and heavy traffic
will most likely still be heard 
52-55Single layer of 1/2" drywall, glued to 8"
dense concrete block wall, both sides painted
Very Loud talk is audible only by
straining to hear it; music and heavy
traffic might still be heard
57-60Double layer of 1/2" drywall on each side,
on wood stud wall, flexible channels on one side, single batt insulation in between
Very loud talk is almost entirely inaudible;
music can barely be heard but bass
notes are still disruptive
Double layer of 1/2" drywall on each side,
on double wood/metal stud walls
(spaced 1" apart), double batt insulation
Music is barely heard- bass notes
make a thumping noise,  but
power equipment is clearly heard
8" concrete block wall, painted, with 1/2"
drywall on independent steel stud
walls insulation in cavities
Music can be heard faintly if it is played very loud- power equipment is faintly heard
75+ Most noises are effectively blocked,
including airplane noise

For more information on STC ratings for various wall assemblies, please visit:

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 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 theatre walls.
• It’s not always practical to test the entire wall configuration of an assembly to determine the true STC.