Explained - STC Rating
STC is an acronym for Sound Transmission Class. It is described in terms of a representative number that rates how well a room or material will insulate acoustic sound pressures such as speech, music or other.
Below is an example of the perceived audible changes for increment STC ratings for wall or room soundproof treatment.
STC Rating of the Soundproofing Material
30-35 Clearly intelligible speech
36-40 Only 50% of speech is intelligible
41-45 Loud speech audible, music and TV’s heard
51-55 Speech not intelligible, loud music and TV heard
56-60 Loud speech not heard, music significantly muffled, bass still heard
61-65 Music barley heard, bass still heard, power tools heard
66-70 Most airborne blocked though very loud music and power tools still heard though structure transmission.