Skyfold Classic, Zenith & Zenith Premium

Demystifying STC Ratings

STC is short for Sound Transmission Class. The higher the STC rating, the less sound is transmitted through the wall.

Below is a chart showing what can be heard through a wall as the STC rating changes:

STC What can be heard through a wall
25 Normal speech is distinctly and understandably audible
30 loud speech can be heard.
35 loud speech is audible but not intelligible.
40 Onset of acoustic “privacy”.
42 loud speech is audible as a murmur.
45 loud speech is not audible. 90% of a typical group sample not annoyed.
48 Skyfold Zenith® 48 tested STC.
50 Skyfold® Classic NRC™, Zenith® NRC and Zenith® Premium NRC tested STC.
50 Very loud musical instruments or a stereo can be faintly heard; 99% of population not annoyed.
51 Original Skyfold® Classic 51™, Zenith® 51 and Zenith® Premium 51 tested STC.
55 Skyfold® Classic 55™, Zenith® 55 and Zenith® Premium 55 tested STC Superior acoustics.
57 Equivalent to sound transmission through a cinder block wall, with a one inch (1″) gap and sheet rock on one side.
60 Skyfold® Classic 60™, Zenith® 60 and Zenith® Premium 60 tested STC – Highest for motor-driven or electric retracting partitions.


Skyfold Classic 60, Zenith 60 and Zenith Premium 60 lead the industry with the highest STC ratings available for a retractable, rigid motor-driven partition. Skyfold Classic NRC, Zenith NRC and Zenith Premium NRC delivers an STC of 50 and an NRC of 0.65, both reducing reflected sound within a space while preventing sound transmission through the wall.

Back to Advantages