Is there any direct relationship between an STC number and transmission loss as indicated by dB values? Does an STC of 50 for example equal a transmission loss of 50 dB?
Many manufacturers, acousticians, government departments say that STC values that are + or – 1 are equal in terms of their ability to attenuate sound. For example an STC of 50 is equal to an STC of 49 and 51. Is this true?
Rather than our simply giving you our opinion and thoughts, below are the opinions and thoughts on both questions, as well as links to web sites, from independent, reputable, experienced professionals involved in Architectural acoustic products.
Question #1: Is a “1 STC” difference equal to a “1 dB” difference?
“An STC rating roughly equals the decibel (dB) reduction in noise volume a wall or partition can provide. For example, if an 80 dB sound on one side of a wall/floor/ceiling is reduced to 50 dB on the other side, that partition is said to have an STC of 30”
“Subjectively the human ear would consider a 1-2 dB (1-2 STC) change as nondiscernible at best which is significant.”
“Partitions with STC ratings within 1-2 points (1-2 dB) of the listed criteria would still be acceptable given the anticipated tolerances in repeat tests.”
Source: NAIMA: The North American Insulation Manufacturers Association
“The STC rating expresses the amount of dB lost through a partition, which means that on average an STC 35 partition attenuates sound by approximately 35 dB”
Source: SoftHub – an acoustical consultant
“The STC rating very roughly reflects the decibel reduction of noise that a partition can provide”
Source: Wikipedia – Sound Transmission Class – STC
“STC is decibels (dB) reduction in noise a material/partition can provide”
Source: Audimute – a manufacturer of acoustic panels & baffles
“When we say STC 35, it means the enclosure, wall partition or door will reduce noise by 35 decibels. The same logic applies to solutions rated as STC 45 and 52.”
Source: From Mecat – a manufacturer of acoustic enclosures and products.
“An Architect who must design a room with a sound source emitting 100 dB and isolate an adjoining adjacent room will need to choose between various STC values when selecting wall construction. A wall with an STC of 38 would not perform as well as a wall with an STC rating of 50. The latter will provide approximately 12 dB more sound blocking performance”
Source: Construction Specifier, Author Mr. Kevin Herreman Owens Corning
Conclusion: A “1 STC” difference is equivalent to a “1 dB” reduction in sound transfer. An STC 50 moveable wall will reduce sound by 50 dB.
Question #2: What change in dB (or STC) can the human ear detect? Is a change of 1 dB (1 STC) noticeable?
|Changes in STC rating||Changes in Apparent Loudness|
|+/- 1||Almost imperceptible|
|+/- 3||Just perceptible|
|+/- 5||Clearly noticeable|
|+/- 10||Twice (or half) as loud|
(As determined by the University of Minnesota)
Page 6, Table 1-2
|Change in Sound Level||Change in Loudness|
|+/- 1 dB||Requires close attention to notice|
|+/- 3 dB||Barely perceptible|
|+/- 5 dB||Quite Noticeable|
|+/- 10 dB||Dramatic; nearly twice or half as loud|
|+/- 20 dB||Striking, fourfold change|
Source: “Quieting: A Practical Guide to Noise Control, National Bureau of Standards Handbook 119” as published by the “U.S. Department of Commerce, National Bureau of Standards”
|Changes in STC Ratings||Changes in Apparent Loudness|
|+/- 1||Almost Imperceptible|
|+/- 3||Just Perceptible|
|+/- 5||Clearly Noticeable|
|+/- 10||Twice as loud|
Conclusion: A person cannot detect a change in loudness of +/- 1 dB (STC).
If we assume that a branch of the United States Government, The University of Minnesota, The Minnesota Housing Authority, prominent acoustical engineers and several manufacturers of acoustical products are correct, a change of “1 STC” is equivalent to a change in loudness of “1 dB”.
Humans cannot detect a change in loudness of “1 dB or 1 STC”
Conclusion must be that STC levels of +/- 1 are equal. For example an STC 50 = an STC 49, 50 or 51.