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.
Source: NAIMA: The North American Insulation Manufacturers Association
Source: SoftHub – an acoustical consultant
Source: Wikipedia – Sound Transmission Class – STC
Source: Audimute – a manufacturer of acoustic panels & baffles
Source: From Mecat – a manufacturer of acoustic enclosures and products.
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.
|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.