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Reduced sound transmission
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'Stone wall' of precast, reinforced, colored concrete. photo courtesy of stonehengewest.com
'Stone wall' of precast, reinforced, colored concrete. photo courtesy of stonehengewest.com
Hearing loss due to prolonged exposure to noise is well documented. Excessive noise also has an adverse effect on personal health and wellbeing, ability to perform quiet tasks, and productivity in general. Because land is becoming scarcer, buildings are being constructed closer together and closer to noise sources such as highways, railways, and airports. As a result, sound or acoustic control is becoming increasingly important.
 
The reduction of airborne sound through a wall is called sound transmission loss (STL). The frequency or pitch of sound has a great effect on sound transmission, since low frequency sound will transmit through a wall more readily than high frequency. Laboratory tests for sound transmission loss are determined over a range of frequencies. Sound Transmission Class (STC) is a single number used to rate walls, partitions, doors and windows for their effectiveness in blocking sound.

 

Concrete walls provide a buffer between:

  • Outdoor noise and the indoor environment in a building
  • Highway noise and neighborhoods with a sound barrier
  • Indoor noise between adjoining apartments or other spaces as a separating wall  
Homeowners enjoy the quietness of a concrete home
Homeowners enjoy the quietness of a concrete home.  PCA No. 15434
The greater mass of concrete walls can reduce sound penetrating through a wall by over 80% compared with wood or steel frame construction. Although some sound will penetrate the windows, a concrete building can be two-thirds quieter than a wood or steel frame building. Concrete panels also provide effective sound barriers separating buildings from highways or industrial areas from residential areas.

Compared to a typical wood frame wall, only about one-quarter to one-eighth as much sound penetrates a concrete wall. Acoustics experts would describe loud speech on the opposite side of a frame wall as “audible, but not intelligible.” On the opposite side of a concrete wall, a listener would “strain to hear” loud speech. Through some concrete walls, loud speech would be “inaudible.”

A 2 x 4 wood stud partition wall with ½ in. gypsum wallboard on each side has an STC (Sound Transmission Class) of about 35. With the addition of furring, insulation, and wallboard, STC values up to 63 are obtained for 6 and 8 in. thick concrete walls. Bare concrete and masonry walls have STCs in the range of 45 to 50. Standard flat panel ICF walls generally have STCs in the range of 55 to 60. A subjective description of STC values is presented in the table.
 

STC -Lab

STC - Field

Subjective description of effectiveness

26-30

20-22

Most sentences clearly understood

30-35

25-27

Many phrases and some sentences understood without straining to hear

35-40

30-32

Individual words and occasional phrases clearly heard and understood

42-45

35-37

Medium loud speech clearly audible, occasional words understood

47-50

40-42

Loud speech audible, music easily heard

52-55

45-47

Loud speech audible by straining to hear; music normally can be heard and may be disturbing

57-60

50-52

Loud speech essentially inaudible; music can be heard faintly but bass notes disturbing

62-65

55

Music heard faintly, bass notes "thump"; power woodworking equipment clearly audible

70

60

Music still heard very faintly if played loud.

75+

65+

Effectively blocks most air-borne noise sources

 
 
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Located at BookstoreSound Transmission Loss Through Concrete and Concrete Masonry Wall (1978)
Albert Litvin and Harold W. Belliston, Portland Cement Association, Item Code RD066
Many building codes require minimum sound transmission loss values, expressed as sound transmission class (STC), of 45 to 50. Tests of sound transmission loss were made on 8-in.-thick (203-mm) concrete masonry walls and on 6- and 8-in.-thick (152- and 203-mm) cast concrete walls finished with materials intended to increase sound transmission loss. Using furring, acoustic insulation, and wallboard attachments, STC values up to 59 and 63 were obtained for the masonry and cast concrete walls, respectively. Selected STC values, reported by other investigators, for a variety of walls are included for reference.
Download DocumentSound Transmission Loss Measurements Through 190 mm and 140 mm Blocks with Added Drywall (1990)
A.C.C. Warnock , National Reseach Council Canada, #IR-586, 32 pages
Available for free. This report presents the results of a series of sound transmission loss measurements carried out under contract for the Ontario Concrete Block Association. The test series was augmented for research purposes by measuring sound transmission losses at different stages in the construction and disassembly of the walls. The report that follows provides an analysis of the information obtained during the complete measurement series. Available as a free download at National Research Council of Canada's Institute for Research in Construction website.