Sound Transmission Loss

The testing of sound transmission loss at National Acoustic Laboratories is the primary use of the reverberation chambers. The test aperture between the chambers consists of a 10 m2 opening in which the test specimen (or wall) is constructed. The wall may consist of masonry, lightweight with stud framing or other innovative products.

The test procedure is carried out in accordance with AS 1191-2002 "Acoustics - Method of Laboratory Measurement of Airborne Sound Insulation of Building Elements". The data obtained in this measurement is then manipulated in accordance with AS/NZS 1276.1-1999 "Acoustics - Rating of Sound Insulation in Buildings and of Building Elements Part 1: Airborne Sound Insulation".

There are two recognised methods of determining sound transmission loss, the first is the American Sound Transmission Class (STC). The second is the International Weighted Sound Reduction Index (Rw).

As a guide, the sound transmission loss for some typical materials are listed below:

Typical Materials   63  125  250  500  1000 2000 4000 8000 STC 
13mm thick
both sides of
76mm steel studs
12 14 27 37 47 49 42 47 38
13mm thick
both sides of
76mm steel studs
plus 50mm
glasswool between
the studs
15 19 32 44 53 56 49 53 43
Single 110mm
24 30 36 39 47 54 59 60 45
Double 110mm
cavity brick
37 40 43 49 59 64 64 70 54

The STC is similar to the Rw. Recently the spectrum adaptation term (Ctr) has become more important as the Building Code of Australia now require products to be rated to determine this value. The Ctr is added to the Rw to obtain an overall Rw + Ctr value. New apartment buildings are required to achieve Rw + Ctr 50 or better for common walls and floors.

Sound transmission loss testing may be carried out over two hours for a single product, however several hours or days may be required for the product to properly cure prior to testing. Laboratory hire rates may be negotiated on a daily rate or for the total number of products to be tested.

Contact Stephen Gauld to discuss your requirements.

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  • Environmental
  • Industrial
  • NAL Testing