What level STC door do you suggest for an office building near an airport?

There are many variables that would determine the proper STC value, including the physical proximity of the office building to the airport. To ensure that the specification is properly developed, an acoustic consultant should be engaged to determine the Outdoor / Indoor Transmission Class (OITC) values.

STC ValueRatingDescription
50-60ExcellentLoud sounds heard faintly or not at all
40-50Very GoodLoud speech heard faintly, but not understood
35-40GoodLoud speech heard but hardly intelligible
30-35FairLoud speech understood fairly well
25-30PoorNormal speech understood easily and distinctly
20-25Very PoorLoud speech audible

Do you recommend a specific type of core for acoustical doors?

No, we recommend that the door selection be made on the basis of the STC value that has been specified. Multiple door core types may be capable of achieving the specified value, and can be documented by Certificates available from the manufacturer.

I have a specification that references an OITC value, is this the same as STC?

OITC stands for Outdoor-Indoor Transmission Class and is a measure of the ability of a building material or product’s ability to retard sound transmission. It is similar to STC, but it is not the same. As the name indicates, OITC is a measure of sound transmission from the external environment into the building envelope. Testing to establish an OITC value utilizes ASTM E-1332 Standard Classification for the Determination of Outdoor–Indoor Transmission Class. This standard uses a range of frequencies lower than the STC testing, to more closely replicate the sounds of rail and vehicular traffic.

What is STC?

STC stands for “Sound Transmission Class”, a measure of the extent to which sound is prevented from being transferred from one area to another. The higher the STC value, the less sound transferred from one area to another.

The STC scale is a logarithmic progression, meaning that a jump of 3 points in an STC rating equates to a doubling in a door’s ability to prevent sound transmission. Acoustical doors are tested as an assembly comprised of the door, frame, hinges, and sound sealing system. See SDI 128 for more information.

The following chart illustrates the sound retardant performance associated with a range of STC values.

What is the difference between STC and decibels?

TC is a single number rating that indicates the sound transmission loss over a defined range of frequencies of a door assembly between adjacent closed rooms. Higher values equate to better sound reduction performance.

Decibels dB, are used to express the intensity of a sound wave. Examples of decibels levels are:

  • 100-120 Deafening industrial machinery, jet engines
  • 80-100 Very loud cocktail party, boom box
  • 60-80 Quiet speech
  • 20-40 Faint soft whisper, recording studio
  • 0-20 Very faint acoustical laboratories, deep caves