It gives the reduction in sound energy in dB, when sound wave passes through the component. In Building Acoustic, it is given as Sound Transmission Class (STC) which is an integer rating of how well a building partition attenuates airborne sound.

  • The STC number is derived from sound attenuation values tested at sixteen standard frequencies from 125 Hz to 4000 Hz.
  • It is also measured in two ways.

 

Normal Incidence Sound Transmission Loss-

  • It is measured in a four microphone impedance tube as per ASTM E 2611. It is again useful for only grading of acoustic materials.

Random Incidence Sound Transmission Loss-

  • It is measured in Two Reverberation chambers as per ISO 10140 / ASTM E90.
  • It is also measured at Field (site) as per ISO 10140-5 and known as Field Incidence Sound Transmission Loss.

 

Sound-Attenuation

 

Sound Transmission Loss in Lab Testing

Sound Transmission Loss on Site Test (Field Testing)