SIL - the Speech Interference Levels

Background noise frequencies that interferes with speech. Speech Interference Levels (SIL) are arithmetic average sound pressure levels at the 500, 1000 and 2000 Hz center frequencies and a measure of the degree to which background noise interferes with speech.

Voice LevelSIL Range (dB)Distance (feet)Distance (meters)Description
Normal30-403-60.9-1.8Conversational speech at comfortable level
Raised40-502-30.6-0.9Elevated voice to overcome moderate noise
Very Loud50-601-20.3-0.6Shouting required in high noise environments
Shouting60+<1<0.3Maximum effort speech in extreme noise

About Speech Interference Levels (SIL)

Speech Interference Levels are calculated as the arithmetic average of sound pressure levels at three center frequencies:

  • 500 Hz
  • 1000 Hz
  • 2000 Hz

These frequencies represent the range most important for speech intelligibility.

Example

If the background noise sound pressure level is 75 dB and the distance between two persons is 6 m, they would need to raise their voice to more than a very loud level to be understood, according to the SIL diagram.

Conversion Factor

1 ft = 0.3048 m

SIL - the Speech Interference Levels | MEPKit Engineering Tools | MEPKit