Use

Determine the insertion loss due to the break-out of energy from a duct.

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User Inputs

  1. Width (mm)
  2. Height (mm)
  3. Length (m)
  4. Duct walls: 0.6, 0.8, 1.0 1.2, 1.6 mm thickness

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SoundSurfer Input

Sound Power Level (red node) from an upstream source within the duct.

Algorithm

Insertion loss is based on ASHRAE 2019 HVAC Applications Chapter 49 Noise and Vibration Control Table 29.

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Reference should be made to the Handbook to assist in determining the appropriate length of ductwork over which break out occurs (noting that it would often not be the full length of the duct over the space being assessed).

The Duct Break Out calculation does not provide for circular (or oval) ducts at this stage.  Duct breakout occurs more readily from rectangular ductwork due to the radiating efficiency in comparison to a circular (or to a lesser degree, oval) containment duct.

Refer to the full text of ASHRAE 2019 HVAC Applications Chapter 49 Noise and Vibration Control for full description of application.

Output

Attenuation (dB) from the duct breakout applied to the input Sound Power Level, with attenuated Sound Power Level (red node) output octave bands in dB(A), dB(Z) and dB(C). Output being the sound power level at the upstream side of the duct less the attenuation provided through the duct walls.

Click on ‘Z’ of the Sound Power Output to see dB(A) and dB(C) weightings.