Circular Duct Attenuators - S / P Seriesnoise

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features  Features

  • These notes apply to both the open and pod type attenuators.

construction  Construction

  • The units are rigidly constructed and consist of an outer cylindrical galvanised steel casing, lined internally with no hygroscopic and incombustible sound absorbent material.
  • This material is retained by an inner perforated metal cylinder.
  • An impervious lining of the acoustic infill can be provided to prevent the ingress of moisture or grease.
  • There is a small performance penalty in high frequencies when an impervious lining is fitted.
  • Refer to our Sales Engineers if more information is required.

Insertion Loss

  • The values quoted in the table represent the difference between the sound power level (Lw) of a fan and attenuator combination and that of the fan alone.


  • To ascertain the sound power level of a fan fitted with an attenuator, the insertion loss should be subtracted from the sound power level (Lw) rating of the fan across the octave band centre-frequency spectrum quoted in the fan characteristic data (obtainable on request).
  • The fan sound power, Lw, ratings and attenuator insertion loss apply to in-duct operation and where an attenuator is connected between the fan and duct system.

Rectangular Attenuators

  • Whilst circular attenuators provide a convenient form of attenuation when used with axial flow fans and have the added advantage of minimising noise break-out, it is often more economical to consider standard rectangular attenuators.
  • Please refer to the pages G-6/10 for details of these.
  • Purpose-designed attenuators can be supplied for particularly demanding applications requiring performances or construction beyond that provided by our standard product.

construction  Suggested Specification

  • Attenuators shall be as designed and manufactured by Elta Fans and shall have the performances as scheduled.
  • The casing and end flanges shall be constructed from high quality galvanised mild steel sheet.
  • The end flanges shall be match drilled and tapped to suit the fan flanges and facilitate installation.
  • Attenuator pods, where fitted, shall be adequately supported and be fitted with a nose cone on the inlet to minimise noise regeneration and pressure loss.

dimension  Dimensions


performance  Performance


technical  Technical Data