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Circular 1D Open Type Attenuators – C1-050
Circular 1D Open Type Attenuators
Detailed Information - C1-050
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Insertion Loss - C1-050

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


The units are rigidly constructed and consist of an outer cylindrical galvanised steel casing, lined internally with non-hygroscopic and incombustible sound-absorbent material. This material is retained by an inner perforated metal cylinder.

When a pod is fitted it is of perforated metal, retaining an infill of acoustic material.

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.

The ends of the attenuators are drilled and tapped to match the Fantech ‘AP’ and ‘FP’ series of axial flow fans.

Non-standard flange drillings or sizes can be supplied to the customer’s specifications.

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 mid-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 betweeen 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 H-13/15 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.

Elta Group