Fan Silencers

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Industrial fan installations, small or large, produce noise. This fan noise is one of the most predominant noise sources in an industrial plant. The magnitude and intensity of noise will vary depending on fan size, horse power, air flow, type and number of blades, static pressure, rotational speed, etc.

Fans normally deliver a large volume of air at relatively low static pressures usually measured in inches of water. The rotating action of vanes produce a broad band noise spectrum however, the noise in mid to high frequency range is heard to be louder and requires to be treated for achieving noise control.

Generally, silencers are used at intake and discharge of fan installations for treating air borne noise. Fan silencers usually require absorptive type design as they are well known for better attenuation in mid and high frequency range (500-8000 Hz). The effectiveness of absorption material progressively reduces at frequencies above and below this range.

The noise control is achieved by means of absorption. The acoustic energy propagating through the silencer is effectively absorbed into the fiberous absorption material and converted into heat energy. These silencers generally employ straight thru design and has a low pressure drop as it imposes very little restriction to the flow.

Silencer Selection

The fan silencers are normally selected on the basis of maximum allowable pressure drop at rated flow and the silencing criteria. These silencers are usually sized for around 5000 to 5500 FPM velocity but not exceeding 7500 FPM velocity to prevent excessive self generated noise and aerodynamic noise generation. While selecting the fan silencer, it must be ensured that the flow area throughout the silencer is sufficient to accomodate the air flow without imposing excessive restriction.

The following table indicates the maximum recommended air flow in CFM for respective silencer size in accordance with the above guidelines.

Select the silencer size based on the air flow from the above table.

Refer to the formulas given here for calculating the pressure drop for the silencer size selected. Check this pressure drop against the maximum allowable pressure drop. If the pressure drop is too high, select the next larger size and recalculate.

Pressure Drop

(These calculations assume air as the flowing gas. For other gases, density and other corrections may be required. Contact our engineers for assistance).

Data Required:

Air Flow Rate (Actual CFM)
Temperature (°F)
Pressure (PSIG)
Maximum allowable pressure drop (inches of water)

If this pressure drop is higher than the maximum allowable pressure drop, then select next larger size and recalculate.

Temperature Limits

Various options for acoustical absorption materials are available with temperature limits ranging from 325°F to 1000°F. Please consult our engineers for your specific applications for selecting suitable absorption material suiting to your requirements.

Pressure Rating

The silencers described herein are designed to a maximum operating pressure of 15 PSIG. For applications where pressure exceeds 15 PSIG, the silencers can be designed to ASME Code, Section 8, Div. 1 for pressure vessel construction. The dimensions are similar to standard models, but the material type and thicknesses are selected to meet code requirements. Consult our engineers for pricing and design information.

Attenuation Curves

Noise attenuation curve showing insertion loss at each frequency is shown here. This represents the insertion loss for airborne noise under average conditions. The resultant silenced noise level will depend on a number of other factors therefore this curve should be used with discretion and can be used as a guideline for evaluating the noise levels after the silencer installation.

We specialize in custom designs and also provide various nozzle orientations to suit your specific requirements.

Axial Fan Silencers

Axial fan silencers are used for many different systems in the areas of industrial and commercial applications. These silencers are specifically designed to be able to complement airflow profiles for axial fans. The acoustical elements get aerodynamically matched with fan parameters to be able to minimize system effects with the outcome in maximize energy savings. An Axial fan silencer is available to fit any fan size, with construction materials suitable towards a system type, a fan size and a higher velocity of a fan type.

The available types of Axial Fan Silencers include media filled with film liner, dissipative media filled and No-Media designs. The E.I. Williams engineering service team can assist in applying an axial fan silencer that is required to meet various noise control requirements.

These application types are for the inlet or the outlet of the axial fans for the return air, exhaust air, and the smoke exhaust installations along with the air handling units, the tunnel ventilation installations and the air recirculation systems.

Axial Fan Silencers can be custom built by E.I. Williams for close coupling towards the inlet and the discharge of these axial fans. Axial Fan silencers are engineered so it can provide top quality sound attenuation to improve aerodynamic performance from the fan.

Contact E.I. Williams today to inquire about our experience and services regarding Axial Fan Silencers. We can assist you today and we look forward to helping you to design and manufacture custom Axial Fan silencers in order to meet specified standards.

To learn more about EI Williams, call us at (905) 428-0950 or toll-free at 1-877-840-3347 or you can also email us at info@eiwilliams.com for further inquiries.