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Attenuator selection guide

ATTENUATOR SELECTION PROCEDURE INTRODUCTION Assessing whether an attenuator would reduce noise e ?ectively enough for a particular situation usually requires complete equipment noise data and attenuator insertion loss SIL spectrums Acoustic calculations then have to be performed to assess the resultant noise levels with the attenuator To give the reader a general understanding of the noise reduction performance of di ?erent attenuators the methodology presented in this section provides attenuator performance as a single noise reduction value against a Low Frequency Biased or General HVAC noise pro ?le The performance of an attenuator in a speci ?c case may vary from these general noise reductions To assess if this general advice applies to a speci ?c case assistance is available through our nearest sales o ?ce and through the acoustic analysis tool in the Fans By Fantech Selection Program and Fantech Website To make an attenuator selection that will provide satisfactory performance there are several criteria that have to be addressed Acoustic attenuation silencing performance The reduction in noise o ?ered by an acoustic attenuator varies according to the source of the noise being controlled Being technically speci ?c it depends on whether the noise is particularly loud in low frequencies tones In the example below two di ?erent noises could have the same overall decibel levels but because one is from a generator set low frequency biased the performance of the same acoustic attenuator varies to that of a general HVAC system General fan noise Example fan coil unit Attenuator noise level reduction dB Low frequency biased noise Example generator set Attenuator noise level reduction dB Fan Attenuator Attenuator Generator H dB dB Noise before Noise after attenuator attenuator dB Noise before attenuator dB Noise after attenuator In-duct SWL -dB In-duct SWL -dB Before attenuator Octave Frequency Hz Hz Hz Hz Hz Hz Hz HZ HZ High Freq Bias Noise dB Overall Level After Attenuator Attenuator Overall Loss dB dB Level Attenuator Noise Level Reduction dB H- NOISE CONTROL PRODUCTS Before attenuator After attenuator Octave Frequency Hz Hz Hz Hz Hz Hz Hz HZ HZ Low Freq Bias Noise Overall dB Level After Attenuator Attenuator Overall Loss dB dB Level Attenuator Noise Level Reduction dB ? FANTECH CATTENUATOR SELECTION PROCEDURE Attenuator Pressure Loss A sound attenuator restricts the passage of air ow through it The restriction of the attenuator is de ?ned in Pa of static pressure loss The pressure loss of the attenuators in this catalogue is charted in two di ?erent ways a Pressure loss at a given air ow For the C C P CC series circular attenuators and POW series attenuators the static pressure loss is charted for each model at di ?erent air ows For example if we select an attenuator model C P- with an air ow of m s the pressure loss is Pa b Variable Face Area Width or Height Some attenuator types are expected to be built to varying widths and heights to suit the duct or wall sizing With