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H © FANTECH 2016 ATTENUATOR SELECTION PROCEDURE Low F Freq Bias N Noise dB Over

H © FANTECH 2016 ATTENUATOR SELECTION PROCEDURE Low F Freq Bias N Noise dB Overall Level Attenuator Loss d dB After Attenuator dB Overall Level 63Hz 75 76.8 4 71 72.0 125Hz 70 6 64 125Hz 65 9 56 500Hz 60 10 50 1000Hz 60 15 45 2000Hz 60 13 47 4000HZ 55 14 41 8000HZ 50 12 38 Attenuator N Noise L Level R Reduction 4.9dB High F Freq Bias N Noise dB Overall Level Attenuator Loss d dB After Attenuator dB Overall Level 63Hz 50 76.8 4 46 64.7 125Hz 55 6 49 125Hz 60 9 51 500Hz 60 10 50 1000Hz 60 15 45 2000Hz 65 13 52 4000HZ 70 14 56 8000HZ 75 12 63 Attenuator N Noise L Level R Reduction 12.2dB In-duct SWL -dB 125 63 250 500 1000 2000 4000 8000 0 20 40 60 80 Octave Frequency, Hz B ef o re at tenuator A fte at r te n ua t or Generator Attenuator Noise before attenuator Noise after attenuator 76.8 dB 72.0 dB Attenuator noise level reduction 4.9dB To m make a an a attenuator s selection t that w will p provide s satisfactory p performance, there a are s several c crite eria t that h have t to b be a addressed. 1. Acoustic attenuation/silencing performance The reduction in noise offered by an acoustic attenuator varies according to the source of the noise being controlled. Being technically specific, it depends on whether the noise is particularly loud in low frequencies/tones. In the example below, two different 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. 0 20 40 60 80 125 63 250 500 1000 2000 4000 8000 Octave Frequency, Hz In-duct SWL -dB Before t at e n u ator Attenuator Noise after attenuator Fan 76.8 dB 12.2dB Attenuator noise level reduction 64.7 dB Noise before attenuator General fan noise (Example fan coil unit) Low frequency biased noise (Example generator set) INTRODUCTION Assessing whether an attenuator would reduce noise effectively 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 different 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 profile. The performance of an attenuator in a specific case may vary from these general noise reductions. To assess if this general advice applies to a specific case, assistance is available through our nearest sales office and through the acoustic analysis tool in the Fans By Fantech Selection Program and Fantech Website. NOISE CONTROL PRODUCTS H-2 H H-3 NOISE CONTROL PRODUCTS © FANTECH 2016 ATTENUATOR SELECTION PROCEDURE 2. Attenuator Pressure Loss A sound attenuator restricts the passage of air flow through it. The restriction of the attenuator is defined in Pa of static pressure loss. The pressure loss of the attenuators in this catalogue is charted in two different ways: a) Pressure loss at a given air flow For the C, C.P , CC series circular attenuators and POW series attenuators, the static pressure loss is charted for each model at different airflows. For example, if we select an attenuator model C2P-071 with an air flow of 4m3/s, the pressure loss is 50Pa. 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 acoustic louvres for example, pressure losses for a given model are graphed against face velocity: Face velocity, m/s 10 20 40 50 80 100 0.5 0.75 1.0 2.0 1.5 SBL1 (500H) Pressure loss, Pa For rectangular attenuators, the velocities are provided for a given model at 20Pa or 50Pa at different lengths as per below: (See Page H-7) Face Velocity of 50Pa Pressure Drop uploads/Management/ attenuator-selection-guide.pdf