RACA Journal January 2019 | Page 69

Essentials
Table 1: System noise calculations
Supply air fan
Octave band centre frequency  
630/150/5 Hz 63 125 250 500 1 000 2 000 4 000 8 000
1.00 dB 92.0 91.0 88.0 89.0 88.0 86.0 83.0 74.0
Attenuator 1.5D and Pod 1.00 dB -6.0 -8.0 -14.0 -21.0 -20.0 -17.0 -16.0 -12.0
Straight d = 630 8.0 dB -6.40 -4.80 -2.96 -1.36 -1.20 -1.20 -1.20 -1.20
Bend d =1 000 1 dB 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Sound power level in W (SWL)
loss at branch 1 dB -12.00 -12.00 -12.00 -12.00 -12.00 -12.00 -12.00 -12.00
Corrections for directivity 1 dB 4.00 4.00 6.00 7.00 8.00 9.00 9.00 9.00
Reflection loss   dB -12.00 -7.00 -3.00 -1.00 0.00 Total SWL before grille 1 dB 60 63 62 61 63 65 63 58
Sound pressure level (SPL) of
difference 1 dB 73 72 70 70 68 64 61 55
SPL radiated into room   dB 73 73 71 70 69 67 65 60
Reverberant room effect   Corrective room surface area
<10 000m^ 2   dB -31 -31 -31 -31 -31 -31 -31 -31
Corrective room acoustic
(average)   dB 11.00 11.00 11.00 9.00 7.00 6.00 6.00 6.00
Reverberant room pressure level
(SPL)   dB 53 53 51 48 45 42 40 35
Direct room effect   Corrective distance listener (m) = 1.0 dB 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Direct sound pressure level (SPL)   dB 53 53 51 48 45 42 40 35
Octave band pressure level NC45   dB 67 60 54 49 46 44 43 42
Required attenuation   dB -13.81 -7.46 -3.36 -0.52 -0.85 -1.57 -3.00 -7.37
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RACA Journal I January 2019
67