Selection of attenuators

Rectangular attenuator KSD

■ General De = Lo – Lm dB ■ Fast selection of an attenuator ■ Key

If the noise level of a fan exeeds Lo: Sound level without attenuator LWA total = Sound power level
the required level, additional Lm: Sound level with attenuator For easy estimating of a retan- of the fan in dB(A) (from table
measures can be taken to gular or circular attenuator the above fan’s performance curve).
reduce it. The use of attenuators, The efficiency of an attenuator is average attenuation figure is
working on the principle of largely dependent on the frequency given in the red underlined Average attenuation =
absorbtion, is a very effective of the sound source, therefore the column (right hand column) of calculated attenuation figure of
method. This type of attenuator attenuation is stated over the the attenuator’s table. This figure the attenuator in dB(A) (red
offers high damping figures octave spectrum. Low frequency is to be deducted from the column in the attenuator’s table).
creating only low additional noise is more difficult to attenuate sound power level (LWA total)
resistances. than high frequency. Therefore a of the fan. LWA reduced = reduced sound
HELIOS offer attenuators that larger or more resistive attenuator level in dB(A) using an attenuator.
are optimal to the HELIOS fan is required. The result is the sound power
range. Circular and rectangular level (LWA reduced) of the fan, ■ Sound level calculation
attenuators are available in It is necessary to know the noise reduced by attenuation. The To calculate the relevant sound
virtually any size. All attenuators spectrum of a fan (octave or tierce difference with this selection level the attenuator sound
can of course be used together spectrum) to choose an attenuator. method (if compared to the reduction must be substracted
with fans by others. When selecting an attenuator for a frequency band calculation) it is from the fan sound level. This
HELIOS attenuators are made system the attenuating effect of an approximation. More exactly should be done in frequency
from galvanised steel, fitted with other components like bends, values can be reached using the bands. For better attenuation
high quality mineral wool, transformation pieces etc. must calculation to the octave band. several attenuators of the same
covered against air flow with be considered in addition to the diameter can be installed one
scrim to prevent erosion. noise level of the fan. ■ Example: after another.
To avoid regeneration of noise Given:
■ Technical information through the air speed over the Fan model VARD 225/2
Attenuation duct surface the air velocity should Chosen: Circular attenuator
The amount of attenuation is be minimised. RSD 225/600 (length = 600 mm)
determined using the principle
of comparison. It compares the Sound power level of fan
noise reduction within a pipe or LWA total = 81 dB(A)
ducting with and without the Average attenuation figure for
attenuator. attenuator
When measuring without an reduction = 15 dB(A)
attenuator, it is replaced by a = reduced soud power level
straight piece of rigid, noise LWA reduced = 66 dB(A)
hard ducting. The attenuation
is calculated to:

■ Rectangular attenuator KSD Dimensionsin mm see table

■ Specification – Installation
Casing made from galvanised
steel with flanges to fit the fan’s
dimensions. To be installed
in-line with ducting on inlet or
exhaust. To reduce vibration
transmission from the fan, a
flexible connector (accessories
VS or VS… Ex) should be
installed between fan/attenuator
and ducting.
■ Pressure drop
The attenuator will add an
∆p
Pressure loss KSD
additional resistance to the duct Pa 3 1 = KSD 40/20
2 = KSD 50/25-30
system (see chart), which must 3 = KSD 60/30-35
4 = KSD 70/40
be considered when selecting a 5
6
=
=
KSD
KSD
80/50
100/50
fan. The figures shown refer to 1 4
an equal inlet into the attenuator. 2 5
Turbulences from the fan’s
exhaust can be reduced if 1 6
metre of straight ducting is fitted
between fan and attenuator.
Otherwise allow for a higher
.
resistance. V m3/h

Type Ref. No. Duct size Dimensions in mm Nominal Attenuation De dB Average

in mm A B C D weight kg 125 250 500 1000 2000 4000 8000 attenuation
KSD 400/200 8728 400/200 420 220 443 240 13 8 11 23 31 31 26 18 17
KSD 500/250.. 8729 500/250-300 520 270/320 540 340 16.5 6 9 19 25 25 20 15 14
KSD 600/300.. 8730 600/300-350 620 320/370 640 390 20 7 10 21 28 28 23 16 12
KSD 700/400 8731 700/400 720 420 740 440 25 6 8 18 24 24 20 14 12
KSD 800/500 8732 800/500 820 520 840 540 31 7 9 19 26 26 21 15 14
KSD 1000/500 8733 1000/500 1020 520 1040 540 35 5 7 16 21 21 17 12 11

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 Flexible circular attenuator FSD
Rigid circular attenuator SRSD

■ Flexible circular attenuator FSD

FSD
■ Specification – Installation
Robust flexible aluminium
ducting with inner perforated
face retaining the resin bounded
attenuation packing of 50 mm
thickness. Spigotted on both
ends to fit into nominal size
ducting or to be fixed with pipe
clamp connectors BM on fan or Dim. in mm
see table
ducting. The flexible body allows
an easier installation.
■ Pressure drop ■ Information Page
The pressure drop is 4 times the
Selection
equivalent normal rigid ducting
noise assessment 318
value.

Type Ref. No. Dimensions in mm Attenuation in dB at Hz Nominal Average

L øD ød l 250 500 1000 2000 weight kg attenuation
FSD 100 0676 1000 210 99.5 60 17 33 48 40 1.1 25
FSD 125 0677 1000 240 124.5 60 13 27 47 22 1.5 20
FSD 160 0678 1000 262 159.5 60 12 26 45 20 2.0 19
FSD 200 0679 1000 313 199.5 60 10 22 31 10 2.5 16
FSD 250 0680 1000 363 249.5 85 8 15 26 8 3.2 12
FSD 315 0681 1000 418 314.5 85 7 15 25 8 4.2 11
FSD 355 0682 1000 464 354.5 85 5 13 19 8 4.7 9
FSD 400 0683 1000 514 399.5 90 5 13 19 8 5.3 9

■ Spigotted circular attenuator SRSD AVAILABLE IN

SRSD
■ Specification – installation
THE UK ONLY !
Robust casing made from
galvanised steel with inner
perforated face retaining the
50 mm thick mineral wool lining.
Spigotted on both ends to fit
into nominal size ducting or to
be fixed with pipe clamp
connectors (accessory BM). Dimensions in
■ Pressure drop mm see table
The pressure drop is twice the
normal rigid ducting value.

Type Ref. No. Dimensions in mm Attenuation in dB at Hz Nominal Average

L D d l 250 500 1000 2000 4000 8000 weight kg attenuation

Accessories
Duct / Rect. fans
SRSD 100/ 300 8901 300 202 98 40 8 13 20 23 20 12 2.6 11
SRSD 100/ 600 8902 600 202 98 40 12 20 37 47 36 17 4.7 18
SRSD 100/ 900 8903 900 202 98 40 15 29 44 50 42 25 6.7 27
SRSD 100/1200 8904 1200 202 98 40 20 33 42 46 44 29 8.8 31
SRSD 125/ 300 8905 300 227 123 40 7 13 20 21 19 12 2.9 11
SRSD 125/ 600 8906 600 227 123 40 12 22 36 44 32 26 5.3 20
SRSD 125/ 900 8907 900 227 123 40 14 26 44 46 35 22 7.7 24
SRSD 125/1200 8908 1200 227 123 40 16 33 47 53 46 29 10.1 31
SRSD 150/ 300 8909 300 252 148 40 5 10 15 22 16 9 3.3 8
SRSD 150/ 600 8910 600 252 148 40 8 15 31 34 22 12 6.0 13
SRSD 150/ 900 8911 900 252 148 40 10 25 43 49 26 18 8.7 23
SRSD 150/1200 8912 1200 252 148 40 13 29 49 52 30 18 11.4 27
SRSD 160/ 300 8913 300 262 158 40 5 10 15 22 16 9 3.4 8
SRSD 160/ 600 8914 600 262 158 40 8 15 31 34 22 12 6.2 13
SRSD 160/ 900 8915 900 262 158 40 10 25 43 49 26 18 9.1 23
SRSD 160/1200 8916 1200 262 158 40 13 29 49 52 30 18 11.9 27
SRSD 200/ 300 8917 300 302 198 40 3 7 15 16 10 6 3.9 5
SRSD 200/ 600 8918 600 302 198 40 7 14 30 26 15 11 7.3 12
SRSD 200/ 900 8919 900 302 198 40 8 20 42 41 18 15 10.6 18
SRSD 200/1200 8920 1200 302 198 40 10 26 48 51 22 16 14.0 24
SRSD 250/ 300 8921 300 327 223 40 2 6 15 13 10 4 4.6 4
SRSD 250/ 600 8922 600 327 223 40 6 12 25 18 10 7 8.6 10
SRSD 250/ 900 8923 900 327 223 40 8 16 30 27 12 9 12.6 14
SRSD 250/1200 8924 1200 327 223 40 11 22 36 38 18 12 16.6 20
SRSD 315/ 300 8925 300 417 313 40 2 5 14 12 8 4 5.5 3
SRSD 315/ 600 8926 600 417 313 40 6 10 18 13 10 6 10.3 8
SRSD 315/ 900 8927 900 417 313 40 7 15 22 17 12 9 15.2 13
SRSD 315/1200 8928 1200 417 313 40 9 20 29 21 15 12 20.0 18
SRSD 400/ 300 8929 300 502 398 40 6 4 11 10 6 4 6.6 2
SRSD 400/ 600 8930 600 502 398 40 5 10 14 11 8 6 12.6 8
SRSD 400/ 900 8931 900 502 398 40 7 13 19 14 10 8 18.5 11
SRSD 400/1200 8932 1200 502 398 40 8 18 24 20 14 7 24.5 16

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 Flanged circular attenuator RSD

■ Specification – Installation ■ Pressure drop RSD

Casing made of galvanised The resistance of the RSD
steel, acoustically lined with attenuators is very low. When
high quality mineral wool covered designing the system consider
with cloth to prevent erosion. twice the pressure drop of rigid
Acoustic lining retained by per- ducting.
forated steel sheet.
Dimensions and tapped flange
holes of all sizes fit fan’s nominal
diameter (R 20). Tapped holes in
accordance to DIN 24155, Pt. 2.

■ Isolation standard
To increase the attenuation, Dimensions see chart
several attenuators can be
installed in-line.

■ Information Page
Selection-
Sound level calculation 318

Type Ref. No. Basic Dimensions in mm Nominal Isolation standard De dB Average

Nominal-ø length L A B Hole ø weight kg 125 250 500 1000 2000 4000 8000 attenuation
RSD 225/ 300 8734 1 300 259 404 6xM 6 7 2 5 9 14 13 8 6 8
RSD 225/ 600 8735 2 600 259 404 6xM 6 12 4 10 17 27 25 17 14 15
RSD 225/ 900 8736 3 900 259 404 6xM 6 17 7 13 25 33 31 20 16 20
RSD 250/ 300 8737 1 300 286 404 6xM 6 7 3 5 8 8 9 7 5 8
RSD 250/ 600 8738 2 600 286 404 6xM 6 12 5 10 16 24 19 14 10 15
RSD 250/ 900 8739 3 900 286 404 6xM 6 16 6 12 22 28 21 15 11 18
RSD 280/ 400 8740 1 400 322 454 8xM 8 10 4 5 8 14 9 8 6 8
RSD 280/ 800 8741 2 800 322 454 8xM 8 18 7 9 16 28 18 17 14 14
RSD 280/ 1200 8742 3 1200 322 454 8xM 8 25 9 12 23 37 23 20 16 18
RSD 315/ 400 8743 1 400 356 504 8xM 8 11 3 3 7 13 8 7 5 5
RSD 315/ 800 8744 2 800 356 504 8xM 8 19 6 8 14 26 16 12 9 12
RSD 315/ 1200 8745 3 1200 356 504 8xM 8 28 9 12 21 36 18 17 14 18
RSD 355/ 400 8746 1 400 395 564 8xM 8 13 3 4 7 11 7 6 4 6
RSD 355/ 800 8747 2 800 395 564 8xM 8 23 6 7 13 22 14 12 8 11
RSD 355/ 1200 8748 3 1200 395 564 8xM 8 33 8 11 17 29 18 15 10 17
RSD 400/ 400 8749 1 400 438 564 12 x M 8 12 3 4 6 9 7 5 3 6
RSD 400/ 800 8750 2 800 438 564 12 x M 8 21 6 6 12 18 13 12 8 9
RSD 400/ 1200 8751 3 1200 438 564 12 x M 8 30 7 10 14 22 18 13 9 15
RSD 450/ 400 8752 1 400 487 634 12 x M 8 17 4 5 8 10 8 7 5 8
RSD 450/ 800 8753 2 800 487 634 12 x M 8 27 6 7 13 18 13 12 9 11
RSD 450/ 1200 8754 3 1200 487 634 12 x M 8 38 8 10 18 23 17 14 10 15
RSD 500/ 600 8755 1 600 541 714 12 x M 8 27 4 5 9 11 9 9 6 8
RSD 500/ 900 8756 2 900 541 714 12 x M 8 36 6 8 14 16 13 13 9 12
RSD 500/ 1200 8757 3 1200 541 714 12 x M 8 45 8 11 22 24 17 16 12 17
RSD 560/ 600 8758 1 600 605 804 8 x M 10 32 3 5 9 9 8 8 6 8
RSD 560/ 1200 8759 2 1200 605 804 8 x M 10 52 6 10 19 19 16 13 10 15
RSD 630/ 600 8760 1 600 674 900 8 x M 10 44 3 5 8 8 8 7 5 8
RSD 630/ 1200 8761 2 1200 674 900 8 x M 10 68 5 10 16 15 15 11 8 15
RSD 710/ 600 8762 1 600 751 1000 8 x M 10 51 3 5 7 7 7 6 4 8
RSD 710/ 1200 8763 2 1200 751 1000 8 x M 10 80 5 10 14 13 13 10 7 15
RSD 800/ 600 8764 1 600 837 1100 12 x M 10 57 2 5 7 6 6 5 4 8
RSD 800/ 1200 8765 2 1200 837 1100 12 x M 10 88 5 9 13 11 11 9 6 14
RSD 900/ 900 8766 1 900 934 1220 12 x M 10 82 2 4 10 9 6 5 4 6
RSD 900/ 1800 8767 2 1800 934 1220 12 x M 10 135 4 9 21 17 13 9 8 14
RSD 1000/ 900 8768 1 900 1043 1350 12 x M 10 96 2 4 8 7 5 4 3 6
RSD 1000/ 1800 8769 2 1800 1043 1350 12 x M 10 157 4 7 16 14 10 7 6 11
RSD 1120/ 900 8770 1 900 1174 1350 12 x M 10 81 2 3 7 6 4 3 3 5
RSD 1120/ 1800 8771 2 1800 1174 1350 12 x M 10 136 3 6 14 11 8 6 5 9
RSD 1250/ 900 8772 1 900 1311 1460 12 x M 10 86 1 2 5 4 3 2 2 3
RSD 1250/ 1800 8773 2 1800 1311 1460 12 x M 10 146 2 4 11 9 7 5 4 6

320