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GENERAL ACOUSTIC INFORMATION
H
H-23
NOISE CONTROL PRODUCTS
© FANTECH
2016
TYPICAL APPLICATIONS AND
BENEFITS OF ATTENUATOR TYPES
ATTENUATOR INFORMATION
STATIC INSERTION LOSSES
BS 4718 : 1971 "Methods of Test for Attenuators for Air Distribution Systems" requires
manufacturers to test and publish static insertion loss figures.
An insertion loss is defined as "the reduction in noise level at a given location due to the
placement of an attenuator in the sound path between the sound source and that
location". A static insertion loss is the insertion loss with no air flow passing through the
attenuator.
Therefore placing an attenuator in between a fan and the measuring position, will
reduce the noise level at the measuring position by the insertion loss.
DYNAMIC INSERTION LOSSES
Fantech test attenuators to BS4718: 1971 "Methods of Test for Attenuators for Air
Distribution Systems". This test standard sets out a procedure for the testing of static
insertion losses; i.e. the measuring of insertion losses without air flow.
Some overseas companies publish dynamic insertion losses; that is the testing of
insertion losses with air flow involved. At higher passage velocities the static insertion
loss can vary from the dynamic insertion loss by a small margin, depending on the
direction of the air flow compared to the noise propagation direction.
For typical velocities associated with a HVAC system, the static insertion losses and
dynamic insertion losses are virtually identical and can be assumed to be the same.
AIRWAY VELOCITY
For a given attenuator size a higher air flow results in a higher airway passage velocity.
Higher passage velocities will increase the regenerated noise level of the attenuator. This
is particularly critical when the attenuator is serving a low noise level zone; i.e. film studio.
A number of suggested maximum passage velocities with the appropriate room NR level
are tabulated. Critical noise applications should be checked by an Acoustics Engineer.
Model
Application
Benefits
Small Circular Type Attenuators
CC
Bathroom and Toilet exhaust fans Lightweight
Tenancy fit outs
Low cost
Apartment fans
Semi-Flexible
Circular & Rectangular Attenuators
C./C.P
&
RT/RS
Car park exhaust fans
Circular: Easy fitting
Return Air fans
Circular Open: Low pressure drop
Swimming Pools
Circular Pod: High performance
Kitchen Exhausts
Smoke Spill fans
Rectangular: High performance
Cross-talk Attenuators
CS/T/U/Z
Room to room air transfer ducts
Different designs to suit a wide range
of wall/roof configurations
Police stations
Office areas
Sound Bar Acoustic Louvres
SBL1/2
ASB
Plant rooms
Short lengths
Weatherproof
Critical noise level application should be checked by an acoustics engineer
Approx.
NR25
Do not exceed
8 m/s
In attenuator airway
NR30
“
10 m/s
“
NR35
“
13 m/s
“
NR40
“
15 m/s
“
NR45
“
18 m/s
“