Acoustical
Benefits of Double-Wall, Insulated
Duct and Fittings
Performance
Ratings
Through extensive testing in acoustical laboratories, we have generated
a large database of insertion losses and airflow-generated sound power
levels for our double-wall duct and fittings. Such information is essential
for optimizing noise control in air handling systems. Our UNI-DUCT®
computer-aided duct system design program, which is equipped with this
data, makes it easy to analyze the acoustical design of an air handling
system while simultaneously analyzing and balancing the airflow performance
of the system.
Fan
Noise Reduction
Fan noise can travel to every air outlet and inlet in an air handling
system and create unacceptable noise levels in the rooms or areas served
by the system. Our double-wall duct and fittings provide exceptional control
of fan noise, often eliminating the need for additional duct silencers.
Reduced
Airflow-Generated Noise
The insulation in our double-wall duct and fittings is located outside
the duct system’s air passage, where it can absorb sound without
interfering with the airflow. Duct silencers, on the other hand, interfere
with the airflow. Turbulent airflow at the inlet and outlet of a silencer
generates noise that can create acoustical problems upstream and downstream
of the silencer. With our double-wall duct, there is very little airflow-generated
noise. In fact, the insulation continuously reduces what noise there is,
effectively creating an air handling system that is quieter than a single-wall
system.
High
Sound-Transmission Loss
Noise traveling along a duct path can radiate through the walls of the
duct and fittings. Sheet metal duct walls have higher sound-transmission
loss than lightweight duct materials such as fiberglass duct board and
flexible duct. Acoustical laboratory tests show that in similar sizes
and shapes our double-wall duct and fittings can reduce radiated noise
by 25 dB or more, compared with fiberglass duct board, and by 30 dB or
more, compared with insulated flexible duct.
Our
double-wall duct and fittings also control radiated noise better than
similar sizes and shapes of externally insulated sheet metal duct. The
internal insulation continuously reduces the noise flowing along the duct
path, while external insulation has little or no effect on this noise.
With external insulation, excessive noise travels undiminished throughout
the duct system and can radiate into rooms or areas served by the system.
Flanking-Path
and Cross-Talk Noise Control
When a duct system passes through noisy environments such as mechanical
equipment rooms and production areas, its walls can pick up flanking-path
noise and convey it to other areas served by the duct system. Openings
in duct systems (for example, diffusers, registers, and grilles) allow
even low-level background noise into the duct system where it can be conveyed
to other openings and radiate outward as cross-talk noise. The internal
insulation of our double-wall duct begins absorbing external noise as
soon as it enters the duct system, effectively preventing the duct system
from becoming a speaking tube.
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