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®
Sound Attenuating Curbs
An engineering concept that provides effective sound absorption with
lower airflow interference than the center baffle sound attenuating curbs.
For use with Centri Master® ® and Skymaster®® power roof
exhausters on exceptionally quiet ventilating applications or
where the specifications require sound attenuating curbs.
Therefore, when working with sones, use 0.60 as the sound
transmission coefficient in attenuation calculations and to
make the proper power roof ventilator selections.
This Acme development utilizes a core of modular type
sound absorbing cells that exposes a very large sound
absorbing surface to the sound transmitted to the curb from
the power roof ventilator.
The sound absorbing material consists of special
acoustical-type glass fibers held in galvanized framework.
The Sone-Master®® curb reduces the audible sound
produced by the power roof ventilator by approximately
40%. In other words, it transmits approximately 60% of the
sound entering the curb.
Sone-Master®® Curb vs. Center Baffle Type
The Sone-Master®® curbs, as previously explained, have a
very low airflow interference. The center baffle type sound
curbs, on the other hand, reduce the roof fan performance
much more than their resistance charts show. A typical
center baffle type curb resistance chart will indicate only 8
to 10% loss in roof fan performance.
The amount of attenuation in decibels of Lw(A) is
dependent upon the eight octave band sound spectrum of
the specific fan being used. The Centri Master®® spectrum
differs substantially from that of the Skymaster®® . In
addition, there are other dissimilarities in sound spectra due
to differences in motor horsepower. The factory should be
consulted when attenuation in Lw(A) is needed.
Low Airflow Interference
Since airflow is the first consideration in ventilation, a “low
loss” sound curb is essential. The Sone-Master®® sound
curb provides a straight-through streamlined air passage
that has an absolute airflow interference of only 2 to 4% for
most all applications.
The center baffle disturbs the airflow pattern at the fan
wheel inlet in a manner similar to an elbow at a blower inlet.
Wind tunnel tests repeatedly show this disturbance reduces
fan performance by as much as 3 times that caused by the
resistance. The result is a total fan performance loss of 20
to 35%. This total loss is called interference.
Form C16L
Section 11
Sone-Master®® Curb Center Baffle Type
Specify Quality.
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Construction
Heavy gauge galvanized steel sound curb has continuous
welded watertight corners. Curb is available as
Self-Flashing type (SF) or as Roofed-Over Flashing type
with built-in cant strip (RF).
All acoustical and thermal insulation materials are fire
resistant glass fiber. Internal sound absorbing cells have
galvanized framework. SF curb includes foam rubber
gasket for field installation to curb top. This gasket reduces
the transmission of any vibration or metal-to-metal
conducted noise. RF curb has a wood nailer as standard.
When used, the backdraft damper may be installed in the
mounting frame opening below the curb or attached to the
sound curb with a damper box.
Curb
Model
IN mm IN mm IN mm
CS14.5 11.00 279 22.50 572 14.50 368 PRN100-110
CS19.5 16.00 406 27.50 699 19.50 495 PRN118-145
CS22.5 16.00 406 30.50 775 22.50 572 PRN163-171
CS19.5 16.00 406 27.50 699 19.50 495 PNN100-135
CS22.5 16.00 406 30.50 775 22.50 572 PL & PU135-145; PNN163
CS26.5 20.00 508 34.50 876 26.50 673
CS32.5 26.00 660 40.50 1029 32.50 826
CS38.5 32.00 813 46.50 1181 38.50 978
CS44.5 38.00 965 52.50 1334 44.50 1130
CS52.5 46.00 1168 60.50 1537 52.50 1334 EC & ECH42
CS58.5 52.00 1321 66.50 1689 58.50 1486
Dimensions
H J K
Fan
Size
PL & PU163-171-200-223;
PNN200
ECH24; PL & PU245-270;
PNN245
EC30; PL & PU300-330;
PNN300
PL & PU365-403; PNN365; EC
& ECH36
PNN425; PNN, PL &
PU440-543; EC & ECH48
transmission factor (0.60) to determine the maximum
allowable sone level of the ventilator to be selected. Then
refer to the Acme catalog to select the model that fulfills the
airflow requirements and that does not exceed the
maximum allowable sone level just determined.
Example: Furnish a power roof ventilator providing
2800 CFM (1.321 m3 /s) at .125" S.P. (31 Pa) that will not
produce over 7.0 sones with a sound curb.
1. Maximum allowable ventilator sones =
desired sones
0 60
.
7 0
.
0 60
.
117
sones
.= =
2. Since in most ventilating applications the
Sone-Master®® curb interference is about 4%,
compensate for this by selecting an airflow capacity of
4% more than desired.
Selected CFM = Required CFM x 1.04
= 2800 CFM (1.321 m3/s) x 1.04
= 2912 CFM (1.374 m3/s)
3. Refer to the appropriate Acme catalog and select an
exhauster providing 2912 CFM (1.374 m3/s) at .125"
S.P. (31 Pa) having no more than 11.7 sones. In
catalog C14, PNN200E will meet the airflow
requirements. The performance curve shows this model
will produce 11.1 sones.
4. Desired sones = 0.60 x ventilator sones
= 0.60 x 11.1 (from catalog performance curves)
= 6.7 sones
Limited Warranty
To select the proper power roof ventilator when using
sones, divide the desired attenuated sone by the sound
Acme Engineering & Manufacturing Corporation reserves the right to change specifications without notice.
These are typical drawings for dimensional purposes only. They are correct within limits suitable for normal installation and do not necessarily show actual construction.
Acme Engineering &
Manufacturing Corporation
P.O. Box 978
Muskogee, OK 74402
Telephone 918/682-7791
Fax 918/682-0134
The Sone-Master®® curbs are subject to the same Warranty
and Terms and Conditions as listed in Acme catalogs C14,
C3, C23 and C13.
Mem ber Air Move ment and Con trol As so ci a tion Au gust 1994 Form C16L
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