1322:
should straddle the wall of the mechanical equipment room provided there are no fire dampers. If a sound attenuator is located over occupied space, the noise control engineer should confirm that duct breakout noise is not an issue prior to the attenuator. If there is significant distance between the attenuator and the mechanical room penetration, additional duct cladding (such as external fiberglass blanket or gypsum lagging) may be required to prevent noise from breaking into the duct and bypassing the attenuator.
226:, provided by the silencer under flow conditions. While flow conditions in typical low velocity duct systems rarely exceed 2000–3000 ft/min, sound attenuators for steam vents must withstand airflow velocities in the 15,000-20,000 ft/min. range. The acoustic performance of a sound attenuator is tested over a range of airflow velocities, and for forward and reverse flow conditions. Forward flow is when the air and sound waves propagate in the same direction. The insertion loss of a silencer is defined as
77:
1321:
Sound attenuators are typically located near ducted mechanical equipment, to attenuate noise which propagates down the duct. This creates a trade-off: the sound attenuator should be located near the fan and yet the air is typically more turbulent closer to fans and dampers. Ideally, sound attenuators
120:
Sound attenuators are available in circular and rectangular form factors. Prefabricated rectangular sound attenuators typically come in 3, 5, 7, or 9-ft lengths. The width and height of the sound attenuators are often determined by the surrounding ductwork, though extended media options are available
1308:
First, the project noise control engineer (or acoustician), mechanical engineer, and equipment representative select the quietest possible equipment which meets the mechanical requirements and budget constraints of the project. Then, the noise control engineers will typically calculate out the path,
579:
For example, if the attenuator doubles in width, while maintaining a constant airflow velocity, the generated noise will increase by 3 dB. Conversely, if the attenuator shrinks by a factor of 10, while keeping the airflow velocity constant, the generated noise will decrease by 10 dB. Since
1317:
Duct silencers are prominently featured in systems where fiberglass internal duct liner is prohibited. While fiberglass's contribution to air quality is insignificant, many higher education projects have adopted a limit on internal fiberglass liner. In these situations, the project acoustician must
1259:
Dissipative silencers attenuate sound by transferring sound energy to heat. Dissipative silencers are used when broadband attenuation with low pressure drop is desired. In typical ductwork, high frequencies propagate down the duct as a beam, and minimally interact with the outer, lined edges. Sound
375:
Some manufacturers report the static insertion loss of the silencer, which is typically measured with a loudspeaker in lieu of a fan to represent a zero flow condition. These values can be useful in the design of smoke evacuation systems, where sound attenuators are used to attenuate exterior noise
1291:
between two closed, private spaces. Their design typically incorporates one or more bends to form a "Z" or "U" shape. This bend increases the efficacy of the sound attenuator without significantly increasing its overall length. Crosstalk attenuators are passive devices and should be sized for
931:
The pressure drop through a sound attenuator is typically higher than the pressure drop for an equivalent length of lined duct. However, significantly longer lengths of lined duct are required to achieve equal attenuation, at which point the pressure drop of large extents of lined duct is
205:
The acoustical properties of commercially available sound attenuators are tested in accordance with ASTM E477: Standard Test Method for
Laboratory Measurements of Acoustical and Airflow Performance of Duct Liner Materials and Prefabricated Silencers. These tests are conducted at
1260:
attenuators with baffles that break the line of sight or elbow attenuators with a bend provide better high frequency attenuation than conventional lined ductwork. Generally, longer attenuators with thicker baffles will have a greater insertion loss over a wider frequency range.
1218:
The perimeter, area, and length of the sound attenuator are also parameters which affect its pressure drop. Friction loss at the sound attenuator is directly proportional to its noise attenuation performance, whereby greater attenuation usually equates to greater pressure drop.
391:
The internal baffles of a sound attenuator constrict airflow, which in turn generates turbulent noise. Noise generated by a sound attenuator is directly related to the airflow velocity at the constriction, and changes proportionally with the face area of the sound attenuator.
1313:
level. If no attenuator selection is feasible, the noise control engineer and mechanical must re-evaluate the path between the equipment and the sound attenuator. When space constraints do not allow for a straight attenuator, an elbow or transitional attenuator can be used.
1279:, and other ventilated equipment enclosures. On certain air handling unit or fan applications, it is common to use a co-planar silencer—a dissipative silencer that is sized for the fan and mounted directly to the fan outlet. This is a common feature in fan array design.
1250:
design of automobiles and trucks. Attenuation is primarily achieved through sound reflection, area change, and tuned chambers. The design of reactive silencers from scratch is mathematically intensive, so manufacturers often have a number of prefabricated designs.
105:
Packless sound attenuators do not include sound-absorptive insulation. As a result, the high-frequency insertion loss of a packless sound trap is greatly reduced. Bagged insulation or packless sound attenuators are typically referred to as "hospital grade"
64:. Unlike conventional internally-lined ductwork, which is only effective at attenuating mid- and high-frequency noise, sound attenuators can achieve broader band attenuation in relatively short lengths. Certain types of sound attenuators are essentially a
927:
Where sound attenuator dimensions differ from surrounding duct dimensions, transitions to and from the sound attenuator should be smooth and gradual. Abrupt transitions cause the pressure drop and regenerated noise to significantly increase.
1075:
923:
provides pressure drop correction factors for different inlet and outlet conditions. These correction factors are used whenever there's a turbulent wake within 3 to 5 duct diameters upstream or downstream of the attenuator.
514:
210:-accredited facilities and then reported by the manufacturer in marketing or engineering bulletins. Outside of the US, sound attenuators are tested in accordance with British Standard 4718 (legacy) or ISO 7235.
754:
306:
114:
The gauge of circular sound attenuators is typically less of a consideration, as circular ductwork is considerably stiffer than rectangular ductwork and less prone to duct breakout noise.
124:
Sound attenuators are typically classified as "Low," "Medium," or "High" based on performance characteristics and/or duct velocity. An example classification scheme is listed below.
1227:
Prefabricated sound attenuators rose to prominence in the late 1950s-early 1960s. Several manufacturers were among the first to produce and test prefabricated sound attenuators:
121:
for improved attenuation. The baffles of rectangular sound attenuators are commonly referred to as splitters, whereas circular sound attenuators contain a bullet-shaped baffle.
1106:
1213:
1179:
1157:
905:
832:
607:
574:
545:
370:
337:
111:
An outer non-perforated layer of sheet metal. The outer layer is typically heavy gauge sheet metal (18ga or stiffer) to minimize duct break-out and break-in noise.
940:
781:
1128:
876:
854:
803:
1621:"ASTM E477 - 13e1 Standard Test Method for Laboratory Measurements of Acoustical and Airflow Performance of Duct Liner Materials and Prefabricated Silencers"
1329:, air intake of emergency generators, and exhaust fans. Larger equipment will require an array of sound attenuators, otherwise known as an attenuator bank.
2161:
1300:
In the early 1970s, American SF Products, Inc. created the KGE Exhaust
Register, which was an air distribution device with an integral sound attenuator.
207:
919:. Catalog pressure drop values obtained through ASTM E477 assume ideal, laminar airflow, which is not allow always found in field installations. The
1942:
1726:
1500:
1946:
1730:
1504:
400:
1309:
without the attenuator first. The required sound attenuator insertion loss is the difference between the calculated path and the target
1343:
2098:
628:
60:
materials. The physical dimensions and baffle configuration of sound attenuators are selected to attenuate a specific range of
1788:
1702:
1581:
1476:
231:
1999:
Advertisement (1961). "Fan Noise
Controlled in Air Handling Systems Quickly & Accurately in less than 5 minutes!".
380:
1918:
1823:
1753:
1662:
1443:
1965:
Doelling, Norman (1960). "Noise
Reduction Characteristics of Package Attenuators for Air-Conditioning Systems".
56:
In its simplest form, a sound attenuator consists of a baffle within the ductwork. These baffles often contain
623:
There is a prediction formula that can be used to estimate duct silencer regenerated noise if no data exists
53:
through the ductwork, either from equipment into occupied spaces in a building, or between occupied spaces.
1878:
1846:
2059:
American SF Products, Inc. (1972). "Meet the KGE: the first exhaust register designed as a sound trap".
1381:
Doelling, Norman (1961). "Noise
Reduction Characteristics of Package Attenuators for Air-Conditioning".
612:
Regenerated noise should always be reviewed, but it is usually only a concern in very quiet rooms (e.g.
17:
2143:
1234:
Though rectangular dissipative attenuators are the most common variant of attenuators used today in
1084:
1235:
2166:
1186:
57:
613:
1527:
1318:
rely on duct silencers as the primary means of fan noise and duct-borne noise attenuation.
1164:
1135:
1070:{\displaystyle Friction\ Loss={\frac {P}{A}}l(K_{f}{\frac {1}{2}}\rho v_{p}^{2}),\ N/m^{2}}
883:
810:
583:
552:
523:
348:
315:
8:
1607:
Development of a mechanical equipment noise-control permit scheme for model building code
65:
2133:
2076:
Fibrous glass duct liner standard : design, fabrication and installation guidelines
1531:
763:
1936:
1720:
1551:
1494:
1113:
861:
839:
788:
620:, music rehearsal rooms) or when the ductwork velocity is greater than 1500 ft/m.
95:
2079:
2041:
1924:
1914:
1852:
1829:
1819:
1794:
1784:
1759:
1749:
1708:
1698:
1668:
1658:
1587:
1577:
1543:
1482:
1472:
1449:
1439:
1405:
2073:
1555:
2138:
1879:
American
Society of Heating, Refrigerating and Air Conditioning Engineers. (2015).
1847:
American
Society of Heating, Refrigerating and Air Conditioning Engineers. (2006).
1535:
1310:
617:
920:
2014:
Farris, R. W.; Young, W. S. Jr. (1955). "All Quiet on the
Residential Front?".
1574:
Noise and
Vibration Control for Building Services Systems - CIBSE Guide B4-2016
219:
1712:
1471:. American Society of Heating, Refrigerating, and Air-Conditioning Engineers.
2155:
2083:
2045:
1856:
1833:
1798:
1763:
1748:. American Society of Heating, Regrigerating and Air-conditioning Engineers.
1672:
1591:
1547:
1486:
1453:
1409:
1326:
1268:
916:
36:
1928:
1231:, Industrial Acoustics Company, Industrial Sound Control, and Elof Hansson.
1539:
1695:
Noise and vibration control engineering : principles and applications
1620:
2124:
American
Society of Heating, Refrigerating and Air-Conditioning Engineers
1609:. Environmental Protection Agency, Office of Noise Abatement and Control.
1338:
1276:
1264:
935:
Friction losses due to dissipative sound attenuators can be expressed as
340:
46:
580:
turbulence generated noise caused by duct fittings changes at a rate of
76:
1908:
1894:
Cerami, Vito; Bishop, Edwin (1966). "Control of Duct Generated Noise".
1272:
932:
significantly greater than incurred through a single sound attenuator.
1984:
Advertisement (1961). "We don't know what noise annoys an oyster...".
1518:
CUMMINGS, A. (January 2001). "Sound Transmission Through Duct Walls".
2035:
1813:
1778:
1652:
1433:
1288:
509:{\displaystyle Generated\ Noise\ (dB)=10\log({\frac {A_{1}}{A_{0}}})}
379:
The insertion loss of a sound attenuator is sometimes referred to as
61:
39:
1692:
1292:
extremely low pressure drops — typically less than 0.05 inches w.g.
609:, airflow velocities are a critical component of attenuator sizing.
1469:
A practical guide to noise and vibration control for HVAC systems
1247:
1228:
223:
32:
2118:
84:
Generally, sound attenuators consist of the following elements:
2074:
North American Insulation Manufacturers Association. (2002).
1431:
99:
88:
An inner perforated layer of light gauge sheet metal (baffle)
50:
749:{\displaystyle Lw=55log(V/V_{0})+10log(N)+10log(H/H_{0})-45}
372:= Radiated sound power from the duct without the attenuator
1435:
Acoustics : architecture, engineering, the environment
783:= sound power level generated by the sound attenuator (dB)
91:
The baffle is then filled with sound-absorptive insulation
43:
2058:
2123:
1605:
Blazier, Warren; Miller, Nicholas; Towers, David (1981).
94:
In high velocity systems, or when there is a concern for
1466:
915:
Similar to other duct fittings, sound attenuators cause
2128:
1402:
Sound Attenuation of Fiberglass Lined Ventilation Ducts
878:= height or circumference of the sound attenuator (in)
301:{\displaystyle IL\ (dB)=10\log({\frac {W_{0}}{W_{m}}})}
222:
of a sound attenuator is the amount of attenuation, in
1325:
Sound attenuators can also be used outdoors to quiet
1189:
1167:
1138:
1116:
1087:
943:
886:
864:
842:
813:
791:
766:
631:
586:
555:
526:
403:
351:
318:
234:
1743:
128:
Sound Attenuator Classification at 1000 ft/min
1604:
1108:= ratio of the sound attenuator perimeter and area
1207:
1173:
1151:
1122:
1100:
1069:
899:
870:
848:
826:
805:= velocity at the constricted cross-area (ft/min)
797:
775:
748:
601:
568:
539:
508:
395:The change in generated noise can be expressed as
364:
331:
300:
1909:Beranek, Leo L. (Leo Leroy), 1914-2016. (1991) .
2153:
1650:
1263:These types of attenuators are commonly used on
1776:
1399:
1303:
856:= number of air passages (number of splitters)
44:Heating Ventilating and Air-Conditioning (HVAC)
576:= Reference face area of the sound attenuator
80:Circular sound attenuator (left of the grille)
1998:
1983:
1693:Vér, I. L. Beranek, Leo L. 1914-2016 (2010).
2033:
1941:: CS1 maint: multiple names: authors list (
1893:
1725:: CS1 maint: multiple names: authors list (
1499:: CS1 maint: multiple names: authors list (
547:= The new face area of the sound attenuator
2013:
1287:Purpose-built sound attenuators to prevent
1238:noise control, other design options exist.
2162:Heating, ventilation, and air conditioning
1945:) CS1 maint: numeric names: authors list (
1811:
1729:) CS1 maint: numeric names: authors list (
1503:) CS1 maint: numeric names: authors list (
1896:Air Conditioning, Heating and Ventilating
1654:Fundamentals of noise control engineering
834:= reference velocity (196.8 ft/min)
213:
1964:
1517:
1380:
1254:
75:
68:used as a passive noise-control device.
907:= reference dimension (0.0394 in)
376:that breaks into the exhaust ductwork.
14:
2154:
1571:
1432:Charles M. Salter Associates. (1998).
1282:
1246:Reactive silencers are very common in
2099:"Controlling Noise from HVAC Systems"
2096:
2029:
2027:
2025:
1960:
1958:
1956:
1874:
1872:
1870:
1868:
1866:
1688:
1686:
1684:
1682:
1646:
1644:
1642:
1640:
1241:
2037:Noise control in mechanical services
1567:
1565:
1427:
1425:
1423:
1421:
1419:
1376:
1374:
1372:
1295:
1222:
386:
49:designed to reduce transmission of
31:, or duct silencer, sound trap, or
24:
2022:
1953:
1863:
1815:Noise control in building services
1679:
1637:
343:from the duct with the attenuator
25:
2178:
2112:
1562:
1467:Schaffer, Mark E., 1949- (2011).
1416:
1369:
1159:= The friction loss coefficient
910:
71:
2090:
2067:
2052:
2007:
1992:
1977:
1902:
1898:. September (September): 55–64.
1887:
1840:
1805:
1770:
1737:
98:in the air stream, a bagged or
1613:
1598:
1520:Journal of Sound and Vibration
1511:
1460:
1400:Albright, Jacob (2015-12-01).
1393:
1355:
1101:{\displaystyle {\frac {P}{A}}}
1040:
999:
737:
716:
698:
692:
674:
653:
503:
476:
461:
452:
295:
268:
253:
244:
13:
1:
2119:Acoustical Society of America
1746:Algorithms for HVAC acoustics
1744:Reynolds, Douglas D. (1991).
1349:
200:
1404:. Digital Scholarship@UNLV.
1304:Noise control implementation
7:
1783:. Elsevier Academic Press.
1332:
1271:, and at the air intake of
10:
2183:
1363:ASHRAE Guide and Data Book
139:Attenuator Classification
102:-faced insulation is used.
1651:Thumann, Albert. (1990).
1365:. 1961. pp. 217–218.
1208:{\displaystyle v_{p}^{2}}
1777:Long, Marshall. (2006).
1780:Architectural acoustics
1236:architectural acoustics
2097:Jones, Robert (2003).
1540:10.1006/jsvi.2000.3226
1209:
1175:
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872:
850:
828:
799:
777:
750:
603:
570:
541:
510:
366:
333:
302:
214:Dynamic insertion loss
81:
2040:. Sound Attenuators.
2034:Woods, R. I. (1972).
1255:Dissipative silencers
1210:
1176:
1174:{\displaystyle \rho }
1154:
1152:{\displaystyle K_{f}}
1130:= length of the duct
1125:
1103:
1072:
902:
900:{\displaystyle H_{0}}
873:
851:
829:
827:{\displaystyle V_{0}}
800:
778:
751:
604:
602:{\displaystyle 50log}
571:
569:{\displaystyle A_{0}}
542:
540:{\displaystyle A_{1}}
511:
367:
365:{\displaystyle W_{m}}
334:
332:{\displaystyle W_{0}}
303:
79:
1187:
1165:
1136:
1114:
1085:
941:
884:
862:
840:
811:
789:
764:
629:
584:
553:
524:
401:
349:
316:
232:
2105:. September: 28–33.
1812:Fry, Alan. (1988).
1532:2001JSV...239..731C
1283:Crosstalk silencers
1215:= passage velocity
1204:
1039:
169:> 0.30 in. w.g.
158:0.10-0.30 in. w.g.
129:
66:Helmholtz resonator
2129:ASTM International
1818:. Pergamon Press.
1657:. Fairmont Press.
1265:air handling units
1242:Reactive silencers
1205:
1190:
1181:= density of air
1171:
1149:
1120:
1098:
1067:
1025:
897:
868:
846:
824:
795:
776:{\displaystyle Lw}
773:
746:
599:
566:
537:
506:
362:
329:
298:
191:> 0.03 in w.g.
180:< 0.03 in w.g.
147:<0.10 in. w.g.
127:
96:particulate matter
82:
1913:. Peninsula Pub.
1790:978-0-12-455551-8
1704:978-0-471-44942-3
1583:978-1-906846-79-4
1478:978-1-936504-02-2
1438:. William Stout.
1296:Exhaust registers
1223:Design variations
1123:{\displaystyle l}
1096:
1048:
1020:
994:
970:
871:{\displaystyle H}
849:{\displaystyle N}
798:{\displaystyle V}
618:recording studios
501:
451:
433:
387:Regenerated noise
381:transmission loss
293:
243:
198:
197:
16:(Redirected from
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2134:Price Industries
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2003:. February: 141.
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2144:Vibro-Acoustics
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2018:. March: 36–37.
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1911:Noise reduction
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341:sound power
339:= Radiated
62:frequencies
2156:Categories
1973:: 114–128.
1851:. ASHRAE.
1713:1026960754
1630:2020-01-11
1350:References
201:Properties
40:acoustical
18:Sound trap
2084:123444561
2078:. NAIMA.
2046:807408333
1937:cite book
1883:. ASHRAE.
1857:315340946
1834:924971315
1799:906254282
1764:300308745
1721:cite book
1697:. Wiley.
1673:301407261
1592:987013225
1576:. CIBSE.
1548:0022-460X
1495:cite book
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1289:crosstalk
1267:, ducted
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161:"Medium"
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47:ductwork
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1229:Koppers
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183:"Low"
150:"Low"
133:Shape
1552:S2CID
1389:(12).
208:NVLAP
100:mylar
51:noise
2080:OCLC
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1947:link
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2158::
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