Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: HVAC Sound Attenuators
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- Shop drawings (dimensions, active length, connections, orientation)
- Silencer schedule cross-referenced to required performance
−default: [Product data (type, size, casing, fill, pressure class), Octave-band DIL, GNL, and pressure drop (forward and reverse flow), NVLAP-accredited ASTM E477 test reports, Shop drawings (dimensions, active length, connections, orientation)]
+default:
+ - "Product data (type, size, casing, fill, pressure class)"
+ - "Octave-band DIL, GNL, and pressure drop (forward and reverse flow)"
+ - "NVLAP-accredited ASTM E477 test reports"
+ - "Shop drawings (dimensions, active length, connections, orientation)"
```
…52 unchanged lines
# Environmental and Service Conditions {toc}
−## The silencer casing material shall be selected for the service environment of the duct system it serves; standard galvanized steel is suitable for typical conditioned-air systems but corrodes in moist, chemically aggressive, or sanitary environments. {note}
+## The silencer casing material shall be selected for the service environment of the duct system it serves; standard galvanized steel is suitable for typical conditioned-air systems but corrodes in moist, chemically aggressive, or sanitary environments.
### Natatorium, kitchen exhaust, laboratory fume exhaust, coastal outdoor-air, and similar corrosive duct runs require stainless steel or aluminum casing; specifying standard galvanized casing in these environments is a common and costly design omission. {note}
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step: 5
unit: °F
−setpoints: [40, 105]
+setpoints: [-20, 40, 105]
```
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step: 1
unit: dB
−setpoints: [15, 25]
+setpoints: [15, 25, 45]
```
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step: 1
unit: dB
−setpoints: [25, 40]
+setpoints: [25, 40, 50]
```
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step: 1
unit: dB
−setpoints: [30, 45]
+setpoints: [30, 45, 50]
```
…5 unchanged lines
step: 1
unit: dB
−setpoints: [30, 45]
+setpoints: [30, 45, 50]
```
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step: 1
unit: dB
−setpoints: [20, 35]
+setpoints: [20, 35, 45]
```
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step: 1
unit: dB
−setpoints: [12, 25]
+setpoints: [12, 25, 35]
```
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## Pressure Drop {toc}
−### Pressure drop is the static pressure the silencer adds to the system at design airflow; it is paid for by the fan in energy and must be reserved in the fan schedule. {note}
+### Pressure drop is the static pressure the silencer adds to the system at design airflow; it is paid for by the fan in energy and must be reserved in the fan schedule.
−### Specifying a long, narrow-baffle, high-performance silencer without reserving adequate static pressure in the fan selection forces fan re-selection during construction and generates avoidable requests for information; the pressure-drop budget must be coordinated with the mechanical schedule at design. {note}
+### Specifying a long, narrow-baffle, high-performance silencer without reserving adequate static pressure in the fan selection forces fan re-selection during construction and generates avoidable requests for information; the pressure-drop budget must be coordinated with the mechanical schedule at design.
### The total pressure loss across the silencer at the design airflow and face velocity shall not exceed the scheduled maximum.
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step: 0.01
unit: in. w.g.
−setpoints: [0.10, 0.15]
+setpoints: [0.05, 0.1, 0.15]
```
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step: 50
unit: FPM
−setpoints: [1000, 1500]
+setpoints: [500, 1000, 1500, 2500]
```
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```
−## The silencer performance configuration shall be selected to match the application: low-pressure-drop where fan energy and static budget are constrained, or high-insertion-loss where attenuation governs and space permits a longer, denser unit. {note}
+## The silencer performance configuration shall be selected to match the application: low-pressure-drop where fan energy and static budget are constrained, or high-insertion-loss where attenuation governs and space permits a longer, denser unit.
```datasheet
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## Active Length {toc}
−### Active length is the acoustically treated depth of the silencer in the direction of airflow; greater length yields greater low-frequency insertion loss but must be reconciled against the plenum, shaft, or mechanical-room space available. {note}
+### Active length is the acoustically treated depth of the silencer in the direction of airflow; greater length yields greater low-frequency insertion loss but must be reconciled against the plenum, shaft, or mechanical-room space available.
−### Silencer active lengths of 5 to 10 ft (1500 to 3000 mm) are frequently not flagged on mechanical drawings and conflict with structure, piping, or shaft height in the field; the selected active length must be coordinated against available space during design. {note}
+### Silencer active lengths of 5 to 10 ft (1500 to 3000 mm) are frequently not flagged on mechanical drawings and conflict with structure, piping, or shaft height in the field; the selected active length must be coordinated against available space during design.
### The silencer active length shall be as scheduled.
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```
−# Construction {toc}
+# The silencer is a sheet-metal casing enclosing absorptive baffles filled with sound-absorbing media; casing construction, baffle construction, and fill media each carry their own requirements. {note}
−## The silencer is a sheet-metal casing enclosing absorptive baffles filled with sound-absorbing media; casing construction, baffle construction, and fill media each carry their own requirements. {note}
+# Casing {toc}
−## Casing {toc}
+## The casing shall be constructed of the scheduled material and gauge, with airtight seams suitable for the scheduled pressure class.
−### The casing shall be constructed of the scheduled material and gauge, with airtight seams suitable for the scheduled pressure class.
+## The casing gauge shall follow SMACNA HVAC Duct Construction Standards for the applicable pressure class, with a minimum of 22 ga for sizes up to 24 in. wide, 20 ga for 25 to 48 in., and 18 ga for sizes over 48 in.
−### The casing gauge shall follow SMACNA HVAC Duct Construction Standards for the applicable pressure class, with a minimum of 22 ga for sizes up to 24 in. wide, 20 ga for 25 to 48 in., and 18 ga for sizes over 48 in.
+## Casing seams and joints shall be sealed to achieve the duct leakage class of the adjoining duct system.
−### Casing seams and joints shall be sealed to achieve the duct leakage class of the adjoining duct system.
+## Connection flanges or slip-and-drive edges shall be compatible with the connection method of the adjoining duct.
−### Connection flanges or slip-and-drive edges shall be compatible with the connection method of the adjoining duct.
−
```datasheet
label: Connection Type
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```
−## Baffles and Fill Media {toc}
+# Baffles and Fill Media {toc}
−### The acoustic baffles shall contain the scheduled fill media, retained against erosion into the airstream at the design face velocity.
+## The acoustic baffles shall contain the scheduled fill media, retained against erosion into the airstream at the design face velocity.
−### Fill media shall be glass fiber or mineral wool at a minimum density of 1.5 lb/ft³ (24 kg/m³).
+## Fill media shall be glass fiber or mineral wool at a minimum density of 1.5 lb/ft³ (24 kg/m³).
−### Where fill media are exposed to the airstream, they shall meet NFPA 90A Section 5.2, with a flame-spread index not exceeding 25 and a smoke-developed index not exceeding 50 when tested per ASTM E84.
+## Where fill media are exposed to the airstream, they shall meet NFPA 90A Section 5.2, with a flame-spread index not exceeding 25 and a smoke-developed index not exceeding 50 when tested per ASTM E84.
−### The fill-media facing shall be selected for the service: a perforated metal facing protects the fill in standard systems, while encapsulation isolates the fill entirely for hygienic and erosion-sensitive systems. {note}
+## The fill-media facing shall be selected for the service: a perforated metal facing protects the fill in standard systems, while encapsulation isolates the fill entirely for hygienic and erosion-sensitive systems.
−### Open (unencapsulated) fiberglass fill shall not be used in healthcare, cleanroom, laboratory, or kitchen exhaust systems; NFPA 90A and infection-control requirements mandate encapsulated fill or no exposed fibrous media in these applications. {note}
+## Open (unencapsulated) fiberglass fill shall not be used in healthcare, cleanroom, laboratory, or kitchen exhaust systems; NFPA 90A and infection-control requirements mandate encapsulated fill or no exposed fibrous media in these applications. {note}
−### The fill-media encapsulation shall be as scheduled.
+## The fill-media encapsulation shall be as scheduled.
```datasheet
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```
−### The fill media density shall be as scheduled.
+## The fill media density shall be as scheduled.
```datasheet
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step: 0.5
unit: lb/ft³
−setpoints: [1.5, 3.0]
+setpoints: [1.5, 3, 6]
```
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step: 0.5
unit: duct diameters
−setpoints: [1, 2]
+setpoints: [1, 2, 4]
```
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# Delivery, Storage, and Handling {toc}
−## Silencers shall be delivered with casing ends protected and fill media kept dry, since wet fill media lose acoustic performance and can support microbial growth. {note}
+## Silencers shall be delivered with casing ends protected and fill media kept dry, since wet fill media lose acoustic performance and can support microbial growth.
## Silencers shall be delivered with factory protective covers over open casing ends and shall be stored indoors, off the ground, and protected from weather and construction moisture.
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default: None
```