Noise is generally accepted as unwanted sound. Noise in a ventilation system is a very complex and diverse phenomenon. There are often many noise sources from each other; however, it is very important to be able to separate them so that the appropriate sound attenuator can be installed.

Noise Sources:
In principle, the noise sources in a ventilation system can be roughly divided into the following main areas:
1. Fan Noise.
2. Duct Noise.
3. Noise from dampers, leaks, etc.

1. Fan Noise :
Noise from the fan can be divided into air noise and operating noise. Air flow noise is a function of the velocity and pressure. Operating noise comes from the fan motor, belt drives, bearings, etc. the air flow noise is usually the worst problem. The critical frequency is often the fan impeller frequency, fs.
fs = n/60 . s, Hz
n = number of revolutions, rpm.
s = number of blades.

2- Duct Noise :
Duct noise is generated primarily when the air flow passes sharp edges, dampers, turning vanes in rectangular elbows and poorly installed saddle taps. Any obstruction to the air flow will cause turbulence and noise. Secondary duct noise may also originate from the transmission of noise through the duct from room to room.

3- Damper Noise, valve Noise, etc. :
Noise may also be caused near valves, dampers as the air flow passes through relatively small holes. Noise may also be caused by poor joints or leaks.

1. The design insertion losses (IL) at each octave and frequency, ranging from 63 Hz up to 8000 Hz.
2. The design airflow rate through each silencer with the maximum permissible pressure drop across each silencer.
3. Duct connection size, and the maximum permissible length for the silencer (if applicable). Maximum static pressure drop.
4. Room Dimensions ( W x H x L).

Please note that Egy air’s standard silencer lengths are 600, 900, 1200,
1500, 1800, 2100 & 2400mm long. Once you have this information you will be able to simply select the silencer size and model that matches your criteria.

Sound Power Level (SWL) Vs Sound Pressure Level (SPL):
The difference between SPL and SWL: SPL is the sound pressure level =20 log P/Pref. P is sound pres-sure in N/m2 and Pref = 20 x 10-6 N/m2, while SWL is sound power level = 10 log W/Wref, where W is sound intensity in Watts and Wref = 10-12 Watt. The sound is is coming out from the source as SWL and when it travels spherically its intensity will be distributed over sphere area which makes it pressure SPL.

Octave Bands:
An octave band is a frequency band where the highest frequency is twice the lowest frequency. For example, an octave filter with a center frequency of 1 kHz has a lower frequency of 707 Hz and an upper frequency of 1.414 kHz. In HVAC Industry, the octave bands in general comprising 63, 125, 250, 500, 1K, 2K, 4K & 8K Hz.

Frequency (Hz):
The pitch of sound. The number of sound pressure waves arriving at a fixed point per second.

Insertion loss:
Insertion Loss is the reduction in the sound power level at the receiver after the silencer is installed (inserted) in the system. Insertion loss is measured as a function of frequency and commonly published in full octave bands ranging from 63 to 8000 Hz.
A silencer’s insertion loss varies depending on whether sound is traveling in the same or opposite direction as airflow. Silencer performance changes with absolute duct velocity. However, airflow velocity generally does not significantly affect silencers giving a pressure drop of 0.35 in. of water or less, including system effects.

Decibel (dB):
The decibel ( dB) is used to measure sound level.
The dB is a logarithmic way of describing a ratio.
The ratio may be power, sound pressure, voltage or intensity or other.

Background Noise & Breakout Noise:
Background Noise is the irreducible noise level measured in the absence of any building occupants when all of known sound sources have been turned off. Breakout noise is the transmission of mechanical equipments or air system noise throughduct walls.

Regenerated Noise:
Regenerated Noise is the sound generated by the duct due to air flow in dB (ref 10-12 watt).
Moreover, regeneration of sound caused by passing of air through duct elements such as dampers, Air outlets, splitters and other installed mechanical components in the Duct.

Reverberant Time:
This is the plus or minus contribution of the room reflections (reverberation) in dB.

Total Pressure Loss:
Total pressure loss is determined by subtracting the differential pressure across the attenuator from the differential pressure across the substitution duct.
A total pressure loss coefficient is calculated for each attenuator by measuring the total pressure loss at five different airflow rates.

Egy air offers all the above Types & Models of Attenuators with a dedicated experience team who can undertake all aspects of computerized sound analysis & do calculate technically to produce a highly engineered solution to your unwanted noise problem and any noise control issue

Flanges
Attenuators fitted with external galvanized steel flanges of 30mm with Corners of 105mm will help in arresting leakages, which also provides firmness & stability to Ducts, thereby creating effective barrier against
pressure drop. Flange corner holes fitted with M8 nutserts to enable easy connection

Single & Multiple Section Assembly
Egy air attenuators are supplied in Multiple Sections, when any of the below dimensions are exceeded :
W=2100, H= 1800 L = 2100 mm.
The assembly of multiple section attenuators will be carried out by others at site, based on the manufacturers instruction & guidelines.

Model : EG-RSA 75/100/150
 

Egy air Circular Sound Attenuator constructed from Galvanized sheet steel, with a peripheral out of airstreams acoustic lining. Casing provided with end ring flanges suitable for direct connection to circular fans or flanged ducts.

Casing
Casing is made of 1.0mm Thick (20 Gauge) galvanized steel. Casing provided with 30mm flanges as standard which will be sealed with Mastic Sealant to prevent leakage of Air. Circular Sound Attenuators are constructed with the following dimensions :
Inner Dia— 300 to 1000 mm
Outer Dia— 435 to 1200 mm
High-pressure duct sealant is applied inside the casing along the length of each seam, and for rectangular casings behind each flanged corner that coincides with a seam, to provide an airtight seal.

Flanges
Attenuators fitted with external galvanized steel end ring flanges suitable for direct connection to circular fans or flanged ducts.

Available Size

Airway Area & Width
Airway area & Width may differ based ontechnical calculations & Attenuator final dimensions.

Flanges
Attenuators fitted with external galvanized steel flanges of 30mm with Corners of 105mm will help in arresting leakages, which also
provides firmness & stability to Ducts, thereby creating effective barrier against pressure drop.
Flange corner holes fitted with M8 nutserts to enable easy connection.
Single & Multiple Section Assembly Egy air attenuators are supplied in Multiple Sections, when any of the below dimensions are exceeded :
W=2100, H= 1800 L = 2100 mm.
The assembly of multiple section attenuators will be carried out by others at site, based on the manufacturers instruction & guidelines

speech level within the receive room is taken to be 70- 7 = 63 dB. B. The Noise criteria for the design of mechanical services in each space
being considered :
• If crosstalk is being assessed between two adjacent room areas with different noise criteria, then the lowest criteria should be used.
• Substract the required NC level from the received speech level to give the additional average insertion loss requirement.
Example :
Air volume 0.09 m3/s ducted crosstalk attenuation required between NC 45 Toilet areas.
Attenuator cross-section required to maintain 1.5 m/s is calculated by (Volume / face velocity) 0.09 / 1.5 = 0.05 m2.
Typical Attenuator cross-sections for 0.06m2 face area :
300 x 200, 400 x 150mm. For NC 45 areas, insertion loss requirements = 63 – 45 = 18 dB, therefore, 600mm long attenuator is
selected.

Egy air Attenuator Selection Method stipulated on the below table shall be kept for an easy & quick assistance to the Design Engineer to carry out a quick selection for the attenuators at preliminary design stage, based on the design Noise Criteria of NC 40. This method should only be used when the required insertion loss has not been determined

Each Modular Joining Bracket (2) incorporates slots for four fixings and nutserts for two fixings. This allows for fixings into the rails through the flanges of adjacent modules as shown. Fix the screws loosely first until all fixings are in and the units have been correctly positioned and aligned. The screws should then be tightened.

B) Joining Centre Sections
The views below given an enlarged view of a Modular Centre Joining Bracket in position. This bracket has a larger front face incorporating four nutserts to allow the joining through four separate attenuator module flanges

C) Completion of Asembly
Once all of the sections are joined together, as shown in the view below, then a system of capping channel sections and pieces (1 and 2) can be fitted. These are used to close off the gaps between flanges in the inner sections of the modular attenuator.

All sound calculations meet international standards ASTM E90,STM E477, ISO 7235, ISO 3741, ISO 140, ISO 3744, ISO 3746, ISO 6798, ISO 8528-10, ASHRAE Handbook & Sound Research Laboratory.

The Construction of all Airwellcare Attenuators are in compliance with SMACNA & DW 144 Standards, ASTM E477, ASTM E84, NFPA 255, UL-723 and silencer dynamic insertion loss and pressure drop ratings in accordance with AMCA & applicable building codes.

Attenuators Acoustic in-fill enveloped with a Melinex Polyester Film coating, which prevents erosion of acoustic fill and/or absorption of moisture by insulation, Bacterial or microbial growth within silencer, as an alternative optional construction, apart from standard supply.

The design flexibility and calculations are based on Attenuator Application & nature of project.

Attenuator casings will comply with one of following pressure classifications:

3 – High Pressure for Class C ductwork systems operating at static pressures between – 750 and + 2000 Pa.
2 – Medium Pressure for Class B ductwork systems operating at static pressures between – 750 and + 1000 Pa.
1 – Low Pressure for Class A ductwork systems operating at static pressures between – 500 and + 500 Pa.
0 – Zero Pressure for static or very low velocity applications where attenuators do not require a pressure classification.

Acoustic Property
Fiberglass / Rockwool of 32-35 or 48Kg / M3 Density.
Thickness & density can be changed according to the Technical Calculations, to obtain the optimum performance of the Attenuators.
Non combustible when tested in accordance with BS 476 : Part 4: 1970, ASTM E-136, NFPA255 and UL 723 testing methods. Fill material is class-1 as tested in accordance with ASTM-84.
Fiberglass shall be density calculated to provide the acoustic and aerodynamic
performace.

Tested for Temp. upto 750° C in accordance with DIN 52271.
Meet the requirements of BS 2972 Sec.22 & ASTM C-871, ASTM-C-795, ASTM C-692. ASTM C-177/C-518 & DIN 52612 for low thermal conductivity.
Sound absorption in accordance with BS 3638 & ISO 0354.
Inert, vermin-proof, weather rated non combustible acoustic infill.
The acoustic infill material complies with Class ‘O’ of the U.K.’s Building Regulations

Combustion Ratings
Combustion ratings for acoustic media shall be equal to or less than the combustion ratings noted below when tested in accordance with ASTM E84, UL723 and NFPA255.
Flame Spread Classification: < 30
Smoke Development Rating: < 25

RSA

SCA

SBA

CAA