Nap Acoustics - The experts in noise control

NAP ACOUSTICS SOUTH EAST ASIA PTE LTD
DESIGNERS & MANUFACTURERS OF NOISE AND VIBRATION CONTROL PRODUCTS

Rectangular Duct Silencers

Introduction

D-Series (formerly named as Dingo) and H-Series Duct Silencers are used wherever it is necessary to control the passage of noise along an air path. They control the noise of ventilation and air-conditioning systems in office buildings, lecture and conference rooms, hotels, hospitals and wherever air-conditioning and ventilation systems are installed.

In industrial applications, D-Series Duct Silencers control noise from fans and blowers, cooling towers, dust extraction systems and generators.
Excellent low frequency performance combined with minimal aerodynamic pressure drop make H-Series Duct Silencers the ideal choice for noise control in applications such as air-cooled chillers, industrial fans, power station ducting, cooling towers, steam vents, diesel and gas turbine driven equipment.

Construction

NAP Duct Silencers consist of a galvanised sheetmetal case containing one or two side panels and one or more splitters (refer to picture above).
Normal low pressure silencers use Pittsburgh seams with attached angle frames step welded to the case. Duct sealer is then used to seal the case to the frames to ensure that the silencer is airtight. For high pressure systems, the silencers have fully welded seams.

NAP Duct Silencers have been used on cooling towers continuously exposed to the weather without any signs of rust or reduction in acoustic performance after many years of use. This is due to the fact that the sheetmetal in the silencer is galvanised to provide long life, free from corrosion.

Installation

When used in mechanical services and air-conditioning systems, silencers are best installed where the ductwork passes through plant rooms, studios or other building walls, and where the ductwork upstream of the silencer is free of bends so that airflow into the silencer will be uniform.

Should a silencer be installed after a bend, there is a right and wrong way of orienting the silencer. Splitters should be installed in the same plane as the radius of the bend.

Silencers should not be installed close to the inlet of fans. This prevents noise generated by the fan blades as they cross the wake from the splitter airways. This phenomenon can increase the fan noise by up to 15dB. Silencers should therefore be placed approximately two rotor diameters from the fan itself.

Where the adjoining ductwork is thermally insulated, allowance should be made for thermally insulating the silencer as they are not externally insulated in standard form.

Flexible couplings should be used between the silencer and adjoining ductwork where there is a risk of vibration transmission or flanking. The material of the flexible coupling should be non-sound transparent material (metal impregnated with fibreglass-reinforced vinyl cloth being an excellent material) which permits vibration isolation whilst minimizing the sound leakage into or out of the ductwork.