What are the types of silencers for duct-mounted fans?

Release time:

2021-07-15

What are the types of silencers for duct-mounted fans?

Pipe fans are commonly used in ventilation systems for high-rise buildings. However, due to the noise generated during operation, pipe fans can disturb residents. The introduction of sound-absorbing pipe fans has effectively addressed this issue. During operation, these sound-absorbing pipe fans significantly reduce the noise they produce by utilizing specially installed silencers. Many different types of silencers can be selected for installation in sound-absorbing pipe fans. Let’s take a closer look at the various types of silencers available for pipe fans.

Porous sound-absorbing materials are primarily used to reduce noise. By fixing these sound-absorbing materials onto the inner walls of airflow passages or arranging them in a specific manner within ducts, we can create resistive silencers. When sound waves enter a resistive silencer, some of the sound energy is converted into heat through friction within the pores of the porous material and is thus dissipated, thereby weakening the sound waves that pass through the silencer. A resistive silencer functions much like a purely resistive electrical circuit, with the sound-absorbing material serving as the equivalent of a resistor. Hence, this type of silencer is referred to as a resistive silencer. Resistive silencers exhibit good noise-reducing performance for mid- and high-frequency sounds but are less effective at attenuating low-frequency noises.

A resistive muffler consists of tubes and chambers with abrupt impedance changes. It functions like an acoustic filter, much as an electrical filter does. Each small chamber containing a tube serves as a mesh element in the filter. The air mass within the tubes is analogous to inductance and resistance in electrical circuits, referred to as acoustic inductance and acoustic resistance. The volume of air in the chambers is equivalent to capacitance in electrical circuits, known as acoustic capacitance. By selecting and combining tubes and chambers appropriately, it is possible to filter out certain frequency components of noise, thereby achieving the goal of noise reduction. Resistive mufflers are particularly effective for eliminating mid- and low-frequency noise. By combining resistive structures and reactive structures in a specific manner, a composite resistive muffler can be formed.

Microperforated silencers are typically made from thin metal sheets with a thickness of less than 1 mm. The perforations drilled into these thin sheets have diameters smaller than 1 mm, and the perforation rate ranges from 1% to 1%. By selecting different perforation rates and varying the cavity depths corresponding to different sheet thicknesses, you can precisely control the silencer’s spectral performance, thereby achieving excellent sound attenuation within the desired frequency range.

The structure of a small-hole silencer consists of a closed straight pipe with numerous tiny holes drilled in its wall. The principle behind the small-hole silencer is based on the frequency spectrum of jet noise. If the total area of the nozzles remains constant and is replaced by many smaller nozzles, when the airflow passes through these small holes, the frequency spectrum of the jet noise shifts toward higher frequencies, significantly reducing the proportion of audible sound components. As a result, the silencer minimizes disturbance and harm to humans.

The basic principle of an active noise canceller is to use electronic devices to generate sound waves in the original sound field that are equal in magnitude to the original sound pressure but opposite in phase, thereby canceling out the original sound field. This noise canceller consists of a set of instruments, primarily comprising a microphone, an amplifier, a phase-shifting device, a power amplifier, and a speaker.

After reading the above introduction, everyone should have a good understanding of the functions of different types of duct fan silencers. When making a purchase, you can choose a fan that suits your needs based on your living environment, floor level, and budget. No matter which type of fan you decide to install, duct fans will provide you with quiet and efficient ventilation.

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