How Does a Duct Silencer Work?

We have all experienced the duct noise dilemma – do you switch off the air-con and swelter or turn it up and be deafened all night?

Ducts can be noisy, but it can be much more than irritating. Duct noise in larger unattenuated systems can impact employee welfare, potentially damaging hearing. Planning applications can be turned down due to incorrect system configuration and noise control. Conference centres, recording studios and concert halls with noisy air conditioning may struggle to deliver quality acoustic environments their users demand. Even if you find the noise tolerable, studies clearly show an inverse relationship between workplace noise and productivity.

Australia has many blessings, but hot weather isn’t always one. Even during clement weather, our HVAC systems are often critical to control dust. Dust accumulations pose long-term fire risks and dust in the air is never good for your health. We need our HVAC systems, but there are scores of situations in which duct noise is counter-productive. It doesn’t matter whether you are from a commercial building, factory data centre or a hospital, it is a problem that you need to investigate and remedy.

Identifying the underlying causes of HVAC noise can be a complex task, but duct noise is certainly one of the most obvious and fitting silencers to them is one of the least disruptive solutions. However, you can’t just stick a muffle over them and expect them to still perform. HVAC duct silencers, or “attenuators” are specifically engineered to suppress the kinds of noise generated in ducts without impeding airflow, or preventing maintenance access.

What Causes Ductwork Noise?

Different vibrations arise from a variety of causes within pipes and ducts. Sometimes specific components contribute to an issue, such as fans or insecure mounting brackets, but more often it is simply a function of turbulent airflow, pressure drops in particular locations and the characteristics of the enclosures. On factory floors, vibrations emitted by particular pieces of machinery can influence resonances and reverberations inside nearby ducts.

Inevitably, the impact and cost-effectiveness of a solution varies according to the cause. There may be several contributing factors, therefore researching your particular noise issue before rushing in with a solution is vital. In most cases, an acoustic survey will quickly establish how and where your noise problem is being generated.

Holistic Noise Control Solutions

Rarely is one single noise-control tactic sufficient on its own, or if relied on exclusively it may impede air conditioning efficiency. Therefore, HVAC silencers should always be part of a systemic noise control strategy.

When machinery used in an industrial application is identified as a significant cause, the most sensible solution is to install a noise control enclosure around it. Frequently that is beneficial in controlling the noise source front the machinery, but additionally the HVAC system that is integrated with it, alongside the immediate working environment. Complemented with attenuated duct silencers to prevent the noise from travelling through the building and, together, they usually provide a highly effective solution.

Types of Silencer

There is a cylindrical type of silencer for ducting, and a rectangular type to fit over noisy HVAC components. In large plants and commercial spaces, attenuators are often fitted in banks.

Attenuators contain a multitude of perforations, leading into small individual air pockets formed by the fibres of the baffle material. Each helps to diffuse the sound by disrupting its wavelengths. The ideal size of those pockets depends on the problem frequencies, so different grades of material can be used. Low-frequency silencers typically focus on the 63Hz region.

In food preparation and medical facilities, additional care is needed. Cleaning access is crucial and silencer systems are designed so no particles should be shed into the air. Filler-less silencers are sometimes the solution, and easier to clean. They are also sometimes appropriate for chemical plants using corrosive or inflammable reagents.

IAC’s attenuator range is featured in our Duct Silencer selection tool, which enables you to build an effective system with guaranteed noise control results.  Our engineers are always happy to provide advice about the best solution for your particular noise control problem.

Jay Owen
Sales Director
+61 (0) 3 5521 1994
jay.owen@iac-australia.com.au