Industrial Noise & Vibration Centre

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Fan Noise Reduction

Fan noise reduction - no silencers, no maintenance, more efficient

How can you reduce the noise from fans without impairing efficiency? Our self-financing fan silencing technology uses innovative aerodynamic noise reduction techniques instead of silencers. Installed in a multitude of fans and blowers across the planet, from 6cm diameter to 4MW behemoths, this technology has and is saving £millions in capital and reduced running costs.

Applicable to both centrifugal and axial flow fans (e.g. chillers), our muffler alternative can be retro-fitted in hours and is particularly effective at low-frequency fan hum noise reduction, providing both stealth and efficiency to eliminate complaints and to reduce energy consumption and carbon footprint compared with attenuators.

Take advantage of our free email evaluation service to determine if you can use our technology in your fans (how Quiet Fan technology works). We provide instant diagnoses from smartphone data (Remote Control of Fan Noise - as used by environmental regulators and Env. Health organisations ) followed by detailed solutions anywhere in the world.

Fan noise reduced by 99% and costs by 80% using new technology

Award-winning fan noise control technology cut capital, installation and running costs by 80% compared with conventional silencers. Applying our noise reduction technology to three 4MW industrial fans at a Tata steel-works eliminated a long-running environmental fan blade hum noise problem and reduced the capital costs (>£800,000) and running costs (c £200k per annum) compared with attenuators. It is equally applicable to chiller and data center cooling fans (where efficiency gains of up to 23% have been achieved) and to conventionally "difficult" applications such as fume extract and scrubber plant fans where conventional silencers cannot be used. Applied more widely, the technology has the potential to contribute to a significant reduction in worldwide CO2 emissions.

Contact us to see if our technology is applicable to your fan noise problem. If it is, in principle you could be running a quiet fan in less than a week from first email at a tiny fraction of the cost and at higher efficiency than traditional attenuators and enclosures.

Quiet Fan Technology – industrial fan noise reduction without silencers

This industrial fan silencing technology reduces tonal noise (hum or drone) at source at a fraction of the cost of traditional techniques such as silencers and enclosures. It achieves this noise reduction without the increased power consumption associated with conventional attenuators, lasts the lifetime of the fan without maintenance and can be retro-fitted in a few hours. Applications include extract fans, ID fans, data centres, chillers, air conditioning plant, fume extract and scrubber systems, process ventilation fans, cooling towers, HVAC, power stations, cement and steel works and most blowers where there are low-frequency noise issues.

Industrial fan noise attenuation: how does the technology work?

Originally developed for the Euro-fighter, we take a similar approach to Formula 1 teams who invest in aerodynamic aids to control airflow round cars. Fan noise is turbulence generated pressure fluctuations shed by the impeller. We reduce these at source by designing aerodynamic inserts that fit inside the casing. This reduces the fan noise at source without the back-pressure often associated with silencers. As source control simultaneously reduces intake, exhaust and blower casing radiated noise, it may eliminate the need for both attenuators and acoustic enclosures or lagging.

Fan noise attenuation: remote control anywhere on the planet

Fan or blower noise reduction problems can be solved anywhere on the planet via the internet - saving the time and money of site visits. The whole world now has instant access to this noise and energy-reducing technology. Successful projects across the globe include 5 large fans at this USA oil refinery where we reduced the noise reduction project capital cost from $1.25 million down to <$0.25 million… Go to Remote Control of Fan Noise for case studies and details of the free smartphone email diagnostic service to diagnose if your project could benefit from this innovative technology. Environmental noise regulators and Environmental Health organisations worldwide routinely use this free service.

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Scrap extract fan noise reduction

Attenuators do not take kindly to the passage of scrap – which is a problem when installing noisy extract chopper fans. Our cutting edge aerodynamic fan modifications, however, are even robust enough to be able to cope with extreme scrap metal. In this example, both occupational and environmental noise problems were simultaneously solved at source.

Three sets of chopper fans are used to pull-off scrap aluminium cans from the production lines to shred them for recycling. These generated high levels of tonal noise (drone or whine), causing both occupational and environmental noise problems. Instead of fitting conventional fan attenuators, acoustic enclosures and noise lagging at a potential cost of £30k or more, our Quiet Fan technology was fitted to the fans in a matter of hours to give an overall noise reduction of 22dB(A) at an installed cost of c £1000/line – a capital cost saving of 90% and with no effect on fan performance or efficiency.

Unlike silencers, the modifications are unaffected by the passage of scrap cans and will last the lifetime of the fans without maintenance – and at less than 1% of the previous noise level… The same technique is equally applicable to silence dust extract, cyclone and filter fans for any form of waste material.

Tata steel gas fan stack noise attenuation

3 off, very large, 4-megawatt steelworks fans had been the cause of environmental noise issues for years. The problem was solved within months at a tiny fraction of the cost of attenuators by implementing our Quiet Fan technology aerodynamic fan noise reduction techniques. Fan power consumption was also reduced, making this a self-financing project.

A second opinion saves a £million…

The fans generated a low-frequency hum (c162Hz) over a wide area. As the fan speeds varied, sophisticated resonator silencers were ruled-out and conventional attenuators would have imposed a heavy penalty in terms of cost and reduced fan efficiency. Tata approached us for a second opinion as to potential alternatives. Our solution was to develop novel fan casing modifications, avoiding the need to modify either the existing ductwork or the stacks to fit silencers - thereby minimising downtime. These modifications have eliminated the noise at source for the lifetime of the fans. Significantly, the new fan modifications require no maintenance and do not affect the efficiency of the fan. Moreover, the willingness of Tata to invest in new and innovative technology has reaped very substantial rewards compared with conventional silencing:-

  • 94% reduction in noise (12dB)
  • capital cost savings of over £800,000
  • substantial environmental benefits (carbon emissions)
  • c £200,000 saved each year on running costs (power and carbon)
Red Bull extract fan noise attenuation

Fitting conventional silencers to this fan extract system seemed a long-winded and crude process to Red Bull who were used to the pace of change and the engineering innovation found in Formula One. Our approach was a perfect fit for their engineering ethos – 1000x less noise installed within a pit-stop of a few hours.

Red Bull found an alternative to traditional attenuators in our Quiet Fan aerodynamic noise control technology. The aerodynamic inserts were designed, manufactured and installed inside the fan casing within a pit-stop window of just a few hours to dramatic effect. The problem 218Hz low-frequency tone was reduced by a factor of around 1000 (30dB – a new world record for the technique), completely eliminating the problem at the source for the lifetime of the fan, without maintenance and without affecting fan efficiency.

“We felt that there had to be a better way to reduce the fan noise other than by compromising the system efficiency and creating additional long term maintenance” said Terry Brice of Red Bull Technology. “The INVC technique not only produced a fantastic result, but it’s also very satisfying as an elegant engineering solution”.

Combustion fan noise attenuation

Despite considerable time and money being spent with the supplier and acoustic consultant installing silencers and reducing fan speed, a noise abatement notice was due because of numerous complaints about combustion fan noise. We resolved the problem overnight via Barry welding in 22dB of attenuation during a normal shutdown...

Combustion fan noise from a new waste heating system at a Palgrave Brown MDF site had caused numerous complaints from neighbours with a noise abatement notice in the offing. The fan system supplier and their consultants had tried conventional measures (additional silencing and reduced fan speed) over an extended period to no avail.

On the point of admitting defeat, they were referred to us by the local Environmental Health Officer. Our solution was to control the tonal fan noise at source using Quiet Fan technology aerodynamic fan noise control. This was fitted during a few hours of scheduled downtime. The next morning, it was hard to tell that the unit was running as the tonal noise from the ID fan had been reduced by 22dB and the overall level by 9dB(A).

palgrave ID combustion fan noise attenuation .jpg

A quick, low-cost and permanent attenuation for the lifetime of the fan without maintenance and without affecting efficiency.

The results were so impressive that the director, Alan Fillingham, recommended that our approach should be used throughout the group.

Compared with traditional attenuators or mufflers, this approach to induced draught (ID) fan noise reduction is not only typically 70% - 90% lower capital cost with significantly reduced running costs, but it is also much more effective at cutting the low-frequency tonal content that is a common cause of environmental noise complaints. It can also be used on fans that run at high temperatures.

Steelworks axial extract fan noise attenuation

Low frequency tonal noise (a 112Hz hum) from 8 very large architectural scale axial fans (several stories up that were already fitted with 8m long silencers!) at a Tata steelworks had caused environmental noise problems over a number of years. We diagnosed, we tweaked – and the problem was solved at virtually no cost…

All the possible conventional fan noise control solutions had been considered (largely additional silencers). These would not only have cost a large fortune (and would not have been effective at 112Hz), but they would also have reduced system efficiency and therefore increased the running costs.

Our detailed diagnosis revealed a system resonance that we addressed at source by slowing the fans very slightly. This reducing the fan tones by 20dB at virtually no cost, with no downtime and with no effect on the system efficiency.

Quarry fan noise reduction - no clogging

A serious problem for the conventional silencing of quarry fan noise applications like this where the air is very dirty is the need to shut-down to clean the silencers on a regular basis with the associated cost implications. Our noise attenuating technology is immune to clogging, so no cleaning is needed - ever…

In this instance, the tonal noise (hum) from this quarry suction fan working under very dirty conditions was reduced by 23dB using our unique Quiet Fan technology - a new record for the technique at the time. No silencers, no enclosure, no lagging, little down-time and no maintenance - ever (despite the operating conditions). Plus, this all comes at a tiny fraction of the capital cost of conventional silencing and without the associated running cost penalty.

This approach to fan noise reduction is particularly effective where the air is dirty as it avoids the need to clean silencers - plus it does not compromise fan efficiency. Consequently, it is the ideal noise attenuation method for dust and cyclone extract and filtration systems.

Paint shop spray booth extract fan noise attenuation

Paint spray booth extract fan noise control poses a problem for conventional silencing in that, even with effective filtration, the silencer will clog and lose attenuation. Moreover, paint fans often generate a low-frequency hum that passes through mufflers with little attenuation. This case study illustrates a low-cost alternative approach to spray booth extract noise reduction that lasts the lifetime of the fan without loss of performance.

A pair of classic industrial paint spray booth extract fan filter systems used on an MDF paint plant generated a very irritating low-frequency drone that was the subject of complaints both from operators inside the workshops and from local residents. At these low frequencies, conventional silencers would not only have been ineffective, but would have quickly clogged.

Moreover, as the pair of fans were not quite synchronised, the sound also had a distinctive “beat” which made it even more annoying. As the spray booth extract fan noise was at a low frequency of 146Hz, conventional silencers would have been very large, very expensive, would have required relocation of the plant and supplementation with lagging and enclosures (and regular cleaning). We bypassed all these issues by reducing the fan noise at source (Quiet Fan technology), eliminating the tones (13dB reduction) and the “beat ” with no down-time outside normal maintenance requirements.

This approach has a broad application for silencing paint plant, spray booth fans and other dust extract filtration systems as a more effective alternative to attenuators…

Schiller biofuel power station fan noise attenuation.jpg

The Power Industry International journal published an article about the application of our innovative aerodynamic fan noise attenuation technology to cut not just the cost of noise control projects to reduce the noise from large fans feeding into stacks in the power industry, but also to improve fan efficiency.

The suggestion was that the widespread adoption of the technology could substantially reduce capital and running costs compared with traditional fan noise attenuation techniques such as attenuators, acoustic enclosures and lagging.

The journalist uses the application of the technology to the 50MW Schiller biomass power station in the US as an example. This is the largest power station of its type and uses a huge, house-sized ID combustion fan connected to a stack. The aerodynamic fan noise attenuation was installed within a time window of just 12 hours - compare that with the costly weeks of downtime required to install conventional mufflers. This cut the fan noise by 10dB at fraction of the cost and the fan efficiency was substantially improved.

An interesting point made in the article is that the noise control installation may seem too simple. The industry is used to the idea of massive noise control structures and extensive downtime. Compare that with the option to install elegant aerodynamic inserts inside the fan casing in a few hours to eliminate the noise problem at source without compromising fan efficiency.

Exactly the same point applies to many other industries such as steel and cement industry fans and the associated signature stacks that broadcast the fan noise far and wide.

Read the Power Engineering International fan noise control article

cement works fan and stack noise attenuation

Cement fan stack noise reduced over a weekend...

Unfortunately, the plant update to improve the efficiency of the exhaust fans in a large cement works created a serious noise problem that generated complaints from miles around. A novel, low-cost attenuation system was designed and fitted over a weekend to avoid the eye-watering downtime cost required to implement conventional solutions.

Conventional stack silencing would have resulted in an unacceptable delay in solving the problem. In addition, it would also have involved massive capital expenditure plus the costs of a very prolonged shut-down and the system efficiency would also have been reduced. Our alternative solution was based on designing a set of bespoke stack silencer elements tuned to suit the noise signature. These were pre-fabricated off-site and then inserted into the stack through a small access door over a weekend.

cement fan stack noise attenuation

The result was a 19dB noise reduction over the critical low-frequency range with zero effect on the fan or stack efficiency. The overall cost was a small fraction of conventional silencing - and without the reduced fan efficiency.

The alternative to costly 19th century attenuators

Large centrifugal cement works fans are a common source of low-frequency (and tonal) noise problems. Where the tonal content is the dominant issue, our aerodynamic fan noise reduction technology is by far the best alternative to fundamentally 19th-century noise control techniques such as silencers, enclosures and lagging. These involve high capital expenditure and extensive downtime to fit with increased maintenance and running costs (due to reduced system efficiency).

Where it is not possible to achieve the desired result using aerodynamics, this new stack modification technology can (and has been) been fitted in a couple of days to cut the noise across a wide range of frequencies without the reduction in fan efficiency often associated with silencers.

View the article published by the Global Cement magazine on this approach.

Thermal oxidiser fan and stack noise reduction at source

Severe noise problems were encountered from the fans in a new regenerative thermal oxidiser plant on an industrial site. The suppliers suggested an earth berm noise barrier, large fan silencers and acoustic enclosures that would not only have cost a 6 figure sum, but would have been a complete waste of money as they would not have worked.

We used accurate and precise diagnosis to isolate the key subjective sound features in addition to the broadband noise. We removed the tones using our aerodynamic fan noise control technology; slowed one fan to remove the “beat” with the other unit; moved and changed the damper to improve flow and added small conventional attenuators to reduce broadband noise. These modifications eliminated all the noise character and reduced the overall noise by 15dB(A) at a few % of the costs associated with the traditional (and largely ineffective) noise control package.

data center server farm fan noise attenuation

Data centres (or "data centers" in the US) require a lot of cooling - which involves noisy chiller fans, air handling units and condensers. Moreover, in addition to the general fan air noise, there are often low-frequency tonal elements (hums) that cannot be silenced using conventional silencers and acoustic barriers. Fortunately, there are low-cost alternatives...

An Abatement Notice was issued re the noise from a large array of chillers and air handling units at this data centre. The company had already spent nearly £100k on noise control with very little success and were considering claiming Best Practicable means (BPM) in court when the council suggested they might like to get a second opinion from us…

Our accurate diagnosis and control technology meant that we could guarantee BPM would be implemented by recommending a range of innovative noise reduction techniques for the AHUs and chiller condenser fans. These reduced the plant noise by 15dB at less than half the previously expected cost. If this approach had been implemented in the first place, the company would have saved over £100k, the council would have saved resources and the complainants would not have had to suffer unnecessary disturbance over a 2 year period.

More on data center, chiller, condenser and heat exchanger fan noise reduction.

Chiller fan noise reduction

Attempts are often made to solve classic low-frequency chiller fan noise using conventional silencers and noise barriers. Despite the fact that there is zero chance that these techniques can work at low frequencies, a fortune is still wasted every year on these useless palliatives. Previous failed attempts on this air cooled chiller (48.5Hz and harmonics) were replaced with aerodynamic techniques that reduced the tones by 95% and improved the fan efficiency – all by email via forwarded video clips and photos.

The company had already tried using a barrier to mitigate the noise complaints to no avail. This is because barriers are almost completely ineffective at frequencies below around 200Hz (drones, hums etc). Chiller and AHU fans regularly generate low-frequency tones as the blade pass hum often falls in this range. Whilst acoustic barriers and attenuators can be used to reduce the overall dB(A) noise level, they do not touch the low-frequency tones that are very commonly the actual cause of complaints. Our analysis of emailed video clips can immediately confirm whether this is the case, avoiding potentially costly mistakes. In contrast, our aerodynamic axial fan noise reduction technology addresses the low-frequency noise problem by reducing it at source with increased fan efficiency as a common additional benefit.

Click this link for more detailed information on the best approach to noise attenuation for chiller, air condenser, HVAC and refrigeration fans.

Rooftop chiller fan noise attenuation

The cost of reducing the noise from air conditioning system chillers on the roof of a large multi-storey data centre facility to meet the requirements of the Local Authority had been estimated at over £300,000. Fitting the proposed acoustic screens round the condensers would also have required considerable planning (closing streets and bringing-in cranes) and the proposed noise control measures and silencers would have reduced the cooling capacity of the HVAC system. We had a better idea…

The communications company involved approached us in the hope that we could provide a better alternative. A very careful analysis of the noise sources and layout of the air conditioning plant plus some lateral thinking resulted in an elegant solution involving a combination of engineering control at source, novel local acoustic treatments and the clever use of geometry. The result was a set of modifications that were easy to implement in convenient stages and provided a reduction in the condenser axial fan noise of c 15dB(A) at a cost of c £40,000 – and with no effect on the normal operation or the overall efficiency of the system unlike conventional noise barriers and silencers.

More details of the best approach to reducing the noise from data centres, chillers and air conditioning plant >

Axial chiller condenser fan noise reduction

Chiller noise control costs were cut by 80% using new technology. The company running a server farm had spent £100,000 on noise control measures (acoustic barriers and silencers) for their HVAC and AHU plant to no avail – the complaints continued as the noise levels were virtually unchanged. We were invited by the Local Authority to provide both parties with a definitive statement as to what constituted “best practicable means” and to sort the problem.

Careful diagnosis allowed us to generate a best practice noise control package that would eliminate the problem at a cost of c £30k.

These measures included purpose designed silencing, geometry changes, improved acoustic screening and internal modifications to the main Air Handling Units. On the air conditioning condenser units, we by-passed the conventional solution of noise barriers and silencers as these are not only high cost control measures, but they can also reduce the efficiency of the chillers themselves. Our alternative was a set of low cost engineering noise control modifications that not only reduced the overall noise from the HVAC plant at source by 8dB(A), but also eliminated the hum (worth an additional 5dB(A) noise reduction with respect to environmental noise limits) – and with no effect at all on the chiller condenser performance or access.

The result was an overall noise reduction of 12dB(A) and the elimination of the tonal content of the noise from the condensers. If best practice had been used at the start, the company would have reduced the cost of the chiller plant noise control project by 70% and avoided several months of management hassle and a sacking…

More information on the optimum way to reduce noise from server farm, chiller, AHU and data center fans >

Cooling tower fan noise attenuation at source

Cooling tower fan silencing by conventional means is often both very difficult and very costly as the problem is usually low frequency in nature so conventional silencers and noise barriers don’t work. Despite this fact, the cooling tower world is awash with placebo silencers and acoustic barriers that are just a waste of money. Alternatively…

… quite often there are low-cost source control alternatives. For example, the dominant environmental noise problem from a food processing plant in the middle of a village was caused by cooling tower noise from a pair of units – despite the large silencers already fitted to the axial fan exhausts. We devised engineering modifications that produced a substantial improvement in the efficiency of the cooling towers that, coupled with measures to reduce the noise from falling water, not only cut the overall noise level from the units by 15dB(A), but also substantially reduced running costs.

Details of how best to silence cooling towers >

Cooling tower fan and pump noise reduction

The noise from a pair of new cooling towers had ignited complaints from residents across the road from the site. A typical acoustic consultant was drafted-in who recommended the industry default silencers and a noise barrier without carrying out any diagnosis. Not good practice, let alone best practice.

The predicted effect on the plant noise of fitting the typical conventional acoustic package of silencers and a barrier along the edge of the site was to reduce the noise level down to around 56dB(A) at the neighbours - still far too high for the area. Despite a total cooling tower noise attenuation package costing well over £40k, not only would the problem not have been solved but in addition, as the acoustic barrier would have caused serious transport access problems, the company had to look for alternatives.

Our solution was based on a very accurate diagnosis and ranking of the cooling tower fan, drive and pump noise sources to develop an engineering source control package. The final noise reduction measures for both cooling towers comprised:-

  • intake and drive motor modifications
  • exhaust and pump silencers
  • local acoustic screening

This package achieved a noise level of <50dB(A) at a cost of only £6k and without affecting normal site operation or cooling tower efficiency. Around 15% of the cost and more than 4 times the attenuation of the conventional noise reduction measures.

How to select the optimum cooling tower noise control measures >

remote control of ID fan noise

A BP refinery in the USA had been quoted $1.25 million for five 1.5MW double entry ID combustion fan silencers to address the cause of extensive noise complaints. Their acoustic consultant had come across our aerodynamic fan noise control technology on the web and contacted us for advice. He sent his noise data to us by email and we identified that our technology would be ideal as an alternative to fitting fan silencers.

ID fan fitted with noise attenuation technology

We used the information provided to design the aerodynamic modifications to generate drawings that would allow the components to be made by local contractors. After an installation process that required a tiny fraction of the downtime associated with fitting attenuators, the 180Hz blade pass tone had been completely eliminated (>12dB reduction), preventing any further noise complaints.

The quotation for fitting conventional silencers or mufflers totaled $1.25 million with additional costs associated with the extensive downtime required to fit the attenuators plus increased running costs.

The total project cost for all the aerodynamic modifications not only saved over $1,000,000 from the $1.25 million quotation for conventional silencers, but, in contrast with traditional mufflers, the modifications had no effect on fan efficiency (reduced running costs) and will last the lifetime of the fan with zero maintenance.

No site visits were required, saving time, resources and carbon (transatlantic flights etc).

Schiller biofuel power station fan noise attenuation.jpg

The efficiency of a 3m, 1.5MW wood-burning industrial boiler combustion fan installed at the Schiller power station in New Hampshire (one of the largest renewable energy projects in the U.S.) was dramatically improved by replacing the traditional silencer fitted to the power station wood burner fan with our aerodynamic noise control technology to cut the noise at source.

Schiller ID fan remote control of noise.jpg

The fan feeds a stack that included a large conventional silencer to prevent noise complaints from local residents. As the silencer had had a drastic impact on fan efficiency, it had to be removed. Our aerodynamic source control technology was retro-fitted instead within a 12-hour downtime window. This not only eliminated the low-frequency tonal noise problem from this large industrial boiler system at a minute fraction of the cost of the silencer it had usurped, but as it also reduced the fan power consumption, the project was self-financing.

"The ID combustion fan created a low frequency tonal noise that could be heard on the other side of the river ans was the cause of complaints. The installation process took only 12 hours, after which we recorded a huge 10dB drop in noise and measured a reduction in the power used by the ID fan.."  Jim Granger, Senior Engineer, Schiller

This international project was managed remotely from our UK offices. By analysing and interpreting data acquired locally to our specifications, we were able to dispense with site visits and reduce the entire process, from initial contact to problem solved, down to a matter of a few weeks.

Axial extract fan silencing at source

4 large axial extract fans caused noise complaints over a wide area in Canada, despite multiple attempts at noise control based on conventional techniques. One email led to the noise being reduced by 99% with no site visits required - the whole project was completed over the internet.

Mitchell, the site engineer sent us an email with smartphone video clips and photos. Soundtrack analysis showed the problem to be high-level tones at the 197Hz blade pass and harmonics. We used the photos to design retro-fit aerodynamic noise-reducing components which the client made and installed to give 20dB attenuation at 100m.

"We are exceptionally happy with the overall results that were obtained, from a noise reduction, cost, and time standpoint. INVC was very professional and prompt on all deliverables. Out of all solutions attempted this was by far the best and cost-effective. The whole process was very smooth from first contact to installation … glad we went with INVC, thanks…"

axial fan tone silencing aerodynamic modifications.jpg

In addition to the attenuation of the primary fan hum sound, the harmonics and associated tones were also dramatically reduced as shown in this frequency analysis plot. Moreover, as the performance of the fans was also improved, the project was self-financing and will pay for itself in reduced running costs.

This technology is very applicable to all types of extract fans where tonal noise is an issue. As it is immune to the effects of the passage of materials or to corrosive atmospheres (it cannot clog), it is particularly suitable to attenuate the noise from fume, scrubber, dust, or other waste extract fans.

Axial mine water spray fan noise attenuation

Proposed £100k conventional attenuators for 10 axial mine water evaporation fans in Australia would have had zero effect in the noise as it was predominantly low frequency tones (hum or drone). A few emails and <£20k gave 23dB noise reduction and improved efficiency.

The Australian mining company had a series of 10 large axial fans that are used to evaporate water pumped from underground. However, these fans had caused complaints over a very wide area. The quote for £100k of mufflers would have provided zero attenuation as they would be fitted only to outlets (half the noise is from the intakes) and they would provide virtually no attenuation at the dominant 200Hz tone.

Our remote noise control service diagnosis allowed us to evaluate the problem using information and recordings provided by email, saving a visit from the UK to Australia... We designed and emailed aerodynamic fan noise control modifications for local manufacture. These reduced the tonal content by 23dB at a cost of <£2k/fan. As fan efficiency was also improved, this was a profitable, self-financing project for the client.

Failure of acoustic lagging in fan noise control

As a result of complaints about noise from 2 large centrifugal fans on a factory roof and the involvement of the Environment Agency, the company spent £50k on traditional acoustic lagging that unfortunately had zero effect on the noise levels. This ineffective expenditure resulted in a prolonged wrangle with the authorities – who eventually suggested that they could get a 2nd opinion from us (based on our free analysis and diagnostic service).

They forwarded a video-clip and analysis of the sound-track proved that the problem was a pair of tones at the blade-pass frequencies of the 2 fans plus 1st harmonics that were interfering and “beating” with each other. We designed the solution in the form of aerodynamic Quiet Fan technology that provides retro-fit attenuation without using silencers. This eliminated the tones as a noise feature and the complaints ceased.

The whole process was completed within a few weeks at a tiny fraction of the cost of conventional alternatives. Moreover, only a single site visit was required – the rest of the work was carried out by email.

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