Industrial Noise & Vibration Centre

+44 1753 698 800

Noise Control Case Studies

An elegant engineering solution to your noise or vibration problem may already be available. Search the largest database of noise control at source case studies in the world for best practice alternatives to conventional, high-cost palliatives such as acoustic enclosures, silencers, barriers etc.

Showing 91 to 99 out of 99
  • vibration control
  • vibration analysis

Mill Bearing Failures

Bearing failures on a food processing mill continually recurred despite careful overhauls. Vibration signature comparisons with a second mill indicated a loose rear bearing. This diagnosis was confirmed in strip-down – the rear bearing was found to be turning in its housing.

  • vibration control
  • vibration analysis

Gearbox Faults

The motor/gearbox on a large fermentation vessel suffered varying motor current and intermittent noise. Downtime would be costly due to the production schedule. Single point vibration analysis indicated excessive input shaft float – very unlikely (due to the construction) but confirmed later on partial strip-down (25 thou v 6 thou specification). Pinpoint accuracy.

  • impact noise
  • damping
  • noise control
  • scrap yard

Impact Noise Control – chutes, bins, conveyors, hoppers…

We have developed a suite of innovative and elegant engineering impact noise control techniques that typically provide 10-20dB reductions. These are both much more effective than conventional technology and very much lower cost and rugged. We custom design the modifications either for new designs or for retro-fit to existing installations. We also have high hygiene versions for the food and pharmaceutical industries.

  • Applications: chutes, hoppers, conveyors, bins, recycling plant, scrap yards, train/truck loading/unloading, quarries …
  • Benefits: large attenuations, rugged (often harder wearing than the untreated surface); very low cost; hygienic

Additional Noise Control Examples

We have a host of other engineering noise control applications across a wide range of industries – contact us to discuss particular plant or machinery in detail.

Coal chute impact noise control

coal chute noise damping

High levels of impact noise were generated by coal falling into a delivery chute on an industrial site. Expensive noise barriers had been considered, but these would have made access difficult and would have reduced the noise by only around 5dB. Our alternative solution was to design highly damped chute modifications to reduce the noise at source.

These low-cost modifications were retro-fitted with very little downtime and not only reduced the impact noise by 20dB(A), but they also substantially reduced the dust generated (solving another problem in the area) and cut chute wear to reduce the maintenance requirements.

This engineering approach is very effective on all kinds of chutes and hoppers where there is impact noise from a wide variety of objects that include rocks and stones, scrap metal and even high hygiene products such as sweets, tablets and vegetables.

  • noise analysis
  • environmental noise
  • stack noise
  • environment agency
  • fan noise control

E-control: stack and fan noise ID analysis

silenced tonal fan

Low frequency (c 149Hz) tonal noise from a large variable-speed ID fan venting via an 83m high stack had caused complaints over a wide area. The company had spent considerable time trying (and failing) to find a practical conventional mitigation solution. We designed a bespoke stack silencing system that completely eliminated the problem noise without affecting fan efficiency. However, complaints then recurred post silencing that, as it turned out, were being wrongly attributed to our clients' site. This was pontentially awkward as the Environment Agency was involved.

Telepresence - using a virtual expert on site

As the Environment Agency (EA) was involved, the site manager wanted to resolve the situation as rapidly as possible. He linked with us via Whatsapp on his phone, using the app to forward a couple of video clips. These allowed us to identify instantly that the complaints were now being caused by a tone at 346Hz and that the source was a small fan on a neighbouring site. After contact, they emailed the fan details and we designed an aerodynamic insert silencer that was manufactured locally and fitted within hours to eliminate the tone. This very rapid process (a few days) avoided the potential further involvement of the EA and ensured that removing the nuisance to the local residents was fast and effective.

stack and fan noise control

This plot shows the overlayed noise signatures of both the stack and small fan noise before and after silencing based on smartphone data. You can listen to the audio at the top of the page showing the effects of the modification - view the video on which the analysis was based here >

  • environmental noise
  • fan noise attenuation
  • noise analysis

E-control: fan noise and wind...

fan with two silencers

A consultant and materials supplier had encountered a complex industrial environmental fan noise problem as multiple rooftop fans were potential noise sources. Whilst on-site, he recorded audio both at the complainant and close to each fan. Unfortunately, it was a very windy day and hence the audio was overloaded most of the time. However, we are able to extract very short samples between wind gusts - as in the sound sample above that also includes the "after the fan noise attenuation" recording during more clement weather...

This enabled us to identify the only fan that matched the frequency of the whine at the complainant - this was a fan that had been previously discounted as a potential problem as it was already fitted with the 2 conventional attenuators visible in the picture.

fan noise reduction via email

This analysis (taken from the sound samples above) illustrates that, despite the wind noise, we were able to extract enough information to diagnose which fan was the cause and to devise a solution that permanently eliminated the complaints. This whole process was accomplished within a couple of weeks without a site visit.

  • noise control
  • noise analysis
  • gearbox
  • environmental noise
  • environment agency

E-control: anaerobic digester noise

anaerobic digester noise control

The noise from a set of anaerobic digesters (AD) had caused complaints from nearby residents that resulted in a Noise Abatement Notice. The company employed noise consultants and installed partial enclosures and barriers round the mixer motors and gearboxes on the AD tanks. The subsequent noise report concluded that there was no longer a significant noise impact from the operation of the plant as the attenuation measures had significantly reduced the noise breakout from the mixer motors.

This conclusion was simply wrong and the complaints continued.

The BS4142 report generated by the consultant was based entirely on overall dB(A) and third-octave band noise level measurements. Despite the fact that the complaints were about tonal noise, no detailed frequency analyses were carried out. This is a common failing in environmental noise reports, as is the lack of knowledge about effective best practice engineering noise control options.

anaerobic digester noise analysis and control

We requested smartphone video clips when the company contacted us. From these, we were immediately able to diagnose that the only problem was a 953Hz tone at the gearbox gear mesh frequency as shown in this plot. We were also able to provide detailed engineering noise control recommendations, including the high-efficiency damping of specific components to reduce the gear mesh vibration re-radiated as noise. The complaints have ceased...

You can view the video on which the process was based here >

E-control: CHP generator + chiller noise

CHP generator set exhaust silencer

The cause of low-frequency hum noise complaints from residents had been misdiagnosed in multiple reports. Consequently, no solution had been found despite extensive resources invested by both the company to whom the problem tonal noise had been ascribed and by the Environment Agency (EA). When contacted, we provided both our client company and the EA with the list of smartphone video recordings needed for the diagnosis, namely a recording close to each potential source plus off-site samples. This allowed us to frequency match the tones at the resident with those from the various items of plant.

Diagnosis showed the noise complaints were due to a pair of tones at 71Hz and at exactly 75Hz. All previous evaluations had mistakenly used 1/3 octave frequency analysis and assumed there was a single tone (despite the "beating" between the 2 tones - see audio and below). We diagnosed that the 75Hz was from a CHP generator on the company site (75Hz is a classic generator tone), but the other 71Hz tone was from a chiller on another site. We recommended a tuned exhaust silencer that eliminated the generator tone. The 71Hz can easily be resolved using aerodynamic fan noise control technology.

Poor noise diagnosis and reporting
narrow band v third octave CHP and chiller noise analysis

This plot shows an overlay of a 1/3 octave analysis of the noise at the complainant and the (correct) narrowband analysis. This illustrates an all too common mistake by noise consultants using inadequate frequency analysis to investigate tonal noise problems. In this case, both problem tones are more or less in the same band (the 71Hz also contributes to the 63Hz band), hence the mistaken diagnosis that wasted considerable time and resources for both the company and the EA. As capable (free) FFT analysis phone apps are available, you have to question the competency of consultants using 1/3 octave frequency analyses to investigate tonal noise sources.

The correct noise diagnosis process
71Hz 75Hz environmental noise tone identification

Narrowband frequency analysis of the tones that are the cause of complaints provides objective evidence of the subjective problem in a form that closely matches the human response making it the ideal metric to assess tonal noise nuisance.

In addition, it also provides very accurate and precise diagnostic information about the noise source. In this case, for example, we know both from calculation and experience that exactly 75Hz is a common tone from generator sets connected to 50Hz mains supplies and that 71Hz is in the common range for chiller fan tones.

CHP generator engine exhaust silencing

A simple off-the-shelf tuned exhaust silencer fitted to the CHP engine reduced the problem 75Hz tone by c 19dB, eliminating this element of the nuisance noise.

E-control: heat pump hum noise control

noise from heat pumps

A newly installed heat pump domestic central heating system immediately generated noise complaints from a neighbour. The owner contact us and subsequently provided the requested smartphone videos of the noise at the neighbour, close to the units and inside the adjacent garage. This allowed us to rule out structure-borne noise (a common noise issue for A/C and pump installations) and to diagnose that the cause was primarily sound reflections that created an amplified 93Hz pumping frequency standing wave.

From the photos provided, we devised a simple solution involving low-cost components available in DIY stores (plywood and loft insulation). Once installed, they reduced the tone at the neighbour by about 30dB (as shown in this noise signature), eliminating the problem. This was a fast, low-cost project completed remotely (no site visits) via smartphone data from start to finish.

heat pump noise control

Showing 91 to 99 out of 99