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.
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.
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.
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.
Why was this air source heat pump so noisy?
A newly installed air-source heat pump domestic central heating system immediately generated noise complaints abut low-frequency sound from a neighbour. The owner contacted us and subsequently provided the requested smartphone video clips (as per the recommended diagnostic proceedure) of the noise:
- at the neighbour,
- close to the units
- inside the adjacent garage
This allowed us to rule out structure-borne noise (a common noise issue for A/C and heat pump installations) and to diagnose that the cause of the noise problem was primarily sound reflections that created an amplified 93Hz pumping frequency due to standing waves.
How was the heat pump noise reduced?
This precise diagnosis coupled with the photos provided, allowed us to devise a simple solution involving low-cost components available in DIY stores (plywood and loft insulation). Once installed, these noise control measures broke up the standing waves and 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 (without any site visits) via the supplied smartphone data.
We have provided a more detailed guide to heat pump noise reduction covering both air-source and ground-source noise control.
The traditional approach to granulator noise control is based on using palliative high-cost acoustic enclosures to reduce the spread of noise without tackling the noise generation at source. This approach is not only expensive, but it also has a substantial impact on access and therefore productivity and maintenance. Typical granulators generate noise levels close to, or above, 100dB(A). As such, they pose a very serious risk to hearing as it is not possible to guarantee adequate protection using PPE.
There is an alternative engineering approach that cuts the noise at source with the following benefits:-
- very low-cost compared with acoustic enclosure
- no effect on access, so no effect on productivity
- no effect on maintenance activities
- rapid deployment with minimum downtime
Granulator noise sources
Granulator noise is usually generated by 3 mechanisms:-
- Airborne sound from the blades or hammers, both aerodynamic (when run without material) and mechanical (impacts)
- Vibration from the granulator blades or hammers radiated as sound by the structure
- Web vibration radiated as noise on web-fed granulators
- Fan or blower noise from dust control and extract systems
Noise control modifications
The airborne sound path can be controlled internally, whilst high performance, rugged structural retrofit damping and impact control cut the vibration radiated noise. Blower noise is usually reduced using aerodynamic noise control technology that cannot clog and will last the lifetime of the fan without cleaning or maintenance.
Granulator noise control case study
The hearing risk posed by the 100dB(A) noise level from this plastic granulator was reduced at source by 98% (18dB) by designing a web damper coupled with internal modifications to the infeed path. Neither modification had any effect on operation or access. The cost of the granulator noise control modifications was c £5k compared with the previously proposed acoustic enclosure cost of c £30k.
The driver noise level of this Manitou forklift truck was 93dB(A) at full engine speed and load. The detailed diagnostic measurements showed the dominant source to be the engine cooling fan.
The somewhat agricultural cooling fan was changed for a more efficient and quieter unit and tuned acoustic absorbent was fitted in the cab roof to reduce the standing waves. These measures reduced the hearing damage risk by 75% (6dB) at virtually no cost. When evaluated over the typical worst-case working day, these noise reduction measures ensured that the operator noise dose was well below 85dB(A).
The remaining noise was dominated by tones from the hydraulic pump as shown here. Interestingly, whilst the hearing damage risk was substantially reduced, at full engine speed you can hear from the recording that the noise actually sounds louder as the characterless broadband noise from the fan that had masked the tonal noise from the hydraulic pump had been reduced.
Whilst it would have been relatively easy to reduce the now dominant hydraulic noise by 5dB - 10dB, the client considered that further retrofit measures were unnecessary.
The manufacturer of air-source heat pumps approached us to use our diagnostic skills and technology help them to reduce the noise from their units without recourse to expensive, efficiency-sapping enclosures and silencers. The objective was to design-in low-cost engineering noise control features to make the units inherently quieter - without compromising efficiency.
Heat pump noise diagnosis
The diagnostic analysis showed that there were 4 major noise sources, all of which would need to be reduced in order to achieve the desired noise reduction. The sources identified were:-
- fan: tones at 70Hz + harmonic - cannot be reduced using silencers or barriers
- mains hum: 100Hz tone
- compressor: several tones
- air noise: broadband sound
Previous resources had been focused on reducing the overall dB(A). However, the low-frequency tones were the dominant noise complaint issue despite only contributing <0.5dB to the overall dB(A). These would not have been reduced by the conventional methods under consideration.
Noise-reducing modifications
These involved the following:-
- fan tones: aerodynamic modifications
- mains hum + compressor: high-performance damping of key components + local tuned acoustic absorbent
- broadband air noise: once the low-frequency components had been cut, a simple small carefully designed screen was very effective
The combined effect was to reduce the 70Hz fan tone by 97% (15dB) and the overall noise by 90% (10dB(A)) without affecting the efficiency of the heat pump as demonstrated by the above analysis and the sound file.
View a more detailed guide to heat pump noise reduction covering both air-source and ground-source noise control.
The hydraulic power pack driving a baler was the cause of both occupational noise issues on-site and noise complaints off-site. Whilst the former was simply a case of the overall noise level at 87dB(A) requiring the use of hearing protection, the latter was a result of the highly tonal - and therefore annoying - nature of the noise. We designed engineering noise control modifications that not only cut the overall noise level to 76dB(A) at 1m (no PPE required), but also eliminated the tonal noise issue.
How was the hydraulic noise reduced?
The noise sources were ranked and modified as follows:-
- Vibration from the submerged hydraulic motor/pump unit into the oil tank: unit vibration isolated from the oil tank to reduce the high-frequency tonal noise
- Valve block vibration into oil tank: high-frequency vibration isolation
- Thin steel panels: damped
- Small local acoustic screen: to reduce noise traveling off-site
Care was taken to ensure that there were no vibration isolation short circuits.
These modifications cut the overall noise from the power pack by 9dB(A). In addition, care had been taken to address the off-site tonal noise problem. The major problem tones were reduced by up to 17dB (98%) as shown by this narrow band frequency analysis.
The engineering modifications were low-cost, easy to install using a local contractor and had no effect on normal operation, access or maintenance.
View detailed hydraulic power pack, pump and motor noise control guidance >
Wet wood pulp fan tonal noise
“I have never seen such an amazing result from a consultant in my career.”
Remote fan noise control, UK to New Zealand, no site visits... New wet wood pulp fibre bulk solids conveyor fans at the Pan Pac facility in New Zealand had caused noise complaints. The company made the very proactive “good neighbour” decision to shut down the plant overnight despite a substantial cost that posed a threat to the business.
“Shutting down 30% of our operation overnight was a significant cost and particularly damaging after the site was flooded and out of operation for over a year and needing investment of over $150M in the site flood repairs.”
Within exactly 3 weeks of googling the options and contacting INVC, noise from all 3 fans had been diagnosed, the solutions designed and installed with zero additional downtime. This resolved the problem and the plant was returned to 24-hour operation.
“On behalf of Pan Pac (and probably our neighbours as per this text) I would like to thank Peter Wilson and the INVC team for the professional service you have given and for helping overcome, in a very short time, a major threat to our business.”
“I have never seen such an amazing result from a consultant in my career. We were going down the acoustic insulation route before I “Googled”. I will call it lucky I found your website. Please make sure you pass on my thanks to your team!” Roger Jones, General Manager.
What fan noise attenuation technology made this possible?
Conventional silencers would not have been practical due both to the low frequencies involved and the passage of wet pulp solids that would have clogged any attenuators very quickly.
Locations: Pan Pac, New Zealand. INVC, UK offices
The 3 week process
- Pan Pac googles “fan noise control”
- Email to INVC
- Smartphone video and fan details requested
- Videos sent, analysed, problem diagnosed, costed proposal provided
- POs received
- Detailed recommendations designed and issued
- 3 fans modified (using local engineers)
- Plant returns to 24-hour operation
- Neighbourhood happiness confirmed!
The diagnosis
The complaints were caused by fan blade pass hums at 89Hz, 95Hz and 280Hz from 3 different fans.
The solution
Designing bespoke aerodynamic inserts for each fan based on the fan geometries and flow paths. These were made locally in New Zealand (simple sheet metalwork) and welded into the fan volutes to reduce the turbulence causing the tonal noise at source.
This is a permanent, low-cost solution with no effect on performance that will last the lifetime of the fan without maintenance, despite the passage of wet pulp solids.
Conventional options?
Conventional silencers could never be practical for this application due both to the required length of around 10m and the fact that they would clog very rapidly. Acoustic lagging of the entire systems would have been very costly and caused problems with both maintenance and corrosion. Moreover, silencers would still have been required…
Solving noise complaints fast at minimum cost
Regulators and other organisations can take advantage of this outsourcing approach to eliminate noise complaints, knowing that the solution will be based on best practice that typically reduces project costs by 50% - 80%. Remote control of noise >>
Pan Pac
For over 50 years, Pan Pac Forest Products has been growing, processing and delivering wood products.
The Pan Pac Pulpmill produces up to 850 tonnes/day of Bleached Chemi Thermo Mechanical (BCTMP) wood pulp.
Pan Pac BCTMP is used in in the production of paper products including packaging boards, paper towel and paper. The Pan Pac Pulp markets include New Zealand, Australia, China, Indonesia, South Korea, Japan, Malaysia, Taiwan, Vietnam, India, and Pakistan. https://www.panpac.co.nz/
Low frequency noise and vibration from a aluminium die casting injection operations had caused extensive complaints from nearby residents. This led to the involvement of the Environment Agency (EA), the local press and the local MP…
The wrong measurements over months...
The noise consultants employed carried out extensive noise and vibration measurements for many months - to no avail. The lack of avail was caused by a poor understanding and diagnosis of the problem that led to them to measure the wrong noise parameter, dB(A).
As the noise complaints were actually caused by "thumps" with a frequency largely below 50Hz they could not possibly contribute to the measured dB(A)...
The rapid diagnosis and low cost solution
We were recommended to the company by the EA as an option for a 2nd opinion. A single day on site resulted in the problem being diagnosed as hydraulic lock in an aluminium injection moulding die cast machine.
Our recommended solution was to fit a small hydraulic accumulator costing c £300 at the correct location, a process that took all of 10 minutes. This not only solved the noise problem as shown in this noise signature, it also reduced the mechanical stresses in the machine, cutting maintenance requirements.
This is a classic (and not uncommon) case of misdiagnosis and a lack of understanding of the causes of noise complaints needlessly prolonging the stress on local residents. It also resulted in unnecessarily high (and ineffective) consultancy fees, not to mention the bad publicity for the company.
