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.
Boiler burner noise complaints
The cause of complaints about environmental noise levels was traced to this dual fuel burner boiler on a Heinz site. The company contacted us to assess the noise control options as the conventional palliative noise control techniques for this sort of problem involve fitting large silencers into the stack and converting the boiler house into an acoustic enclosure – eye-wateringly expensive with extensive downtime (which would have caused serious production problems).
The (blackcurrent) solution
The source was diagnosed as a 116Hz low frequency “drone”, a very common type of burner noise control problem. We developed a stunning simple alternative solution that comprised a set of aerodynamic modifications that fitted inside the combustion head. The initial trials were conducted using an adapted yoghurt pot fitted inside the burner head – as far as we know, this is the only known yoghurt-based noise control application…
The modified pot reduced the drone by 16dB, completely eliminating the problem.
The cost? Less than £2k with a downtime of a few hours (aluminium version of the yoghurt pot). This new approach and technology can be an incredibly cost-effective solution to many burner or combustion noise problems.
Industrial boiler burner noise attenuation
There are usually only 2 noise sources on industrial boilers and burners:-
- combustion fan: broadband and/or tonal noise at the fan blade pass frequency. Easily controlled using a simple silencer and/or aerodynamic fan noise control technology
- combustion noise in the boiler burner: broadband sound - but very often with a pronounced low-frequency signature (and sometimes pure tones) that can travel large distances (a common cause of complaints). Traditionally, the suggestion is often to spend a large fortune to turn the boiler house into an effective acoustic enclosure. Our alternative is to address the problem at the source - as above...
A detailed environmental noise impact assessment established 24 hour target noise levels for a new quarry as part of the planning submission. This was supported by predictions of the changes in the local noise environment throughout the working life of the quarrying project and a detailed compliance verification procedure.
Detailed Buy Quiet noise purchasing specifications were provided for every piece of plant to be installed within the quarry. These included the measurement procedures and the best practice noise control measures that should be used by the suppliers to ensure that the target noise levels were met as cost effectively as possible (most suppliers have very little knowledge of noise control engineering technologies).
£250 000 cost saving on environmental noise control…
Everyone knows that massive noise barriers are the only solution for noise from scrap yards and recycling centres. Everyone knows wrong...
We saved a scrap recycling company over £250 000 on the proposed noise barriers by controlling the dominant scrap impact noise at source. This is new technology that can reduce the impact noise from crushers in quarries, dump trucks, shredders, trains, manual handling etc by up to 15dB(A). Compared with conventional noise control techniques, the cost is miniscule, it is incredibly rugged, can be fitted very quickly and has no effect on plant operation, maintenance or access.
Noise levels from a power station were uncomfortably close to their environmental noise planning conditions. Detailed diagnosis proved that the dominant contribution was high-frequency noise (>500Hz) radiated by the Gas Reception Facility. Vibration measurements narrowed-down the source to the reducer, expander and associated valve section of the facility.
Sound Damped Steel was brought in to fabricate our innovative, high-performance acoustic lagging. This has an outer skin constructed from highly damped laminated steel, making it very tolerant of installation practicalities. Moreover, options are available that eliminate the corrosion problems inherent in conventional lagging designs. The diagnostic process illustrates how costs can be kept to an absolute minimum by precisely ranking noise contributions from different components, even amidst complex arrays of pipework, valves and other sources. The effect of the treatment was to reduce the noise from this source by 16 -19dB(A), eliminating it as a contributor off-site. Occupational noise levels in the area were also reduced by an average of 8dB(A). More information is available on the Sound Damped Steel installer website here.
From regular noise complaints to less than zero complaints…
As the station is overlooked by apartments, nighttime noise from underground track maintenance activities had given rise to regular complaints from local residents. The contractor, Balfour Beatty, decided to be proactive by asking us to introduce our new Acoustic Camouflage technology.
This solution involved relocating welfare facilities to take advantage of existing site screening features coupled with temporary acoustic barriers – not just for the facilities, but also for the vehicles and workforce at the station entrance. Then a pair of Acoustic Camouflage systems were installed at the station entrance and near the welfare area to dispense non-directional, shaped signature background noise. Despite raising the background noise by 8dB(A) at key locations, it was subjectively inaudible on the other side of the street. As a result, these systems were very successful at camouflaging the key annoying elements in the noise from the site activities.
The end result was not just to reduce the number of complaints to zero, but congratulatory emails were received from previous complainants complimenting the company on the effectiveness of their noise management...
The most compromising and common issue we encounter is that plant noise data (fans in particular) never includes frequency signatures. Octave bands: yes. Narrow band (that defines if there is a tone): no. If there is a tone, in the UK it attracts a 6dB penalty – which only puts your predictions out by a factor of x4! Consequently, if you want to play safe, you over-engineer mitigation which adds a massive cost overhead. This is unacceptable. We try to get round this by asking for a smartphone recording from an installation anywhere in the world so we can design the optimum noise control measures.
This is a ridiculous state of affairs considering that you can do an accurate narrow band tonal analysis with a smartphone app for free. Noise consultants are also to blame as only a very small proportion of them carry out tonal analyses.
These water pumps generated 95 – 99 dB(A) and were the subject of a dispute with the suppliers re the agreed noise levels. Various acoustic barriers and partial enclosures were being considered – at high cost and with considerable access issues. Our detailed vibration analysis proved that the required noise reduction could be achieved simply via constrained layer damping plus laminated close shields. These provided a 12dB(A) noise reduction with no effect on access, operation or maintenance – and at a tiny fraction of the previously proposed costs.
This is an example of the efficacy of accurate diagnosis coupled with good engineering and knowledge of materials. More information is available on the Sound Damped Steel installer website here.
Machining of alternator end castings produced 104 dB(A) at the operator, dominated by a “squeal” radiating from the casting. Overlapping hanging strips had been fitted round each machine in an attempt to reduce noise – but in every case they had been cut down at the operator location to improve access. Frequency analysis showed the dominant tones were excited by cutting forces with evidence of chatter-marks on some of the machined surfaces. We designed a low cost damper to reduce the casting vibration.
This reduced “squeal” tone by 32 dB and the overall noise level by 16 dB(A) at source, improved the quality of cut and reduced the machining cycle time to improve productivity.
Noise from a power station was uncomfortably close to their environmental noise planning conditions. Detailed diagnosis proved that the dominant contribution was high frequency noise (>500Hz) radiated by the Gas Reception Facility that also contributed to occupational noise exposure. Vibration measurements narrowed-down the source to the reducer, expander and associated valve section of the facility. Sound Damped Steel was brought in to fabricate our innovative, high performance acoustic lagging.
This has an outer skin constructed from highly damped laminated steel, making it very tolerant of installation practicalities. Moreover, options are available that eliminate the corrosion problems inherent in conventional lagging designs. The diagnostic process illustrates how costs can be kept to an absolute minimum by precisely ranking noise contributions from different components, even amidst complex arrays of pipework, valves and other sources. The effect of the treatment was to reduce the noise from this source by 16 -19dB(A), eliminating it as a contributor off-site. Occupational noise levels in the area were also reduced by an average of 8dB(A). More information is available on the Sound Damped Steel installer website here.
The 96 dB(A)Leq recorded from a 250 ton Rhodes billet hydraulic guillotine was cut by 17dB(A) – without using an acoustic enclosure. This was not only very low cost, but it also avoided the associated access, maintenance, and temperature issues.
Dominant hydraulic power pack noise reduced
Diagnosis showed that the overall noise from the guillotine was dominated by high levels of vibration transmitted from the hydraulic pump into the machine frame (and through rigid pipework to the remainder of the machine). In addition, there was also a significant transmission of impacts from the hydraulic valve bank.
The engineering solution was to mount the hydraulic motor-pump unit on a damped rigid frame that was then isolated from the machine body. The valve bank was also vibration-isolated from the machine frame using a tuned section of rubber-cork composite.
These modifications reduced the hydraulic power pack noise from 96 dB(A) down to 79 dB(A) at a fraction of the cost and without the operational and maintenance issues that would have been introduced by the previously proposed acoustic enclosure.
View detailed hydraulic power pack, pump and motor noise control guidance >
12 burners on a malt drying oven generated 95dB(A) with an 82Hz combustion generated “boom” as the dominant component. This was not only a very annoying occupational noise hazard, but also a potential environmental noise issue.
An acoustic enclosure was being considered, but was deemed too costly and too impractical. Building modifications were also under consideration, but were prohibitively expensive. The company contacted us to see if there was an alternative noise reduction technology. We diagnosed an organ pipe resonance caused by combustion mixture problems that caused pulsing of the flame front that excited the resonance. We solved the problem by sourcing and modifying off-the-shelf weld extract motor-controlled valves that were used to control the flame dynamics.
This provided a 21dB noise reduction at source for less than the cost of a single acoustic door…
Building a new terminal 3 multi-storey car park above the Heathrow Express underground station was a major technical challenge. As part of the process, piles had to be bored 40m into the ground very close to access and train tunnels – without disturbing structures or personnel. There were also additional complications arising from the necessity to carry out work at night within a very limited time-window and without interfering with the station operation or the marring the look...
BAA selected us to carry out an extensive vibration and noise monitoring programme over several months. The turn-key project involved developing a bespoke vibration monitoring system and installing an array of transducers in the tunnels with detailed analysis and continuous remote monitoring of the piling vibration. The INVC designed system also included a facility to alert key personnel automatically via SMS text message if the vibration exceeded threshold trigger values.
Noise monitoring and mitigation programmes were also initiated to ensure the minimum disturbance of passengers during working hours,
Adjacent to London Bridge Station and Guy’s Hospital…
Whilst the Shard is the tallest building in the UK, we were involved when it was just a hole in the ground. The location abuts London Bridge Station with Guy’s Hospital just across the road. You could scarcely have asked for a site that was potentially more sensitive to noise and vibration.
Explosive demolition
Keltbray, the demolition contractor, wanted to use the technically advanced explosive demolition techniques developed by the Controlled Group to remove the pile cap in the basement of the office block on the site. Breaking up this massive slab of concrete by conventional means would have extended the project by c 2 – 3 months - and the consequent noise and vibration were potential deal-breakers. Explosive demolition offered the opportunity to minimise both the noise and vibration from the site and the programme duration.
Noise and vibration predictions
We were asked to provide the noise and vibration predictions, logging, monitoring and mitigation expertise required to justify the decision both in terms of potential risks and to minimise both the duration of the process and the environmental impact.
Noise and vibration presentations and PR
We also generated and presented multi-media presentations to all the parties involved (station, hospital, security, police etc) to present the predictions and to provide the technical reassurance necessary to assuage any concerns about noise and vibration issues.
The project was very successful with zero complaints re the pile cap demolition.
Demolition vibration was causing problems in the adjacent lightweight steel construction office block. A very extensive and costly array of conventional vibration monitoring systems was in use as part of a time consuming and unsuccessful vibration complaint management process that led to potentially very costly delays to the project.
Our detailed building and operational vibration analyses proved that the cost and hassle of the extensive vibration monitoring programme could be completely eliminated. We developed and introduced a number of innovative - and sometimes counter-intuitive - demolition vibration management procedures that substantially reduced the problems in the offices. Coupled with developing a purpose-designed project vibration management software tool, the “best practice” noise and vibration management process for the project was simplified and re-defined to minimise the likelihood of further costly delays.
One of the open-plan office floors in the very prestigious new Mailbox office development had been designed with a very low profile floor to provide more space within the building. Unfortunately the design had a natural frequency of 3.6Hz and had very low damping.
Consequently, as staff walked across the floor, the vibration amplitude would rapidly build-up and after a few steps, the whole floor would be oscillating with quite high amplitude. This caused PC monitors to sway and some staff to complain of incipient motion sickness.
Based on a detailed analysis of the structure and response, a minimal set of disguised stiffening beams were designed and fitted (to avoid impinging on the open feel of the office). These increased the vertical stiffness by 70% and introduced more damping, solving the problem.
