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.
A Local Authority had been investigating complaints about ground vibration from residents near a factory using rolling mills. Narrow band frequency analysis of the vibration revealed two distinct and separate types of vibration – tonal vibration at 18.25 Hz (and harmonics) plus a regular “thump”. The source of the “thump” was traced to roller backlash caused by bearing wear at the transfer gear end of a particular mill.
The tonal component was diagnosed as excessive vibration at the tooth mesh frequency of the pinion on another mill caused by worn teeth on the gear. The “thump” could be eliminated by replacing the bearings. However, as production requirements precluded immediate down-time, the interim solution recommended was to avoid running at idle and to adjust the clamping force to minimise the backlash. Inspection of the pinion gear source showed very worn pinion drive tooth flanks in mesh with “new” flanks on the driven gear. The tonal vibration was eliminated “on-the-spot” by reversing the pinion.
This case study illustrates the benefits of sophisticated diagnosis coupled with engineering expertise. A low cost solution to a complex and intractable problem was implemented within hours of arriving on site.
We have considerable experience in the establishment of ground and building borne vibration limits and specifications for a range of vibration sensitive equipment. These range from computer systems and hard disks, servers, metrology equipment, electron microscope and nanotechnology facilities and electronic fabrication plant.
Our speciaiist expertise allows us to determine the best practice building vibration monitoring and control regimes for these vibration sensitive facilities and, if necessary, to design bespoke vibration monitoring and control systems.
A detailed vibration assessment of the impulses from a drop-hammer piling operation was carried out in response to concerns from local residents about potential structural damage to their houses. The results showed that the vibration level was very close to the DIN 4150 damage limit guidelines which posed a question as to possible claims for compensation.
Instead of halting piling operations, a detailed vibration analysis allowed modifications to be developed for the pile helmet. These reduced the ground vibration by 65% to well below the structural damage criteria, allowing the project to continue on schedule. In a similar case involving piling near a railway line, we reassured the residents by demonstrating that whilst the piling operations were subjectively very evident, the passage of trains actually generated a very similar level below the structural vibration damage criteria.
The ProTest production test system was used to update the facilities and performance of Gleason gear test machines used to check the quality of differential gear sets. The system was developed to provide fully automated production testing based on gear vibration that not only provides pass/fail warnings for gear quality, but it also automatically evaluates the optimum pinion position for the quietest operation of the given gear pair. This information is then stored with the gear pair and used during assembly to determine the shims required to provide the quietest running condition.production noise and vibration testing of gears
In addition to evaluating the quality of the gear sets, ProTest also automatically acquires vibration data to assess the mechanical condition of the gear test machine itself to ensure the repeatability of the quality testing process.
Minor damage to a single gear tooth is classically a very difficult defect to detect using conventional analysis. We developed our own "knock" detection algorithm that provides the basis for a very sensitive production test system.
An automotive gearbox assembly line was fitted with our gear “knock” detection system in parallel with a vision gear-mark test. This uses our algorithm that has been designed to be auto-calibrating with a very high immunity to other vibration sources. This makes it a very reliable test for minor single tooth imperfections (usually introduced on the “green” gear) that can cause an audible problem once installed in the vehicle.
ProTest is used to test the sound quality of automotive warning sounders in the dashboard for different types of vehicle, including the BMW Mini. Initially, we carried out the initial engineering diagnosis on “good” and “faulty” units to develop the test technique that is well correlated with the subjective impression of the noise from the sounders. This was integrated into the electronic binnacle test system.
ProTest incorporated these specially developed algorithms that reflect accurately the subjective impression of the customers hearing the sounders and with no increase in the standard test regime time. As the 100% sounder testing regime eliminates potential warranty claims for this type of fault the system payed for itself within a few weeks.
Electrically operated steering columns and their motor / gear components can produce unacceptable levels of noise and vibration that may only become apparent after installation – a costly warranty issue.
We not only provided engineering consultancy to reduce the problem at source, but also installed a semi-automated version of ProTest to provide 100% production testing of both components and assembled columns. A fully automated system has also been installed on another production line to predict noisy units and to provide vibration statistics for the customer.
If an incompletely filled crankshaft damper is fitted to a large diesel engine, the crankshaft will fail – which can cost well over £20000.
We carried out extensive tests on a wide range of dampers and devised an impact noise test that can be used to detect the rare faulty dampers in production. ProTest systems fitted to the lines generate controlled impacts and analyse the response of each damper – only operating the welding machines if the dampers are correctly filled.
A bar code driven ProTest installation has been used to automate the 100% production testing of vacuum pumps. It not only provides 5 channel 1/3 octave sound power plus vibration signature analysis, but also includes test control functions and parallel capture of temperature and other data.
The vibration analysis facilities have proved to be invaluable. They have been used to identify faulty components and the subtle effects of assembly techniques to improve build quality. Consequently, the system pays for itself several times a year. The vibration signature database is also used to aid fault identification in the field. Whilst the test regime has been continuously extended and updated in-house, the system has proved to be 100% reliable – vital for a production critical application.
ProTest provides turnkey, automated sound power measurement, with systems ranging from simple, very low cost versions (a complete installation for the cost of a sound level meter) up to more sophisticated multi-microphone installations.
Capabilities include octave, third octave, narrow band and additional vibration analysis. The system developed for JCB is used all year round in all weathers to provide automated sound power measurements from an array of 6 microphones (noise levels are captured and displayed in real time).
It not only worked perfectly from day one – “straight-from-the-box” – but it was also customised to suit precisely the requirements of the test programme and engineers.
The noise from a 3m, 1.5MW wood-burning biomass boiler combustion ID fan installed at the Schiller power station in New Hampshire (one of the largest renewable energy projects in the U.S.) was dramatically reduced using innovative technology to replace the traditional silencer fitted to the power station fan. Our aerodynamic noise control technology not only cut the noise at source, but also substantially increased the fan efficiency.
The ID fan feeds a stack through a system that included a very large conventional silencer to prevent noise complaints from local residents. As this muffler had a drastic impact on fan efficiency, it had to be removed. This had a serious impact on the local environment, generating a host of complaints for which a very urgent solution was required.
Our aerodynamic source control technology was retrofitted instead of the attenuator within an incredibly short 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 and 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, to a matter of a few weeks.
Filtration (bag filters etc) and conventional attenuators reduce fan efficiency by adding back pressure. We use Computational Fluid Dynamics (CFD) modeling and past experience to determine exactly where changes can be made to reduce back pressure and hence improve system efficiency. For example, it is often possible to modify existing silencers to reduce back pressure - or even to eliminate these attenuators altogether by using alternative techniques to cut broadband noise without the hit on fan efficiency associated with conventional noise control measures..
The approach not only reduces noise, but it also cuts running costs and increases productivity. This renders noise control projects of this type highly profitable so that implementing the modifications would be a valuable exercise, even if there was no noise issue...
The manufacturer of hydraulic power packs for offshore use had to meet a very tight customer Buy Quiet noise purchasing specification. The unit had to include an acoustic enclosure within a very tight space for environmental reasons. In order to meet the requirements, we designed a combination of engineering control measures to reduce the power pack noise at source combined with an acoustic enclosure that included features to provide the required attenuation within significantly less space than a conventional soundproof box.
Hydraulic power pack noise sources and noise reduction features
The hydraulic power pack noise sources are listed below in rank order:-
- hydraulic pump and associated vibration
- oil cooler fan
- pump motor, including fan
The noise from each source was reduced at source as far as practical to ensure that the dimensions of the acoustic enclosure were within the space constraints without compromising cooling. The following were the design features:-
- hydraulic power pack pump noise: control at source using high-efficiency damping
- oil cooler fan noise: geometric features coupled with compact, bespoke silencing to provide high attenuation without compromising cooling
- acoustic enclosure panels: included high-performance damping and tuned acoustic absorbent.
The detailed design was developed in conjunction with SoundDampedSteel who supplied both the highly damped laminated steel used and the enclosure itself to our specifications.
This project was carried out entirely remotely (no site visit) by email and smartphone using streamed pictures from site.
View detailed hydraulic power pack, pump and motor noise control guidance >
Analysis of the smartphone video sound-track shot outside the complainant’s house and close to potential noise sources on an industrial site allowed us to pin-down the source of the low frequency tone that had been the cause of long term complaints. Based on the mechanical information provided, we proved that the culprit was not the fan previously diagnosed locally, but a vibratory sieve. We then provided a virtually cost-free modification (mechanical disconnection from the building steelwork) to solve the problem. The whole process cost a few hundred pounds and only took a few days.
We have also generated a comprehensive technical note on all aspects of vibrating feeder, hopper, conveyor and screen noise...
A pair of air compressors installed in a plant room were generating noise levels well above the specified 80dB(A). We discussed the installation with the contractor, who then took some basic noise measurements plus photographs and smartphone recordings which were forwarded by email. As we have extensive experience of these types of compressor, we could use our noise control database as the basis for developing the solutions.
We designed retro-fit silencers and wall treatment, returned the recommendations and solved the problem by reducing the noise to well within the purchasing specification within a few days. The whole project cost less than a single site visit…
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.
