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.
We were asked to look at improving the acoustic design of Custom Design speaker stands for up-market Hi-Fi aficionados. As a result of vibration testing on the stands, we recommended replacing the top and bottom plates with laminated “dead-metal” versions. These reduced the vibration response of the stands by up to 40dB (a factor of x100). According to the review in Hi-Fi Choice:-
” .. switch to the acoustic steel plates and the sound is even better, with a deeper, quicker bass and a more open mid-band. There’s definitely a neutralising effect with the acoustic steel that zaps a lot of colouration, giving a far more neutral sound … Top value upgrade .. 5 stars.”
This suction fan used in a newly designed, automated pick-and-place system for food packets on a production line generated high levels of noise. Conventional fan silencing would not only have posed a hygiene problem (attenuators make use of porous acoustic absorbent materials), but would also have required acoustic enclosure.
We re-designed the fan mounting system (interestingly, the fan itself was designed for model aircraft engines) and modified the geometry slightly. This reduced the fan noise at source by 8dB(A) without affecting the efficiency of operation - and at zero cost once designed-in to the unit.
A major customer implemented our Buy Quiet purchasing policy and passed-on to the supplier a request to reduce the operator noise levels from 90dB(A) down to below 85dB(A) in the production environment. We were retained by the manufacturer to provide design improvements as part of the of the machine development programme. Our engineering recommendations reduced the machine noise down to 82dB(A) at a cost of around £300 per machine (c 2% of the capital cost) without affecting normal operation or access. Modifications included sewing machine damping, control of exhaust air and minor changes to the machine base.
The purchaser of several multi-spindle auto lathes was on the point of cancelling the order as the first completed machines did not meet the agreed noise level of 83 dB(A) (3000 rpm) – they were typically generating 87 – 90 dB(A). We used the results of sophisticated noise and vibration analysis to recommend a change in the assembly procedures used that reduced noise levels to <83dB(A) at negligible cost.
The diagnosis and recommendations were completed in less than 2 days and, as a result, all purchasers now receive quiet machines. This illustrates the benefits of effective policing of purchasing requirements.
Weighing machines for the confectionery industry are a very common noise problem. In this case, the purchaser had implemented our Buy Quiet policy for new plant, with a target of 75dB(A) for this particular installation. One of our engineers attended the new machine proving trials at Easiweigh as part of the purchasing policy process to determine what would constitute best practice to meet the noise specification. We developed a set of modifications that reduced the initial 83dB(A) Leq noise level down to the required 75dBLAeq.
The low cost, high hygiene modifications included replacing the conventional (and non-hygienic) damping materials with much higher performance stainless constrained layer damping. This has since been adopted as standard practice on all new weighing machines.
Variable Frequency (VFD) drive cooling fan noise is often the major source from these systems. Reducing this element of the noise is a non-trivial project given the space limitations and the fact that cooling efficiency must not be affected.
Reviewing the noise attenuation options for their product range led a major VFD drive manufacturer to approach us to help them to design noise attenuation modifications for the cooling system based on our aerodynamic technology. They could then use the technology across the entire product range.
The whole project was carried out remotely via internet, saving time, money and carbon.
How to reduce VFD drive noise - the cooling fan
The low-noise product design process is outlined below.
- Provide a detailed set of baseline measurements and procedures
- Create a Computation Fluid Dynamics (CFD) model of the fan
- Design the aerodynamic modifications
- Test the results and copy the design across the product range
VFD noise reduction - the result...
Our final low-cost design modifications cut the annoying fan tone by 99.5% (23dB) and the overall noise by 50% whilst simultaneously increasing the airflow by 3%, ready to be copied across the entire product range.
The key to the successful noise attenuation was to combine aerodynamic expertise with CFD modeling in order to optimise fan efficiency whilst, at the same time, eliminating the annoying fan blade pass tone.
The top figure shows the velocity output from the CFD model for the standard fan. 3 iterations of design and simple testing resulted in modifications to alter the flow through the fan as illustrated in the second picture that reduced the blade pass tone by 23dB in parallel with increased airflow.
Fan noise reduction in product design
This approach is ideally suited to improve the noise profiles of products that include fans. Our aerodynamic fan noise control technology often makes it possible to cut noise at little or no increased product cost and with increased fan efficiency - neither of which applies to conventional silencers. Our current record holder is a dust control fan noise reduction project: 17dB tonal noise attenuation with over 20% improved performance...
The noise from this 115T Bliss power press was reduced by 90% (10dB) by analysing the flywheel vibration and then bolting £15 worth of small steel blocks mounted on gasket springs at specific points. These tuned dynamic vibration dampers cancel out the flywheel vibration, fit inside the existing guards and were installed in a few hours. Compare this with the cost and access problems associated with the only alternative noise control measure – a high cost conventional acoustic enclosure.
Similar dynamic vibration dampers fitted to the main gear wheels on a wire draw bench reduced the overall noise by 5dB(A) – again with no effect on normal operation, access or maintenance and at a cost saving of c £13000.
We have developed and applied the same technology used to solve the Millennium Bridge sway to control noise and vibration for industrial applications with great success. The solution involves attaching small dynamic vibration absorbers (or dynamic vibration dampers) to the structure that cancel the vibration at the point of attachment. On the famous bridge, these add a virtual stiffness equivalent to large concrete piers (spoiling the ride…).
Our industrial noise control uses include 10 – 20dB of noise and vibration reduction on power presses, grinders, gearboxes, dynamometers, pipe lines, pumps and pipe-work.
We have developed an elegant dynamic vibration absorber that can simply be bolted to pipe work or other structures to reduce vibration by 90-99%. Technically, this is very satisfying as the absorber is small, efficient and “sexy”…
Installed on petrochem pipe work attached to a reciprocating compressor generating high levels of vibration (illustrated here), this not only killed the vibration (eliminating wear and potential fatigue problems), but also produced a constant stream of curious staff wanting to see how such a small device could have such a big effect!
High levels of vibration on this water pumping station unit had caused maintenance problems and necessitated motors being sent away for refurbishment. The dominant element was at the 10.7Hz pump running speed with an amplitude of over 8mm/sec.
After detailed diagnosis, a pair of tuned dynamic vibration absorbers were designed that could be bolted to the motor whilst it was still in service. Once tuned, they all but eliminated the vibration – not only a very elegant and effective technique, but there is also a hint of magic about it…
“When I went down there afterwards, it was so smooth I thought the motor wasn’t running…” Alan England, maintenance engineer
Vibration analysis indicated that the compressor was surging which would cause damage and probably require a strip-down. However, by identifying precisely what was happening mechanically within the compressor and discussing the results with an AC expert, the fault was diagnosed as a gas shortage causing liquid to flash across the expansion valve – cured by re-charging. This example illustrates the power of non-invasive fault identification.
Persistent propshaft failures were compromising engine test programmes. Vibration analysis was used to diagnose the problem as strong coupling between the response of the engine on its mounts and a structural mode of the engine pallet. The solution was designed and fitted within an hour (a simple steel channel welded across the pallet was all that was required).
A gravure coating line was producing striations on the thin aluminium web (due to film thickness variations). As the marking wavelength was independent of line speed, a resonance was diagnosed. This was traced (using a non-contacting probe) to web vibration at a specific point in the coating head. The solution designed was a simple, low cost web damper.
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.
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.
