Annual report 2004-2005
|Every year the Institute of Sound and Vibration Research
publishes an Annual Report. This is the entry for ISVR Consulting
covering the year May 2004 - April 2005.
Manager: Mr S J C Dyne
ISVR Consulting offers a comprehensive consultancy service in acoustics, vibration, modelling and testing, and serves a wide range of public sector and industrial clients. The automotive and aerospace sectors still dominate our order book but the unit is working increasingly with the marine and chemical industries, and is active in building and architectural acoustics, litigation (particularly hearing loss claims), occupational noise assessments (especially where headsets are worn such as in call centres) and industrial noise control.
ISVR Consulting operates on a commercial basis, with twenty full-time engineering and support staff, and is a founder member of the Association of Noise Consultants. The unit maintains close links with the ISVR research groups and a number of projects are carried out in collaboration with academic and research staff. The Unit website www.isvr.co.uk includes full details of the range of services and facilities available.
Environmental noise and building acoustics
Environmental work continues to be concentrated on planning issues and expert witness activities. The unit has been involved in Public Inquiries into the reconfiguration of the docklands at a major UK port, and into extending the operating hours for an air-support helicopter. The continual demand for more land for housing development has provided a stream of projects for environmental assessment according to ’Planning and Noise Guidance Document PPG 24‘.
In addition, the testing of dwellings according to the Building Regulations continues to provide a regular series of projects, and the unit is registered for Schedule E testing. The Unit has provided guidance to a number of developers on suitable building designs to meet the regulations and has advised some builders when their chosen designs have failed the regulations. Work continues in assisting a petrochemical company to resolve environmental noise problems around a refinery. Further remedial measures are proposed which will require further testing on-site and in the community.
Test and experimental work
The space around the anechoic and reverberation chambers has been fully refurbished and is now highly presentable with a small office set aside for visitors to use while their tests are carried out in the chambers. The Unit has started a programme of replacing some of the specialised, but rather old, instrumentation and sensors. Recently purchased equipment, based principally around the B&K Pulse system, significantly enhances our multi-channel laboratory and field test equipment and in many cases reduces the time between initial measurements and final reporting.
Vibroacoustics and modelling
Work on aircraft airframe noise has continued to develop, providing an excellent model for the interaction between EU-funded contracts and commercial contracts. Two valuable new tasks have been approved and started in the ‘SilenceR’ project. The first task, a development from a commercial project last year, concerns modelling of slat noise radiation and has enabled us to develop our capability with ‘SYSNOISE’. The second task, which requires testing of a scale model landing gear in the 7 foot x 5 foot wind tunnel and uses the source location capability of the Aeronautics department, is expected to lead to further commercial contracts in the future. Two new EU projects have also been approved: ‘NACRE’ on new commercial aircraft concepts and ‘HISSAC’ on high-speed business jets. Aerodynamically induced noise and vibration is an area where there is potential for significant future consultancy business. A large project to study the use of microphone arrays to identify a source of aerodynamic noise on an aircraft was completed during the year, and there have been a number of smaller projects and enquiries for future work. The EU-funded aircraft noise projects provide useful experience for these commercial studies.
Noise at work, subjective acoustics and communications
A custom-made sound-moderator (silencer) for a rifle has been tested to provide evidence in a legal case. Sound levels with and without the silencer during test firings were measured on a shooting range. ISVR Consulting also carried out an assessment of noise exposures and hearing protection for police firearms instructors on an indoor firing range. Although such work is infrequent, we have assessed many firing ranges over the last few years. Comparative measurements of active noise reduction (ANR) headsets have been made to determine their passive and active performance. This work was carried out for a local company which provides headsets and noise-cancelling modules for in-flight entertainment.
The Control of Noise at Work Regulations 2005 are due to replace the Noise at Work Regulations 1989 in April 2006. The new regulations will place some new obligations on employers and generally reduce the noise exposures or sound levels at which actions must be taken. Over the last year we have been assessing noise exposures for compliance with both the current regulations and the draft new regulations so that our clients are well prepared for the change.
Noise at work assessments have been carried out in call centres in Plymouth, Cardiff and Cheltenham. The work at Cardiff also investigated the maximum sound levels from the headsets, for simulated ‘acoustic shock’. The sound levels produced by various makes of headsets were compared, to assist the selection of new headset types to be introduced within that call centre. We have also assessed noise from headsets in three police control rooms during the year. The introduction of the new Airwave or TETRA radio system for the emergency services has led to further measurements of sound levels from earpieces. Some of this work has been carried out for police forces and some for the manufacturers and suppliers of radio and earpiece equipment.
The first phase of a project with Cranfield University on behalf of Transport Canada into the use of sound to guide passengers to aircraft exits when visibility is poor has been completed. Last year we reported that we had designed highly distinctive complex-tone sounds that were optimised for localisation. These sounds were tested at ISVR and Cranfield and are as effective as broadband noise for localisation. The work was presented at the Fourth Triennial International Fire & Cabin Safety Research Conference, in Lisbon.
A high-frequency noise assessment has been carried out in a newly refurbished biology research laboratory. The assessment included some noise sources that are audible to animals but not to humans.
Locally, we have we performed a survey to assess compliance with current and proposed noise regulations for cargo-handling staff of a shipping firm operating roll-on-roll-off ferries at Southampton Docks. Even more locally, we have carried out a noise assessment for the University’s gardens department.
Personal injury claims
ISVR Consulting has continued to prepare expert witness reports and evidence for Courts dealing with personal injury claims for noise-induced hearing loss. The more unusual cases included a person alleging hearing damage from exposure to extremely high levels of ultrasound; instructional officers in a prison woodworking shop; an infantryman undergoing live-fire battlefield training; a person wearing covert earpieces for surveillance; a military bandsman, and a mobile telephone user. Other more conventional cases involved several brothers all working on tugboats in Southampton Water; workers making cans for aerosol spray products; a printworker; a machinist in the tool-making industry; a swimming pool manager; and a number of ex-miners.
Despite the current financial woes of much of the automotive industry, interesting and challenging research and development tasks continue to be forthcoming. As in recent years, the projects are seldom aimed purely at reducing absolute overall levels of engines and vehicles, but more at reducing specific sounds generated by the various ancillaries and secondary sources which have been judged to be a negative component of the vehicle’s sound quality. In most cases these sound quality issues fall into two acoustic categories, namely tones and impulses.
One of the Unit’s most researched areas of automotive tonal noise in recent times has been that produced by the turbocharger. In the past year projects have again been aimed at improving the understanding of the transmission mechanisms of the various sources of turbocharger noise with particular interest in the transmission and radiation properties of the attached reinforced flexible air hoses. Another recent commercial project that investigated some of the psychoacoustic issues relating to a tone (turbocharger whine) sitting amongst a harmonic series (higher engine orders) has revealed some interesting, and possibly controversial, findings.
Impulsive noise studies this year have been related to the ever present topics of combustion and injector noise of diesel engines. Sadly, the dream that fully electronic fuel injection systems would eradicate combustion noise through appropriate rate shaping has been largely killed by the ever increasing emission demands. To meet future emission levels, injection pressures and rise rates are being increased, resulting in the high frequency injector excitation forces exceeding those of some of the primary sources, i.e. combustion and piston slap. Studies in this subject area have demonstrated the importance of appropriate cylinder head and injector clamping design if intrusive injector noise is to be avoided. The banger rig structure attenuation studies have increasingly focused upon various aspects of diesel engine sound quality. The cylinder-to-cylinder differences in both the vibration and the noise transfer functions are now being studied in great detail in an attempt to understand the potential for creatively controlling the ½ order NVH content at the design stage.
The past year has seen a significant move from test cell to in-vehicle engine testing. What was until recently considered as delicate instrumentation that was nursed through static test bed projects, is now being routinely used in vehicle under full road conditions. Robust techniques for power unit operating mode shapes as well as the measurement of torsional vibration of crankshaft, camshafts, oil pumps, etc., are now regularly being used for on road tests.
Rapid source ranking methods for vehicle interior noise continue to be developed where the contributions of power unit noise, wind noise and tyre noise are separated with the minimum of instrumentation. Although the technique has now been successfully demonstrated on a number of vehicles, the application of inverse methods still requires further development for the full potential of this rapid technique to be realised.
As control methods for the major sources of vehicle noise mature, so attenuation is increasingly being focused on some of the more minor, but just as challenging, sources of interior noise. One such issue studied this year has been the noise of active suspension actuators. Some of the more sophisticated suspension systems incorporate highly loaded hydraulic actuators which can on occasion generate significant stick slip settling noise. Although the resulting interior noise levels are very low, they can be perceived and do not portray the image sought by the luxury vehicle manufacturers who fit such systems.
The major marine activity last year was associated with the two-year ‘SoundBoat’ project that has now been completed. The project has been a great success both technically and politically. The findings with regards power craft exterior noise are now regularly used and quoted throughout the industry and have become the dominant technical input to a number of developing ISO standards. Perhaps the most significant outcome of this project has been the contacts made throughout the luxury powerboat industry both in the UK and overseas. ISVR Consulting is now seen throughout much of the world as an authority on small craft noise. Specific marine projects have predominantly been related to exhaust system design, where in many cases the boat builders are highly constrained with regards silencer packaging volume.A new aspect of marine noise recently studied by the Unit is that of watercraft annoyance. It has become clear that annoyance caused by power craft is not only related to absolute noise level and sound character (as in the case of road vehicles), but in many cases is also related to the individual’s perception of the type of people who drive the different sounding boat types. Developing metrics for this situation is proving challenging.
The Mark II High Frequency Sound Source continues to attract customers, with all five units this year being delivered to overseas customers. One very practical outcome from the ‘SoundBoat’ project was a simple on-board exhaust noise measuring kit called the SoundBoom. An extending boom with a microphone at its outer end and a pre-amplifier and a USB sound card at its handle end is connected to a lap top which runs a customised version of the ISVR EngWaves spectrum analyser. The software instructs the user where to measure on-board exhaust noise, acquires this noise, averages the recordings and corrects for propagation effects. It then combines this exhaust noise contribution with an empirically derived water noise contribution to give a prediction of the vessel’s pass-by noise. The technique has been shown to be very robust, and considerable interest has been shown by the industry for a production version of the SoundBoom.
Customised software development activities continue to grow, many being based upon the well established ISVR GenView and EngWaves packages. Although most of the software is developed for the automotive industry, other interesting uses occasionally surface. One of the most unusual applications of a version of EngWaves has been for the study of milk leaving a cow’s udder. The ‘Listening to Routes’ software for simulating the sound and vibration as it travels down the numerous routes through a vehicle from the various sources to the driver’s ear continues to be the major software development task.
The three automotive short courses run by the Unit again attracted good numbers last year with the Intake and Exhaust course so over subscribed that a modified timetable running into a second week had to be introduced to accommodate a second separate practical design exercise.
Ironically, as NVH activities within the industry become progressively more sophisticated, so the demand for evermore basic training courses increase. Perhaps this signals an untapped opportunity.
Dyne, S.J.C. Weakness of CVR recordings. ISASI Forum, 37(1), 2004, 20-3.
Gemmell, I*. and Lawton, B.W. Hearing standards for firefighters. In: Williams, T. and Rayson, M. eds. Medical and Occupational Evidence for Recruitment and Retention in the Fire and Rescue Service, London, Office of the Deputy Prime Minister, 2004, 5-23 to 5-26.
Lower, M.C., *Kay, A.M., *Thomas, L.J. and *Muir, H.C. Localizable sound and its application in guiding passengers towards exits during aircraft evacuations. The Fourth Triennial International Aircraft Fire and Cabin Safety Research Conference, Lisbon, Portugal, 15-18 November 2004. Available on-line at http://www.fire.tc.faa.gov/2004Conference/files/evac/M.Lower_Localization_of_sound.pdf
Joseph, P.J. and Smith, M.G. Chapter 7. In: F.J. Fahy and J.G. Walker eds. Advanced Applications in Acoustics, Noise and Vibration, London, Spon Press, 2004, 292-346. Smith, M.G. Sound radiation from a vibrating surface under a boundary layer, 2004. Complete ref please
Smith, M.G. and Morfey, C.L. Directivity and sound power radiated by a source under a boundary layer. American Institute of Aeronautics and Astronautics, 10th AIAA/CEAS Aeroacoustics Conference, Manchester, UK, 10-12 May 2004, AIAA 2004-3014, 2004, 11pp.
* - Not working in ISVR
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For further information contactStuart Dyne ISVR Consulting,
University of Southampton,
Telephone: 023 8059 2162 (+44 23 8059 2162 from outside the UK),
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