ISVR Consulting - Annual report 2007

Every year the Institute of Sound and Vibration Research publishes an Annual Report. This is the entry for ISVR Consulting covering the year January to December 2007.



Group Developments

ISVR Consulting is the commercial consultancy division of the ISVR. We provide services to industry and the public sector in a wide range of aspects of acoustics, noise and vibration. Our service includes environmental acoustics, litigation services (particularly for hearing loss claims and audio tape analysis), specialist measurements, noise control and automotive design. In this report we describe some of the more interesting projects for the reporting year.

Research

EPSRC Project for a Soundscape Instrument

ISVR Consulting has continued work in partnership with the University of York and Newcastle University on a three-year research programme investigating the measurement of soundscapes. The ISVR contribution to this project is a consideration of the possible impact on environmental noise assessment and legislative noise controls of a tool that can discriminate and localise sources in a variety of environments.

Currently most impact assessments, standards for the environmental noise measurements and planning guidance are based on statistical parameters derived from measurements of environmental noise, particularly the A-weighted Leq (equivalent continuous sound pressure level) and the L90 (the level exceeded 90% of the time). Technology advances, particularly in digital signal processing, may mean that it will be possible for a sound level meter to discriminate between and localise sound sources. This makes it possible to characterise a sound field in terms of the relative contributions of different sources instead of characterising the effect of the sources.

We are looking at the potential impact of such a meter on planning guidance and noise controls through discussions with stakeholders to establish the most useful functionality and possible applications.

Refurbishment of a Prestigious Hotel

ISVR Consulting is currently assisting in the acoustic design of the refurbishment of a prestigious hotel in London. The work involves desktop design work and extensive testing on site to ensure a high level of sound insulation is achieved. One of the complications of the project is that our client’s domain is from level 2 and upwards of the building while the lower floors are retained by another hotel that also owns the adjacent building.

Hearing Loss Claims

We have worked on several projects over the reporting year, some more interesting than others! In one case, an individual was working on the tarmac at an international airport, underneath an aircraft that was being prepared for departure. His radio vibrated to indicate an incoming call. While walking away from the aircraft, the individual removed the hearing protector from his left ear, and held the radio against that ear to take the call. The call terminated after a pre-set period, making a loud piercing bleeping sound in his left ear. For about an hour after this incident, he reported deafness in his left ear. As his hearing returned, he became aware of a constant ringing in the left ear. This constant ringing sensation (called tinnitus) has remained with him since the radio incident.

ISVR Consulting tested the radio using our Kemar (Knowles Electronics Manikin for Acoustic Research) manikin — this has been designed to be geometrically and acoustically representative of a median adult human and incorporates microphones to measure sound levels at the eardrum positions. The radio was applied to Kemar’s right ear in an attempt to simulate the acoustic incident. Sounds were made at maximum volume from the radio.

The greatest sound level recorded for the call-termination beeps was 125.5 dB(A). Calculations indicate that such a level would have to persist for over 60 seconds to produce a noise exposure recognised as potentially harmful to hearing. The acoustic incident described in the incident lasted less than one second; it would not have contained enough acoustic energy to produce a predictable noise-induced hearing loss. The possibility of tinnitus due to the reported incident was left as a matter for the medical examiners.

Noise in Train Cabs

ISVR Consulting has been working with Greenstreet Berman on two projects for the Rail Safety and Standards Board (RSSB).

The first project was the design of a set of ergonomic alarm and alert sounds for the GSM-R cab radio system for communications between drivers, signallers and others. The sounds are designed to be easily and quickly identified, to be readily heard above the noise in the driver’s cab, to convey an appropriate degree of urgency, and to not conflict with or interfere with sounds from existing equipment already fitted in cabs, such as the ‘Automatic Warning System’ (AWS) and the ‘Driver Safety Device’ (DSD). The GSM-R system is currently being trialled in Scotland.

The second project concerns sound levels from warning devices in train cabs, such as the AWS and DSD. We are preparing a practical guidance document which will allow train operators or manufacturers to set sound levels of current and future warning devices in each type of cab, so that the sounds will be heard reliably, but will not be so loud as to cause annoyance or even discomfort.  We have recorded and analysed the ambient noise in driver’s cabs of electric passenger trains and diesel-electric freight trains to test the procedures, and these measurements will be included as example case studies within the guidance.

Noisy Buildings

Whistling buildings have been in the news on a number of occasions recently, and this has raised awareness of the risks of wind induced noise and the costs of rectifying problems. Partly as a result of this publicity we have had a number of projects relating to existing buildings with exterior or interior noise problems, and also several projects aimed at preventing problems prior to construction.

An example of the latter was wind tunnel testing to ensure that a louvre screen proposed for a commercial development would not cause problems. The development included several kilometres of the screen, to be positioned at high level and so exposed to strong winds from all directions. The first wind tunnel trials identified a problem almost immediately; the slats vibrated at high level, even at moderate wind speeds, and this caused non-linear impact noise from the end fixings. The likelihood is that over the longer term there would be fatigue problems as well as environmental noise issues.

Working with the designer of the louvre enabled us to find a way of stiffening the slats and adding mid-span supports without preventing the use of the extrusion process that was required to make manufacture of the many kilometres of slat material cost effective. A follow-up test ensured that the modified structure did not resonate under any reasonable conditions of wind speed and angle of incidence.

Automotive and Marine

The majority of activity still centres very much upon the internal combustion engine generally, and on the diesel engine in particular. However a recent project has involved a study of electric motors as used in small mobility vehicles. These vehicles require a high level of refinement, especially those intended to be used indoors.

A fundamental study into the noise generating mechanisms of electric motors has been undertaken, and the usual automotive techniques for quantifying airborne and structure borne transmission paths have led to some significant noise reductions.

A major aim has been to find methods of maintaining refinement when switching to lower cost drive motors manufactured in China. ISVR is working with the manufacturers to provide the noise and vibration components of an ambitious end of line quality monitoring system. This will enable the noise performance of every single motor to be quantified, and should also allow the detection of a number of known issues. However there is a particular interest in controlling sound quality. To achieve this it will be possible to easily and rapidly transmit full test results to engineers in the US and UK so that more detailed analysis can be performed on selected motors whilst listening to high quality digital recordings.

Publications

Brown, K.T. and Smith, M.G.
Time domain measurement of sound power output from a vacuum facility. Proceedings of the Institute of Acoustics, Autumn Conference, Oxford, UK, 17-18 October 2007, 29(5), 7pp.

Smith, M.G. and *Whale, S.
Acoustic measurement of boundary layer flow parameters. Journal of Sound and Vibration, 301(1-2), 2007, 278-96.

Smith, M.G., *Kim, K.B. and Thompson, D.J.
Noise source identification using microphone arrays. Proceedings of the Institute of Acoustics, Autumn Conference, Oxford, UK, 17-18 October 2007, 29(5), 8pp.

Smith, M.G., Carrilho, J., *Molin, N., *Piet, J.F. and *Chow, L.C.
Modelling landing gear noise with installation effects. Proceedings of the 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), Rome, Italy, 21-23 May 2007, Paper 2007-3472, 16pp.

*Li, Y., Smith, M.G.,*Zhang, X., *Chow, L.C. and *Molin, N.
Noise sources control of an aircraft landing gear. Proceedings of the 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), Rome, Italy, 21-23 May 2007, Paper 2007-3465, 14pp.  

* indicates authors who are not in the ISVR

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