Aircraft internal noise, sound systems and communications

ISVR Consulting has carried out many unusual projects relating to noise and communications in aircraft. The following examples illustrate the wide diversity of projects and our range of capabilities.

Measurement of ambient noise levels and noise levels from crew headsets on the flight decks of civil aircraft

We measured ambient noise levels on flight decks and the noise exposures of flight crew from their headsets in each type of aircraft in the British Airways fleet. The measurements were carried out using a manikin, or artificial head and torso, during normal scheduled flights to Europe, the USA and Canada. The potential benefits of Active Noise Reduction headsets were demonstrated in flight and the airline re-equipped with new headsets.  From April 2006 the Control of Noise at Work Regulations 2005 apply in aircraft flying over British soil, and airlines will need to carry out a risk assessment for cabin and flight crew.

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We subsequently carried out similar measurements for two further airlines, based in the UK and Ireland, in light aircraft used for training pilots, and in fixed-wing and helicopters used by police air support units.  (See also our page on Headphones and noise exposure)

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Design of warning sounds for military and civil aircraft

In collaboration the MRC Applied psychology Unit, Cambridge, we have carried out research and development of ergonomic warning sounds for both military and civil aircraft use. These sounds are designed to be quickly and easily recognised, to convey the appropriate degree of urgency and to be loud enough to hear instantly above background noise, yet not so loud as to startle, distract, induce panic or interfere with communications.

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Development of a specification for the passenger public address system in helicopters

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A Puma helicopter

A specification was prepared for the CAA to cover the intelligibility of passenger public address systems in helicopters such as those serving the North Sea oil rigs. Announcements must be audible and intelligible through cabin loudspeakers and through noise-excluding headsets, sometimes with the passengers' ears covered by the hoods of waterproof immersion suits. The specification covered the methods of measurement and the required standard of performance. Following on from the above project we assessed the performance of public address systems against the draft specification for three helicopter operators.

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Design assistance and testing of passenger public address in aeroplanes and helicopters

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The public address system was tested in this aircraft

We have assisted with the selection of public address (PA) loudspeakers for an aviation company redesigning the interior of two aeroplanes, one with a fifty seat and one with a thirty seven seat capacity. We verified the performance of the PA against CAA Specification 15. We are able to assess intelligibility using either the Articulation Index or the Rapid Speech Transmission Index (RASTI) method.  We have also evaluated PA systems in helicopters, see above.

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Design and testing of sound systems to guide passengers to exits of smoke-filled cabins

Our first study was carried out in 1992 in collaboration with the MRC Applied Psychology Unit and the Applied Psychology Unit of Cranfield University, who conduct aircraft evacuation trials for the CAA. We installed loudspeakers close to the doors of a test aircraft at Cranfield and used sounds to guide passengers to the exits of a dark smoke filled cabin to speed up the evacuation.

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We also undertook a further study in collaboration with Cranfield University for Transport Canada.  We developed sounds that were optimised for localization and have shown that well designed, complex-tonal sounds can be localized effectively.  The best of these complex-tonal sounds is comparable in accuracy of localization to broadband pink or white noise in tests. Although broadband sound is generally regarded as the most accurately localised sound, complex-tonal sounds have distinct advantages over broadband noise as audible alarm and warning or guidance signals. 

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Assessment of the effect of the noise from cabin water sprays on the intelligibility of instructions shouted by cabin crew during aircraft evacuations

Recordings were made and noise levels measured during trials of water sprays in an aircraft cabin. The effect of the noise of the sprays on the intelligibility of shouted instructions from the cabin attendants was evaluated during trial passenger evacuations. The project was carried out with the Applied Psychology Unit of Cranfield University at the Fire Research Station at Cardington for the CAA.

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Loudspeaker selection and layout for entertainment systems in VIP aircraft

We are able to advise on the selection of loudspeakers, design of speaker enclosures and coverings and the location of loudspeakers in VIP aircraft. We have designed loudspeaker layouts for four separate VIP aircraft including a Boeing 747, a Boeing 757 and an Airbus. Each of these aircraft was undergoing refit in the USA. The forward half of the cabin in each aircraft was partitioned into separate rooms, including a bedroom, office and lounge. Each room was equipped for stereo music and Dolby Pro-logic surround replay of Laserdisc movies. Loudspeakers had to be concealed from view. By making full size mock-ups of selected rooms in our laboratories and installing the full music and video system we demonstrated the quality of the sound systems as heard from the critical seats under quiet conditions and with the noise of the aircraft in cruise. This gave the customer's representatives and the main contractors the confidence to proceed with each installation.

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Electroacoustic measurements

We also carry out laboratory measurements of aircraft communications components, including frequency response, distortion, and directivity of cockpit voice recorder microphones and communications headset microphones, and frequency response and distortion of headsets and handsets. (See our page on electroacoustic measurements)

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