Racing single seat hovercraft may be a fun thing to drive but with a 2 stroke engine and a high revving industrial cooling fan they can be noisy. Identifying the loudest sources on each craft quickly and easily is challenging because of the variety of noise sources, and because each craft is different and mostly homemade. A low cost, homebrew, beamforming system has been built and successfully used to identify around 95 % of sources on 100 hovercraft from across Europe during the 2007 season. The system uses a highly portable 2 metre radius semicircular array of 16 microphones with comb filter software to focus on tonal noise, a delay and multiply algorithm to improve 'noise picture' definition and a simple inverse technique to estimate the db elimination value of individual frequencies. It pinpoints sources in the range 30 hz to 800 hz, typically within about 100 mm and about 5 hz, even though several similarly loud sources are present within the space of about a 1.5 metre cube. The common sources are engine air intakes, exhaust silencers, and various fan obstructions such as pulleys, radiators, stators, engine covers etc causing airflow turbulence and thus noise. It has also provided early warnings of bearing and crankshaft failure. The system doesn't use a conventional camera and although the simple cartoon cross section of a craft on the noisepic has proved very effective there are registration issues if the craft is not precisely in the correct place during the test. It's proposed to fit a loudspeaker emitting a 500hz tone as a marker beacon on top of the fan duct as an aid to more accurate registration. A ring of 8 microphones at the standard 25 metres around the craft will be added in 2008 to measure far field noise in accordance with club rules and to provide a reliable calibrated total power measurement between one test and another.


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    Title :

    Noisecam - Using beamforming to identify noise sources on hovercraft


    Additional title:

    Lärmkamera - Identifikation der Lärmquellen von Luftkissenfahrzeugen mittels Strahlformung


    Contributors:


    Publication date :

    2008


    Size :

    6 Seiten, 7 Bilder, 2 Quellen



    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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