Beyond the global target of reducing the sound pressure level in a vehicle interior, it may be desirable to affect the interior sound quality and to grant the vehicle a strived interior sound character, i.e. 'pleasant', 'sporty', 'powerful', etc. In most cases, achievement of such targets by means of usual hardware modifications is difficult, time consuming, costly, often not feasible and, least of all, sometimes not possible. Conversely, application of the Active Noise Control (ANC) techniques has the potential to skip these disadvantages and may help to achieve the anticipated sound quality. The sound quality improvement strategy for a passenger car applying ANC may be set in 3 steps: reduction of annoying high SPL engine orders (i.e. second Engine Order (E.O.) of 4-cylinder, 4-stroke engines); reduction of annoying random type noise (i.e. road noise); reduction and/or balancing of even, odd and half E.O. In the past, various car manufacturers have already experimented and proven out the technology of reducing the high-SLP E.Os. (i.e. booms) with using an ANC system. The experience shows that these boom frequencies are very often coinciding with the vehicle interior cavity modes, therefore the mode shapes of the interior cavity are to be taken into consideration in positioning the actuators, error microphones, etc. In many cases the loudspeakers of the vehicle audio system may be used as ANC actuators. lf the road noise issue is at very low frequencies and mainly addressing the first interior cavity mode, an 'analogue' modal approach as above may be striven. However, in case of higher frequencies 200 ... 600 or 800 Hz, the mainly radiating body areas should first be identified and then treated by using flat ANC actuators diminishing the strength of the respective dominant local source. Appropriate 'composition' strategies for the even, odd and half E.Os. will enable a desired sound quality being granted to a vehicle. lf a 'smooth and pleasant' sound is required, the even E.Os. should stand in proper ratios to each other and the levels of odd and half orders should be reduced. On the contrary, if a 'sporty' sound is required, some odd E.O. may be raised during accelerating the car. Thus, in course of 'tuning' the desired sound quality, the SPL of some orders may be reduced and some of them even be raised. On principle this kind of tuning can be deployed by means of ANC techniques. As the higher engine orders mean higher frequencies, a modal approach as mentioned above will not be functional, as the modal density of the interior cavity increases exponentially with increasing frequency. In this case, the space in the proximity of each passenger's head may acoustically be treated. That can be reached e.g. if Electro-Mechanical Film (EMFi) and error microphones are positioned in the headliner of the vehicle or a loudspeaker and a microphone is integrated into the headrest.


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    Titel :

    Prospects of improving vehicle sound quality by means of ANC


    Weitere Titelangaben:

    Aussicht auf Verbesserung der Schallqualität in Fahrzeugen durch ANC


    Beteiligte:
    Necati, G.A. (Autor:in)


    Erscheinungsdatum :

    2001


    Format / Umfang :

    2 Seiten, 7 Bilder, 4 Quellen



    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch




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