Active noise systems could put acoustic diagnostic equipment into production cars. Most car manufacturers' acoustic concepts rely on some level of noise absorption to remove interior noise. But this adds mass. Others go to greater lengths with varying mixes of sound absorption materials, sophisticated engine mounts and stiffer oil pans, but there is only so much that this can do. An alternative is to use materials that dissipate the sound instead, lighter weight materials with complex layers, but these have their limitations too. Engines are getting more sophisticated and hybridisation and cylinder deactivation give the engine two or more distinct noise profiles. Also at certain speeds or under certain conditions sound pressure can still build up, causing unpleasant "booming" effects.
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