Vehicle Noise Regulations

A: Governing principle: Pass-by noise is a system response combining airborne and structure-borne paths under a defined excitation. Applied here: A thinner shell can amplify panel breathing and radiate noise even if acoustic insertion loss looks good on a bench, pushing levels over the limit during the test acceleration. Distractor trap: Option A appeals to engineers who treat the regulation as muffler-only acoustics and forget shell radiation isn't filtered out by the test.

A: Governing principle: Coast-by noise is sensitive to lightly damped structure-borne paths when engine torque reverses. Applied here: Overrun excites exhaust modes differently, and a hanger rate shift can line up a boom at a specific order without affecting full-load pass-by. Distractor trap: Option A sounds plausible to NVH generalists, but tire noise wouldn't create a narrow exhaust-correlated tone.

A: Governing principle: Safeguards only act within their defined operational design domain. Applied here: PWS is active at low speeds and isn't credited during type approval pass-by tests, so it has zero effect on those results. Distractor trap: Option B confuses a warning function with an active safety system, a common SIL boundary mistake.

A: Governing principle: Test geometry directly affects measured sound pressure and is fixed by regulation. Applied here: Microphone position is non-negotiable because small deviations shift SPL more than typical vehicle design changes. Distractor trap: Option B catches engineers who recall environmental limits but forget geometry outranks them.