Vehicle Noise Measurement Kit SV 971A VN ISO 5130 ready

ISO 5130 is the acoustics standard for measuring the sound pressure level emitted by stationary road vehicles. It applies to categories L, M and N with internal combustion engines and is used for type approval, checks at the manufacturing stage, official testing stations and roadside testing. The level is measured close to the exhaust outlet, with the vehicle stationary.

A sound level meter meeting Class 1 of IEC 61672-1, used with A-weighting and F time weighting, together with a Class 1 sound calibrator to IEC 60942 and an engine-speed instrument accurate to at least ±2 %. The SV 971A Vehicle Noise Kit brings all three together — the SV 971A meter, the SV 33B calibrator and rpm reading through the OBD interface or the SP 73.

At 0,5 m ± 0,01 m from the reference point of the exhaust outlet and at 45° ± 5° to the vertical plane containing the flow axis of the pipe. The microphone sits at the height of the reference point, never lower than 0,2 m above the ground, with its reference axis aimed at the outlet. Assistant PRO shows the geometry for the vehicle's tailpipe layout.

The target engine speed depends on the rated engine speed, S. For categories M and N it is 75 % of S up to 5 000 min⁻¹, 3 750 min⁻¹ between 5 000 and 7 500 min⁻¹, and 50 % of S from 7 500 min⁻¹ upwards. Category L uses 75 % of S up to 5 000 min⁻¹ and 50 % above it. The tolerance is ± 5 %.

Engine speed is raised gradually from idle to the target value and held steady for at least one second, then the throttle is released rapidly and the engine returns to idle. The sound pressure level is measured across the steady phase and the whole run-down, and the maximum reading is taken as the test value. Assistant PRO displays live rpm and signals the release moment, so the operator is not estimating.

The test is repeated at each outlet until three consecutive values fall within 2 dB of each other. Their arithmetic mean, rounded to a whole decibel, is the reported A-weighted sound pressure level L_Arep. Where a vehicle has several outlets more than 0,3 m apart, each is measured separately and the highest average is reported.

The complete measurement chain is checked with a Class 1 calibrator at the start and at the end of every measurement session. If the two checks differ by more than 0,5 dB without any adjustment in between, the results taken since the last valid check have to be discarded. The SV 33B supplies a 114 dB reference at 1 kHz for both checks.

A level, hard outdoor surface — concrete, dense asphalt or similar — free of large reflecting objects within 3 m of the microphone and of any point of the vehicle. Wind, including gusts, must stay at or below 5 m/s, and background noise at least 10 dB below the level being measured. A semi-anechoic chamber meeting the same acoustic requirements may be used instead.

A statement that the test followed ISO 5130, the test site with ground and weather conditions, the measuring equipment including the windscreen, the typical A-weighted background level, identification of the vehicle with its engine and transmission, a description of engine and exhaust outlet location, the microphone position and orientation, the engine speed used and the resulting level L_Arep. The SP 74 wireless printer produces it on site.

ISO 5130 does not set general noise limits. A vehicle in use is assessed by comparing its result with a reference measurement made by the same method — for example at type approval, or the figure recorded in the registration documents. Because of measurement uncertainty (1,9 dB site-to-site at 80 % coverage probability), differences below 5 dB should not be treated as significant.