CCA丨BMW 3 Series NVH Analysis

China Customer Audit (CCA) is an evaluation, before a new car launches, on the product’s “marketability” from various dimensions. Standing in customer’s shoes, experts figure out issues that don’t match customer’s aesthetic about car quality and offer suggestions to R&D department and quality department of auto enterprises for issues improvements in the early period.

The CCA team of Car Research evaluated BMW 3 series (320Li M Sport) NVH performance based on their CCA dynamic evaluation system.

The evaluation is conducted when the car is idling, which car owners most frequently experience, focusing on the conditions of air conditioning on and off when in P gear and D gear. The objective test data shows that the overall noise level of BMW 3 series at idle speed is good.

When the A/C was on, the noise was lower than 40 dB(A), and the driver and passengers in car didn’t feel discomforted. Meanwhile, the difference between the noise of A/C on or off is less than 1 dB(A), which was not obviously perceived.

A detailed analysis about noise spectrum inside the car when idling shows that the engine noise of 2, 4, 6 and 8 orders, which generally causes passengers’ complaints, is relatively small for BMW 3 series, and there is no abnormal phenomenon of any order under each working condition.

After testing the blower noise and air volume at the outlet, in combination with the overall performance of A/C system during test, the team found that the noise of BMW 3 Series’ A/C system is good: noise kept stable in different options without any abrupt change; the cooling capacity of A/C met the use demand; the A/C pipe noise stayed at a normal level under different settings of the blower without obvious pipe noise or whistles.

To fully assess its noise level, the CCA team took the car for a two-day and 300-km test drive. It’s found that and the noise level and inside phonetic intelligibility are great when BMW 3 series is at constant speed, which is in upper-intermediate level among models in the same class. In addition, there are the following findings during the test drive:

1. When the car was at high speed, the wind noise level sounds acceptable, and phonetic intelligibility in car was good, which didn’t cause obstacles to the communication of the occupants.

2. There was no abnormal sound and leakage sound inside caused by wind noise.

3. When the car passed rough roads with medium-size particles, there was distinct low-frequency noise in car, causing a sense of constriction to the occupants’ ears.

4. The tire noise level is average: the occupants can hear the tire noise, but they didn’t think it a must to complaint about it.

During acceleration, the engine has a slight roar near 1000rpm, but its rotational speed will exceed 1000 rpm soon, which won’t cause any complaint from the driver according to the subjective evaluation. On top of that, the noise and vibration of engine at other rotational speeds keep average good.