All doors and sunroofs were closed and the average sound level over 10 seconds was measured. The idling testing took place in CAR‘s garage (representing a controlled environment), with the vehicles’ stop/start systems disabled to keep the engine running. Note that all additional noise generators in the cabin, such as the audio system and climate-control fan, were switched off. That is why the A-weighting scale is applied by measurement equipment to evaluate the human ear’s perception of loudness and the unit is then dBA.Įach vehicle’s cabin noise was measured using two sets of equipment for 10 seconds during the following conditions: idle 60 km/h 80 km/h 100 km/h and 120 km/h. Perceived loudness is a complex field because the human ear is not equally sensitive at all frequencies (it’s most perceptive between 2 and 5 kHz, and less so at higher and far lower frequencies). The hearing threshold of 20 μPa (micropascal) is the 0 dB reference and the pain threshold is about 130 dB, which equates to a military jet taking off from an aircraft carrier. Therefore, the decibel (dB) scale, which is logarithmic (meaning not linear higher numbers represent vastly louder sounds than low numbers), is used instead. A sound’s magnitude is the amplitude of the pressure fluctuations and these can be measured in Pascal however, because of human hearing’s extensive range, this results in very large numbers. Sound travels at 340 metres a second (1 224 km/h) at standard atmospheric conditions. The number of pressure variations per second is called the frequency of the sound, and the normal detectable frequency range of a healthy ear is between 20 and 20 000 Hertz (Hz). Sound is any pressure variation (in air, water or other medium) that the human ear can detect. ![]() We decided to choose three vehicles from three divergent automotive categories: Recently, however, we acquired a modern Casella digital sound-level meter and, to test its accuracy, we did some side-by-side assessment with state-of-the-art HEAD Acoustics equipment from Stellenbosch University to determine if we should once again include this procedure as part of our road-test findings. In the past, CAR magazine has experimented with the measurement of interior noise level as part of the road-test regime, but because the analogue equipment failed to show significant differences between vehicles at the time, it was decided to abandon the test. To see how effective – or not – their efforts are, we decided to choose three vehicles from different segments to evaluate their cabin noise levels. To provide a quiet cabin, noise, vibration and harshness (NVH) engineers spend vast amounts of time in sound laboratories evaluating the selection of insulation and absorption materials, and the appropriate quantities.
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