Automotive NVH Testing
Commonly known as NVH test, this measures the amount of noise you can hear in the vehicle – at the driver’s seat and at the passengers’ seats, which will also determine the level of comfort in a vehicle. The test also measures vibrations felt at various points in the vehicle, which are a major contribution to “driver fatigue” on a long trip. (Ever travelled in a rattling old state transport bus? It will give you an idea of what vibrations can do to you). Our automotive NVH testing which are categorized into Noise, Vibration, Vibration Isolation under which we offer .
Automotive NVH testing equipment:
Data Acquisition system – This is the “brain” of the NVH testing equipment.
Connectors –Ensures no noise in the signal transmission.
Microphones – These are high sensitivity microphones that are set up at just about ear level (always maintaining same distance from seat H point) near the driver’s seat and rear left passenger’s seat, and in the case of MUV/SUVs with three rows, they are set up at ear level in the third row too. These capture actual noise in the cabin just how the human ear would hear it.
Seat pad vibration sensor – These high sensitivity pads are set up on the seat to measure how much vibration filters through the seat – which means how much you would feel on your body. Seats with good cushioning usually insulate vibrations pretty well.
Uniaxial and triaxial accelerometers – These are attached to the steering, to the gear lever and on the floor to measure just how much vibration a driver will feel. Diesel engines for instance tend to throw up far more vibrations through the steering and gear lever than a petrol would generally.
Normal standards of measurement:The actual output is measured in dBA (decibels A-weighted) which is the relative level of sound as perceived by the human ear. Up to 70 dBA is a comfortable, accepted noise level in a car when it is moving at about 80-100 kmph. For perspective, 115 dBA is how loud a truck’s air horn is, and anything over 120 dBA is painful. In general among premium hatchbacks, petrol variants have ambient noise levels below 60 dBA, when driving at normal speeds, while diesels are around that mark. The lower the dBA level the quieter the car.This test is also a measure of the “Articulation Index” or the level at which normal conversation can happen in a car without having to raise ones voice to overcome engine noise and wind noise in the cabin. Low frequency sound in the cabin, such as a ‘booming’ noise that happens when you drive at low rpm in a high gear and also high frequency sounds such as an over-revving engine, both affect your ability to have a comfortable conversation in the car.Vibrations are picked up by the accelerometers and the seat pad sensors – these vibrations are measured in metres per second-square. The measurements of noise and vibration are recorded to cover both city and highway driving conditions one would normally encounter.
What affects this test:
NVH tests results will vary from car to car considerably. The cars we use for the test usually don’t have more than 15,000 km on them and are in stock condition – the way they are made by the automotive OEM. NVH results can get affected by aftermarket tyres, suspension modifications and even with seat covers or extra carpeting in the car. The thickness of the seat cushion, the type of door beading (single or double layer) and even the thickness of the roof liner or door pads will affect the readings of this test. Hence, cars that have much thicker roof liners, seats and better quality door beadings are usually the quieter ones. This is one of the reasons car manufacturers give you a padded engine cover (also known as an NVH cover) to reduce noise especially with diesel engines.
The tabulation of results:
Now for a consumer the frequency graphs and numbers visible on the laptop screen would make little sense. There are just too many figures getting churned out every second. However, what our team does it to analyse that data and compare it with data from other cars in the same segment. This gives a car a relative score on a 0-100 scale. For example, car Y scored a 70 on NVH for the driver (the noise the driver can hear). Car Z, surprisingly, proved to be quieter – with a figure of 60 for the driver. The actual dbA levels against a particular RPM or vibration levels at certain RPM can also be recorded – this data is of immense value to car manufacturers. But for you, the car buyer, you just need to look at the relative score for each car.
Since this data would mean nothing to the average consumer, our team does the number crunching to give you a rating on a 0-100 scale, where lower the figure is better. The Car Y, for example, scored 70 for the driver on noise, and 20 on vibration, while the Car Z scored 60 on noise for the driver and 25 on vibration. For the passenger the Car Y scored 78 on noise and 10 on vibration, while the Car Z scored 50 on noise and 18 on vibration. If you look at these relative scores, the Car Z is perceivably quieter than the Car Y under test conditions.
Additional Automotive NVH testing for development
- Frequency Response Functions
- Operational Modal Analysis
- Experimental Modal Analysis
- Noise level measurement according to various standards
- Mode Shapes and ODS animation