With the shift to electric cars and their near-silent drivetrains, the pressure to scrutinise noise generation from wind, tyres and vibration is getting even stronger, especially for premium manufacturers.
BMW recently opened a new test facility called the Aeroacoustics and Electric Drive Centre (AEC) to replace its acoustic wind tunnel, which is almost 40 years old.
Located at the BMW Group Research and Innovation Centre (the FIZ) in Munich, the new facility follows the addition of the Environmental Test Centre to the FIZ back in 2010.
Geared up for the fast development of electric vehicle drivetrains, the AEC consists of two parts.
One is multifunctional, housing workshops for prototype work and testing equipment, the other an aeroacoustic wind tunnel, which is claimed to be the quietest and largest in the world, at 100m long, 45m high and 25m wide.
Not surprisingly, designing a wind tunnel to be capable of measuring the noise levels of and in cars that are already intrinsically quiet poses challenges not just in terms of the equipment used but in the construction too.
The two buildings were built in a giant pit to decouple them from the surrounding area, with a 3m-thick fl oor slab and a sound-insulated façade to isolate them from external noise and vibration.
The buildings are partially separated from each other, with the second building (which BMW likens to a “semi-detached house”) housing workshops, testing and measurement stands and prototype assembly lines.
This section occupies 15,000 square metres over several floors, with a further 800 square metres set aside for manufacturing future inverters in cleanroom conditions.
The main test chamber has a background noise level of 54.3dBA with a car travelling at the equivalent of 87mph on the built-in rolling road, which BMW describes as the equivalent of speaking in hushed tones or the noise made by a quiet air-conditioning system.
With intrusive noise being at such low levels, measuring the noise of headwind accurately is much more precise.
The maximum wind speed the tunnel can generate is 155mph, thanks to a 4.5MW blower, which at that speed is moving 100,000 cubic metres of air through the tunnel every minute.
The chamber is rated as an acoustic semi-free-fi eld space, meaning none of the surfaces apart from the floor reflects any sound at all.
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It would seem counterintuitive to start trying to make EV cars as quiet as possible when they were quite happy to sell people noisy diesel cars in the not so distant past and that people were more than prepared to put up with it. I suppose the masking effect of the engine noise was why they didn't bother.
Going to be a bit weird sitting in a car where there little noise inside or out,and if all the eltromechanical stuff is so quite and virtually vibration free, how will we know if there's an imminent failure other than permanently monitoring screens in front of you , I think it's getting towards cars any cars being just wheeled white ( not racist) goods , it's just transport from A to B .