^ MB uses their own aeroacoustic index. Not sure if or how that can be compared to the test AMS performs. Here's an article about S-Coupe testing. Not yet in the new aeroacoustic windtunnel they now have in Sindelfingen next to the design studio.
emercedes-benz
New S-Class Coupe sets wind noise record
The world’s quietest car through the air is also one of the biggest
Size isn’t everything, but it helps to slip through the air more calmly than anything else, if Mercedes-Benz’s new S-Class Coupe is any indication.
At the car’s launch in Florence this week, Mercedes-Benz claimed its two-tonne coupe generated less wind noise than any other series production car in the world.
Measurements taken at the Unterturkheim wind tunnel prove the S-Class Coupe has lower wind noise even than this year’s new S-Class limousine, according to the Head of Aerodynamics at Mercedes-Benz, Dr Teddy Woll.
“The S-Class limousine is second, according to our measurements, and the Audi A7 with the acoustic glass and the Bentley Continental GT would be tied for third, though the old Maybach is close,” Dr Woll insisted.
“The Lexus cars are good up to 100km/h but drop away at high speed, and the higher the speed the more they drop away. They don’t seem as focused on this as they were a decade ago,” he claimed.
Mercedes-Benz ranks interior wind noise using its own aeroacoustics index, which takes into account the interior sound level, psychoacoustic variables (like the sharpness of the sounds and the ability to hear conversations over the background noise) and different frequencies.
It uses the Untertürkheim wind tunnel, designed in the early 1940s to accommodate cars as well as fighter planes, to deliver its baseline test and has a database of tens of thousands of cars and model variants dating back to 1954.
“We measure the wind noise with a dummy head, but not with a rolling road. With a rolling road you have road noise and you have the hydraulic noise of all the systems as well,” he explained.
“We measure at 90km/h, 140km/h and 200km/h and in all speeds we are the quietest, but we have a greater advantage at higher speeds. The faster we go the higher the advantage.
“We don’t measure at 130km/h because nobody goes at 130 km/h. If the speed limit is 130km/h they all go at 140km/h.”
Dr Woll said the aerodynamics team worked on the S-Class Coupe from very early in its development, working on cleaning up the bodyshell and the door sealing along with the underbody.
“We have done so much progress in exterior noise, which obviously helps the interior noise, and then we have 6mm of laminated glass, so it’s by far the quietest inside,” he said.
But there are limits to what can be done on current technology, he warned.
“You can’t do noise cancelling, like a Bose headphone set, for the sheer volume of the car’s interior. Those things have to do their cancelling close to the source.
“For other steps, you can do engine-order cancellation, which Honda is talking about.
"They want to cancel engine noise at lower revs and high torque situations via noise-cancelling electronics, but we have dual-mass flywheels that basically do the same thing mechanically.”
http://www.motoring.com.au/news/pre...ew-s-class-coupe-sets-wind-noise-record-44369
