Re: Changing the TDi badge on a Bi TDi - but what for? –
03-01-2016,06:35 PM
One correction to my post below.
I'd assumed they were using a similar approach to active noise cancelling headphones by using a microphone to detect noise frequencies to suppress. This is not the case. What they appear to have done is worked out a "map" of what frequencies need suppressing at various engine RPM and load and that information gets passed to the active sound exhaust unit controller.
Nice explanation here Making tailpipe music - SAE International if anyone is interested.

Originally Posted by
ukgroucho
Not sure this would add any value on a BiTdi as the exhaust system is very different to a conventional exhaust - and no it's not really like the GTD where fake noise is pumped through the cabin speakers. The exhaust in the BiTdi is an active sound system - basically instead of baffles and the accompanying weight and 'restriction' to gas flow, the active sound exhaust uses inverse sound waves to reduce noise in the exhaust. This is done by using microphones in the exhaust to listen for the current engine noise and then using speaker (also in the exhaust) to generate an appropriate inverse sound wave to largely cancel (or moderate) the engine sound. The basic reasons for doing this were all about a free flowing exhaust with less weight....you can read more detail on Eberspachers web site, they created the technology
Exhaust Technology - Eberspächer
The happy side effect of this is that with a bit of clever sound engineering you can also do a little 'more'. For the BiTdi this means you that 'out of the box' you can have the exhaust in 'comfort' (quiet) or 'dynamic' (pseudo V8 growl). But there are aftermarket boxes that give you lots of other options and basically plug into the existing system.
One of the things that you'll notice with a BiTdi is that if you stand by the side of it when it is running with the exhaust in dynamic mode the pseudo V8 rumble is much more apparent to the back of the car - where the speakers are in the exhaust system.
A6 allroad BiTdi (MY14, July 2013 - DAB & power tailgate). Glacier white, tech pack (HDD Nav, colour DIS, Parking Plus), sports seats, 4 zone climate, heated seats front and rear, ambient lighting, 75L fuel tank, adaptive Bi Xenon headlights