10 Jan 2013

BMWs M5 is the new Milli Vanilli (with its synthesised engine noise)

Matt Hubbard investigates synthesised engine noises, such as VW's Soundaktor and BMW's Active Sound System

Imagine you've just bought your new BMW M5, which has a 4.4 litre V8 with twin turbochargers, and makes a fantastic noise.  The next day you drive the M5 to a concert by your favourite band.  But a couple of songs in to the concert you realise the band is just miming.

The sound you hear is from the studio -  recorded and refined sessions, which a top producer has cobbled together, and the band themselves are just acting along with it, because in reality they can't play their instruments very well.  You leave early, in a huff, and soak up the awesome V8 wail generated by the BMW's engine.

Except, that sound is not the engine.  It is pre-recorded engine noise being played through the car's audio system.  In reality the induction noise made by a modern M5 is muffled by the turbochargers and the exhaust sound is muted by the silencer.

It's all a con.  Don't believe it?  Have a listen to this,

That is the sound of a 2012 BMW M5 with the BMW Active Sound System on and off.   And it's not just BMW who are fooling us.  Volkswagen have done the same with the Golf GTi.  Listen to this for an even more stark difference between before and after VW's Soundaktor system has been disabled.

So basically you've bought a performance car for it's power, handling and noise - and one of those components is missing in it's natural state.  So the manufacturer created it and provided it via the stereo system.

And matters are only going to get worse.  Emissions regulations, and consumer power, means performance cars have to get greener so engine sizes are shrinking and turbos are added.  Induction noise is a direct result of the sound of combustion being emitted, but with the addition of turbochargers comes extra pipework and sound insulation.  So the noise is reduced.  Stock exhaust pipes, with their muffling, also reduce engine noise because the sound literally has to travel further to get out of the tailpipe.

Take Mercedes-Benz for example.  The old 6.2 litre naturally aspirated AMG engine makes an incredible sound.  But the new 63 AMGs come with a 5.5 litre twin turbocharged engine which naturally makes a much reduced sound.  Mercedes' engineers have had to engineer flaps in the exhaust to shorten the route to the tailpipe, when the throttle is pressed and the revs are high.

Jaguar do the same with the XKR-S.  A flap in the exhaust gives us the incredible noise generated by the snarling, spitting 4.2 litre supercharged V8.  Otherwise it would produce a much more muted sound.

Porsche have developed a rather elegant solution.  They have fitted something called a Sound Symposer to the 911.  When the Sport button is pressed the engine sound level in the cabin increases.  This is due to a pipe which is connected to the air intake, just before the throttle valve.  The pipe passes through the bulkhead and into the cabin.  When Sport is pressed a valve in the Symposer pipe opens and some of the induction roar is heard in the cabin.

Ford and Lexus have developed similar systems to Porsche for their Mustang and LFA.  Lexus' system was created by Yamaha.  Not the bike division, but the musical instruments division.

BMW and VW should be ashamed of themselves.  Instead of learning how to properly tune and play their instruments they have got session musicians to record a better version, which they then play back to us - and pretend it's the real thing.

If car companies are going to play pre-recorded engine noises back to us maybe, in the future, we will be able to specify what sounds we want.  A Toyota Prius that sounds like Concorde at take-off anyone?

What do you think?  Are you happy with pre-recorded engine sounds in the cabin or would you prefer to hear the engine itself - no matter how it sounds?