Today is a good day for your ears. At the LA Auto Show, Jaguar has unveiled the most powerful and fastest cabrio in its history: the XKR-S convertible. Happy birthday, aural canals!Like the fixed-roof XKR-S, the convertible Jag uses a 5.0-litre V8 with a twin-vortex supercharger to develop an eardrum-rupturing 542bhp. Though it weighs a full 1800kg – damn you, structural reinforcement – the XKR-S cabrio will bolt from 0-60mph in just 4.2 seconds and run all the way to an electronically limited 186mph.The cabrio gets the same chassis reinforcements as the XKR-S coupe (the car that, earlier this year, we took to the world’s greatest road in Norway), with sharper springs and dampers, along with revised steering. Jaguar claims the XKR-S is the stiffest car in its class, a claim we’ll be very happy to put to the test very soon.The concept of an XKR-S cabrio might sound strange – why go to all the trouble of stiffening and sportifying a coupe, only to chop its roof off? – but it makes sense. The hard-top XKR-S isn’t an out-and-out hardcore track special, but a somewhat more rounded take on the fast coupe formula. We have a sneaking suspicion it may be rather excellent in cabrio form.It’ll certainly sound good. When we thrashed the XKR-S coupe up the Stelvio on our Performance Car Of The Year shootout this summer, we discovered it made one of the finest noises in the known universe, a vicious sawtooth soundtrack that’ll only be improved by the removal of that irksome sound-buffering roof.Have a listen to this SuperValueBargainBasement video of the XKR-S coupe – filmed on a 1980s mobile phone at the very top of the Stelvio by un-named TG staff – and just imagine a cabrio on a full-bore tunnel blast....