I use earplugs with speakers which I got for my motorbike - custom moulded from a company in the US - I have the rear speaker wires wired in to a 3.5mm socket and connect the speaker earplugs to it. They only cut out the wind noise and still allow you to hear horns / engine noise etc. They greatly enhance a long journey!
Cheers!
_________________________
Robbie
Plus4 Aston Martin Mendip Blue
09-WX-2269
"Lord Plus Faw of Kilgibbon"