I measured 87 db at ear height on the highway. That's with a hard top and the behind seat foam. I have aftermarket exhaust, but I can't hear it over the wind noise.
Understandable. Then I would not recommend this mod for you. If the noise level is not loud enough to your liking you could drill some holes in the firewall to let more through.I find this interesting.
I have the same car as you, a 2009 Saffron Yellow Elise Purist Edition.
With either the softtop or hardtop in place I find the noise level is both fun and fine.
I am running the stock muffler and I have the normal Elise carpets.
In the summer without either top on, the noise level rises significantly.
I've never found the desire to have the noise level be less and I'm a daily driver.
I guess I've been driving an older car for more than 20 years and have gotten attached to noisy rides.
My post about noise levels on a stock Elise being "fine" was not meant to say I'm critical of your choice to make the ride quieter.No one is holding a gun to your head. It's only for those who are wanting a quieter ride.