In all seriousness, you could alwys get a set of those noise-cancelling headphones. Bose and others make fairly effective sets, available by mail-order and a gadget places like Brookstone.
I've used them, they work well against the very low frequencies that will be present in your car.
A principal reason for the "boominess" in C4's (and C5 fastbacks) is that there are exhaust pipes that have acoustic resonances that coincide with acoustic standing waves in the cabin.
That is, one of the resonant frequencies of the pipe is the same as one of the resonant frequencies of the cabin, and the pipe resonance "drives" the cabin resonance.
One analogy is a kid swinging on a swing: if you're pushing at exactly the same rate he is swinging, he'll swing higher and higher. If you were to map out his swinging on a piece of graph paper vs time, you'd see a nice sine wave, looking like a sound wave, with peaks and valleys corresponding to height of the forward and backward swing. (see the picture)
A muffler in the exhaust system robs acoustic energy; in the swingset analogy, it's as if something were holding you back, preventing you from pushing the kid very hard, so that friction (damping losses in your exhaust) prevented him from swinging very high.
The resonators aren't very effective mufflers, although they're better than nothing! so you'll hear a bit of noise inside.
Your best bet if it's more than you care for is to use a cross-over pipe just ahead of the rear axle.
Regards,
Robert
Art
Anyone running straight cat converters on their C4???
Dennis
40th Anniv. Registry Member. Original Build Sheet/Window Sticker/Service Records.
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