I'd always assumed that "buttkicker" was an affectionate term for a sub. I'm intrigued now: trying to learn more about their effectiveness, and cost...
The biggest problem with reproducing car sounds is that they are very loud in real life and, as I've said before, we feel sounds just as much as we hear them. Thus, to fully recreate the experience, you need to feel it, too.
Most of the thrill from hearing sounds in person comes from that feeling, rather than the sound itself, which, in fact, is rather uncomfortable on the ears! Even live orchestral music has that effect - it's astounding, really.
I guess that's why NFS:Shift gets so much positive feedback for its sounds, since it artificially conveys this "violence" - the physical aspect - and tricks our minds (well, not mine...) into being just as thrilled.
Whether or not the buttkicker is actually a decent replacement for pure volume (
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"there aint no replacement, for [air] displacement!"
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) remains to be seen...
I shall have to see about testing one.