Quote Originally Posted by ehansen007 View Post
Having gone through this open air experiment with the hot rod, putting the sub anywhere outside the cabin was useless. The 818 trunk is fairly close and you could run some ports into the cabin. In the hot rod, Strangely enough I was able to fit an 8" inch bazooka under the passenger side dash and it was awesome. With the V8 and the wind noise it took about 700W to be able to listen to anything on the freeway with the sub and two kicker coax 6" in the lower door. I think the kick panel/under dash sub box will be your best bet for anything in the sub category but the doors are also pretty cavernous so you you might be able to get frequencies as low as 100Hz to work there with the right setup and insulation. Just my experience.
Thanks for the info, Eric! That pretty much jives with my plans: a good pair of component speakers in the doors/dash/kick panel area crossed over around 100Hz, and a sub, all with 'enough' power. If I can fit a bazooka tube in the frunk and port it to the cabin, the would be great, otherwise, hopefully a slim (3") sub or two under or behind the seat(s). I won't know for sure until I have my kit in hand, or someone else tries it.

As another point of reference for noise in a topless car, I find the upgraded factory Harmon/Kardon system in our 135i vert quite effective. This has a pair of 1" tweeters and 4" mid-woofers front and rear, an 8" sub under each front seat with 'only' 300W of total power (not stated if this is RMS continuous or peak). At first I was a bit skeptical on whether or not this fairly modest hardware would be adequate in an open top car. I did tweak it with an SPL meter to flatten the frequency response, and got it dialed in quite well. Below 60mph, the factory system sounds great. It's only over 80mph that the wind noise becomes an issue. On the freeway, tire noise can be the biggest factor; on a back road with no other vehicles around, or a concrete barrier to reflect your car's noise back at you, it's fine.

Yes, our BMW is quieter than any 818 will likely be, however the exhaust on the M-sport package is surprisingly throaty (we get comments and compliments on it all the time), and with the top and windows down any open car is noisy. We have a wind deflector, which helps immensely, and I expect the 'speed humps' on the 818 will function similarly by reducing turbulence around the head. That being the case, I'm getting more confident that a fairly modest audio system like I'm planning will do well in an 818.