Just a response to the 3 way system (or 4 if you count sub)...
Although I am not doing this in the NSX, I currently have a 3 way set up in my TL, with an oversized 6.5" mid bass in front door (stock location) and a 5.25" & tweeter set up in kick panels....they are all older school MB Quart Q series (the good stuff) components, and are designed to work together , with two very good crossovers as opposed to just one. It used to be called "the Add a woofer" system, when you added in the mid bass.
Basically, it allows the 5.25" and tweeter, which are positioned directionally very good for imaging, to cross over at a higher Freq. than would be needed if matching to a larger subwoofer only. The 6.5" which is less important for direction due to the lower fq's it plays, takes a lot of the higher end bass notes, allowing the actual cross over point to be lower for the subwoofer. (I'm running two 12" R series in trunk)
I can't put into words how sweet and smooth this system sounds....the imaging is terrific and the "hitting" bass is also very forward , and of course the ultra low frequencies , are belended in very nice , even though they are from the trunk.
The key to this I beleive is that the entire 3 way system was designed to work this way with each other, so crossovers are optimized for perfect transition between the drivers.
OF note, the speaker placement in the NSX is actually quite good for imaging also. BUT, the interior of the TL vs. the NSX are night and day difference for road and wind noise, and of course engine, so as nice as it is for setting up in a sedan, it would be defeated in the NSX, at least while driving....but a novel convept for sure. I am curious to see the results of a 3 way system in the NSX for sure.
I don't have any pics of mine handy, but here is one from the net that gives you a rough idea..
http://www.onlinecarstereo.com/CarAudio/p_16051_MB_Quart_QSC_164.aspx
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