I'm not going to get into some deep technical discussion on acoustics, because I don't want to confuse everyone. This is a simple question, that has a relatively simple answer. I'll talk in simple terms.
Good luck.
Golly gee if that isn’t a condescending comment.
You make it sound like everyone who posts here is an idiot. Some of us are pretty well versed in acoustic theory. Unfortunately while all that you have said is true, you can throw 99% of it out the window when it comes to a harsh environment like the interior of a car. Like the comment on concave VS dome and the distribution of each. By your own admittance of wanting the most direct path to your ear, with the least amount of reflection…would you not want a dome? How does that make the concave superior? It doesn’t, at least not in a car environment. They are just a different way of building a driver, which for what its worth the dispersion of the tweeter in that configuration is secondary. The primary reason for building the concave dome is power handling, at least when it was first designed. It does have its own dispersement issues; this is why 99.9999% of the time they have a bridge over them with a phase plug on it.
While the time alignment you speak of is important, the issue is the blocking the higher frequencies. In the car, especially the NSX when mounted low in the door, your legs, clothes and early reflections of the door panel all disrupt the tweeter more than the arrival time of having them mounted in the pillar. 99% of people will hear the tonal “hole” from a blocked high frequency long before they will here the “shifting” from arrival time.
Sorry back to the OP question,
I recommend the pillars; you can use the “bad harsh reflections” to your advantage by using the windshield to load the tweeter, kind of like a compression driver, or horn. This will give an even “stage” across the front of the car, while maintaining an even frequency range (at least better than your leg blocking would). You will want to attenuate the tweeters 5-7 DB sometimes more. This is the biggest mistake people make by not lowering the output of these drivers. The reason for this is three fold, the first being they are horn loaded up against the windshield, creating a boost of up to 3 db (this is a guestimate).
The second would be they are closer to your ear, this makes them seem louder. (I know someone asked if the human ear can here such small differences….If you take 2 speakers @ one meter the ear will here both, move one 3 mm back, and the ear will only here the one closer.) Makes you wonder how a row of speakers seems louder huh….that’s another topic.
The third and final reason is the woofer/mid is mounted 2-3 inches behind a door panel, behind metal mesh and grill cloth. Since sound is just the movement of air….you have to realize these things will lower the output of the speaker. All the people who say this isn’t true…go grab some grill cloth, just grill cloth…not the door, or metal mesh and talk to your wife thru it, ask if there is a difference.
Back in the day I used a lot of Focal drivers. Mostly the TLR tweets that were like $1500 a pair, and sometimes the bigger brother to those, GULP $$$$. They were so efficient we would knock them down 12-15 db, even when matched to the TLR woofer. These tweeters should fire directly across at each other, not angled back or up. Just straight across at each other.
I think most people dont mount them there because it is not easy to do...seems like most people mount them high and back on the door...which is about the worst place to mount anything.....you will not have a mount with the focals that will put them at the right angle, so you have to go custom. You will only be able to knock them down by 3-6 db so you might have some issues there also. and because most people try and bring room accustics into play in the car and but them close to the other driver, so they never even try out a pillar. Look back at all the great sounding cars from Iasca....more that 1/2 had tweets in the pillars, and/or manipulated early reflections..... Of the other halk, half of them had a horn loaded driver configuration.
It has been my experience, with over 15 years in the AUDIO industry…not home theater, but 2 channel audio that it is easier to make a car sound really good than it is a room..
But it is FAR easier to make a room sound GREAT, than it is a car. Since your driving your car anyway, with road noise, engine etc etc really good is really good enough.
