Originally posted by ophidia31:
you definitly dont want your highs bouncing off of the front windshield. it will break up the pattern and make your highs sound harsh. high frequencies are more directional than lower mids-bass frequencies. ...
So long as the glass is locally flat, it won't break up the (beam) pattern -- the pattern will be completely maintained. Locally flat means, for example, you can see the optical reflection of the tweeter in the glass and it's an undistorted image of the tweeter.
... so for highs you want them as close to relation as possible.
Well, close isn't really relevant inside a car. You'll always be closer to the speaker(s) in a car than in a living room. What's more important is that the tweeters are pointing more-or-less at the heads (or ears) of the riders starting with the driver.
there are cars where they calculate the angle that the sound would reflect off the angle of the windshield but that is in major competition cars and dont think you have the time or patience to want to do something like that. ...
Instead of calculating it, just use optics..... that is, use the optical reflection of the glass to help pre-position the tweeter before you finish the install.
If there is any downside to using tweeters that reflect off the windshield it is that you could actually have two sound sources there: one for the tweeter, and the other from the sound reflection of the tweeter. This always happens btw, but it's not a problem if the tweeter is directional enough (large enough in diameter compared to the lowest wavelength it radiates) so that you don't get interference between the real sound source (the tweeter) and the image source (reflection of the tweeter). A tweeter will be directional enough if the crossover network is set to a high enough frequency. I know that's vague, but it is true.
If you got significant interference, then you would hear a fluttering of sound amplitude at high frequencies as you move you head laterally
within the car. To show this in more detail requires math, and this isn't the place for that. So it's a lot easier to place them (temporarily) and test/listen.
In some sense, car audio is driven by the locations where the speakers can be placed, rather than placing them where they ought to go. A car interior is a very lousy listening room because it's so small and there is so much glass (which reflects but doesn't significantly absorb), so quality
car audio is much more of a business of compromises than it is in home audio. High SPL car audio is a different animal with completely different goals.
Door placement of a tweeter would seemingly eliminate the reflection source (giving you only the direct source from the tweeter itself), but you still get reflections from the tweeter at longer delays from the other hard surfaces in the car. In underwater sound and in auditorium acoustics, this would be called reverberation. In a Grand Canyon sense, it's just called an echo. It still affects the quality of the sound, sometimes it can be helpful (if cleverly done) or it can be a nuisance (if not done smartly).
Your ears can be very useful tools to decide if it sounds good or not. So I suggest you try the tweeter placement using double-sided sticky tape as a temporary measure and see how you like it. HTH. - Ken