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Playing around with test tones, you can hear some weird anomolies as you move the head around, especially sideways. A 400 Hz tone intensity varies quite a bit depending exactly where your head is.

Also notice different response peaks in the midrange (using TrueRTA and an Audyssey calibration mike) in different vehicles, but using the same components. My Corolla has a strong peak in the 440Hz range, but my Camry has the same strong peak at 1.2Khz....using the same HU and speakers (Dayton RS180/Vifa NE19VTS).

Another odd find -- in the Camry, using Polk db 651 coaxials in the stock locations, that 400Hz tone varied strongly, but less so with the Dayton RS180s installed in the same location. I did notice that the center image with the Polks was less stable if my head moved slightly, and the Daytons seem to cope with this better.

I guess what I am trying to say is that it is notoriously difficult to get good, consistent sound in a vehicle. Flat freq response is a goal, but that is only a part of the picture. I am thinking that the above anomolies have something to do with standing waves, interference from opposing speakers in a small enclosed space, and phase issues (especially with the Polk coaxials above). The RTA mic only gives a specific picture in a specific slice of space and will not always confirm what the ears hear. Perhaps I should come up with binaural mics mounted on a form the exact size of my head :laugh:

I am getting to the point of stopping at just good enough and simply enjoying the music....
 

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Well, im unaware of what you are experiencing. Everything has a resonant frequency, and at that frequency, all hell breaks loose. Check out the old vids of the tacoma narrows bridge. The wind passing it, hit its resonant frequency and as you can see its amplitude increased greatly causing it to break. This resonant frequency of a car should not change by simply swaping drivers out though.
 

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Playing around with test tones, you can hear some weird anomolies as you move the head around, especially sideways. A 400 Hz tone intensity varies quite a bit depending exactly where your head is.
Comb filtering

Also notice different response peaks in the midrange (using TrueRTA and an Audyssey calibration mike) in different vehicles, but using the same components. My Corolla has a strong peak in the 440Hz range, but my Camry has the same strong peak at 1.2Khz....using the same HU and speakers (Dayton RS180/Vifa NE19VTS).
Different mounting, different "box" volume, different PLD, different boundaries (doors further apart, console different size etc)

Another odd find -- in the Camry, using Polk db 651 coaxials in the stock locations, that 400Hz tone varied strongly, but less so with the Dayton RS180s installed in the same location. I did notice that the center image with the Polks was less stable if my head moved slightly, and the Daytons seem to cope with this better.
Better off axis dispersion on the Daytons, see if you can find on/off axis FR graph for both-I'll warrant the Daytons have a better output off axis

I guess what I am trying to say is that it is notoriously difficult to get good, consistent sound in a vehicle. Flat freq response is a goal, but that is only a part of the picture. I am thinking that the above anomolies have something to do with standing waves, interference from opposing speakers in a small enclosed space, and phase issues (especially with the Polk coaxials above). The RTA mic only gives a specific picture in a specific slice of space and will not always confirm what the ears hear. Perhaps I should come up with binaural mics mounted on a form the exact size of my head :laugh:
Comb filtering is the big issue, driver placement can help reduce this. Reflections are also big issues that in turn may cause more comb filtering; 400Hz has a wavelength of 86.17cm, 1200Hz 28.72cm-check what could be reflecting in these distances from the driver in each car.

You "should" have less phase issues with coaxials than components.

Alpine UK have an £Xthousand "head" with binaural mics-was there the other week and the tech guy stated that the Imprint set up was a fraction away from the set up using the binaural mic head

I am getting to the point of stopping at just good enough and simply enjoying the music....
Yup, there's always that point. I'd have loved to go 4-way active, but would have need to spend an extra £1k on stereo, £600 on amps and another £290 on drivers. Plus the extra install work and I couldn't justify it. Installed my system and am very happy with it, no major issues-slight dip at 200Hz and slight peak at 1250Hz-but otherwise near as damn it flat. Now just need to tune it and have a play with tweeter locations-when i can find the time!
 
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