I've recently upgraded my car system. I added:

 

A Hifonics 4 channel amp, 100Wx4, 2 channels driving the fronts, and 2 channels bridged driving the sub.

 A HiFonics Plato 10 band quasi-parametric EQ. It's different from a 10 band graphic EQ in that each band has an additional knob for adjusting the center frequency of that band. This gives a lot more control than a plain 10 band, without the complexity and cost of a 30 band (1/3rd octave) EQ.

 A (temporary) Coustic active XO for the fronts to sub transition. I plan to build a custom 4th order filter. The Coustic is only 2nd order.

 The sub is an Rockford 8-incher in a homemade vented box, 0.5 cu.ft, tuned to 31 Hz. The resulting response curve is close to a sealed box with an F3 of 55Hz, which many say yields a very high quality, audiophile sound in a car environment, because it complements the natural bass boost in a vehicle. I hope to put up a page describing this in the future.

 All the above I bought on sale :-):-)

 

 

Fronts are 6.5" Vifa P17WG-00-06, and 1" aluminum domes, LPG 26NA. I bought them from Madisound and Solen. They are excellent drivers, and only cost around $35 each. The LPG's are especially sweet, with no metal-dome zing. These drivers are not of the car-audio name brand variety, which I find to be overpriced. Vifa is one of the world's largest suppliers of drivers to hi-end audiophile speaker manufacturers, and sell to the hobbyist market too. The name-brand car speakers which I've heard that sound good good are Dynaudio, Focal, Morel (aka Macrom), Eton ( aka Diamond Audio), and A/D/S. Interestingly, all of them are hi-end suppliers except for A/D/S. Sorry, MB Quart and their ilk don't impress me. See email with Dan of Avatar.

 

For the fronts I built a passive elliptic crossover, here is my elliptic filter page.

 

Elliptic filters feature much more rapid rolloff. In a car where the tweeters and mids are separated by relatively large systems (unlike a home system where they're separated by a few inches), this yields interference between the mid and tweet in the crossover frequency region. A 2nd benefit is that the xover frequency can be set very low, very close to the frequency at which it begins to distort. My LPG 26NA's distort at 1.8 kHz, and I set the tweet hipass freq cutoff point at 2.4kHz. The filter gives something like -28dB at 1.8KHz. In contrast, a 4th order filter would have to be set >4kHz to get 28 dB of attenuation at 2 kHz. Letting the tweeters play low improves the imaging in my car because the tweeters are on the dash and the mids are low in the doors.

 

The reason I put separation rather than some overlap is because I thought interference would be more audible than a narrow notch. (I'm guessing of course, it would take a lot of effort and time to test both and compare. I'd love it if somebody would, or tell me if my assumption is wrong)

 

I didn't have room to put additional amps for the tweeters for a biamped front setup, that's why I went passive XO. I could've done it active, otherwise.

 

I then fired up my LAUD to adjust my active XO and EQ.

 

I set the bass XO to 80 Hz. I also found that the adjustable xover built into the amp is 1st order - pretty lousy - and I couldn't seem to get it to work with the Coustic active XO to get a nice total rolloff. So I disabled the amp's xover and just used Coustic. I still get a little bit of bass-coming-from-the-trunk effect that's why I will build a 4th order xo. I built one for my home system and it sounds great - no bass localization on the sub.

 

To adjust the EQ I placed the mic in the drivers head position and took readings of the left channel alone, the right, and both together. I set the time markers from 10 mS to 150mS, and also tried changing the mic position by several inches around the general area of the driver's head. The differing mic position produced different peaks and dips, but a few showed up in most or all of the positions. I brought down the peaks and lifted the dips.

 

End result, wow! Humongous improvement.

 

 

I can say the EQ worked because it sounds great for the passengers (car's a 2 seater), but terrible if you move your head to between the passengers. And, disabling the EQ makes it sound comparatively terrible.

 

Comparing the sound of my Grado SR60 headphones and the car system, (playing a portable MD player and switching between 'phones and plugging into the head unit aux input), I can almost say the car sounds better ('96 Miata).

 

Oh, and I was surprised that reversing the right channel phasing made images move up above the dashboard. I discovered it by accident, when a test CD I was playing had a voice saying "in-phase, out of phase" and "out of phase" sounded better! This one helped imaging big-time too.

 

Most people who hear my system say "wow, such clarity". Other comments include "how do the images come from the dash and not the speakers?". Ambience reproduction is also surprisingly good. Downside is that it can play loud, even with the top down, but not *really loud* (but then I don't really need that). Bass power could be improved (will investigate), and there's an upper mid harshness on some CDs that I can't find in the measurements. This is the one that annoys me the most.