I'm the oposite... I want it to
sound as good to my front passenger as it does to me..... this is difficult to achieve, but not impossible..... to me there is nothing worse than getting it to sound sweet to the driver, & crap to the passenger...
I use hlcd's, horn loaded compression drivers, waveguides as there commonly known by the popularity of image dynamics own brand name.... there biggest plus is the driver point source is way under the dash, & the pathlengths are about as close to even as your going to get, mechanically, without going through the firewall, if I couldn't use these then, yeah, I guess I'd be a kickpanel kinda guy for my highs.... although there are now some real sweet alternatives, namely the byriliums...
edit:, & if you think that cause the drivers are down low, the front stage is going to be low, your mistaken.... my front stage is right in the center eye level of my windshield, & pinpoint acurate, to both driver & passenger..., when you close your eyes, the stage is out 4' past the windshield, I like to say that it sounds like maria or donna summers is stradling my hood

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