how can i get fuller bass range

seems like some real pros runnin behind the scenes here. finally someone might be able to help me.

ive got an 04 monte carlo with 2 alpine type r 15s runnin off a pair of hifonics brutus 1200 watt amps. i got them wired to 2 ohms each on the 1 ohm stable amps, and a clarion crossover. my box is sealed and, sadly, i do not kno the size of it (which is probrably VERY important to my question. i will look the dimensions up if i get any responses).

how can bring out higher bass tones?

i finally chose the 15s after much trial and error, seeing as i could not get a deep hard bass sound outta 12s in my trunk.(ive tried pioneer 3k watts sealed, mtx 7500 sealed and ported, kicker l7 sealed and ported to be exact).  the 15s SLAM. my problem is i seem to be getting super high energy from the 20 to 35hz range (estimated, not metered) which i LOVE... but  everything over 45 or 50 hz or so sounds very weak. ive been workin on car audio for years and ive always recomended sealed box in general based on my love for deep low bass, but never have i encountered such a steep cutoff of higher toned bass.

ive tried over and over adjusting the xover levels on the amps, the crossover, and the bass boost, but it seems like the accoustics for the sound just isnt there.

do i really need to find a ported box? is there something im overlooking? im not lookin forward to the lack of trunk space. and if i DO get a ported box, how should it be built to match my love for low bass AND still be able to hum the higher notes?

basically ive tried all the settings. radio, external crossover, amplifiier crossover. with all them on high, i still dont get the response. i mean, it makes it a LIL better, but it seems like it draws a whole lot of extra energy.  no my amps do not have any subsonic filters (which im upset about).

the hpf on my car speakers is set relatively high (prolly 150 or so), i dont like a lot of bass going thru them. as for the woofers, i got my estimated signals via usac bass test tones. i got one for every 10 hz, 20 to 100, and also a 20 khz to 20 hz signal test. the 20 , 30 and 40 sound great, the others, as i mentioned, sound weak. granted louder than my car speakers but u can feel the pressure get released after 40 to 50 hz or so.

ive been in sounds for about 10 years since i had 2 10's hooked up in my room via converter box. ive done hundereds of installs. im not NEW but there are some things i never learned by the book. for instance ive never learned how to build or tune a box. i always just bought one from the sound shop and hoped i liked the way it sounded.

thanks for all the help, and even reading any of this. sorry im not quite so technical, im a hands on person. if i could, i would sit u in my car and play u a song so u could see just what im talkin about.

ok i jus went and ran the sound tests again... 20 thru 40 sound FANTASTIC. the 50 is faltering, by the time it gets to 60 to 80 its more of a buzz than anything. the part that worries me is the woofer is really vibrating, as if its getting the wattage, but not producing the sound.

all xrossovers set to high (200 or so) on amp and passive,  radio sub output has been on thru (i thought i had this turned on, but i guess not).

what happens is, the 50 to maybe 100 hz actually play, but the volume at which they play levels off at a point. the lower tones play MUCH louder, and can be overbearing at times. dont get me wrong, i LOVE this earth shattering low bass response, but i wanna kno why its costing me so much of my higher bass.