Subs are makin me scratch my head

I have a 10" rockford he-2 i beleive, i'm not lookin at it so i'm not 100% sure but its a 10" sub from rockford fosgate that is a 400 watt peak single 4ohm sub, i'm running an old la sound malibu 120 amp to it, i've got 8 ga power wires, 12 ga speaker wires, and a 1.3 cube sealed box with a ton of poly fill in it, i recently pulled all of it out because this box is from wal mart since i was on a budget at the time, i pulled the sub and poly fill out and resealed all the edges with silicone and sealed around all the mounting hardware that goes in the box, the terminal cup the handles and such i beleive the box is about 1/2 inch mdf but i'm not sure it seems pretty brittle and i'm wondering if this might be my problem. 

Now that you know all the details heres my problem, my sub has certain frequencies that it doesnt like at all, with my crossover on my stereo set at 78hz for the high pass and the low pass off since it doesnt seem to effect the sub channel at all and the rear speakers turned off completely/fully faded forward the subs higher notes are constant distortion, it just buzzes more than it hits a note and it sounds like total crap, i've retuned my whole system several times, turned the gain down and back up messed with all the settings the amp has to offer trying to cure this problem i beleive its starting to buzz around 180hz maybe 190 and it starts to have some balls around 110-90hz  the sub hits alot fuller since i packed more poly fill but i cant get rid of the sharpness that the bass comes on at or the buzz that goes along with any usuable bass. The only thing that sounds remotely good on my system is really deep bass almost beyond what songs nowadays are playing any rock/metal has this buzz in it but linkin park sounds pretty good for most of their bass lines, the subs still distorting but its liveable and what i'm trying to figure out is if its my box or my amp as the amps getting upgraded asap  along with the box but i want to make sure its not to small before i make another box with pretty much the same basic sq area to it.

J~

actually i'm glad you posted that as now i recall where i got those numbers from, i had a tester cd i made from various testers i had found and kept the tracks i liked i had one that counted down in cycles and its not hz its 180 cycles,  i'm about half dead at the moment from bein tired i should of caught that real quick since i'm going for a lower range than that anyway... the issue i'm having here isnt out of the normal bass spectrum,  lets use songs from groups as an example, old 80s hair bands like ratt and motley crue, most of their bass including the drum tracks cause my sub to distort horribly, even with as much limiting as i can possibly have going on even with the amps crossover turned on and my stereo crossover set at 78hz hi pass and low pass ( which as i said low pass doesnt seem to do anything for the sub at all) i still get the high end buzzing sound from the sub when it hits on a bass note, even with my gains turned almost all the way down it still does it, now on say some tracks from bubba sparxx, or lil jons get low the sub seems to hit very clear and very hard, has lots of power behing its thump as it will vibrate the back of my seat very nicely, it used to only hit like that for a 40 cycle band, from 130 or 120 to around 90 or 80 cycles, whatever that breaks into on hz i'm not sure but once it was beyond those numbers it had no power at all, around 100 cycles it hits very strong almost kind of hurts your head compared to the rest of the time and it would hit like that till 80 cycles, now that the box has a ton of poly fill the numbers are alittle better it stil ldoesnt come around till 140 cycles or so, but it carries down to around 70 cycles and it carries that power all thru the range and really starts to gain power around 90 cycles on down till it falls off abruptly about 70 or 60 cycles.

the issue thats bugging me with this, is that while i have a nice deep bass sub, i have no real useful sub as most of my metal such as fear factory falls in a range that some of it distorts and some of it doesnt, its very annoying to have a very tight bassline thumping along only to have the chorus buzz horribly or to have a bit of double bass drum lines turn into a buzz filled rattle from the trunk. hopefully this helps make things a tad clearer

J~

Several remarks:  subwoofer freqs up to about 100, crossing over at about 80 Hz (aka cycles).  Set lowpass at 80 Hz for the sub...everything higher goes to mid-bass woofers and tweeters.  It is true that some, a lot of, popular music has just a little bit of sub frequencies.  The midbass drivers should be pounding the back of your seat as well.

Tuning your setup does not involve turning the amp gain up and down, etc.  Set the amp gain to match the input of the deck, then leave it be.  Tuning then involves setting crossovers, matching speakers up for best all-freq playback, sound damping, location of drivers....

The quality of the sub enclosure is suspect, or the placement of the woofer into the box.  Make sure it is tight and sealed.  Or have someone who can pinpoint problems by listening take a look at it..

thanks for the starting points, i was aware that most subs dont hit very well up high, which is my my crossovers are set at 78hz and the sub frequency selected on the amp( as i said crap amp i'm aware) which cleans up alot of it, i've also spent alot of time "listening" to what my sub is doing in the box, what the rear speakers are doing and which is contributing to what noise i'm hearing as i first thought this was an issue with my rear deck having loose parts or somethin of the like so i started hunting for vibrations in that area when i found out it was coming from the sub, which is why i pulled my box apart and resealed all mating edges as well as all mounting hardware and double checked to make sure i have no stripped screws or loose parts on the box itself, i wasnt aware that a 10 hitting around 180hz was a huge issue as the average rating on subs is up to 200hz and above for their limit, this box has smaller area as far as recommended sizing of the box so i figured it would be alittle tighter thus allowing me to push up into higher frequencies, as i'm semi new to actually designing a high end system i realize i have some things to learn, which is why i'm here, but as far as hearing things i've been a musician for 7 years and spend hours perfecting my setups to get just that perfect sound with my equipment, so i'm used to hunting around for the source of a misplaced buzz, rattle, squeel,muted harmonic, or any other variable that comes with adjusting amps and effects to work in harmony.   now i guess the questions i should be asking are, will cheap wood cause higher notes to come off distorted or cause noise issues in general, will to small of a box mute the highs, and anyone have a good setup for a sony mdx850mp?

J~

If you would break your marathon posts up into digestible chunks (paragraphs), your readership will grow in leaps and bounds...and your points won't get lost in the crowd.

You said crossovers are set to 78 Hz...then said your sub is playing freqs at 180 Hz.  I don't get it.

Yes.  I would love to help but your sentence construction is non-existent.

sorry for the bad english.

I am also wondering how my sub can be picking up anything higher than 78hz as the low pass and high pass filters have an option to limit to 125 or 78 and both are set to 78hz, its a sony mdx850mp  so anyone that knows this system alittle better than me could maybe explain what exactly i need to do to get my sub in order.

The sub should not see these higher frequencies so maybe my bigger issue is the head unit after all, the high pass filter has alot of effect on the sub, i can hear it pulling out the higher frequencies but when i run a tester cd with all the sound faded forward the eq set flat and the crossover set at 78hz it will still pick up the higher end of things.

Now i know a few songs i've heard the sub cut out completely because the notes being played where to high mostly old 80s songs but the limit seems to be a soft limit as it bleeds thru and crackles and pops from the sporadic signal being sent to the amp.

I'm trying to overhaul the whole system a peice at a time, the head unit has always bugged me for lack of adjustability so is there something about sonys head units that i'm missing? i read the instruction book cover to cover but i guess i must of missed something simple.

I'm wanting to upgrade to a pioneer hu, anyone have any recommended hu's?  is their premier line any good?

J~

If you're going to spend the money to get a Premier (I wouldn't, but that's me,) you might as well get at least a mid-level Alpine or even better, an Eclipse is money allows.

You also may want to look into some "blockers", or I believe they are called F-mods. They connect in-line with the speaker wires or RCA's (depending on which style you want) and simply block out whatever frequencies above or below that level that you don't want.