Crossover points for a true 4-way system

I'm sure I'll get flamed and ridiculed by this, and it'll be deserved as this is a toy project, but here goes...

I'm building (as best as possible) a true 4-way driver setup in my 2004 Jeep Grand Cherokee (WJ) from ONLY Polk equipment. Just because. and with the goal of almost perfect stealth install.
The factory system was the Infinity 'premium' (a word I just loathe) with amp under the back seat, on the dash were 2" paper tweeters, door 6x9 paper 'woofers'. There are a set of 6.5's in the back door that we are going to totally ignore for the purpose of this project (they'll get db651's or something later)...

I'm keeping the factory stereo unit... it came with lifetime sirius radio and the cd changer and the truck is wired where the speaker line outs are twisted pair and run to the back where the factory amp picked them up and then a second set run back out to the dash and doors. Some aftermarket crap would look stupid with that nice rosewood trim anyway. The factory wiring from head unit to amp location is practically a 4v true balanced audio cable (like an XLR) with twisted pair and ground... can't argue with that. My temporary old 4ch Kenwood amp has line level input which I'll have to lose if/when when I upgrade to a 5CH :-( As it is now, I run the rears off the head unit directly as I don't really give two **** about them and fade the off unless the kid is with me.

In the front dash I am modifying the trim and installing Polk DB351's hidden under an almost factory-looking metal mesh grille. This isn't easy, but it will get done... sadly, the DB402's just wont fit. They'll get mounted and sealed to the trim panel itself, rather than under and away from the grille as the original 'tweeters' were.

In the front doors I am going to put in -only- the mid-range half of the DB6501 set, which I hope to source used (with an adapter plate).

Somewhere in the back will go my original set of Polk DB12 subs. I might keep them in their 1.2CF/sub divided sealed enclosure for now, and I -might- keep the 1000w Directed amp running them -for now-.

This should give me a 4-way system provided I properly separate the components I am using into their proper ranges.

So Here's what I'm thinking for ranges:
17wRMS(?) - 5khz(?) to 22khz - 0.5 in. silk dome
35wRMS - 600hz to 5khz(?) - 3.5 in. polycomposite cone
75wRMS - 100hz to 600 hz - 6.5 in. polymica cone
150wRMS - 20hz to 100hz - 12 in. oldschool cone (made of 100% real oldschool)

So here's a few questions I have (note the corresponding (?) in the list above:
1) On the DB351, I would like to know the frequency split that the built-in capacitor operates at (with and without the supplied bass-blocker installed), AND what the frequency the supplied bass blocker is intended for (even with the amp crossover points, a series capacitor will still be installed on the 3.5 to block startup pop. I may very well scrap them and compute my own, but maybe not... depends on what data I can get.
2) What is the separate wattage handling of the tweeter and the mid-range on the DB351? is there a difference accomplished by a higher resistance wound into the tweeter coil than the mid-range coil?
3) Would any of you suggest -different- crossover frequencies for the above components?
4) How many of you are laughing at me already ;-)

As you'll notice, there's about a double of power for each step down in range, which is about right as each step down involves a driver with about half the sensitivity. The end result power to each one will probably have to be adjusted in the field with an spl sweep.

I'm probably going to drive the system with a D5000.5 with amp1 to the Front DB351's, amp 2 to the rear DB652's (almost always faded off), and amp 3 to the front DB65x's. The amp has useful crossover adjustments.

The DB12's have a dedicated 1000w Directed amp at the moment, but it might get swapped for a Polk Monoblock just for the hell of it.

Also... Hi.
This is my first post here on Polk Forums. I used to be pretty active on other audio forums back in the 90s.


  • FestYboy
    FestYboy Posts: 3,861
    I think a better bet would be some Audio Control hardware and 2 4-channel amps. Do the XOs on the line level side. Run the amps in 3 channel mode. Mono block a single 12 below 40Hz.
  • JLStice
    That would be nice, FestY. I could probably amp up a stale cookie and Christmas tree tinsel and make it sound good with that kind of equipment. ;)
    I'm used to doing installs with a 'scope and LC networks, isn't an Audio Control cheating?

    I'm trying to keep this install small, clean, and hidden. Piping those high-level inputs through a nice pad hidden under the rear seat would work, fit in the middle, being much thinner than the amps - sure would save me a lot of headache, especially if I change components later on. What AC pad were you thinking?

    Also, I only have one set of wires up to the dash, so I can't amp the dome tweeters separate from the 3.5s, but I can tweak the RLC values there at the dash between the two. While I used to tear down entire interiors for mobile SQ installs back in the 90s, I'm not going that far on this one for tweeter wires.

    This is my surf-fishing Jeep as well as my daily driver. There's not much room to work with - I don't want exposed equipment as I work in the city, and have to have room left for my beach chair and tackle box. I commute a lot, and in DC and Baltimore traffic, and the sound staging right now is about knee-level and it's driving me up a wall. While I loved my Infinity RSi's off my Teac at home, I just can't leave this 'Infinity' system in this Jeep and remain sane.
  • FestYboy
    FestYboy Posts: 3,861
    In a car interior, there is no such thing as cheating. ;)

    The DM-608 is looking like it has everything discussed, plus a few other features. As for the amp, soundstream's ST3.1000D x 2 should do the trick. They'll easily hide away.
  • JLStice
    So I got the db351s in the mail today... no specs on the voice coils so I just measured them.

    The tweeter coil reads in at just under 3 ohm, with a 3.3uF cap (as labelled)
    The 3.5" cone reads in at just above 3 ohm, with a 200uF cap (as labelled)

    The 200uF cap supplied measured at 214uF. I didn't bother unsoldering the 3.3uf to check it.
    214 -is- within the 10% component QC range...

    The cone rides on that 214uF cap which puts it dropping out ~250hz, below where I plan to cross over into the 6.5" in the door (somewhere between 300hz and 600hz) which seems reasonable and safe for a 3.5" cone and gives me protection against start-up pop.

    With the 200uF in series with the 3.3uf we end up with a 3.25uF on a 3 ohm coil.
    Line resistance aside, that puts the tweeter fading in at-3db at 16khz. There's not much sound information above that, and that's about the point at which most people can't hear above.
    Am I wasting an otherwise useful tweeter? Should change that cap out for something a little more sensible between 6khz and 10khz, or does that 3.5" cone really perform up to 16khz at -3db? I'm not worried about warranty, here.
    Thoughts? Any official Polk weigh-in here?

    The 3.5's are now mounted to the backside of the crescent moon that goes between the dash and the windshield, with plain metal mesh grills (much thinner and holey-er than the plastic 'grille' mopar used. They sound okay for a 3.5s and definitely brought the apparent source up above the dash which was the main goal. My old trusty Kenwood class A/B (does anyone even still use those?!?) can only give them about 30 of the 35 clean rms watts they want. It was ear-spitting fwiw. I'll have to do pics when the sun is back up and snow is off the truck.

    Soundstream Stealth amps... its so tiny, yet plenty of power. Things have come a long way in the class D market, do they really perform that clean at the upper end now?
    Two of those and a monoblock could run a KW continuous, at about 330w a piece. Will make a really nice rear seat warmer... the kids are always complaining that we have heated seats up front but not for them in the back. I'm going to say I -need- these amps, I mean, think of the kids, right?

    That AudioControl is a really nice signal processor.
    !! But so expensive !! <--- mandatory complaining :)
    I'll save that much on not buying a head unit. I don't think a head unit at the same price point would have anywhere close to the same processing power, do you?
  • FestYboy
    FestYboy Posts: 3,861
    Agreed, a basic CD/BT HU is all that's needed here.

    As for the tweets, I'd cross them a bit lower and band-pass the 3.5, or just put an L pad on the tweet since it seams that the 3.5 and tweet will remain passive (but if the urge overwhelms you, the SS Stealths and AC will easily allow each speaker to be controlled separately with all XOs completed prior to any amplification).

    I also wouldn't worry too much about the heat from those Stealths, they're very efficient... SS amps are typically underrated too.
  • JLStice
    I was considering building a butterworth-ish thing to put up in the dash with the 3.5's and run wires to each coil separately from there. It's been ages since I have wound my own inductors, but my parts bin is looking scarce. This is the kind of project I like... buy new thing... immediately take it apart and make it 'better' ;-)
  • JLStice
    Eh... I did sweeps on the tweeter alone with the factory cap, it's still quite sensitive well into the hearing threshold crossed over at 16K, it is just a 1st-order passive so it's quite audible a decade below that - fine. I did split the caps to each coil so tweeter and mid caps are parallel not series now. Staging is clearly dash-height now, much better!

    Newer Jeeps have pillar-mounted t4's which make sense... you sit up pretty high in a Jeep. The WJ's are a mess: If you have the base system, the 6x9's in the doors are just parallel wired with the 2.5's in the dash, putting the muddled sound stage below your knees, with the infinity amp the 6x9s are at least filtered, but the paper 2.5's lack both crisp highs and a full vocal range in both cases. Some say the Infinity Reference 3.5's and the Kenwood 3.5's will drop in if you cut a mounting tab off. Not only do those two not handle the same power as the Polk, they still would have to bounce sound through that tiny little hole. NOPE.

    "Pics or it didn't happen"
    Old Infinity 2.5" paper 'tweeters' and their high-class 1/8" thick mopar plastic honeycomb -

    New DB351's mounted into the dash with plain metal 'nothing-to-steal-here' grilles:
    I might hunt around for some black screw-caps for those holes.
    Non-descript mesh cover:

    If you own a WJ and want a challenge, and understand this is a one-way street...
    To get the Polk DB351 in the WJ dash:
    Pull the crescent moon up and out (just clips), remove the cardboard speakers.
    Then cut off both mounting tabs and then all expendable plastic you can find just shy of the mounting bolts for the dash itself, and cut backwards almost up to the dash edge.
    Cut the holes out of the crescent moon trim part (old hole outside edge is out-side most edge of new hole, it is -not- centered over the old 2" hole).
    I used a thin rod tip on a soldering iron as a hot-knife against a cardboard outer-ring template from the back side, and a lot of patience.
    Speakers get mounted through the trim piece with the grille screws clamping it together using clips behind the edge of the basket.
    Make sure to rotate them because the wires can't face directly towards the back because...
    The magnet has to be forced past the edge of the dash (even after all that cutting).
    Once you force them in, the magnet sits right against the fire-wall rubber-mat, no rattles.

    Here's a shot of the trim lifted up:
    You can see the small chasm that I had to create to fit these.
    There is double sided automotive 3M tape holding the caps to the basket in just the right place - The caps have to be wrapped around and fixed to the side of the basket facing the middle of the Jeep. I tried to fit a set of RF4's in there first, which is how this project got started, doing so would require cutting the firewall. DB351s fit just-barely.

    Next step:
    Finding an orphaned pair of 6.5"s from a DB6501 set to put in the front doors and a set of DB651's in the back doors.
    -OR- I get creative again and squeeze a set of DB840's in the front doors... Should I? Do I dare?
    840's are a total inch taller than the 6x9's with the glass limiting the back depth, but there is an inch of space behind the door panel where it bumps out toward the seat...