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Thread: Aftermarket Sub

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    Aftermarket Sub

    So i've got rid of the useless Bose sub, and upgraded with a rather lovely JL Audio W3. I bought this through the internet recently and the item was new. I've wired in an Apline amp, and obviously the whole lot is running through an aftermarket (Pioneer) headunit.

    Now the issues, i'm getting loads of interference through the head unit, hissing, whistling, buzzing when the lights/indicators are used. I'm aware that this is likely to be the ground, though i've yet to find a decent earthing point either.

    Main issue though, the sub works well, though makes a weird rattling noise, at all volumes (almost sounds like a screw has been left on the cone and is rattling about). When pounding out serious volume the sub seems fine, though the rattling is still audible. The cone is still well attached to the basket and there is no obvious issues.

    I've tried amping another sub, which worked normally, does this sound like a terminal problem?

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    If you press the cone in with your hand can you feel any roughness to the movement? It should be totally smooth.
    Is the JL unit a dual vc sub and if so how is it wired up at the moment?
    If the cone is in one piece then the only other damage is the voice coil, and these will always burn out before before the cone becomes damaged. Could be a slight fracture to the VC which is audible but not preventing the unit from working. If the VC is totally shot then the sub wouldn't work at all.

    Regarding the interference, how is the Pioneer wired up? Is it running all speakers on it's own internal amp or are you using a seperate amp for them as well?
    Presumably you've run new RCA's for the Alpine amp.
    What Alpine amp is it?
    If everything is wired up correctly then the first place to start is to add in your own earth lead to the chassis of the HU directly onto the bodywork of the car, behind the glovebox - the Audi earth on the black ISO connector is not very good, and this will give you a ground loop if the earth on the Alpine is better.
    Likewise with the earth on the Alpine. Where is this connected and how well?
    You usually need to grind off any paintwork from the surrounding area.
    I've installed plenty of Alpine V12 amps in S3's and by mounting them behind the rear speaker panel you are able to use the big allen nut on the seatbelt slide bar as a pretty good short ground.
    Failing all of the above then you'd nee to buy a ground loop isolator, but you really shouldn't need it

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    Just went out to test the bass, i can't really judge if it's rough or smooth to be honest. It's strong though and feels quite tight if that makes any sense.

    It is a JL W3V2 D2 (Dual VC 2om). I think it's currently wired up as such if memory serves me right.



    The amp is an Alpine MRP-M450, Monoblock that produces 400W RMS at 4ohm, so i'm trying to draw 4ohm, though it took a lot of head scratching to work out the correct wiring.

    My concern straight away was voice coil when i heard the noise, it was listed as new on eBay but looks to have been an ex-demo or something.

    About the headunit, i shall try another few earth points to see if i can get a cleaner signal. The headunit is connected up to the Bose Amp and RCA's connect up to the Alpine amp. The Alpine amp has a solid earth, onto the chassis, i rubbed down the paintwork for a cleaner connection.

    I'll sort the headunit wiring another day, but i'm guessing it rather sounds like my sub has had it
    Last edited by A3Andy; 10th October 2007 at 18:18.

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    I meant push down on the cone without it turned on. The cone should move smoothly in & out, if you feel any roughness or if it's not totally silent then the voice coil is damaged.
    the mrp-m450 is 2 ohm stable, so maybe worth just wiring up one voice coil, and see what it sounds like, and then the other, as only one might be damaged.
    That amp is actually only pushing out 220wrms @ 14.4v with a 4ohm load, so is a bit underpowered for that sub, you'd actually get better results running it at 2ohm via a single VC. Not sure if running just one VC is recommended though.
    It's really the wrong spec for that amp - you need the 4 ohm version which wired in parallel would give you a 2 ohm load = 400wrms
    Not surprised you're getting interference on the Bose system - how have you connected the RCA's to the pre-outs on the HU?
    Does it have it's own sub out pre-out?
    What adapter have you used to plug into the Bose amp?
    The Bose system doesn't really work well with aftermarket HU's, you'd be better ditching the Bose amp and upgrading the front components an running them directly off the HU. Forget the rears, the Bose rears are a complete joke, my 2 year old has better quality units in some of his toys.
    Last edited by AndyMac; 10th October 2007 at 19:49.

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    Definately looks that way...bugger. What a mess...

    Back to the Headunit anyway...the Bose Amp is wired through one of the preouts of the new Headunit. It's connected via an autoleads splitter thing. I would go through and add new components but i really cant be dealing with stripping the doors/car apart again, i'd rather limit the noise tbh.

    The rears are already disconnected, definatley not worth the overpriced upgrade, absolute crap

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    That's the right way to do it but unfortunately the Bose system is far trickier to upgrade than the non-Bose, you really have to ditch all the Bose stuff for best results. You can't even run the front Bose speakers off the Pioneer HU as they are 2ohm, and to upgrade the fronts also requires rewiring, or at least running new cable all the way back to the Bose amp and pick up the speakers there.
    If you disconnect the RCA's going to the sub amp is the interference still there?
    Effectively you've got 3 different earths, one for the HU, one for the Boe amp and one for the Alpine, so any imbalance between the 3 will cause a ground loop. If the interference disappears when you disconnect the sub RCA's then the easiest route is a ground loop isolator on the sub RCA's.

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    That's a very good point.

    If i disconnect the RCA's for the Bose amp, there is no sound whatsoever. Is it more than likely the ****ty Bose amp causing all this trouble then?

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    Well it's the unique way the Bose amp is connected to the HU (really crappy unscreened wiring), but I meant disconnect the sub RCA's (not the Bose ones).
    This will tell you if it's related to the sub amp.

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    Nope noise exists without the sub connected.

    The wiring for the Bose set up did seem a bit...'rubbish' when i was installing the sub & amp...

 

 

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