Troubleshooting why a sub isn't performing well

[rogersmj]

Hi, first post here, and I'll say up front I'm not an expert at car audio so I'm looking for some helpful advice. The problem is that I think I have a pretty decent sub and amp, but I'm barely getting anything out of them.

I upgraded the audio system in my wife's 2011 Ford Edge (SEL, non-premium stereo) because the stock system was absolute crap; that's the car we travel in, and I wanted something decent.

Basically I replaced all the door speakers with Infinity Reference 6x9s at the suggestion of some people on the Ford Edge forum. When that didn't offer nearly as dramatic an improvement as I had hoped, I set about installing a sub.

I've attached the diagram below, but one additional piece of info is that I built my own box using MDF and hid it behind a trim panel in the rear cargo area (where the stock sub goes, if we would have gotten the factory premium audio system). The box is right at the bare minimum Polk recommends for this sub, but I did also stuff it with polyfill which I understand is supposed to help the box "seem" bigger for the sub.

The problem is that while everything sounds decent in the back seat, up in the front you can hardly get any real bass notes. You can pick up some of the "punch" from a bass drum, for example, but you barely hear anything more than that. And I have the amp and the gain on the RE-Q5 turned up to the max.

Right now, from the front seat everything basically sounds flat and lifeless, with a lot of the bottom end missing. I was hoping I could get close to my other car's factory Infinity system (which I think is quite good) with these upgrades in the Edge, but right now it doesn't even sound as good as the stock system in the old 2004 Accord I used to have.

My question is, what do you guys think the culprit is? Others have reported success using similarly-sized and similarly-powered equipment in the Edge, and I'm not looking for head-banging loudness. I just want a full, rich sound stage with nice bass at moderate volume. Could the box I built be bad? I tried to seal it up tight with glue and joint sealer. What could be the problem?

Thanks in advance for any advice.

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Technical details:

- Polk MM840 4-ohm DVC sub wired to 2-ohm load

- Sony Xm1S 900W (290W into 4 ohms) mono class D amp

- RE-Q5 signal processor takes speaker-level out from the factory head unit and cleans up/separates into line-level outs

- Infinity Reference 6832 6x9 door speakers with bass blockers

See attached diagram for the setup

Click to read more...

 

[wenn_du_weinst 10+ year member]

you need to use both the left and right for the line level

 

[Kangaroux 5,000+ posts]

^ this. Your box could also be the issue if you just bought a prefab. Check your amplifier's grounding point to make sure it is secured well i.e. tight and sanded down to bare metal (protecting from corrosion using silicone is a good idea). If none of that works it could be something as simple as you wired the sub wrong. For shits and giggles try switching the phase switch on your amp, or if it doesn't have one, swap the pos and neg wires going into the amp's speaker terminals

 

[rogersmj]

Thank you both for the fast response! When I got home last night I wired up the right rear channel into the RE-Q5 line processor as well, and that definitely made a difference. I should have thought of that.

So it's better, but a lot of the mid-frequency bass notes still don't fill the cabin. They're quite pronounced in the back seat, just not all the way in front. The sub is working hard -- in the cargo area, it's deafening. I'm thinking my homemade box just isn't big enough and/or sealed well enough, so I'm going to try rebuilding it at some point here.

But for now, hooking up both LR and RR made a big difference. Thanks!

 

[Heeltoeclutch 10+ year member]

I think it very well may be the box -

I tried an experiment in my car with an 8" sub - I used a Sundown E8 d2 with more than 400 extremely clean watts going to it, built the smallest sealed box sundown recommended, and bolted it to the rear deck of my car. It had polyfill. No matter what I did, I couldnt get hardly ANY bass out of it. And I know it was moving fine - I could see it in my mirror //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif I did this because I wanted to add the least amount of weight possible. But i just wasn't getting anything out of it. So after MUCH deliberation I got a 10" SSA DCON and built a 1 cube PORTED box for it, ran it from the same amp with approximately 1/4 of the power that was going to the 8" (4 ohm load vs. the 1 ohm load of the 8") and it sounded AMAZING. and that's what I'm running now.

So my advice to you would be to try and build a bigger, ported box for the current sub first, and if it that does not make the improvement you desire, perhaps go for more cone area (10" sub).

//content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[rogersmj]

Well, unfortunately I don't think a ported box is an option. As I understand it, those need significantly larger volume, and space is something I just don't have (I'm hiding this sub behind a trim panel, where the factory sub normally goes). I do think I can build a slightly bigger/better sealed box though. I might be able to do a 0.6 cube box, perhaps a bit more if I get really creative. The frustrating part about building this box is that it's irregularly shaped, and I can't exactly tell if it will fit behind the trim panel until I tack it together and actually try to put it back there.

 

[Heeltoeclutch 10+ year member]

Where did you get the box specifications for the sub? I'm looking on Polk's site with little luck //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif

edit: just found it. 0.35 cubes??? that's incredibly small. It is true that ported boxes do require more airspace, but with a sealed space that small you might be able to build a 0.6 cube ported box with a tube port and achieve what you're looking for. I'm no expert - but there are plenty around here //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[IonRL205 10+ year member]

I think it's a combination of having a small box, a small sub and low power that's just not giving you the bass you're wanting. I would look into something a different, an 8" sub like that is more like a midbass than anything. I doubt that sub will hit low in a small sealed box like that.