X5M E70 - Subwoofer (Invisible but not Stealthbox)
 

I just bought my first BMW, which is a 2011 X5M with premium sound (16 speakers, 600W) and it sounds ok, but I am not sure I get the "premium" point as with 600W there is no deep bass, there is base, but it's not deep. System is loud, but bass is not deep. My computer speakers (Logitech 4.1) have a deeper base. I have never had an aftermarket sub in a car before, but looking to have one or two added (do not expect to swap any of the existing speakers bur rather to add). The goal is to keep the trunk stock/empty and hide sub in the spare wheel space as I have it free. I was kind of sure on the JL Stealthbox, but read online that it rattles the lid that covers the trunk area. Also, I would rather use the wheel well and keep the close storage compartment available as it's more useable. I would not want to modify the lid in the trunk with wholes/openings/meshes installed and would prefer to keep that lid as is. If I am looking to spend ~500-1500 just for sub(s) with enclosures (and then amp with JL RD500/1 in addition to that) what are my best options? I am thinking of the way to have JL's W7 either one 10" or 2x 8" in there in a custom or prefab box but not sure it will fit. I have seen Audioson flat box with 10 for 400, but not sure how it compares to JL as JL seems to be the best.
My targets are:
1. good base that adds to music, not just a boomy disaster
2. empty trunk and the lid with no wholes
3. removable/transferable to another vehicle sub
4. preference not to change/upgrade any other elements of the system at this point so the added sub should sound good with the stock premium system

Can JL W7 be hidden underneath? 8 or 10? 8x2? Audioson? Anyone has had good results on 1-2k budget by adding to premium system?

I don't think you can have your cake and eat it too. If you recognize that a decent sub in the spare tire well is going to rattle the thin cover, then if you want the sub in there, it will require a more sturdy cover, very possibly with a cut out/grill. And a grill in the middle of the cargo floor will definitely collect dirt or debris.

If it were me, I'd have a car audio shop build a custom fiberglass enclosure that replaces the removable panel that covers where the audio equipment is. If you want to use a W7, even the smallest ones are fairly deep and would have to be built out a couple of inches. But a good shop could make it look somewhat 'factory'. Or get a flat style subwoofer...they do exist, and will never match a W7, but will still be a huge upgrade. Just make sure the custom enclosure is easily removable in case you need access behind it.

Another option that I used in a prior car was I got a single W7 in a JL wedge shaped enclosure and just kept in the corner of the trunk. If I needed 100% of the trunk for a trip, I just took it out.

Thank you Skyline. If I stick a flat sub under the lid, will it rattle you think? I mean without modifications to the lid. Whats the best flat sub out there?

I can't answer either of those questions. I think a sub in the left rear, (or both left and right rear hatches,) would allow you to have a sub with nothing but speaker cloth hiding it...you would not be forcing the sub to vibrate the floor panel. I know there are some decent flat subs, (by flat I mean 2-3" deep instead of 6+" deep for an 8" W7.) Ask a car audio shop.

Thank you, I have seen some youtube videos with some expensive custom jobs and 2x10" under the lid with ni mods to the lid and saying if there is "enough" space between the subs and the lid the air will move around without rattling. I guess one way to find out).
One other thing is that i would want to buy a good sub and keep the sub after I sell the car in a couple of years. This leaves me with generic shapes whether pre built or custom. It may be that I end up just putting it in a trunk. Would prefer to avoid it. Whats worse compromise, design flaw with a box in the trunk or buying a sub I dont want just cause it fits. Decisions...

That 8" W7 in the JL wedge box puts out quite a lot for its small size, and it can handle plenty of power. The JL wedge box is built VERY solidly. I had a separate 300w JL mono amp running it. You could just strap it down in the cargo area.

Thanks Skyline, I was looking at JL RD500/1 as base case. I read that lights dont deem with it while it gives good power. How did you decide on 8 vs 10? And one vs two subs?
did anything vibrate, like the trunk itself? I mean the actual trunk lid. It is awkward when you here the whole car including the license plate is shaking. )

I’ve installed subs in several of my past BMWs that didn’t have good low end and never had a bad issue with vibration. I even built a custom enclosure that fit in my spare tire we’ll just like you’re talking about for an old three series. Couple rattles here and there, but I was after quality sound and not boom noise and with a little bit of finesse got rid of any issues. I haven’t messed with anything on the X5 though. It’s not theater quality or anything but it’s fine compared to what I used to have to modify.

I just used a single 8" W7 in their very strong JL box, and had it in the trunk of a G35 sedan. It did vibrate things a little in the trunk, especially the trim on the trunk lid. I solved that by removing the plastic trim, covering the entire (now exposed) trunk lid with Dynamat, and replacing the trim panel. I had the doors of the car completely lined with Dynamat as well....MB Quarts in all the doors. That was a really great sounding car stereo. I had two JL AMPs, 4x75w for the doors, and a 300w mono for the sub.

But I'm not keen on heavy bass; I'm more into natural sound so YMMV.

Just visited another audio shop today (for the total of 2 over the last week) and nobody is keen to install a sub under the lid. The preference is to stick a box into the trunk. I really liked the look and feel of the all-across-shelf style box with 2 downfiring subs, but it blocks the ski hatch, prevents me from lifting the lid and prevents me from using the space if I need to fold down the seats. Started considering a box in the trunk and thought of 8" W7, but the owner told me it's too much of a speaker and its inefficient and for me as to sound good I would need at least a $1000 amp and for a cheaper amp (~C$500) I would need a different speaker, like Alpine or at least something more modest. I was also told that JL RD500/1 is by far inferior to Alpine and Rockford dollar-for-dollar and was offered a 750W Rockford for C$400or a 1000W Alpine for the comparable to JL RD $450...

The best part is that I got quoted $500 labour for amp install + $100 for wiring.. I was rather shocked as even though I want the knob wired to the front, the battery is in the back, the stock amp with connections is in the trunk area (left hatch). I was told 8 hrs of work.. not sure it's true. Another place quoted me $200 installation (all in) but not sure if it's the same quality work.

Overall when I imagine a big box in the trunk:) now seems like more of a burden than anything else... when I think that I also have to pay for it:) my excitement disappears! Back to the concept of a flat sub under the lid...

Back to the original decision - will the difference be worth C$1.5k - C$2k? for a sub given I am running premium system to begin with.. kind of gamble.