Modifying factory sub box enclosure for 10" sub
 

Hi guys.
I know a few members have modified their boxes to accept a shallow mount 10" sub (I purchased an MB Quart Discus DS1-254 to play with, as it was new on Amazon.ca for $72) but I haven't seen any write-ups.
I'm still in progress with it but figured I'd share my journey with you, including pics.

I have a factory sub box in its hidy-hole but I hated the "sound" so I unplugged the harness and enjoy my aftermarket sub and box but as of late I'm noting, that even tho it's a low profile box, it's still taking up more room than I'd wish.
So whilst at a pick-n-pull spot, I got a broken sub box for free (was missing speakers already, and the bolt tab at top was broken, but all else was dandy...so I decided to modify that and if it sounds good, I will modify my factory one and use that in place of aftermarket setup. So here I am playing with the "busted" box first to see if it's doable with my sub selected.
I also read that since the factory sub box is tiny for a 10", you can make the sub THINK it's in a larger box by putting poly-fil inside to achieve better (larger) sound. I also read ppl push the loose poly-fil inside BUT that loose fill can actually lodge itself between the sub come and voice coil and heat up the sub and damage it, SO I decided to buy sheets of This poly-fil and spray adhesive it to the inside of box first. I did a few layers in the deeper areas and the lower body section.
Before any modifications, I put the speaker side of box onto a sheet of cardboard and traced outline of it. Easy.
Then I cut off the "higher elevations" of plastic till I had a flat perimeter. This took a while and was a PITA honestly. Cutting, grinding flat, checking flatness, regrinding more... Lather, rinse, repeat... I eventually got it.
I then had to determine the new sub cut out diameter and depth of sub and measure a few places inside box where the deepest and widest parts of box were.
Basically the new sub perimeter will be touching up against the lower BOX section as that's the deepest section of box.
So my cardboard template now needed a diameter cut out. Then it was done
Time to transfer this template to actual 5/8" thick MDF
I then used a clear adhesive. More expensive than DAP or other brands, for sure, but the cure time is much shorter than the 7-14 day cure time of others too.

ADVANCES: Aug 30, 2020

So I finally got back to cutting a 7cm by 7cm square out of the same 5/8" MDF to cover over the factory harness hole.
I also bought long Binding Posts (speaker terminals) and installed into new cut square block, after I measured out size of hole (approx 4.5cm) and then determined where to drill two holes for these binding posts.
I installed the modified box into my x5 sub area and then found out where I could mount the newly cut block with binding posts. Great success. No interference at all.
Then I removed the box and block with binding posts and then I (newly learned) soldered the 10 gauge wire to and then ran inside tiny hole.
I temp held the new block of wood to the box and then outlined it with silver sharpie markers to show where the adhesive.needs to at LEAST be.
Then I used the No More Nails Ultimate and smattered on the adhesive and pressed the two parts firmly for a few seconds. Then for good measure, I caulked the box perimeter.

In a few hours/tomorrow, it's time to mount my sub into box and then test :)

ADVANCES: Aug 31, 2020
OH SWEET JESUS, IVE CREATED A MONSTER.
This stereo is SICK, in a good way, not a Covid-19 way.
Super tight bass. ZERO rattles from box.
So glad I can hide my sub away now, giving me my trunk back.

PS: the black plastic tray that sits in front of sub box and the cargo shelf clips into, it needs to be trimmed for sub surround. See pic below.

ADVANCES: Sept 13, 2020
Finally cut the factory cover to make a hole for sub and then put a speaker grill over hole for protection. A pic showing how much of the front and bottom lip of cover that I cut (if I had my time back, I'd have made even smaller cuts on the bottom lip but in my application you can't see the extra wide cuts (mistake) so I'm happy.


Final Thoughts:
So extremely worth doing this (since I had the boxes) but now I'm torn, as this box was just meant to be a temp box to see if I enjoyed the sound and if so I was going to modify a perfect box. This box has no ear tab at the top so it can move in place and a bit of rattling from the entire box moving does occur from time to time.
So...do I find a way to attach the top of this box to the top bolt and secure tightly OR take my learnings and do totally same thing on another box? It's very time consuming and I'm thinking the Basser brand boxes have even more cubic ft interior as they don't have same curves as factory but are also more difficult to get into place apparently.
I'd recommend this to someone who HAS a good condition factory sub box already, but if a person needed to procure and then modify, I'd say just buy the prebuilt Basser brand box and be done.

Here are the pics finally.

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That actually looks pretty solid! Nice job with leveling the face of the factory box off, I'm amazed that you cut it flat, in my mind I was thinking build up the low spots, or lay a face over everything and then seal the gaps - your way will probably net you a much longer term solution and probably a better fit under the factory body panels as well - NICE JOB!!

Cool project. Subbing for results.

Subscribed!

Ok, decent update.
I will continue to update the first post, so all info is in one post

Enjoy.
Getting excited to see if this is a bust or bonus.

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Nice work. Cant' wait to hear your opinion on the results. This is by far the cleanest way of getting good sound in an X5. Having a sub box in the corner that is, whether modified OE, or aftermarket box.

Interesting binding posts. Did they take to the solder fairly easily? Some of those I find I have to use acid and/or grind the gold coating off them before the solder will bind.

I actually like these binding posts.
I melted a drop of solder in the post/cup first.
Then, I was able to push the 10 Ga wire in the hollow post, about 1" and then I heated up the bottom side of the gold post, while the solder wire was pressed on top of 10 Ga wire and eventually the post and wire got warm enough to melt the solder into wire and to post. Seems like a solid connection.
Time will tell :)

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My other option for wiring the sub to box and box to external amp wiring, was to use the factory harness and connector BUT those wires are much smaller gauge and also the connector was meant for a smaller 6" set of subs and those will not be as violent on the plastic connection as the single 10" (if it works properly) will be, hence why I decided against reusing factory harness and connector.

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heres is my set up

eonon stero with ibus usb dsp dummy signal aftermarket stealth box and amp in driers side cargo bin

check out my video

https://www.youtube.com/watch?v=W3XOwNBQTUc

All done. Post 1 updated!!

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