[M3Tuner44]

So I wanted to build a sub box for the 335i but didn't want to pay $300 for whats already out there. I have built a bunch of these before and I knew I wanted something stealthy and not to abrupt when you open the trunk. So I went for a simple corner sub.

To start lay blue tape in the area you decide to make your box, lay the tape beyond where you want the box to go and you can even put a couple layers on if you want. Also put some oil on the tape so the mold doesn't stick to the tape.

Apply the fiberglass resin to the tape and then start to apply your fiberglass on top of that, then put more resin on top. You really only need 1-2 layers of fiberglass while its in the car. You car will smell for a couple weeks, so you don't want to do all layers in there or else it will get pretty bad. I did 6 layers.






So I knew I was going to use a capacitor with my setup and like I said I wanted it all to be clean when you open the trunk so I decided to put the capacitor in the trunk. I first used construction paper to cut a template for the break point and then transferred the template to 3/4 mdf. Also at this time you can trim the box and cut it to how you want it to sit in the car.







Then I fiberglassed the breakpoint section and also fiberglassed the capacitor holder.






Then it was time to make the sub ring. My routing bit on my dremel wasn't working so I used a marker to make the outline and then cut out the ring with a jigsaw. I wanted the subwoofer to be flush so I also cut a 3/4" trim ring.






Then decide how you want the sub to sit and hot glue wooden dowels in order to hold the speaker ring in place.





Now after you have that all placed take some stretchy fabric or shirt and cut it in half so its not layered. Spray 3m 77 glue onto the sides of the box and stretch the fabric tightly over and give it time to settle, this glue tacks right away so you can apply to fabric immediately. Then apply resin to the fabric and let it harden, don't apply to much pressure at this time or else the fabric may collapse. After its hardened apply a few layers of fiberglass. After thats hardened put some fiberglass between the sub-ring just for added strength.



It was raining this day so I used my electric heater and an air purifier/pusher.



After 2 layers of bond and a lot of sanding. If your going to lay carpet over it, then it does not have to be completely smooth and filed in but if you are going to paint it then you will have a lot of work getting the waves out and filling in each pinhole because it will show.





Carpeted and fit perfectly. It sits right in the tray about the logic7 amp. This setup does not move at all even under aggressive driving. It holds in there really well even without bolts or velcro.






I will be covering this with a carpeted grill so its hardly noticeable

[335iJWC]

Very nice! hows the sound?

[M3Tuner44]

Originally Posted by 335iJWC

Very nice! hows the sound?

It sounds good. Definately better then stock. It's the proper size box for the sub

[blingman]

How much to make another? or group buy?

[2turbodinan]

Well done lad! Sometimes it seizes to amaze me how creative people could get on these forums

[M3Tuner44]

Originally Posted by blingman

How much to make another? or group buy?

I've made a few for others and i've charged $240. It depends on what car you have. If you have an e92 I can use my car to make the mold, but if you have an e90 ill have to use your car.

[import36]

looks great! but this is definitely something i wouldn't attempt to DIY!

[CharlieBear]

looks good! yeah not a DIY for my at least.

[illrider]

Great write up. Wish I had the tools/experience to pull it off. Too bad you aren't local otherwise i'd pay you to make me one for my E90!

[kiwi29]

EPIC.

[Ch3ss]

great diy very helpful. just wondering can you tell us how much you spent on materials.

[M3Tuner44]

Originally Posted by illrider

Great write up. Wish I had the tools/experience to pull it off. Too bad you aren't local otherwise i'd pay you to make me one for my E90!

In the process of possibly making one for another member, I can ship!!

[taz2ko0]

Where did you mount the amp?

[M3Tuner44]

I put the amp right under the decklid. You can't see it unless you duck down and look into the trunk. If you just standing you can't see anything. For only a 250w amp it hits very hard. I have a PAC trunkloc connected to my factory suns so I can adjust the bass for the sub right from the front and don't had to adjust the amp. I have the bass boost on the amp off and the bass completely turned down on the factory settings and it still hits very hard.

[lightning_x1]

Originally Posted by illrider

Great write up. Wish I had the tools/experience to pull it off. Too bad you aren't local otherwise i'd pay you to make me one for my E90!

Very nice work indeed!

[Delusive]

Great DIY Guide

I was wondering where are you located and will you be taking orders? cuz i'd buy one, maybe two.

I'd do it myself but no tools or garage to work in.

[M3Tuner44]

Originally Posted by JS-NA.E92

Great DIY Guide

I was wondering where are you located and will you be taking orders? cuz i'd buy one, maybe two.

I'd do it myself but no tools or garage to work in.

I am on Long Island. Yea PM me if interested.

[onesuperboi]

Awesome bro!

Do you have any more pics of how you wired the sub?

[Jat_E92]

I've started this too, at the stage of displaying the matle for the sub. Need to go and get a heat gun and some putty tonight and will hopefully have it placed up and puttied. Sanding tomorrow!

[bootleg]

Ill buy one too if your still willing to make them for e90s

[Jat_E92]

My effort, slightly different but I am chuffed with it! Can't wait to get it connected this week.

[Jat_E92]

I'll try that again