Zero-modification custom built square Subwoofer for under rear seats

[ardjr20]

I’ve seen a lot of posts here with custom built boxes for under the seats. I wanted to show the setup I made since a lot of the builds involve a non-square box or modifying the space in some way to make it fit. I wanted to do something very straightforward and simple that could slide right in. The Sub I got was the Skar VD8 2ohm. Running a 1200 watt RMS amp that pushes 800 RMS at 2ohm which is perfect to run 2 Skar VD8’s which have a RMS of 400 each.
For the box I used some sanded half inch plywood I had laying around. Half inch isn’t ideal for larger sub but for an 8” sub it will work. And for my purposes I couldn’t use 3/4” because this was built to just above the minimum in terms of required volume. Dimensions are 7.25” tall. Can’t make it any taller and still have it fit under the lip by the door. This also gives you room for a 2” tall sub guard to be installed to the box. Haven’t installed that yet but will.
Box is 15 in length. Again really can’t make it any longer because of the design of the bottom of the bin. Width is 8.5”. Cutout for the sub was just under 7.5” so with 1/2” on each side and the bottom of the bin is exactly 8.5” so really can’t make it any bigger or smaller. Going to build a platform to mount the amp between the subs on the hump in the middle.
Just wanted to show that you can make something very simple and clean that will fit with no modification or building a weird shaped box.

Links:

Sub: https://www.skaraudio.com/products/vd-8-inch-car-subwoofer

AMP: https://www.skaraudio.com/products/rp-1200-1d-car-amplifier (If running 2 subs)
https://www.skaraudio.com/products/rp-800-1d-car-amplifier (If running 1 Sub)

High Level Input adapter for connecting AMP to Front door speakers: https://a.co/d/h5JeB8J

Speaker Box Fabric: https://a.co/d/aQp7npF

Sound Deadening Material: https://a.co/d/48VvDO9

Video on how to tune your amp:


All in cost including the tweeters, midrange door speakers, and coaxial 4x6's in the rear columns, adapters, materials, amp, sub, sound deadening. $650 This can change very quickly as you change brands. I went with Skar as decent budget option.

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[BingoDingo]

Interesting! Can you detail wiring and head unit integration?

 

[Chris_G]

Details on sub? Part number

 

[ardjr20]

Interesting! Can you detail wiring and head unit integration?

Sure thing. I haven’t wired everything up yet. But this is my plan. I’m running 2ohms subs and my final load at the amp will be 2ohm so I will wire like this.

These are 2 coil subs so they have 2 positive and 2 negative. You connect the a positive to a negative on each. Then I ran the other two to the wiring cup. Then from there to the mono block amp. If it has two sets of outputs on the mono block amp then you can hook up 1 sub to each. If you have one then you need to get both positives and both negatives into the same wire output.
As far as amp input I bought a kicker RCA to high level input adapter like $20 on Amazon. That requires you run speaker wire to the front door speakers and tap into the positive and negative run the wire back to the adapter and then from there it’s just a simple RCA plug in. Use the front speakers not the rear because factory head-units often reduce the base signals going to the rear speakers. I’m replacing the front door speakers anyway so it’s not a big deal to run the extra wire.

https://www.amazon.com/Kicker-KISLO...ocphy=9007478&hvtargid=pla-568052270134&psc=1

 

[ardjr20]

Details on sub? Part number

https://www.skaraudio.com/products/vd-8-inch-car-subwoofer

This is the one I bought. It’s a shallow mount 8”.

https://www.skaraudio.com/products/rp-1200-1d-car-amplifier

This is the amp I’m using.

https://www.skaraudio.com/products/rp-1200-1d-car-amplifier

 

[Chris_G]

https://www.skaraudio.com/products/vd-8-inch-car-subwoofer

This is the one I bought. It’s a shallow mount 8”.

https://www.skaraudio.com/products/rp-1200-1d-car-amplifier

This is the amp I’m using.

https://www.skaraudio.com/products/rp-1200-1d-car-amplifier

Thank you @ardjr20

 

[MavDave]

I’ve seen a lot of posts here with custom built boxes for under the seats. I wanted to show the setup I made since a lot of the builds involve a non-square box or modifying the space in some way to make it fit. I wanted to do something very straightforward and simple that could slide right in. The Sub I got was the Skar VD8 2ohm. Running a 1200 watt RMS amp that pushes 800 RMS at 2ohm which is perfect to run 2 Skar VD8’s which have a RMS of 400 each.
For the box I used some sanded half inch plywood I had laying around. Half inch isn’t ideal for larger sub but for an 8” sub it will work. And for my purposes I couldn’t use 3/4” because this was built to just above the minimum in terms of required volume. Dimensions are 7.25” tall. Can’t make it any taller and still have it fit under the lip by the door. This also gives you room for a 2” tall sub guard to be installed to the box. Haven’t installed that yet but will.
Box is 15 in length. Again really can’t make it any longer because of the design of the bottom of the bin. Width is 8.5”. Cutout for the sub was just under 7.5” so with 1/2” on each side and the bottom of the bin is exactly 8.5” so really can’t make it any bigger or smaller. Going to build a platform to mount the amp between the subs on the hump in the middle.
Just wanted to show that you can make something very simple and clean that will fit with no modification or building a weird shaped box.

Links:

Sub: https://www.skaraudio.com/products/vd-8-inch-car-subwoofer

AMP: https://www.skaraudio.com/products/rp-1200-1d-car-amplifier (If running 2 subs)
https://www.skaraudio.com/products/rp-800-1d-car-amplifier (If running 1 Sub)

High Level Input adapter for connecting AMP to Front door speakers: https://a.co/d/h5JeB8J

Speaker Box Fabric: https://a.co/d/aQp7npF

Sound Deadening Material: https://a.co/d/48VvDO9

Video on how to tune your amp:


All in cost including the tweeters, midrange door speakers, and coaxial 4x6's in the rear columns, adapters, materials, amp, sub, sound deadening. $650 This can change very quickly as you change brands. I went with Skar as decent budget option.

What 4x6s did you use? What adapter did you use for this? I would like to go to 5.25s in the rear pillar but I doubt there will be enough room. Any details would be great.

 

[OleFordGuy]

Well Done

 

[ardjr20]

What 4x6s did you use? What adapter did you use for this? I would like to go to 5.25s in the rear pillar but I doubt there will be enough room. Any details would be great.

https://a.co/d/g1l16QO I've seen other people use these with no mounting adapter.

I'm trying these. https://a.co/d/cl9MoWS

I Haven't gotten to actually replacing all the stock speakers as I have been focused on getting the sub boxes built. Hoping to get to installing everything this weekend. Will update you on if they fit.

Edit: Sorry I realize you might mean the wire adapter. You will want https://a.co/d/gv5ga7M. Ths is the one for the rear and tweeters.

 

[ardjr20]

Well Done

Thank you. Was my first time building speakers boxes. Carpet looks great on the tops and the long sides. Not as pretty on the two ends I can for sure see the seams but with the way I am putting the amp in the middle no one will ever see that. Building furniture is one of my hobbies so building the box was the easy part for me. I haven't carpeted the second box yet so hopefully that one comes out cleaner.

 

[colinl]

First of all, congrats and nice work regardless, but definitely great for your first box. The box in my Maverick was also my first.

Did you happen to take any pics of the box after you cut the hole for the sub, but before you installed it? It looks like you're very near the edges of the box.

People have built wedge-shaped boxes that fit in the area without removing or modifying the plastic insert. If Ford hadn't molded in those nearly-useless FITS slots, we would have at least another inch of space to use. Maybe closer to 2.

 

[ardjr20]

First of all, congrats and nice work regardless, but definitely great for your first box. The box in my Maverick was also my first.

Did you happen to take any pics of the box after you cut the hole for the sub, but before you installed it? It looks like you're very near the edges of the box.

People have built wedge-shaped boxes that fit in the area without removing or modifying the plastic insert. If Ford hadn't molded in those nearly-useless FITS slots, we would have at least another inch of space to use. Maybe closer to 2.

I don’t have any pictures of the cut out but it was right against the edge. We are talking maybe a 1/16th of an inch between the end of the cut out and the inside of the side wall. Sub wasn’t rubbing against the side though. It helps that the sub is just under 7.5” so that little bit of play makes it so it doesn’t rub.

I honestly thought very long about cutting out the Fit things in the bins to get the extra space. But ultimately decided I wanted to avoid any permanent modifications. I also considered going with wedge shape but with never having made a speaker box before I didn’t want to over complicate it. Would have gotten a little more volume that way which I know makes for a better sound. I’m excited to install everything this weekend.

 

[MikeyG]

Looks great! What the ct ft? Also do you have pics of the build and what did you use screws or nails to put the box together?

 

[ardjr20]

Looks great! What the ct ft? Also do you have pics of the build and what did you use screws or nails to put the box together?

I don't have any pictures before I put on the carpet. I used pocket screws for the first one because I wanted to dry fit it before gluing. If you use pocket screws you have to fill all the holes. Took way too long so for the second one I shot it with my nail gun. I used a lot of glue for both and ran a nice bead over every seam on both the inside and outside. I cut out the hole for the top first so I could still reach my hand inside to seal that seam. Gave it a nice sanding after that to get rid of any sharp edges. If you were going to use screws I would only use the very very skinny screws since it is only made out of 1/2". I did drive a few finishing screws that I had left over from another project into both for a little extra strength. You absolutely have to predrill or you will split the wood. These are similar to the screws I used. I'd probably go with 1" rather then 1 1/2" but I used what I had. I'd recommend gluing and nailing first. Then coming back with the screws at the end.

https://www.lowes.com/pd/GRK-8-x-1-...O374NiJCySe7IV0ftkoaAjTAEALw_wcB&gclsrc=aw.ds

Cubic feet: (8.5-1) * (15-1) * (7.25-1) = 761.25 / (12^3) = 0.44 ct ft.

 

[MikeyG]

I don't have any pictures before I put on the carpet. I used pocket screws for the first one because I wanted to dry fit it before gluing. If you use pocket screws you have to fill all the holes. Took way too long so for the second one I shot it with my nail gun. I used a lot of glue for both and ran a nice bead over every seam on both the inside and outside. I cut out the hole for the top first so I could still reach my hand inside to seal that seam. Gave it a nice sanding after that to get rid of any sharp edges. If you were going to use screws I would only use the very very skinny screws since it is only made out of 1/2". I did drive a few finishing screws that I had left over from another project into both for a little extra strength. You absolutely have to predrill or you will split the wood. These are similar to the screws I used. I'd probably go with 1" rather then 1 1/2" but I used what I had. I'd recommend gluing and nailing first. Then coming back with the screws at the end.

https://www.lowes.com/pd/GRK-8-x-1-...O374NiJCySe7IV0ftkoaAjTAEALw_wcB&gclsrc=aw.ds

Cubic feet: (8.5-1) * (15-1) * (7.25-1) = 761.25 / (12^3) = 0.44 ct ft.

Ok thank. Figured the screw would most likely split the 1/2” looking forward to seeing everything done.

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