# Fiberglass box + subs in eco trunk



## maxxve (Jun 22, 2012)

Hey everyone -

I'm starting a project to put a custom fit fiberglass box & sub in the trunk of my wife's Eco. I figured I'd document it here so that others can use the information to do something similar if it turns out well.

Amp: Kenwood KAC-8104D 300w RMS @ 4ohms and 500w RMS @ 2 ohms. 
Sub: Kenwood eXcelon KFC-XW1200​F 12" Shallow Mount Sub
Wiring: knukonceptz 8 gauge OFC kit

Materials
1/2" MDF board 2'x4' pre-cut @ Home Depot ($8) (used for top & bottom)
1/4" MDF board 2'x4' pre-cut @ Home Depot ($6) (used for final top sheet)
Fiberglass cloth 16 sq ft (2 packs @ $5ea from Walmart)
Fiberglass mat 8 sq ft($5 walmart)
1 gallon fiberglass resin ($35 @ Home Depot) *Probably only need a quart or two

I still have to buy carpet to try to match the trunk but I've got some time before I'll need it.

I'll post pictures of the project along the way.


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## maxxve (Jun 22, 2012)

What about two of these? I know the are marine subs but they have a very low mounting depth and come with grills. 
MB Quart NLP254S 10" Single 4 ohm Flat Nautic Marine Subwoofer


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## XtremeRevolution (Jan 19, 2012)

Those tangband and dayton subs were recommended earlier for a very good reason; they model well in that airspace. Not all subs work well in that small of a space. In fact, very few subs do. Have you modeled any of these subs to check how they would sound?

If not, post in my sub box modeling thread asking for a sub box model and I can help you out.

Sent from my Bulletproof_Doubleshot using AutoGuide.Com Free App


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## edro (Apr 18, 2012)

It's funny that marine subs were mentioned, I'm looking at getting this: http://amzn.to/Nka4tS for $200 enclosed JBL 10" sub with built in 250 watt amp & just mount it in the back dash. what do you guys think?


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## XtremeRevolution (Jan 19, 2012)

edro said:


> It's funny that marine subs were mentioned, I'm looking at getting this: Amazon.com: JBL MPS1000 10-Inch 250-Watt Powered Marine Subwoofer: Car Electronics for $200 enclosed JBL 10" sub with built in 250 watt amp & just mount it in the back dash. what do you guys think?


I think it's overpriced and will not sound good in a car. The reason for this is that they're designed for two completely different environments. One is designed in a car with cabin boundary loading and pressurization gain factored in, while one is designed to be played in practically open air.


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## edro (Apr 18, 2012)

cool... Thanks for the info man


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## maxxve (Jun 22, 2012)

*Update*

So far so good. I'm going to focus on the box build in this thread because others have covered wiring for the amp. Basically what I did was take 1/2" MDF to make a bottom plate and a top plate to fit exactly in the hole. 1/2" is a little thinner than I would have liked but I needed it so I had enough volume and mounting depth for the sub that I chose. I'll add some bracing to help.

I've got lots of fiberglass cloth, mat & resin along with my fleece so tonight's project will be wrapping it so I can fiberglass the walls.

Before:










Currently:


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## XtremeRevolution (Jan 19, 2012)

Which subs are you using, and have you modeled them in your predicted airspace?

If you're concerned with the 1/2" MDF, add bracing.


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## maxxve (Jun 22, 2012)

I'm using a Kenwood eXcelon KFC-XW1200​F 12" Shallow Mount Sub. I found a great deal that I couldn't pass up. 

More pics:


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## amalmer71 (Apr 5, 2012)

Pardon my stupid questions as I've never done fiberglass, but is that gonna stick to the wood like that? Or is there a way to attach it to the wood?

Perhaps these questions will be answered as you progress, but that doesn't mean they're not popping up in my head, now.


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## XtremeRevolution (Jan 19, 2012)

Should have passed up on that deal and modeled the sub like I recommended earlier. Now, you'll have a boomy sealed sub in a box much too small for it. I figure you'll have about .8 cubic feet net to work with in that area after subwoofer displacement. I honestly don't know what Kenwood was thinking when specifying that interior volume. I guess like most box models by big name brands, it's full of compromises. The motor simply isn't strong enough to sound good in that small of a volume. 

But enough of my take on big name subwoofers. Here are the models to prove it. A Qtc of 1.08 is way, *way *too high. The highest Qtc I've ever designed a box for is around .78. If you had asked me to model this earlier, I would have told you to avoid this sub.

In-cab frequency response:









Densely stuffing it with mineral wool or fiberglass pad will help, but it's still not that great. If you insist on keeping it, I'd very highly recommend you stuff the box well with a good sound absorption material, and I don't mean polyfill, but I'd return it if I were you. 









That sub ideally needs 2x the amount of airspace you're giving it. Just because it's shallow mount doesn't mean it does well in small boxes.


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## maxxve (Jun 22, 2012)

Amalmer - the resin does act as a glue but you'll see in the next pictures I will overlap the fiberglass so it's directly on the wood which helps hold it. 

Xtreme - I know you are trying to help and I appreciate it. However, the goal of this project is to detail the process of building the box so others can do the same. I know you've got the software to create your graphs and you've obviously got a ton of experience but I've got the sub already and I'm sure it'll sound just fine. I did take your advice on the knukonceptz wiring and it was great wire.


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## XtremeRevolution (Jan 19, 2012)

maxxve said:


> Amalmer - the resin does act as a glue but you'll see in the next pictures I will overlap the fiberglass so it's directly on the wood which helps hold it.
> 
> Xtreme - I know you are trying to help and I appreciate it. However, the goal of this project is to detail the process of building the box so others can do the same. I know you've got the software to create your graphs and you've obviously got a ton of experience but I've got the sub already and I'm sure it'll sound just fine. I did take your advice on the knukonceptz wiring and it was great wire.


If you discover at one point that the sub sounds boomy, uncontrolled, difficult to integrate, muddy, thick, or just plain bad, you'll know why. I just never saw a reason to put so much time and effort into building a box, only to fit an unsuitable sub into it. It's quite rare to find a 12" sub that works well in this small of a volume, let alone a shallow mount 12". I'm glad you're posting this so others can see how it's done. I just wish you would have picked a sub that would actually sound good in that volume. 

I'm glad you liked the KNU wire. It's high quality stuff.


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