question for those that build fiber sub boxes

[stich626]

hello.. this isn't for a truck but.. a good cause
my monty SS it's an 86, now these cars in the trunk ,right behind the rear seat, have a shelf thats higher than the rest of the trunk floor..
I want to build a box that sit here and the drivers facing the seat .
I will be sealing the box face to the seat back cars framework(not the seat back itself) the rear deck(that on this car is tiny) and the shelf and the rearseat support frame crossbraces. as I really hate cars that boom boom boom just as loud in the trunk as the seating area..I want it all in the seating area, not the trunk(well as much as I can,HA)
I plan on cutting the seat back foam(junkyard seat back) and recovering the cloth. so that the sound doesn't have to fight to get through the foam..
now remembering "lite is good" I was thinking alum angle to build the basic frame(bones) then make fiberglass panels that cover that.. the shelf is 4'+ long would I have to brace the lenth so the fiber panel doesn't flex with the air movement, and if so, every foot, 18", whats a good standard, the box will only be 15" tall at the most (ballpark figure)
now the front panel that the drivers are screwed to..something tells me just fiberglass isn't gonna hold up all that long. without stress cracks and then failure.. mdf is heavy as hell.. would 1/4 plexy work, or would something else be better(chip board/plywood)?? then cover in fiberglass, tho, that is somewhat pointless as no ones gonna see it..
I say lite as this car will see solocross like events and drag raced at times and a box that is lite helps here, 1) it won't totally screw with the set up and 2) lite enough to take out for those times you want it out..

it will be a dual driver box.. may or maynot port the box. if ported it will port into the cars factory 4by10 deck holes or ?? a tuned port in the face fire'n at seat??
with te area each driver would have a sealed box would more than likely be best(and tighter).. but power hungry..


thanks for any input on this.. fill my gray mater with ideas..

[jimmydean]

Fiberglass won't stick to plexy, but if you use 1/2" MDF for some of the structural with glass, it will be solid. Use the glass to form braces that will reduce flex, as well.

One option I did in a VW bug was cut a section out of the rear seat for the face of the drivers (4 - 8" subs) then built a grill with the edge padded. It was very comfortable and the subs had nothing to fight through.

Another option was a single sub in a bandpass enclosure and the ports went through the rear deck speaker holes. Looked factory, sounded awesome. Could be done with 2 subs if you wanted to, or the same concept applies for a ported box with the ports in the speaker holes.

[tubbedII]

Sounds time consuming, but I've never done fiberglass. I would think once the speakers and amps are all mounted, the car would probably still be better off on track days without it inside the trunk.

I'm not trying to say you shouldn't do the fiberglass, but have you considered just designing a regular MDF box that's easy to take out. It might be heavy, but incorporating some handles or ledges for grip should make it simple enough for 1 person to do it since it's just a rectangle.

[jimmydean]

I play with fiberglass all the time. If you use the fiber mat (not the woven mat) it has great structure. If you take your time, use as little resin as possible and get all the air out of each layer, you'd be surprised at how sturdy and light it can be.

Woven mat works, too. But if you want sturdy, I would use the thicker fiber mat (used to make showers and tubs).

I'm having a tough time with the mental image, post up a picture of the area and design.

[pockets]

Plexiglas won't be nearly strong enough. Even with fiberglass you want the speakers mounted to mdf rings.

If you wan good sound quality then you want a really rigid enclosure. That means thick mdf or a pretty solid fiberglass enclosure. The worst thing for subs is flexing and you'd be surprised at how much pressure a sub can generate in a sealed box. Fiberglass isn't really good on flat panels if you don't want it to flex. Chip board and plywood have the same problem which is why mdf is used so much. Mdf's density makes it ideal.

You could go with a pair of 10s or a single 12. You be surprised at how much sound you can get out of that. I even had a box with three 8s that rocked pretty good and was easy to take out.

If you wanted to be really different you could put 8's in a small door panel enclosure and just have a simple amp rack in the trunk. It will be tight but u can get enough airspace on a custom door panel. I've done it and it is pretty sweet.
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[pockets]

One other option is to use one of the shallow subs out there to reduce space needs. I hve a jl audio 13tw5 in my truck and it sounds great. Just over a cubic foot of air if I recall. I have that and two amps behind the seat in my 87
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[stich626]

thanks for all the replies..

[motornut]

i built boxes for my 81 lemans
same rear area
10.5 high slight incline to match the seats(fit under the 4X10 in stock spot)
cut foam outa the back of the seat
cut the metal straps holding the seat back in so i could lift up and out removing the seat back and see the subs
even with the seat in it moved my hair.....but i had more then lol
i made the boxes with 5/8 MDF with ported Crunch 10 inch subs
port was 3 inch wide 7 long i think pvc pipe
made to the "right" size the box should go into the trunk space maybe a foot
a sub needs the right size box to sound good
cut and glued the box seams with wood glue
the maker of the sub would be able to tell you the size needed
this is one pic i have still but i still got em if you wana see em
prob got the plans still too

[stich626]

thanks, I won't be cutting out the cross bracing.. but.. was your's 10.5" because you mounted the amps above it.

[motornut]

the amps were mounted on the back
10.5 to fit under the rear speakers in the stock location

[AceX]

I wouldnt bother with modding the rear seat. Instead, I would run a port into the rear deck. I dont care how small it is, its big enough to run a port for any sub or series of subs you plan to run.

You also dont have to get crazy with fiberglass OR plexi. Design the box so the sub fire into the trunk, and the magnet sit above the 'shelf' so you can retain as much trunk space as possible, With this consifguration, the box will look kind of like an 'L' block on Tetris, but it will be rigid and sound pretty good. Make a "filler panel" for the front face of the box in the trunk, add some accents or amps.

[stich626]

Originally Posted by AceX

I wouldnt bother with modding the rear seat. Instead, I would run a port into the rear deck. I dont care how small it is, its big enough to run a port for any sub or series of subs you plan to run.

You also dont have to get crazy with fiberglass OR plexi. Design the box so the sub fire into the trunk, and the magnet sit above the 'shelf' so you can retain as much trunk space as possible, With this consifguration, the box will look kind of like an 'L' block on Tetris, but it will be rigid and sound pretty good. Make a "filler panel" for the front face of the box in the trunk, add some accents or amps.

thanks, but if you read my post, I don't want the trunk to go boom boom boom.. so the sub "fire'n" into the trunk is a no go..
removing the foam from the seat infront of the subs themselves will allow more sound into the cabin ,and less in the trunk.. if I was sitting in the trunk ,then I may want the sound there, but I'll be in the cabin .
if I wanted a buzz'n deck lid/lic plate I'd just through anyold box in the trunk..
the fiberglass was for weight.. mdf is heavy as hell,
I like my cars to handle, but looks like mdf is what I'll end up use'n..

it'll be b/a pros 5.25 in the kicks/ b/a pro 6.5.3 in the back and 2 jl subs
I like clear strong tight sound.. but also believe the db meter shouldn't read as high outside a trunk as inside the cabin..
thats just me..