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Old     (scott76310)      Join Date: Sep 2009       12-16-2009, 9:38 AM Reply   
My wonderful wife is getting me a Boston Acoustics SPG555 sub for Christmas and I want to install it in the factory location in our Centurion Typhoon. There is all ready a fiberglass enclosure built into the floor but it is 2-3 cubic feet in size and the 555 needs exactly 1 cubic feet. I have done a lot of fiberglass work in the past and I feel very confident that I can build a new enclosure floor and sidewalls INSIDE the current enclosure to make it exactly 1 cubic feet. Once I get the new box built inside using the original front, back and top wall then it should be pretty easy to lay enough fiberglass in there to make it as thick as I want so here are my questions:

If ĺ MDF would be considered the minimum thickness, what would be considered the equivalent thickness in fiberglass taking into consideration that the box is very small. Seems like ĺ inch fiberglass would be overkill in such a small box.

My main question is will it be strong enough screwing the sub straight into the fiberglass. I plan on making the fiberglass very thick at the sub mounting surface so there will be plenty of fiberglass for the screws to bite into but I see most enclosures have MDF mounting rings. I canít figure out if they use the mounting rings to make the enclosures easier to build or if it is necessary to get the sub mounted securely without the screws coming loose. The original sub was just mounted into the fiberglass and it isnít near as thick as what I will make it but this sub is much better and I will be putting 1000 watts RMS to it and I just want to make sure that I do it right.

Any advice will be greatly appreciated, I really donít want to cut the whole thing out and build a new enclosure like I have seen some do.



(Message edited by scott76310 on December 16, 2009)
Old     (timmy)      Join Date: Jul 2001       12-16-2009, 11:45 AM Reply   
I put (2) 12's in that location in my boat in a fiberglass box. Used 1 layer of woven mat followed by somewhere around 4-6 layers of chopped strand mat. The box is definately sturdy enough. Used wooden mounting rings, might have used plywood rather than MDF but can't remember at this time. If you are going to have any large flat surfaces, consider using a sheet of wood in that area.
Old     (duffymahoney)      Join Date: Sep 2008       12-16-2009, 12:14 PM Reply   
I have an avalanche (basically the same boat) and the previous boat owner installed another 10 on the other side of the stock box. So I have 2 apline 10's in the stock box. You can't see the sub unless you look under the front bow cushions but they both pound! I think you could do something like that very easily.
Old     (grant_west)      Join Date: Jun 2005       12-16-2009, 1:31 PM Reply   
The Bostin 555 is pretty light. It uses a Neo magnet so the regular rules of trying to support a 30 to 40 pound magnet off the back of the sub Via a 3/4 inc mdf front are not as important. If it were me this is what I would do or how I would build it.
I would use a MDF face for your sub no matter how light it is. Your gonna have a nice flat surface with the mdf to mount the sub to and the screw's are gonna hold real tight into mdf. In fact I would make a MDF ring that's fiberglassed into the stock sub box. This ring would be the point where you attached the baffle (that's what the piece that's attached to the sub is called) The front of the box it's called a baffle. This baffle would hold your sub. You would screw into the MDF ring you fiberglassed and into your stock box. That way if you ever changed sub's all you would need to do is make a new MDF baffle. I know it's a bit more work but not by much.
Old     (scott76310)      Join Date: Sep 2009       12-16-2009, 1:59 PM Reply   
Thanks for the info guys.

Grant, I really appreciate your advice and have read many of your posts. I am not sure I understand 100%. I would like to retain the current baffle like in the picture with the 10 inch kicker in it and leave it carpeted preferably. When you are talking about the MDF ring are you talking about mounting it on the backside of the current baffle or the frontside? I was thinking of trying to fiberglass a ring into the backside but the way that I am picturing it, it will be there forever and not removable. Due to the size of the box needing to be only 1 cubic foot the walls of the enclosure will not be much wider than the ring. It will just be so much easier to build the enclosure inside the current enclosure using all fiberglass. I will be able to make the baffle very thick using fiberglass, the baffle itself will only be slightly bigger in diameter than the speaker, in fact mounting screws may almost go into the side walls of the enclosure. I am just wondering if the fiberglass will hold the screws securely without coming loose and if they do come loose then would it be possible to oversize the holes and fill with epoxy and redrill. Since it will be a large oval hole, I don't really see changing out to a different speaker.

I feel pretty confident that I can make a very solid, sealed 1 cubic foot encloure with a thick baffle what I am not sure about is if the MDF is required for the screws to hold. The current outer surface of my stock baffle is smooth and flat. Thanks again!
Old     (timmy)      Join Date: Jul 2001       12-16-2009, 2:30 PM Reply   
Thinking about this situation more....out of sheer laziness if it were me I would consider putting the T/S specs into a box modelling program and seeing how the speaker would perform in the box as-is. My second route would be to consider filling additional volume in the box to effectively make it a smaller box, the main consideration there is making sure whatever you put in there is secure and isn't going to rattle around.
Old     (soundbox)      Join Date: Oct 2007       12-16-2009, 3:02 PM Reply   
Ever thought of porting the existing enclosure?
Old     (grant_west)      Join Date: Jun 2005       12-16-2009, 3:31 PM Reply   
The ring I was talking about would be on the inside of the box.And you would make it as large as possable. Think of that ring like the foundation of your house and that stays there forever and you build off or from the ring. So if you ever changed subs you could just unscrew the front of the box from the Ring you have fiberglassed into the stock box. when getting a differnt sub you would just make a new baffle. Like what Ben said. Ryan said a 555 with a Radiator pounds like Hell. I'm intrested to hear how a 555 sounds with a radiatior in the right size box and a Powerfull amp.
Old     (azwakekid)      Join Date: Apr 2005       12-16-2009, 5:16 PM Reply   
i bought two 555's for my boat last winter. ended up selling the boat. and i sold the subs to my brother. he put them in his little vw jetta. each one on 1200rms amp, so he says. holy cow. its the loudest and cleanest sounding bass i have heard to date. the bass is super tight and clean. very little distortion. i think he had the 4 ohms at first. but ended up getting the 2 ohm coils. but boats are cars are not the same thing so its really hard to compare open air in a boat to a trunk in a car.
Old     (scott76310)      Join Date: Sep 2009       12-16-2009, 5:26 PM Reply   
Ben, No I haven't thought about porting it because I think the output will be plenty for me with a sealed box and from what I could find it sounds best in a sealed box. If it isn't enough then I may consider adding the radiator. I really like tight, quick bass so I think I would prefer sealed.

Does anyone know if the screws will hold well in thick fiberglass without any wood?


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