Fiberglass Sub Enclosure

[volkdent]

I'm in the process of building a sub enclosure for (1) JL Audio 12W7 in the spare tire well of a '98 BMW M3. I have a few ideas for rigidity which include internal bracing and using the spare tire mounting bolt to tie the whole thing together, but I'm in new territory here with the kind of abuse the W7 will be giving it being driven by 1000W. I don't mean to be rude or anything here, but I'm really only looking for responses from members that really know what they are talking about, ie good references or hands on FG experience. I'm looking for very little resonance out of this box, but I'm also trying to keep the weight down, as this is a drivers car. So far I will be mounting the sub towards the front of the well, tipped slightly forward. The mounting point will be a MDF ring, attached to two vertical ribs running front to back. That's all I have for now. Serious responses only please.

Jason

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[Alaxan 5,000+ posts]

Think about the question you are asking. How can you make it more rigid and still maintain a lighter weight? Form a ridge structure in the fiberglass molding as the box is taking shape. I sometimes also will create a frame to either mold into the fiberglass or attach the FG to. Sounds tho like you have a good idea of what you are looking at getting done and doing. Any more specific questions feel free to drop a line here.

 

[volkdent]

Well, I think I know about how to make it rigid, it is getting the resonant freq. of the box down that I'm worried about. I was thinking about making a fiberglass shape shell, then lining the shell with a veneer of MDF tiles, but that will get pretty heavy. A shop that does a lot of high end installs with high end cars says they can do it with no trouble, but I can't justify the $2k they want for the box. I figure a couple of hundred bucks in supplies and some collaborative good advice and I should be able to lay it up myself. So besides the MDF tiles, the other option was a lot of deadening material added to the tire well itself. Whadya think?

Jason

 

[bean 10+ year member]

I didn't respond earlier because I, like Alaxan wasn't sure of your real question....sorry dude.

I've made quite a few fiberglass enclosures. It sounds like you are going to have pretty good success....Here are my recommendations....

Yes, use a sound deadening material under the enclosure. (on the car, not the enclosure).

MDF tiles are a good idea, but if you are REALLY concerned about weight, lay one or two more layer of fiberglass.

Make as much of the top out of MDF (3/4") as you can........ If nothing else, it's easier to finish.

Mix your resin a little hotter (add a bit more catalyst) than recommended, it will dry faster. I've also seen resin that never hardened completely.

Also, use a fiberglass resin that is designed to be poured in layers. Other wise it will crack and peel apart.

I like working with the fiber versus the mat.

If the enclosure is super strong, rigid, and most important air tight you probably won't experience any coloration from the box. Those resonant frequencies most likely won't be heard........ Good luck! If you need more, just ask.

 

[bean 10+ year member]

It's difficult to calculate the space of enclosure when you do something like glass in your spare tire well. So, build (or find) a 1 cubic foot box and fill it with sand (or something like sand). Then dump it into your fiberglass tub and you'll know how big it is.

 

[volkdent]

Thanks Bean,

I usually use kitty litter, as its a little easier to clean up, but the results are the same.

Jason

 

[volkdent]

I'm sorry, Bean, I didn't mention this, but I've been into car audio for a long, long time. I have all the basics down, its the trickyness of the incredible pressure this woofer will be putting on the box, and my absolute abhorence of resonance that I'm asking for assistance. I do appreciate your effort though, so please don't be offended. I guess I'm looking for out-of-box ideas to make this box totally dead, strong enough, and light at the same time. I understand the usual mass increase/resonance decrease rule, but I always try to think of new ideas and look for new ideas from others. For example, one idea I was thinking about trying to copy was Lexis's metal/plastic/metal idea to get very dead luxury cars like the LS400. Perhaps fiberglass with layers of Dynamat sandwiched between, with areas open that bond the layers of fiberglass together. Or sound deadening tiles, like on ceilings in between. I don't know, I'm just looking for NEW ideas. I've deadened kick panel enclosures by running a layer of resin in side the enclosre, then putting a bunch of MDF sawdust in and shaking it around, then another bunch of resin. The enclosures were incredibly dense, but were ported and only servicing MB Quart 160 midranges. Go on, let your minds take a walk on the wild side and give me some sweet ideas! Whatya think?

Jason

Some of my really old installs, some from the late '80s! The blue kickpanel enclosures were my last, about 3 years ago.

http://www.geocities.com/volkdent/CarAudio.html

 

[Alaxan 5,000+ posts]

Actually having just built an enclosure for two Orion HCCA 12's out of all fiber and mdf framing. What is the shape of the tire well? Is it perfectly round or basically as such? can utilize the shape of it since apaprently your taking that tire out and will not have to worry about too much presure. Use a layer of dynamat on the well then fiber over it in a couple of layers with a ridge structure running thru it. The dynamat "sandwich" idea is also a fairly good idea. I used that on the rear portion of my boxes since they ran right against the fenderwall and rear quarter panels. One layer of fiber with ridge structure....on top of a layer of dynamat....another layer of dynamat laid once cured....then another layer of fiber running over that for the inner box wall.

 

[volkdent]

Alaxan, as I recall your system is up and running. When you have turned up, is it just dead, low, bass, or do you ever get the sense that the box is giving it just a little coloration? I'm just wondering if that point ever arises, and if so, how loud are we talking here, relatively speaking. If it doesn't, you must be a very, very happy man. Or is everything else shaking so much you can't tell whats making noise! I'm not looking forward to chasing down all the buzz's and rattles after the subs in. I love the Civics around here with boxes boomin in the hatch, and their license plate frame making more noise than anything else! Did you use matt or weave? I prefer weave for less mess, but as I understand, the matt provides the ability to handle stresses in all directions. I don't know if it makes a difference in this application, just curious.

Jason

 

[Alaxan 5,000+ posts]

Originally posted by volkdent Alaxan, as I recall your system is up and running. When you have turned up, is it just dead, low, bass, or do you ever get the sense that the box is giving it just a little coloration? I'm just wondering if that point ever arises, and if so, how loud are we talking here, relatively speaking. If it doesn't, you must be a very, very happy man. Or is everything else shaking so much you can't tell whats making noise! I'm not looking forward to chasing down all the buzz's and rattles after the subs in. I love the Civics around here with boxes boomin in the hatch, and their license plate frame making more noise than anything else! Did you use matt or weave? I prefer weave for less mess, but as I understand, the matt provides the ability to handle stresses in all directions. I don't know if it makes a difference in this application, just curious.

 

Jason

I use matt and yeah I do feel it provides a bit more stress handling. So far so good I dun have any issues with the box causing any resonance. I also used a sturdy fram structure tho internally in building the box I was not worried so much about weight tho. No I do not have much of anythign else rattling around because I am in a spankin new ford explorer. I also stripped out the entire vehicle before install to dynamat and make sure everything was well tightned and not going to jump loose on me. My pet peeve is also the boyz and their toyz runnign around and not being able to utilize it properly..........have not had my SPL tested yet tho am guestimating 145's or so... very possible a good bit higher, but would wrather stay on low side so as not to be disapointed LOL. Take a glance at my signature here and it shows the full run down of the main equipment in the truck.

 

[bean 10+ year member]

On top of any deadening you do to the box those nasty resonant tones can be interupted if we eliminate any odd standing waves inside the box.... Right? What I've done in the past is created little squares made of a dense foam. Make these squares the same, maybe three inches or so but of different heights. Adhere the foam squares of different heights inside the enclosure and it'll break up any standing waves inside the enclosure.

Kitty litter is too dusty........Unless you buy the expensive kind.

I don't know that dynamat will do what it's supposed to if you sandwich it in between layers of fiberglass. Dynamat is actually a transducer...... It takes a vibration energy and converts it to heat energy (very low heat)........ So, I'm wondering if it will do that encased in a hardened resin.

I'm sorry, I didn't realize your experience level........

 

[ramos 5,000+ posts]

I would say use kyntex biaxial mat instead of regular mat. It will cut down on the number of layers needed to build up the strength you are looking for. Less layers also mean less weight another thing your looking for. To add more strength you might also want to use some strands of rope resined in between layers. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[Dynboy 10+ year member]

You might try terry cloth. Light weight and very strong when done in layers.

 

[Alaxan 5,000+ posts]

Originally posted by Dynboy You might try terry cloth. Light weight and very strong when done in layers.

Or Kyntex as originally posted by Ramos here.......//content.invisioncic.com/y282845/emoticons/satan.gif.9c6a335ed7aeeed3ee273e573f1fcaac.gif