Fiberglass vs MDF enclosures.

[highfihoney]

Anybody have any experience with custom molded fiberglass enclosures for trunk mount subwoofers in a car ?

I have 2 jl audio 12" wm3 subs that i have mounted in a standard MDF dual enclosure in this car & its a great sounding sub box but it looks like crap so ive been looking at a guy who makes custom molded fiberglass enclosures to fit mustangs,the enclosures look strong enough to handle the pounding it will take but im wondering about how fiberglass will sound vs mdf.

 

[Sheep]

It's not ALL fiberglass. Theres an MDF frame underneath it, and sometimes, its just a fiberglass baffle.

SheepStar

 

[highfihoney]

It's not ALL fiberglass. Theres an MDF frame underneath it, and sometimes, its just a fiberglass baffle.

SheepStar

Hi sheep,ive been looking at both the kind with a frame made from MDF & the kind that is one solid molded peice of fiberglass poured in a mold then finished these are light weight & contain no MDF anywhere,all 4 sides,top & bottom are all made from resin.

I would really like to go with the light weight 100% fiberglass models to keep weight down but im not sure that it can take serious hard hitting bass for prolonged periods without splitting & im wondering how well it will sound.

 

[Sheep]

What kind of car? I'm sure the makers will build it so it can withstand what the subs will dish out (W3's aren't that hardon boxes anyway).

SheepStar

 

[highfihoney]

The car is a ford mustang & weight is a big concern at this point with over 100 lbs of amps in their allready plus the weight of the jl's im really leaning twords the glass enclosure.

 

[Jack Hammer]

My experience with fiberglass in general is that different people make different qualities of fiberglass for whatever the intended purpose. Someone who knows what they are doing will make a durable product that is strong and vibration free (think: artists). Others can offer a poor product that is not strong and/or may introduce annoying vibrations, even if it doesn't crack.

I don't know if it applies and it may be expensive. Have you looked into carbon fiber or a composite of carbon/ fiberglass/ or possibly kevlar?

Jack

 

[Nestor]

Fiberglass and mdf perform equally well...when used properly. Fiberglass flexes over large, flat, unsupported surfaces. MDF doesn't have this problem, obviously, but doesn't conform well to curved, uneven surfaces.

The sub box I built for my King Cab Titan used both MDF and 'glass. Fiberglass was used for the bottom and most sides, with wooden dowels for reinforcement on the bottom. Since I required a long, flat surface for the top, I used 3/4" MDF.

I could have used 'glass for the top surface as well, but it would have been a pain trying to reinforce it. A big slab of MDF did the trick.

Given the acoustical challenges presented by a vehicle, I think you'd be hard pressed to tell the difference between a well-designed box of either or mixed materials.

 

[Sheep]

For sound purposes, MDF is not as rigid as needed for an inert enclosure by itself. For a 2 12 enclosure you will need a center brace as well as others. I'll see if I can get picture of a sealed enclosure my buddy made for 2 12inch JLW3v2s.

SheepStar

 

[Buckle-meister]

Fiberglass flexes over large, flat, unsupported surfaces. MDF doesn't have this problem...

Are you comparing like with like when you state this?

 

[Nestor]

Are you comparing like with like when you state this?

Am I comparing the same thicknesses? No. In practical terms though, 3/4" of fiberglass would make for an awfully heavy enclosure.

1/4" to 3/8" usually suffices.

 

[highfihoney]

Ive talked to a few car audio guru's over this & spent some time talking with a custom instal shop & from what i gather all the best boxes are made from wood & fiberglass is then used to mold & form the cabinet to the interior.

There are too many issues to overcome with a total fiberglass enclosure for my liking & a combination mdf/fiberglass enclosure will only add to the weight in the a$$ of the car so it looks like im sticking with mdf.

 

[Buckle-meister]

Am I comparing the same thicknesses? No. In practical terms though, 3/4" of fiberglass would make for an awfully heavy enclosure.

It's quite difficult to find approximate properties for fibreglass or, as I suspect is actually meant here, glass reinforced plastic (GRP) as opposed to the loose fibreglass used for insulation. Are you sure that the density of fibreglass is greater than that of MDF? Light aircraft are made from GRP and material strength aside, my gut's telling me that it'd be lighter than a similar aircraft made of MDF. D)

What little I could find out about GRP revealed that its stiffness is approximately 3 to 8 times greater than that of MDF. If correct, and conservatively adopting the factor 3, a panel of any given thickness made from GRP could be seven tenths the thickness of an MDF panel yet deflect equally under uniform load. Just thought you'd like to know.

 

[furrycute]

Do you really NEED to have 3 subs mounted inside your car? And 100lbs of associated amps, my old home amp doesn't even weigh this much.

 

[Nestor]

Do you really NEED to have 3 subs mounted inside your car? And 100lbs of associated amps, my old home amp doesn't even weigh this much.

Oh boy...

 

[Nestor]

It's quite difficult to find approximate properties for fibreglass or, as I suspect is actually meant here, glass reinforced plastic (GRP) as opposed to the loose fibreglass used for insulation. Are you sure that the density of fibreglass is greater than that of MDF? Light aircraft are made from GRP and material strength aside, my gut's telling me that it'd be lighter than a similar aircraft made of MDF. D)

What little I could find out about GRP revealed that its stiffness is approximately 3 to 8 times greater than that of MDF. If correct, and conservatively adopting the factor 3, a panel of any given thickness made from GRP could be seven tenths the thickness of an MDF panel yet deflect equally under uniform load. Just thought you'd like to know.

Haven't seen many planes shaped like my Klipshch Chorus

As I mentioned, from a practical standpoint, large FLAT 'glass surfaces are susceptible to flexing and require reinforcement of some sort. Even airplanes require structural reinforcement of some sort.

GRP in auto sub enclosures allowed me to construct a box that completely conformed to the rear floorboard of my truck. Using tape, foil and mold release, I constructed the base of the box right onto the floor. (See pic)

Even after more layers during construction, I still found the base flexed with a simple push of my hand, and required some sort of reinforcement.

The other advantages I gained was maximum enclosure volume for the space taken by the box, and a box that followed the contour of my rear seat, a stealth installation, if you will.

I agree with you on the numbers you mention, though. I'm speaking from how that ratio interpreted and implemented in the car audio world.

 

[Buckle-meister]

GRP in auto sub enclosures allowed me to construct a box that completely conformed to the rear floorboard of my truck. Using tape, foil and mold release, I constructed the base of the box right onto the floor. (See pic).Even after more layers during construction...

Ah! If I understand rightly, you built up a series of fabric layers of fibreglass and bonded them together using some kind of resin - correct? I was thinking of actual manufactured panels (GRP) similar in form to a window pane.

Wasn't your material really thin, even when finished?

 

[highfihoney]

Do you really NEED to have 3 subs mounted inside your car? And 100lbs of associated amps, my old home amp doesn't even weigh this much.

Hmmm,good question,see i knew this would happen once i got into car audio so i tried to stay away from it for as long as i could but this mustang is just screaming for a killer system so i couldnt resist,i hate buying anything that will loose value after i buy it so mcintosh amps were the obvious choice & mcintosh does not make anything that dont weigh a ton.

When i was just starting to think about what gear to use in this car system i made a decision that if i was going to have a good car audio rig in this car then it had to be able to keep up with the high spl's that the kids have in their systems & to be close to show quality when it was done.

Right now the amplifier weight is still under 100lbs but with the dry cell battery in the trunk & the new 2 channel amp thats speeding its way to me via ups i'll be over 100 lbs in amps.

This amp should be here by the first of next week & will run my fronts & rears along with the 2 300 watt monoblocks i allready have running the subs.


http://www.mcintoshlabs.com/mcprod/shopdisplayproducts.asp?hid=2&id=22&cat=Power+Amplifiers&prodid=1063&product=MCC602TM

 

[furrycute]

That's a nice looking amp. And it's a darn kick *** audio system you are building for your car.

But with 3 subs, have you ever thought about hearing protection? Sustained exposure to SPL's above 85 decibels will cause permanent, irreversible hearing damage. In addition to overall decreased sensitivity to sound, hearing damage will also result in tinnitus, a constant ringing in the ears, really not something you would want to experience.

 

[highfihoney]

That's a nice looking amp. And it's a darn kick *** audio system you are building for your car.

But with 3 subs, have you ever thought about hearing protection? Sustained exposure to SPL's above 85 decibels will cause permanent, irreversible hearing damage. In addition to overall decreased sensitivity to sound, hearing damage will also result in tinnitus, a constant ringing in the ears, really not something you would want to experience.

Very true & not something i would like but,i have read a bit on hearing damage & i tend to lean more twords the belief that its not only the db level that causes hearing damage its the type of sound,studies conducted with symphony orchestras have shown some interesting things about the effects of certian types of sounds that the ear finds offensive at the same db levels that the same ear finds pleasant.

Im not so sure that the whole hearing damage issue is as cut a dried as using a fixed db level to assertain what sounds are dangerous,i think it has alot to do with the mix of the music, 85 db can be obscenely loud if the mix is bad but if the mix is perfect than its not very loud,maybee this is why i hate rap so much

On a serious note though i really just want a stupid system like this one purely for adding to the look & feel of the car plus it will be sweet to be able to drown out a rap lover at a stop light

 

[Nestor]

Ah! If I understand rightly, you built up a series of fabric layers of fibreglass and bonded them together using some kind of resin - correct? I was thinking of actual manufactured panels (GRP) similar in form to a window pane.

Wasn't your material really thin, even when finished?

Thickness at most points is about 1/4". Fiberglass is generally a layer of cloth, dabbed/rolled with resin until the cloth becomes clear (the telltale sign). Repeat until satisfied.

It's thin, but sturdy on the curved sections, but needed reinforcing on the base. To save time (and headaches) I used 3/4" mdf on top. I wanted a flat surface there anyways.

Oh, and please disregard any reference to GRP in my previous posts. I was still referring to fiberglass!