I read in a car audio magazine (can't remember which one) that FG was not very good for build sub enclosures as it was not as dense as MDF. Is this true? because it seems like everyone is using FG for sub boxes now.

although it is stronger, fiberglass flexes more easily than MDF, so care needs to be taken to brace the box and apply plenty of layers of fiberglass to minimise flex.
though i imagine if you had enough layers of fiberglass to make it 18mm thick, it would be as stiff as MDF..

If built properly a FG box will be easily stiff enough and heaps lighter than an MDF box...they are fine for SQ IMO

is it true they have problems with resonance?

[ May 05, 2003, 13:42: Message edited by: Sathid ]

what if only small section were off FG?
how many layers?

Roughly 40% thickness will yield the same strength as MDF (18mm MDF = 7-8mm FG). Some say less, some say more...i prefer more as you can never have a strong enough box.

FG does resonate more than MDF, but the irregularity of the internal shape should offset this to the point of being negligible. A layer of dacron would also aid in minimising internal surface resonances. For sub-frequencies, the resonance shouldn't pose a problem.

thanks everyone

FG boxes are great...ive used FG in heaps of installs that ive done

As long as it's braced correctly and the layers are thick enough you shouldnt pick the difference.
I find in certain cars it works better beacause the surface area of the box makes contact with more of the cars structure,which sometimes makes bass transferance throughout the car better

It also allows you to use space that you couldnt normally use(eg:smooth areas around the edge of the wheel well )

My box is FG'ed into my wheel well and sounds great

looks sweet 2

damn that looks sweeet only thing i see bad with fibreglassing in wheel wells and stuf is that it's really hard to tune a box bcos of the lack of info on the size of the box

As the size is an approximation, a solution would be to build the box to the largest recommended size.

Test the box out as normal, and if the volume is causing too much bottom end, then take out the woofer and glue a block of solid material (wood, etc) that has a known volume to the inside of the box. Keep performing this until the desired frequency response is acheived - pain in the ass, but it will allow you to get the sound right including the transfer function of the cabin (which adds too much bottom end in hatches for my liking).

mj

I had resonance issues with my FG box but fitted a heap of deflex panels. This cured resonace problems instantly.

Anyway FG offers several advantages in some situations but can be far more complex than using MDF, so stick with MDF if you can, as its very easy to use and provides predictable results
peace
Cyberpunky

if you have a fibreglass box, and want to know the volume, why not just weigh it, fill it with water, and weight it again.
simple.
each cc of water (1000cc per litre) weighs one gram.
then u just take into consideration the displacement of the sub (as you would any normal box ) and bob's your uncle.

ahhh 1ml of water doesn't equal 1 gram at room temperature.

thats at 4°C.

but its close enough. and i'm just being a smartass

lol buy why weight it why not just go hmmm i just put 30 litres in here and its full i dont suppose the enclosure size is 30 litres ? ok my im just being to smart for my own good buy it make sence to me (ive even been know to fill an mdf box full of water to work out the volume juts dry it straigth away no worries)