Sub upfront and fiberglass

Im planning to put a 10" or 8" sub upfront, on the passenger footwell. I'll be using fiberglass for the enclosure.

Questions:

1) Does fiberglass differ too much from MDF in terms of sound quality?
2) If I put in polyfill (or fiberfill, whateverl that pillow-fill material is really called), should the internal volume be the interior of the enclosure without the fill, or with the fill? (ie, if the requirement is 0.66 cu ft, should it be a little over 0.66 to make an allowance for the fill?)
3) Has anyone ever trie this before? Would the sub produce a solid "thump" in that location?


Im planning to use liters on the actual project so I'll just use water to estimate the volume of the prototypes. Its too much hassle to compute for the volume in an irregular shape enclosure.

1 - No

2- Build the box to the proper spec without the fill. Actually, if you build the box to the recommended spec, you wont need pollyfill.

3- As a matter of fact, in this months Car Audio and Electronics, there is a Benz that has a JL 8W0 in the passenger footwell. It has a piece of MDF in front of it to protect it and also allow the sub to build off it. It wouldnt affect the "thump" really. The main advantage would be having the bass up front with the rest of the music like its suppost to be. Youll get more thump from a bigger sub which would have to go in the back of the car more than likely.

you'll get deeper bass from a 12, but that'd be kinda tough to put up front :). the advantage of up-front bass is that you can xover at like 150, and still have no localisation issues... that's happy times, right there...

yes, glass will be different than mdf insofar as it's bendier - you'll need quite a few layers of glass (as in 9-12 depending on the glass and the sub) to get it as stiff as mdf, which is why you use mdf on any straight runs. you're using 3/4" mdf to make the mounting rings in any case, yah?

polyfill can help the box if it's a little small, or if it's got a too-peaky response, but like mac said, it's better to build to spec then stuff according to taste.

Thanks guys. yup, I'll use MDF for the side where Im mounting the woofer. I'll build it to spec then.

I did get one other suggestion, and Id like to hear your thoughts on it. Instead of te usual fill, someone suggested that I use dynamat or similar materials. Would that do anything to improve the response, if not anything detrimental?

Oh, yeah, for this project I wouldn't use a 12 - probably a 10 or 8.

well, polyfill and dynamat do 2 totally different things. polyfill makes the box 'look' a little bigger to the sub, which can smooth the response of a too-small box. dynamat (or its much cheaper cousin, secondskin @ www.secondskinaudio.com - make sure you type the 'audio' bit :)) is a vibration dampener... not a bad idea to throw down a layer of something - liquid would probably be easiest - inside the box...

You can get truck bedliner spray in an aerosol can from wallmart for 7 bucks, use that on the inside of the box, I think it makes a world of difference in fiberglass enclosures.