vented fiberglass enclosure?

Hi, I am currently in the process of planning my next car audio system and I need some help on a few things.  I am completely new to fibreglass building.

I have 2 MTX T9512-44 Subwoofers – each at 1000 watts RMS

http://www.mtx.com/caraudio/products/subwoofers/thunder9500.cfm

First question is this:  Does it matter with this sub or any sub if I have them mounted with the magnets up, instead of in the box.  Also if you can mount them upside down like that can you have one mounted with the magnet in the box and the other with the magnet out?

Second, when figuring out box sizes do you need to subtract the size of the sub that will be inside the box to get the total volume?  So say that the sub needs 12 cubic inches and the magnet takes up a space of 2 cubic inches do I need a box with 12 – 2 = 10 inside or the 14 – 2 = 12 if you understand what I’m getting at.  I’m not sure I understand myself lol.

Third, from most of the installs I’ve looked at on this site and on others the fibreglass enclosure is sealed.  Can you still make a vented enclosure?  Also if you can and you do make one is there anything that I should avoid doing?  Like not making the box very narrow and long for instance?  Pretty much will a weird shaped box with a vent have a different effect than an actual box with a simply designed vent.

I hope you can understand what I’m getting at with all that.

All help will be appreciated.

twobig86 wrote: Hi, I am currently in the process of planning my next car audio system and I need some help on a few things.  I am completely new to fibreglass building. I have 2 MTX T9512-44 Subwoofers – each at 1000 watts RMS http://www.mtx.com/caraudio/products/subwoofers/thunder9500.cfm First question is this:  Does it matter with this sub or any sub if I have them mounted with the magnets up, instead of in the box.  Also if you can mount them upside down like that can you have one mounted with the magnet in the box and the other with the magnet out?

With MOST subs you can mount them either way. There are some subs that can only be mounted one way or the other, but those are few and far between.

twobig86 wrote: Second, when figuring out box sizes do you need to subtract the size of the sub that will be inside the box to get the total volume?  So say that the sub needs 12 cubic inches and the magnet takes up a space of 2 cubic inches do I need a box with 12 – 2 = 10 inside or the 14 – 2 = 12 if you understand what I’m getting at.  I’m not sure I understand myself lol.

Don't worry about getting confused dear... we're here to help you and I am more than happy to answer that. The box size with include everything going into the box. For example, say the sub needs 1 cu ft. of space, uses .5 cf for itself, and uses a port (for ported enclosures) that uses .25 cf of space. Then you will need to make a box that is: 1 + .5 + .25 cf inside to make it the right size, or 1.75cf of space. I hope this makes sense.

twobig86 wrote: Third, from most of the installs I’ve looked at on this site and on others the fibreglass enclosure is sealed.  Can you still make a vented enclosure?  Also if you can and you do make one is there anything that I should avoid doing?  Like not making the box very narrow and long for instance?  Pretty much will a weird shaped box with a vent have a different effect than an actual box with a simply designed vent.

Part A: Yes!Part B/C: If you decide to put in bracing or whatnot, make sure that the area where things narrow is no less than 80% of the surface area of the cone of the subwoofer. For example, if you have a 12 inch sub with a 11" cone, you'll have a surface area of ~95 square inches (radius squared times pi) Take 80% of that: ~76 sq inches. So as long as you do not have a part of the box that has less than 76 sq inches cross section, there will be no affect on the subwoofer. Long and narrow is ok as long as it follows this rule (Think bazooka tubes)

twobig86 wrote: I hope you can understand what I’m getting at with all that. All help will be appreciated.

I hope this answers all your questions. If you have anymore don't hesitate to ask.

Ganbatte ne!

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The difference between ordinary and extraordinary is that little extra.

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Thanks for all the answers --- it clarified alot for me, as I get closer to install time im sure ill have more questions.