First off this is my first ever subwoofer box, so go easy on me...


Hi,

I recently bought an Infinity Reference 1230W subwoofer. It is a 12" driver with 300WRMS power handling. I went to the infinity site and found the box specs for it here:

http://manuals.harman.com/INF/CAR/Bo...ch%20Sheet.pdf

In the manual, it shows a pretty weird picture of the sealed box:

http://ca.geocities.com/mladen-g@rog...m/infinit.jpeg

Notice that the driver looks like it's inside the box. Does this mean I should screw it in from inside?

Also, what does "All sides lined with 1-inch fiberglass or fiberfill mean" Do I really have to put 1-inch thick fiberglass all around the outside of the box? And how would you put on "1 inch" of fiber fill? I thought you were supposed to pack the entire box if you're using fiberfill.

I plan to make my box with 3/4" MDF, with a double front plate making it 1.5" where the driver mounts. I think it's gonna look like this:

http://ca.geocities.com/mladen-g@rog...nity-mybox.jpg

As you can see it's quite different from the Infinity design, but at least it's realistic. The walls aren't paper thin and the driver isn't inside the box. The internal dimensions should be around 14" x 14" x 11"... just slightly less than Infinity's recommended 1.25 ft3, because of the extra airspace around the basket due to the double wall at the front.

Last question: do I need bracing for this box? If so what type should I make it? And do I need to make the box larger to accomodate the volume that the bracing panels take up?

Any input would be appreciated,
molo

[ September 22, 2004, 09:47 PM: Message edited by: molo ]

Umm, it's just a picture, they don't want you to necessarily mount the sub from behind. Also you can buy polyfill in sheets, they are saying get it in 1 inch thick sheet and staple it to the INSIDE walls of the box.

You'll also want to avoid shaping the box like, well, a box. This usually involves offsetting the front and rear wall angles of the box to avoid standing waves/cancellation (correct me if I'm wrong on the terminology). You'll usually see enclosures with the rear wall angled for this reason. Quick explanation: if the enclosure is a 'square' box, then the bass notes (waves) that travel rearward will reflect off the rear wall and back in the same plane (ie., towards the woofer); this is not good for sound. An angled rear wall avoids this. It makes for slightly harder volume calculations, but I'm pretty sure it's a must do for sealed applications. Good luck...

[ September 22, 2004, 11:17 PM: Message edited by: timmyturtle ]

^^^^^^^^^^^^^ Doesn't really matter. You could make the box a perfect cube and mount the woofer dead center and it won't make a lick of a difference. The waves are so long that they will be bigger than the box no matter what, so you won't get standing waves.

Does the polyfill "count" when calculating volume? I mean, do I have to extend the internal volume by 1 inch on all sides if I'm putting in 1 inch of polyfill?

Also, would I need to put any kind of bracing on this box?

timmyturtle: Some reading I did on JL Audio's site:

http://www.jlaudio.com/tutorials/boxdesign/index.html

suggests that the box shape is not so important as long as it's not a perfect cube. However, they say that perfect cubes should still be avoided, even though the waves are too long to make a difference [img]graemlins/dunno.gif[/img] . I wish they would give their reasoning.

I guess maybe I should slant the front a bit to be sure. It may even fit better behind the rear seat...

[ September 23, 2004, 12:08 PM: Message edited by: molo ]

Bracing is always a good idea.
No don;t worry about compensating for the polyfill displacment.

- Shape not a big deal, its the volume that counts

- Might as well calculate the volume interior of the box before adding the polyfill, it wont be ab audible difference in volume


- I wouldnt worry too much about making sure its exactly an inch, just add approximately the same to all side, im sure you'll be fine.

Im running the 10" version of that sub sealed right now, i actually stuffed the box with polyfill because its a little under the recommened size, still gets good low end extension.

Best of luck.

Sealed boxes flex the most brace the **** out of it!

In a box that small I would just do a few triangular braces on a few sides, I usually don't brace from opposite walls until I am over 1.5 ft3. Dont add the one inch onto the sides. And if you can fit it, the recomended ported box blows the sealed one away.

Well according to the charts it "blows it away" in decibels, but if you look at the group delay it is 20 ms max for the ported and 12.5 ms max for sealed.

Correct me if I'm wrong, but doesn't this measure the "tightness" of the bass? The ported box should sound more boomy and have less resolution, even though it's louder. Is this not correct?