[Mike P.]

I think I'll go with an LLT design.
my budget will be ~$1000, + or -
area=6'w x 2't x ~3'd. total area allowed.
I like to watch movies @ high volume.

You have the option to go with a pair of 18 inch LLT's. The Mach 5 Audio IXL-18 in 12.5 cu.ft tuned to 15 hz would qualify as a LLT. A pair of these would more then fulfill your "high volume" needs. The subs are $265 each, shipping included. Powered by a Behringer EP2500 amp for $300, you would be well within your budget.

 

[Mike P.]

The volume required is dependent on the specific sub. The IXL-18 requires less volume then other 18 inch subs. 12.5 cu.ft works well for a IXL-18 but you can increase the volume if you wish since you do have the room to do so. It's entirely up to you, but why limit yourself to one 18 or two 15's when you have the budget and box volume necessary for two 18's that would be far superior in low end output especially since you like it loud in a 12'w x 23'd room. The IXL-18 is out of stock at the moment but should be available shortly. The IXL-18 is known as the "best bang for the buck", I have a pair myself.

I'll ask Steve to join in here to put your mind at ease. Being nervous is a good thing since it makes you cautious, less chance of mistakes being made.

Port diameter and length correlate to the box volume. Port length controls the tuning frequency. Port diameter controls the air speed.

To give you an idea, click on the link in my signature to see a Database of what subs have been built.

 

[Mike P.]

Your port length calculations are right, however, if the Q18 is your sub choice you're giving up a lot of low end out put in a box that small tuned that low. Both models shown are the Q18 D2 with 650 watts input. (one channel of a EP2500)

 

[Mike P.]

Is 13ft^3 as big as you want to go? You do have more space available. If 13 cu.ft. is your limit, the CSS SDX15 would work well. The model is with one channel of the EP2500 (650 watts). Porting would be one 6 inch diameter tube 21.5 inches long. No high pass filter would be required.

 

[Mike P.]

One sub for $300 or 2 subs $300 each?

 

[Mike P.]

There is a 21 inch Maelstrom-X coming. With 1500 watts if would produce over 120 db down to 12 hz. :blink:

 

[Mike P.]

A Fi Q18 D2 wired for 4 ohms in 23 cu.ft tuned to 15 hz looks good. A 10 inch diameter port 33.5 inches long would keep the air speed under 20 m/s. With 1000 watts input you can expect 120 db down to 14 hz, with room gain.

 

[Mike P.]

If you tuned it to 13 hz Xmax wouldn't be exceeded until under 12 hz, less chance of bottoming out the sub without a high pass filter. A 10 inch diameter port would need to be 47 inches long. If you get 6 db room gain, you'd have 120 db down to 12 hz. :blink:

Although it's debatable, lots of people line the cabinet walls with egg crate foam, I use it on all my subs.

I'm not familiar with the EP2500, someone else will have to chime in here.