The JL Audio F112 is a smaller version of the F113.
The F112 has the same feature set as the F112 with a smaller 12" driver and 1800 watt amplifier. By comparison F113 has 13.5" driver with a 3000 watt amplifier.
In general we recommend the jump to an F113 because of the relatively small difference in cost within an overall stereo and the considerable addition of power and low frequency added. A pair of F112's costs $7800 and adds 3,600 watts, a pair of F113's costs $9400 and adds 6,000 watts to your system + can go lower.
That being said, if you have a medium sized room that a pair of F113's would overpower, or you are just trying to add a single sub to a home theater and/or meet a budget, a single F112 is an very effective medium sized room addition to home theaters.
We still encourage everyone, including those with theaters, to put two subs into a system and are happy to show people the difference if they visit our store.
The JL F112 is 18.5" Tall, 15.1" Wide, and 17.8" Deep, 117 lbs.
The JL F113 is 19.3" Tall, 16.5" Wide and 19.3" Deep, 133 lbs.