Can I mismatch subs?

I have a JL Audio Fathom 113 and would like this baby to have some company. I have a budget to manage. I was thinking about th Fathom 110 or 112.

Is this practical? I am favoring the 110 for space and financial reasons but I could step up to the 112.

Personally, I think as long as both are good subs, this will help even out the bass in your room. The minus is you have 2 subs to move around and try to integrate with your main speakers. 2 crossovers, 2 volumes, and 2 placements. They probably both have 2 different sets of strengths. It might depend upon why you are thinking of adding another sub. More bass, or even bass,etc. I'm sorry if I've raised more questions than I've answered but you didn't give us much info. good luck. Dan
Subs in the same series will generally work well together. I think a second smaller sub will improve your system.
i did something similar some time ago with two sunfire subs, only because i wanted a larger sub; i had a ten inch and acquired their twelve inch. as dlr alludes to, both have differing strengths.

in my case, the smaller sub filled in what the larger didn't in terms of impact and speed, while the larger sub filled in what the smaller didn't in terms of the lower octaves and inaudible rumble. together, the two were greater than the sum of their parts.

two subs have to be heard (and felt) to be believed. simply incredible!
I'd save up and get another 113 or sell and match the 112's.If your system is 2 channel then smaller is beter.Less depth but and dynamics but more tonal accuracy.Placement and integration is a bitch no matter what and mixing and matching probably isn't a good idea.I think TBI had a great ides when they offered their subs powered or passive.Passive you could get their amp/x-over box and when you added the sub it was parallel and power to each box went up.Great idea that I wish more companies would have tried.I haven't done what Eric said worked but think it would be easier wot integrate same subs.That said I like multiple drive subs.
I used to sell Velodyne and latter after I left biz I became fan of multiple drivers to move large amounts of air.Light work the Vandertseen could fill in smaller Maggies.REL did same and speed and tonal accuracy is great with Quads etc.For HT and music Martin Logan has multiple driver speedy subs.I'd like to hear the Totem Thunder with 8" and two passive 8's.But you have a deep sub and might not want to give up depth.Still two Martin Logan Descents or Depths would be my choice especially if I was doing HT.
depends on what you are trying to do--where your xover will be --if you want the sub to xover in the 100-120hz range then the smaller sub will cover that better if you are going to use these in stereo and xover below 80 --I would go with 2--F113--I have my 2 F113 xover at 50hz in stereo ---which sounds much better than summed bass.
I had a F113 and an F112 in the same room at one point and I thought they worked together well. The F112 seemed to be a little faster to my finicky ears, but it was barely noticable.

I actually ended up selling the F113 and buying another F112 because i thought that the F112 did better with movies in my room and so they would match.