Instruction: Given a question and the related document, and generate the answer to the question based on the information provided in the document.

Input:
Question: how many cubic feet of air space does the box need to have for this subwoofer ?
Document: I just replaced an old Memphis Power Reference subwoofer with this one. If you don't know about Memphis, look them up, they make quality subs that hit hard and sound clean. Well this Hifonics HFX12D4 sounds almost as good and handles more power. It's only getting 250 Watts RMS, it hits very hard, and it's not broken in yet. I can't wait to hear how hard it hits after break-in, and then how much harder it will hit when I can give it the 400 Watts it needs. I have it in a generic 1.25 Cu Ft sealed box, it's being powered by a Directed 250d amplifier, and I have it set to hit up to around 125Hz and it handles the high notes moderately well (I need to improve my mid-bass section so that I don't need to rely on the sub for the higher bass notes).
These subs can get down low decently. Honestly they need a bigger motor setup but that's not 3 Kings Audio's problem thats HiFonics problem. I'm using an ARC Audio fd2200 to push these and sometimes I smell voice coil throughout the car but I think thats due more to clipping/slight overpower. I have these in a ported box tuned to 33 hz and they will get ridiculously loud. They will rattle houses from 100 to 200 feet away as people on my street have complained to me already. It's a good cheap buy, however I'm switching to Audio Technix Tropo 12's this week.
If you are on a budget and you need some quality bass the hfx12d4 12&#34; subwoofer is for you. name brand quality at a dime store price...
Bought these expecting to get good low bass and I wasn't disappointed. Just need to buy a MDF box to fit them and they'll bump even harder.
I reccommend this to anybody with not much power, and needing a cheap sub. Like any subwoofer, It sounds x10000000000 in a proper ported box for your vehicle.
I ordered four of these but only use two. fast shipping and were delivered all in one box. skeptical at first. there light compared to my alum12n. I am running hifonic hfi1000 mono amp at 2ohm 750 watts wired parallel. these are clean and hit really nice. my audiobahns hit way harder but these have a nice clean sound and reproduce bass wonderfully. for the price there awesome. if you want spl of course you need to spend more. you will be heard with these. get a pair you will smile.
So far i have bought One subwoofer and i installed it into my box in my 1992 Mazda B2200 just the one subwoofer was very impressive it was more tha enough for me i love it, It came ontime on the delivery and the pacage came undamaged i loved the speedy delivery i am definetly going to buy another one of these and definatly recomend it to whome ever is reading this and to all my friendsIt was makeing all my mirors rattle Just thinkof two of them(p.s. it is only one subwoofer for $36 just so you know)
Excellent sub! Recently had two Sony Xplod 12's that went out after years of use bought one of these and out it on a 1000w Sony Amp and it hits hard and its underpowered. Just one 12 underpowered amp says 400x1 rms bridged running at 8ohms since its a 4ohm amp and i can rattle things on my roof in an 05 Dodge Stratus. Actually turned my gain up to match and had smoking coming from the box. Not sure if its the wires or the subwoofer itself but still bangs so all good!
Now, my wife and I both have Ford Explorers, with Crunch 800W amps, and 4 Polk DB571 Door Speakers with Sony 660UP dash receivers so everything's pretty much identical in our vehicles. I recommend this stereo receiver as well because you can personally tune just about every setting(EQ, HPF,LPF,Subwoofer Level,ALO, DM+, Loudness, and a bunch of other sound options to get your music sounding just right). Our subwoofer box designs are a little different, both ported,  but we still get a bunch of head turns when we're out driving.
I purchased this subwoofer along with an Atrend 12' ported box a little over a week ago, and wow I must say what a nice little combo. This subwoofer is perfect for people on a budget, or for a starter subwoofer. You could even use it if something were to happen to your current subwoofer until you get a higher end replacement like me. I didnt really have high expectations, but I am plesantly surprised to say that this little guy hits pretty hard. As long as you tune your amplifier and your equalizer settings on your stereo correctly it will sound really solid.
Answer: Hey robert. That sub needs at least. 1.25 cubic feet for a sealed box.   1.6 cubic feet for a ported box.. as per intstruction man,