Stiff foam bottom, plywood in middle and acoustic mat on top. And then you place your subwoofer on top of the platform. It should look like this: http://www.auralex.com/wp-content/uploads/2013/11/SubDude-II-020-500x500.png How ever I only have 4" wide and 2" thick foam on 2 sides of the platform and it works just as good. The idea here is that the stiff foam will dampen the vibration and thus isolate from the structures. This only removes the cabinet vibrations but it does nothing to sound waves.

For the sound waves you could treat your room with sound isolation but in apartment it is not worth the money / work to do so.

Opinel Folding Knife
Michael Graves Tea Kettle
Le Creuset French Oven
Pyrex Measuring Glass
Greek Diner Coffee Cup
Panton Plastic Chair
Planner Group Compact Furniture
Hunter Rainboots
One Fifty Vacuum Cleaner
Track Lighting System
Thermos Vacuum Flask
RC-M90 Boombox
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Bic Ballpoint Pen
Phonosuper Phohograph and Radio
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CIFRA 3 Table Clock
Glass Coca-Cola Bottle
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Predicta Television
Apple IIc Personal Computer
Model 302 Telephone

how much cheaper would it be to make that myself instead of just buying that product lol?

and i think mentioned how this really only helps if the sub is played at higher volumes? not so much at a middle listening level right? cause my subwoofer is only the dayton 1200. im debating if its worth it or not for my lower end subwoofer?

It all depends on prices you can find the foam for and if you have the tools for it. Of crouse it is easier to buy ready product but I personally made 6 of these and it was way cheaper to build my own and I got them in size I wanted them as well.

There will be some vibrations at mid level as well and this occurs more with lower end subs as they are ligh weight compared to higher end models that have more weight. Is it worth it is another thing, if you are with budget and neighbours are not a problem then I would say no. But if you worry about neighbours then it might be worth it. And like I said, this wont help with the actual soud waves getting trough.

ok thanks, makes sense.

there are obviously 4 feet that hold the subwoofer up. one of the feet is shorter than the other 3. this seems somewhat like an issue as well. but ill just have to get like an extra rubber 1 inch by 1 inch square to place under it, and i guess that should help to raise it to the normal level of the other feet