What the Auralex SubDude and GRAMMA risers offer is decoupling. Nothing more and nothing less.
ShadyJ is well off his rocker on this one. Decoupling is a basic principle of acoustics and mechanics. If decoupling is "snake oil BS", then so are shock absorbers on car wheels. His stance is utterly ridiculous.
But whether or not the Great GRAMMA will be of any benefit to you or worth the price is all a matter of your particular situation. If your subwoofer is already decoupled, or it produces extremely little physical vibration due to a force-balanced design, then a GRAMMA riser isn't going to add or subtract anything. And you don't have to use the Auralex brand specifically. Any form of decoupling will do. The GRAMMA risers just happen to be effective decouplers and not insanely expensive, so they're easy to recommend. But you can certainly build your own, or find some other means of decoupling your subwoofer - such as a few layers of thick carpet pad, or even just a stack of blankets or something.
All you're after is some way to prevent the physical vibrations of your subwoofer or speakers from reaching the hard surface on which they are sitting. So you just need to suspend the sub/speakers, or put some sort of shock absorber underneath them. That's all the GRAMMA risers are: shock absorbers. So anything that is squishy enough to act as a shock absorber, but still stiff enough to not get crushed and compress to the point of basically being solid under the weight of the sub/speakers will work just fine. Like I say, that can be carpet pad, blankets, mouse pads, packing foam...whatever. Just something to damp any vibrations.
Where people go wrong is in thinking that ANY floor is inert. There's no such thing as an inert floor. Every floor, no matter what it's made of, can transmit physical vibrations. Concrete, wood, stone, marble - doesn't matter. None of them are inert. So if your subwoofer vibrates (and it does), and it is coupled to the floor, then your floor will vibrate. Simple as that. And your floor is connected to the walls. The walls are connected to the ceiling. And those vibrations will carry throughout your entire home's structure. Just like you'd feel every tiny bump in the road if you didn't have squishy rubber tires and shocks in your car. That's why we need decoupling, and that's what the GRAMMA risers offer. Whether they're worth the asking price is dependent on what you personally think is affordable.
The final bit is understanding what happens when your subwoofer or speakers have "feet" of any kind. These might be "spikes" or hard rubber feet, or just little nubs that protrude from the bottom, etc. It's all about surface area. Pounds per square inch. The downward force is just the weight of the sub or speaker. That downward force is going to act upon the given surface area. If you have a flat bottom on the sub or speaker, the weight of the speaker/sub is distributed over the entire surface area of the bottom of the speaker/sub. That means low pounds per square inch.
When you have any sort of "feet" or spikes or whatever, now you have the same downward force - the weight of the sub/speaker - acting upon a much much smaller surface area. A tiny surface area. Just the little "feet" or the points of the spikes! Now you've got very very high pounds per square inch. Same number of pounds. WAY fewer square inches of surface area.
One way to picture it: bed of nails. Would you rather lay down on a bed of 10,000 nails. Or a bed of just 4 nails? That's what's going on when your subwoofer or speakers have "feet" or spikes. You're basically sitting them on the bed of 4 nails. Way way higher pounds per square inch.
So any sort of "feet" or spikes work to COUPLE the subwoofer or speakers to the floor, or whatever surface they're sitting on. This is the opposite of what you should do. Coupling is great for physical stability, but it's horrible for sound because you're now ensuring that the floor or desk or stand, etc. will vibrate in sympathy with the speakers/sub. The only thing that should be vibrating is the sub or speakers. Not the surface on which they're sitting.
So, should you buy a Great GRAMMA? Answer is: it depends.
If your sub is already decoupled, then no. If you'd rather spend less on some other form of decoupling, then no.
But your subwoofer definitely SHOULD be decoupled somehow. It vibrates for sure. I'm pretty sure the model of subwoofer you own has "feet".
If you wanna "try before you buy", just fold up a few thick blankets and put them under your sub temporarily. Obviously, don't block any of the drivers or ports with the blankets.
If your floor was coupled to the subwoofer before, and thus vibrating in sympathy, having the "shock absorber" of the blankets will result in lowered room distortion, and fewer rattles and hums from other objects.
The biggest difference though is often in other rooms of the house. Decoupling's greatest benefit is a reduction in the bass that "travels" or "bleeds" into other rooms via structure-borne sound transmission. As opposed to the airborne sound transmission, which obviously still remains.
Anywho, it's a cheap and easy experiment. Certainly easy enough to try for yourself and decide whether the results warrant a more physically stable and better looking decoupling device than some stacked blankets
