Q - What product suggestion you would have to decouple or isolate the sub off a hollow stage or concrete floor? I’m seeing isolation pads, pucks, spring isolator devices. What would you recommend to decrease that “boomy” sound?
The short answer: Avoid using overlapping presets; use lower numbers on the subs, higher on the tops for a less boomy sound.
The rabbit hole A- In the case of a hollow stage, the boomy sound is most likely related to the resonance of the stage deck itself, in combination with the resonance of the cavity beneath it. The best way to avoid that resonance is to minimize the energy being fed into the structure, and the best way to do that is to not make any physical contact with that structure. The trouble is... gravity. That said, there will be supports running under the decking, and placing subs on those supports rather than between them is a good place to start. Since the decking moves vertically to re-radiate the energy, in this case gravity can help. More weight on the stage can help shift the resonance lower, potentially below audibility. If the sound is escaping through openings in the stage, block the openings. That’s if you can’t fill the cavity with sand or insulation, etc. Probably not, but it had to be said…
Back to the panels. They move vertically because they are lying horizontally but their acoustical center isn’t necessarily the same as the subwoofers’, and vibrations move faster through wood than air, meaning you can mis-align the waves in time, causing cancellations instead of reinforcement. Try moving the subs around until you get the least bad effect. For instance, you might get less "boomyness" if both subs are on one side rather than one on each side or both in the middle. Stack the subs vertically instead of side-by-side… Face the subs towards each other, (leaving a gap at least a woofer wide) or back-to-back, rather than forwards so that the energy transferred into the stage floor of one is cancelled by the other.
As a cone moves forward, the cabinet mass and the friction between the feet and the ground mostly prevents the cabinet from moving backward. The friction between the feet and the floor is where more of the energy is transferred. Putting the subwoofer on a foam pad will allow the cabinet to rock back and forward a bit, allowing the foam to absorb some of that energy. The foam pad needs to be soft to absorb the energy and big in order to distribute the mass of the cabinet over enough area that it won’t compress until it’s ineffective. A thick couch cushion is a good visual. A yoga mat won’t help.
A concrete floor isn’t going to resonate or cause boomyness. Odds are that the boomyness in that environment is related to parallel wall reflections and floor-ceiling reflections. Decoupling won’t help. There’s not a cure but the remedy is to try different subwoofer placement to minimize the worst effects. Think in 3D, in other words, in rooms with hard ceilings and floors, elevate the subs to halfway between them if you can.
Try locations for each sub that cause peaks and valleys in different areas. In a symmetrical room, place the subs asymmetrically. The bad areas caused by one location can be filled in from another location. Figuring this stuff out is easier if you can have a sub playing while it’s on a cart and someone can roll it around while someone else is in the listening location. Or you’ll be able to use our simulator soon…
PS: You can use more than one method in a room.