Originally Posted by sholling
I didn't see the shimmy with with my 10" 250w front firing subs either. But I did see it big time with the ULS-15. I suspect that it has everything to do with the mass of the driver. However there are other solutions. For example I've used 3/4" layered rubber/cork/rubber isolation pads ($4ea) successfully with a high mass driver front firing sub. But for front firing subs I find that 1" spikes work best with thick carpet over concrete. The spikes isolate while locking the sub in place. Naturally your millage may vary.
As I said the improvement with a down firing sub was huge. The bass was much tighter and the walls stopped shaking. I have another down firing sub on order and already have a SubDude HD ready and waiting for it.
Interesting, once again. I don't have my system on a first floor concrete floor as it is upstairs in our family room which is of course wood frame. In my instance, with the massive driver the F113 uses, I have never witnessed what you describe with your 15" driver. The subs wiegh about 130 lbs each so they are pretty massive for their size. The JL even though it is a 13.5" driver with its rolled suspension equals a 15" acccording to JL. However, having said that, I have cranked them (2) to full live rock concert levels on a few live concert blu-rays I own, one of which is known for its bass response (Police - Certifiable) with 24/96 blu-ray encode. The dynamics and slam of that particular recording are excellent, as is the definition and with the best subs, at high volumes the Sting's bass line is clearly discernable and easy to follow separate from the kick drum. Upon moving both JL's to the Great GRAMMA isolation stands, I found similar improvements noted by others and never have seen any jiggle or movement by the foam feet. Tight and solid. These subs have 2,500 watt amps in each so they are, to say the least, dynamic, fast, clean and tight. Those attributes only improved another degree of magnitude isolating them from the room.
Isolation spikes, while a distinct improvement over laying the sub directly on the floor also introduce their own problems. All isolation devices are not perfect as is pointed out here abut the SubDude and GRAMMA stands, as with spikes. Spikes seem to be the perfect device, on the surface. But they do still direct couple the speaker or sub to the floor and as such will resonate with the concrete's own response frequency. Something I experienced with my main speakers years ago and their own integrated spikes. I ended up placing them on isolation bearings and the improvement was nothing short of startling and much different in the bass response area than one would have otherwise thought. the JL's are too heavy for me to work with in their size now at my age to be able to place them on isolation bearings so the Great GRAMMA was the only other reasonable solution which has worked much better than I expected.
As noted, though, all should remember, no isolation device is perfect including the SubDude and GRAMMA's. They all will to varying degrees upon the specific situation, room and circumstances work to varying degrees. They all are better than nothing, though.
The bottom line, enjoy what they do improve.