Yuppers.
I'm very glad that you were willing to talk to Brian over at Rythmik and try out his suggestions. Also glad that you gained a little bit of improvement so that I'm sure you'll now be willing to adjust settings and placement in the future with other subs to try and get the best performance out of them.
But ultimately, it looks as though $500 just isn't going to get you what you're looking for. With the Legend and the FV12, you've seen first hand what $500 can buy you. I think you'll agree that it is not bad! But it is also still very much a limitation.
I think you'll also agree with what I was saying earlier where this sort of $500 and under budget basically demands that compromises be made. The Legend, for example, by your own listening might do very well in extension and output, but it gives up something in the way of accuracy and tightness/transient response. You'd find a very similar compromise being made with Elemental Design's less expensive subs.
I personally strongly feel that the FV12 is the best $500 sub out there right now because it delivers good accuracy, flat frequency response, good tightness/transient response, it is well engineered so that you cannot damage it or cause it to distort badly (which it sounds as though the Legend can be driven into distortion), and the FV12 plays linearly quite deep. You'd find that HSU's and Outlaws subs that are in the same price range are similar, but the FV12 plays just a touch lower than them, which, combined with its slightly lower price, is why I favor the FV12 so strongly at $500.
But you've also discovered that the compromise that the FV12 has to make is sheer output. It is a fairly light-weight 12" driver in a medium-sized box with a 300 Watt amp. There's no magic. I honestly feel that Rythmik has done about as good a job as can be done with this price point and the components that are available for such a price point. But there's just no way to get the same output from such components as what more expensive components can provide.
So, your Velodynes have the benefit of being more expensive. They also have the benefit of not even trying to reproduce the deepest bass, which frees them up to have no limitations placed on their output in the lower mid-bass where it is easier and more efficient to move the driver.
I was saying earlier that I pretty much recommend just saving up and jumping straight to an SVS Ultra. The reason I say that is because it's where I think most people who aren't satisfied with an FV12 or a slightly more expensive sub like the SVS PB12-NSD DSP ultimately WANT to go. Make no mistake, there are plenty of subs in between that are better than the FV12 and less expensive than an SVS Ultra. And it's entirely possible - highly likely, in fact - that one of those $800 - $1300 sort of price point subs will give you what you're looking for in terms of improvement over your Velodynes. But I'm just saying that if you start to eek your way towards something like a Rythmik FV15HP or SVSound PB12-Plus DSP - both of which cost just north of $1300 once you include shipping - then how much more does it really take to save up another $400 and get yourself the PC13-Ultra DSP cylinder?
I took the steps of an Axiom EP500 and a pair of Epik Sentinel subs myself. I regret both of those purchases. Not because the subs themselves are "bad". I still use the EP500 in my bedroom setup. The EP500 plays ruler flat with great transient response, but only below 90 dB or so. As soon as you start to turn up the volume with the EP500, its aggressive DSP really kicks in. It limits distortion to inaudible levels, which is great! But it also keeps the low bass output clamped down. Mid-bass output goes up, but you end up with a big, downward sloping output because the DSP is keeping the output way down on the really deep stuff. Still, at 90dB and lower output levels, the EP500 sounds really great! So it's perfect for a bedroom system where reference output levels are not necessary and I don't require the huge output.
The Epik Sentinels had similar compromises to your Legend (which I still find surprising since the Legend is sealed, but so it goes). The Sentinels could play way down low - really dig out the 20-25Hz stuff. But the biggest problem was overhang. Attack transients (the start of a note) was pretty good, but the decay of the note was WAY too long. Notes that were supposed to stop did not, and it led to an overall "muddy" sound, where notes would just overlap and run over each other. Bad transient response, in other words.
Both the EP500 and Sentinels were meant to be "upgrades" over my aging HSU VTF-3 MK2. Much like your situation here with the Velodynes, it was a disappointment because I felt that the VTF-3 MK2 was still better than either of the "upgrades" in some areas. The Sentinels played lower - no question - but not as accurately or "tightly". The EP500 was better overall so long as the volume was below 90dB. But above that, the VTF-3 MK2 remained more linear, and in my theatre, I like to hit reference levels.
The FV12 is quite similar to my old VTF-3 MK2 - or the current VTF-2 MK4, as I mentioned earlier. And, again, that's why I recommended the FV12 so strongly. Even substantially more expensive subs like the EP500 are not necessarily better in every way.
So, regardless, I'd say you're back to the position of simply being forced to spend more to get what you really want. You seem to be very used to a very, very tight and controlled sound - you'd probably favor a sealed design with a lightning fast driver. My vote would go for the SVSound SB13-Plus DSP if you don't want to go "whole hog" for an SVS Ultra. And, naturally, you've got Rythmik's larger F15HP as a fantastic alternative, although you'll have to check if those are available, as parts shortages have put many of Rythmik's models on back order for the time being.
Again, my gut reaction is to just say to save up, go "whole hog" and get yourself an SVS Ultra. The PC13-Ultra DSP cylinder at $1700 is the steal of steals. And you can put it into "sealed" mode if the ported modes don't quite satisfy your tastes. Below that price, the SVS Plus and Rythmik "15HP" models are neck-and-neck. And below THAT price point, you'd be looking at HSU/Outlaw for something like the VTF-3 MK4/Outlaw LFM-1 EX or the HSU VTF-15H, which actually might suit your tastes quite well since it excels in mid-bass output. Certainly though, just in terms of physical size, the SVS SB13-Plus DSP sealed box is the most compact and it has the "tightest" response out of basically anything below 2 grand.
