I'm sorry, I just don't see it. Looking over on data-bass comparing the Reaction PV15X and the Powersound Audio XV15 (I don't think Josh measured the SE version of this one) there are several metrics we can compare.
First of all, in my post I meant to type XS15se in comparison to the PS15x, not the XV15se, as the two sealed subs are much more comparable, so that was a typo on my part. As for the XV15 and PV15x, yes, we can compare them, even though the XV15 is a discontinued model.
Long term output compression: The shape of the XV15 just makes much more sense to me. Is has a very gradual trail off from 100 Hz down to 30 Hz, where it then starts to roll off more rapidly. But, the more rapid roll off starting at 30Hz makes sense because it is possible to place this in an appropriately sized room and begin to get room gain to fill in, to where you will get a pretty flat frequency response down to 20 Hz or further. The PV-15X from 100 Hz down starts to increase to a peak output at about 55 Hz and then fall off kind of rapidly to where it is down by 10 dB at 20 Hz and then rolls off like a cliff. In the 40 to 70 Hz range, the PV-15X beats the XV15 by quite a large margin in terms of raw output, but it seems like I would have to end up EQing that range down quite a bit to get it back to a somewhat linear frequency response to where the output in those ranges are more close between the two subs. In that case the long term output curves, to me look like they would then be quite similar. If I were to buy the PV-15X, it just means I would maybe need to by something like a miniDSP to fix its frequency response, where I might not need to bother with the XV15
Neither sub holds their shape terrifically well in the long term output compression graphs. Here though, one point in favor of the PV15x is that its long term output numbers are just a hair beneath its burst output numbers. The XV15's output diminishes quite a bit more in long term output and its compression varies more according to frequency. As for the XV15's gradual rolloff, note that it gets that shape in long term output where compression sets in, and in the deep frequencies in that measurement the output is largely harmonic distortion and not the fundamental. At that output level, it would have benefited more from a steep rolloff.
Also note that all but the highest output levels, the PV15x has a relatively flat response with the notch filter engaged. You have to push it to the limit to get that long term output response shape, and if you are pushing your subs that hard, you need either a bigger sub or more subs. Also note that the PV15x hold a substantial output lead over the XV15 over not just 40-70 Hz, but almost the entire range.
Total harmonic distortion sweeps: The XV15 maintains THD below 10% on the 105 and 110 dB sweeps until you get down to the mid to low 20 Hz range. The PV-15X only maintains THD below 10% until you get down to about 32 Hz. I'm not comparing THD in sweeps above that, because that is when they really start to get to unacceptable levels for both.
As for THD, neither measurement is a thing of beauty for either sub, and in your very focused analysis, yes, the XV15 has a bit less THD in for a narrow band of deep bass within a certain level of loudness. The PV15x looked to be under-ported. Audibly, I don't think that slightly extra amount of THD would have been very significant to human perception.
Group delay and waterfalls: Both subs perform very well, staying under one cycle until below 20 Hz. Below 20Hz the XV15 maintains its composure in this area for the most part, but the PV-15X doesn't. The PV-15X starts to show signs of extra stored energy and ringing. Yes, we can't "hear" things below 20 Hz, but the extra ringing is going to continue to more pressure in your room in some scenes of movies than was intended, for example. This might be cool to shake the whole room, but not when it is not intended.
As Josh says in his write-up, " If this ringing was up near 35Hz it would possibly be audible but with 16Hz being such a low frequency, down where our ears are so insensitive, this is a complete non-issue." Anyway, I don't think anyone would mind a bit of extra acoustic energy below 20 Hz in the type of movies that have heavy content at those frequencies. That is not going to be what ruins the magic of scenes with autobots punching decepticons in Transformers part 9.
Appearance: Neither are winning beauty contests here. I don't care about this as much, but some people do.
I will definitely take the Reaction sub here. The finish is much nicer, a smooth matte black. The XV15 stock finish is much closer to a truck bed liner finish than their claimed 'satin black'. If you want to see what satin black is supposed to look like, look at Hsu's standard finish. I don't know how PSA can claim their standard finish is anything close to satin black.
Cost: The PV-15X was $1000 and the XV15 was $800.
With higher CEA numbers, much higher long term output numbers, and a nicer finish, you are definitely getting your extra money's worth with the PV15x. That being said, I think it is a good performer but not a great performer. It was under-ported and bore a fairly notable inductance hump in the response. I also agree its THD performance isn't amazing either. The improvements made in the Echo 15 look like they go a long way to correcting all of that.
To sum up I don't know how much of these subtle differences are audible, but I would say that the Powersound audio XV15 measures better than the Reaction PV-15X and is (was) cheaper.
I am not seeing better measured performance from the XV15 where the PV15x merits 115 and 120 dB output sweeps when the XV15 taps out at 110. Look at it this way, there is a lot more that the PV15x can do which the XV15 can't than vice-versa.
I'm not saying that the Reaction sub is bad by any means. Purchasing a MiniDSP to help shape its frequency response, to get a flatter response in room just makes the price difference larger between the two.
Again, you seem to be ignoring the effects of the notch filter in the PV15x which makes for as linear response as the XV15.
Also, Powersound audio is now on their 3rd iteration of the XV15 with the V1500, where they moved to using an ICE amp and I know they have been making improvements with each iteration. Yes, the price increased in doing so, but it is now neck and neck (in terms of price ) with the Reaction sub in discussion and I just think that it will be the more polished of the two if we were to measure them head to head. This is why I think that Powersound Audio is about a generation or two ahead of Reaction. But, I really am excited about the price/performance ratio Reaction is offering (just as much as with Powersound audio). We are getting performance that I never thought possible at these price points 10 years ago.
I think in terms of business finesse, PSA is ahead of Reaction, seeing as how Reaction is a much smaller and newer company, and also seeing as how their manufacturing operations isn't as smooth as PSA's, but as far as product performance goes, I would rather have a Reaction sub. One more thing, its interesting you should put as much emphasis in your reply on long term output and now mention ICE amps, I have a sneaking suspicion that both Reaction and PSA's move to ICE amps might not be much of an upgrade when it comes to long term output, but we will see- I could be wrong here.