So I finally got the two SVS PC-2000 Pros and the Denon receiver, and for posterity's sake, thought I would let future forum inquirers know:
I am keeping the SVS subs (or at least one--not sure yet whether I will keep the second). The Dynamo1600x is great, and if you can get a really good deal on it, I would highly recommend. But (a) $2000 would be crazy to spend for this sub (I spent $1350 and I think that is a little high, too) and (b) unsurprisingly, it can't match the low-bass output of the SVS PC-2000; it was pretty obvious. It is not a subtle difference. In the mid bass, the Dynamo is fantastic, but at least for my movie-watching tastes, the extra oomph from the SVS is more important.
I do have a few questions for anyone interested, relating to the subs and Audyssey, which I did not have before getting the Denon 3700 last week.
(1) Is it normal for Audyssey to put the subwoofers waaaaay down? I had to have the gain on one at -30 db and the other at -22 dbs to get into the range that Audyssey approved, and the receiver still put the subs down another 7db itself. I then turn the subs' gain back up after I am done with Audyssey, but does this indicate something is wrong? Should I handle this another way? (Like leaving the gain up, regardless of Audyssey's preferences, during the test?) It checked around and it seems like this might happen to other people as well because Audyssey is just trying to match db levels, but it seems odd, nonetheless.
(2) This is sort of a silly question, but can moving one of the subs about two or three feet from the corner make a huge difference? I got excellent response when I put the first sub in the front left corner. Just to see if I could, I move it about two feet inward for aesthetic purposes. That also allowed me to move my tower speakers further apart (they were a bit too close before, I think) and so I ran Audyssey again. The bass seems a bit less authoritative now, and I am wondering if I am just imagining things, if Audyssey changed something drastic (although I don't think it did), or if, yes, moving it two or three feet away from the corner really can make that much of a difference. I assume the latter, and I am going to move it back and try again, just wanted to see if that is really a thing.
(3) This is more a question for curiosity's sake, but what is the advantage of, say, a PC-4000 (or PB-4000) as compared to a 2000? Is it just filling up bigger rooms? I can't imagine ever needing more volume than what the PC-2000 Pro is providing in my large-ish basement (albeit, with a low ceiling, only about 8 ft). If anything, I have to hold them back lest I annoy the neighborhood. I haven't ever tried such a large sub in my basement of course, but I am just wondering what extra value it would have (if any), or if it is really just a matter of using it for a bigger space.
There’s been so much written about these questions... just on AH alone, much less the other forums out there.
For the most part, everything you describe is pretty normal.
Sub gain is usually recommended to start at about 50% and adjust from there. Audyssey is having you target about 72dB iirc. Having your gain down and trim down gives you a lot of headroom for dynamic peaks.
The other thing you will see is the distance for your sub is different. This is Audyssey managing delay for al the signals. I find that Audyssey does a very good job of this and recommend leaving them as Aud sets them.
You mentioned corner loading. This placement will augment the sound of the subwoofer, but may also create some boomy/muddy qualities. If I put a sub in the corner of my room it is almost unlistenable.
Every bodies room is different, even if you are in a closed rectangular shape. There are different ways of dealing with the acoustics in your room. I favor the Geddes approach to placement and multiple subs.
He recommends strategic asymmetric placement where the subs will excite as many room modes as possible to help eliminate any nulls or cancellations. He also recommends getting the subs away from your mains, as they are likely producing some low frequencies of their own, even crossed at 80.
By distributing your LF sources around the room you are able to smooth out you bass response across many seats and improve the overall experience...
Which leads me to your second sub:
Keep it!!! For the love of all that’s holy, keep it.
Learn to set them up right and take advantage of the acoustic boon it will offer.
Anyway... moving a speaker(sub included) even a couple inches can make a significant difference in performance. Likewise, moving your LP. Acoustics is a fickle mistress.
If you are serious about maximizing you HT and Musical enjoyment; getting the most out of the gear and this hobby: learn about acoustics! You don’t have to master it, get a degree in wave theory... but just learn how sound works in a room. I like the Master Handbook of Acoustics... lots of good info there and a valuable resource.
Master Handbook of Acoustics, Sixth Edition
https://www.amazon.com/dp/0071841040/ref=cm_sw_r_cp_api_glc_fabc_VMKZFb6Z1DFFG
Lastly, the 4000 series subs are larger drivers and boxes. The larger driver is able to move more air (greater displacement) and thus requires a larger box, which is also tuned to a lower frequency (giving you lower extension).
Where the 2000 series is rated for medium to large rooms, the 4000 series is rated for large to extreme rooms. Performance will increase accordingly: higher output, more headroom, deeper extension...
It can be nice to have more sub than you need, especially multiples.
That said, if you really wanted a bigger sub but find the budget for the 4000 series too high, consider Hsu subs. Two of their VTF3s cost less than 1 PC4000, iirc.
For now, though, I recommend you take some time to get to know the Subs you just got. Do the subwoofer crawl and learn about how Bass Frequencies actually perform in your room, and where the best locations are for placing the Subs. If you do this with an open mind, you may be very surprised at the results.
Also, an often overlooked aspect of high quality subs is that they are subtle. Usually, it is distortion that you hear and most people come to expect. When you remove distortions from the equation, you almost think the sub isn’t working... until all the sudden your foundation starts to settle!
Hope this helps!