I'd go with your last choice - separate x-over. If the high pass filter in your DD12 is the same as the one in my Velodyne SMS-1 controller - and I believe that it is - it ain't great. It subjects the main signal path to A/D/A processing and has a fixed turnover and slope. By contrast the low pass is incredibly flexible and IMO the A/D/A is much less objectionable way down there in the deep bass.
I use an NHT x-2 x-over to feed my SMS. It works like a charm, is inaudible (to my ear) AND it's inexpensive, to boot.
BTW, even though your main speakers have decent bass extension, you should experiment with crossing over at 80, 100, and 120 hz. This will allow the DRC in your sub to do its thing. I suspect you will be amazed by the improvement in sound.
I recommended experimenting with higher x-over frequencies because my experience with room issues has usually revealed the most audible problems lie between 50hz and 150hz, especially 80ish to 120ish . These are pretty common and usually very, very audible.
I use bass busters which are pretty effective at knocking out the hump between 80hz and 120hz in my current room. I cross at app. 75hz and the DRC in the SMS-1 does the rest. Without bassbusters, I'd start at 120hz to judge the effects of the DRC, then directly compare the sound to a much lower, audiophile approved x-over point. You may be surprised.
Note: if you use bass busters (or similar treatments), you can probably safely cross as low as 70hz - 80hz and get most of the benefit of DRC in the DD subwoofer. If you cross any lower, the DRC won't get a crack at the worst nasties in the room.
Marty -- yes thanks, your thoughts are very similar to mine. And in fact, with my previous pre-amp, I used the Velodyne exaclty as you noted -- by setting the crossover higher and having it reinforce the speakers output below 100 hz, I got better bass, and was able to use the parametric eq in the sub to smooth out the bass response. My problem is that the Nagra is a wonderful piece but for it's lack of output options. I've been pretty happy running the speakers full range, and the SMS unit built into the Velodyne confirms that, properly tweaked, I've got a nice flat response (except for one null at about 165 hz that I can't do anything about). So the crossover, while interesting, is largely a glorified output doubler. I am not convinced the NHT unit will be inaudible (based on some inquiries I've made in this respect) in my system, but it's not all that expensive an experiment to try.
looks like you already know the dd12 has a great interface allowing for some fantastic dialing in of the bottom end. if you take the time (many hours in my case), it can end up sounding pretty darn good.
i'm in an similar situation as you and chose the rca amp to dd12 route. didn't want to complicate/add stuff to the system/path of separates i just upgraded to. i actually tried to go without a pre altogether but my system sounds better with one. regardless... got the results i wanted while keeping it simple with the dd12.
i think the key here for me(us?) is the sub's background use and wanting to "round out the bottom octave". my 3 painstakingly customized pre-sets vary in volume from 16 too 22. this on a scale of 100 or 150 i believe, so i'm barely using the thing. just a little bottom end fill for the most part. i'm not using mine to "create" bottom end. just giving it a little bump instead.
Martykl: you're spot on regarding the 80-120 hot spots. mine was at about 85-100. set the dd12 x-over to 93 and it helped flatten it out fine (along with some other fine adjustments).
i'd try simple first and see how it goes. you can always add gear later. good luck.
Thanks Lev. Yes my volume settings on the DD12 are right where yours are. From a volume perspective it is "barely being used" but that little bit of volume does great things for the sound (after a lot of time getting the parameters tweaked properly).
Very good answers. The NHT X2 is surprisingly transparent for it's price and, in my case, cleaned up the crossover area. Beyond that, the difference it made was less than changing a single pair of cables.
If you're looking to maintain the "purity" of the main signal path,
what are your choices?
I can pretty much assure you that the high pass in the NHT is less audible
(and much more flexible) than the high pass in the SMS-1 as I have
extensively A-B'd the two. The Velo ain't terrible, but I knew it was there.
Also, the added flexibility of the NHT allowed for a better crossover function,
as I can high pass at my chosen turnover frequency and steeper slope than
the SMS allows. So, what can you do?
1) Use the active x-over of your choice (you might be more comfortable re:
transparency in the main path with Bryston or Marchand, but there's the $
2) Run the Curves full range, bypassing the DD's high pass and try to
"snug up" the DD from below, using only it's internal high cut
filter. You might get a good x-over function, but you've blown the
opportunity to maximize the benefit of the DRC.
My point is: Cable adaptors won't improve "purity" in the main
path (DD's high cut ain't great) unless you forgo DRC (low x-over point). If
your question is: "Is DRC worth some slight (in my case, inaudible to me)
degradation of the main signal path?", my answer would be "Without
Question, Yes, Yes, Yes"
Sorry I missed your intervening post re: the smooth bass response you're already getting from the Curves. My room makes such a result impossible. So, as Emily Litella once so aptly put it "Oh...never mind".
Hey Marty, no apologies necessary -- I appreciated your additional post. But actually, running the Curves full range and using the Velodyne it is still possible to get some benefit from the DRC in the Velodyne. By setting the low pass in the Velodyne to around 100, it actually reinforces the Curve's bass response below this level (and of course handles the low bass where the Curves drop out). As a result the main system is playing at lower volume to prduce a desired loudness. With the sub producing some part of the loudness, it is possible to tune the bass response of the room using the DRC in the sub. True, I'm not affecting what the Curves are doing at all, but according to the SMS software the response is considerably flatter than just running the Curves full range without the sub. Maybe someone will tell me this is sonically impossible, but I don't think so -- and unless the measurement microphone software (and my ears) are lying, it works.
I may try the external crossover still. But may wait to find a Bryston 10b. Or I may go ahead and try the X2. Still think about it.
Good point. It never occurred to me to try this. That's probably because, IME with measuring system response in room, I've found that almost any speaker with extended bass response will produce significant excess energy somewhere above 80 hz - in most rooms. Taming this can't be done with DRC in your proposed set-up. You could use bassbusters or maybe you don't need to if your room/speaker system is different than any I've measured - which seems to be the case here.
I'm pretty sure that the NHT X-2 is available direct (oand IIRC from AudioAdvisor.com for a few bucks less) with a money back guarantee for a home trial period. There's little at risk if you're tempted to check it out.
XLR Y-splitter out of the preamp.
Run the speakers full-range, they sound great right?
Tuck the sub underneath, less is more.
Clean and simple solution, takes advantage of what you already have.
FYI - someone has just listed a used Museatex active/passive switchable high pass filter for sale at $275. I haven't heard this model first hand, but I knew a guy some years back (generally reliable) who swore by it. Just FYI.
David, Marty, thanks for the additional replies. Your two posts bracket my thinking. So....I'm gonna try both and see which works better. Hey, it's a hobby afterall.