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Sub setup for HT/2ch mixed system

Discussion in 'Audio Visual' started by srey, Jun 26, 2022.

  1. srey

    srey Member

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    Looking for some advice. I'm going down the path of adding a 2ch integrated to my current AVR driven HT/music setup to do dedicated music duties. Setup will be as follows:
    • Marantz NR1602 (until I pickup another avr to get rid of the stupid DD+ decoding issue)
    • NAD C368 (waiting for it to arrive)
    • Revel M16 as mains
    • Focal CC800V as the centre
    • SVS SB1000 (non-pro)

    So all my AV sources will run into the AVR, which will drive the centre directly and send a pre-out signal to the HT bypass input of the NAD, which will drive the Revels. Music sources will be fed directly to the NAD and the avr won't even be on for that playback.

    My question is about the sub: I'd like to be able to use the sub for both AV and 2ch listening, and my preference for AV playback is to drive it from the dedicated sub output on the AVR, as from my testing so far with the Hegel amp I currently have, that produces better results than just feeding the sub from the 2ch's preouts with the AVR seeing the integrated as full range mains.

    My initial thought is to do this:
    • sub output on AVR to low level input on sub
    • preouts from NAD into 2>1 RCA cable and into the other half of the low level sub input
    • sub LPF and levels tuned to blend with the mains for 2ch listening (I expect to be around ~60-80Hz)
    I know that will work fine for 2ch, because it's how it needs to be setup regardless. But what I'm hoping will also work is that when I setup the AVR using audyssey, I can set it's internal crossover to match what I have set on the sub itself and it will send all the LFE plus the low end of the other channels to the sub via the direct cable it has. It'll then send the remainder of the crossed signal to the NAD which will drive both the mains and the sub, but that extra signal to the sub should be filtered by the LPF at the sub, so really the sub is only being driven by the signal coming direct from the AVR.

    I'm thinking though that I might end up with a spike just below the crossover freq, since that attenuated portion will be coming from the NAD and get past the LPF on the sub, but I'm hoping that the (admittedly crappy version) of Audyssey on the AVR will be able to largely account for this in its DSP.

    Thoughts?

    Alternative options include using the NAD's built in HPF instead of the dual setup, but it seems to be fixed at 150hz which I think is going to be too high. I could also get an RCA switcher I guess and so long as it has an IR remote I can get it to switch the sub intput as part of my Harmony activities, but I'm not sure how reliable they are.
     
  2. Audionut

    Audionut Member

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    I'm not sure what value the NAD is bringing!

    I would rely on the Marantz entirely for the routing. Else you're likely to have various issues such as;
    • differencing crossover points
    • differencing crossover slopes
    • double crossover
    • delays in the time domain
    You can still route the mains through the NAD if you desire.
     
  3. OP
    OP
    srey

    srey Member

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    You mean specifically in the AV playback chain or just in general? As far as AV goes for telly and movies I tend to agree, it's not adding anything other than maybe a slightly gruntier power stage, but I'm not sure that's going to make much of a tangible difference. The reason it's involved though is that I only have the space for one set of speakers in the living room and convenience is a big (big big) factor, so swapping speaker cables or using a manual switch box isn't a good option for toggling between TV and music usage.

    In general terms, I'm hoping the NAD will do a better job than the AVR for music playback. I previously had a denon 4520, their flaghsip from ~2012, still made in Japan and all. I heard a lot of 'an AVR is never going to sound as good as even an entry level 2ch amp' but really, the Denon absolutely did the job for me and I was very happy with it. But I've moved apartments and already given up the surrounds and consolidated my sources, and the Denon kinda seemed like a bit of overkill for a 3.1 setup with only 3 video sources. When it shit itself I picked up this cheap slimline marantz as a stop gap whilst I decided what to do to replace it.

    Straight up it became apparent that whilst the cheap AVR was ok for watching netflix and a few movies, the music playback was seriously lacking: much less body in the mid range and definition in the upper bass, and nowhere near the same detail in the top end. I thought maybe it was time to give up the centre channel too and just get a decent stereo integrated with a DAC that I could feed from the TV itself, but after testing just 2.1 I found that the setup of the room is a problem - half the seating on the couch is left of the left speaker, so the center staging is way off and dialogue gets badly smeared; I really do see an improvement in this space from a centre speaker.

    So now we're here, trying to integrate a dedicated 2ch amp for music and an AVR into one setup, with hopefully nice simple control from one remote.

    Your points about the crossover differences are all what I'd been thinking may be problematic, and I dunno whether the filters in the cheap audyssey implementation in the AVR are going to be nearly capable enough to smooth it out. When you say 'delays in the time domain' do you mean the delay created by the sub receiving part of the signal that has also run via the input on the NAD?
     
  4. flu!d

    flu!d Motoring and Intel forum admin

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    So effectively you're running the NAD as a power amplifier for the fronts?
     
  5. OP
    OP
    srey

    srey Member

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    For TV etc, yep. For music use the NAD is the only amp involved, the sources run directly into its preamp inputs.

    This is basically what I'm planning to do:
    [​IMG]
    [​IMG]
    [​IMG]
    The dashed line is the one in question, as ideally I'd be able to run separate, switched inputs on the sub itself, but it doesn't support that so I'm trying to figure out if there's a way I can get the same sort of behaviour without another switching box.
     

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  6. flu!d

    flu!d Motoring and Intel forum admin

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    I guess what really needs to be explained is: What are the preamp inputs and how do they work? Because, technically speaking, if you increase the volume on the AVR, you also increase the signal level from the line out of the AVR; If the volume control on the NAD is still functional when running a signal into the preamp inputs, than you will likely push the amplifier into a clipped state as the input gain from the AVR could go too high.

    I mean, realistically speaking, every RCA in is a line level pre amp input (not including the fundamental difference regarding real photo inputs).
     
  7. OP
    OP
    srey

    srey Member

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    Oh yeah right I see what you mean. It's one of the reasons I'm going with the NAD, it allows for a fixed gain to be assigned to an input. Other brands have dedicated 'HT Bypass' inputs, but in this case it seems like you can modify almost all of the inputs.

    So in practice, when I hit the 'watch stuff' activity on the harmony the NAD will switch to whichever line-in I've setup with fixed gain and default to that setting, then the AVR will control volume as per normal.
     
  8. flu!d

    flu!d Motoring and Intel forum admin

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    So if I'm reading you correctly, the NAD should essentially become a power amp and the volume control/tone controls on the NAD should do nothing? Because that's essentially how you need things to run to avoid clipping on the input stage.
     
  9. OP
    OP
    srey

    srey Member

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    Yeah correct, it essentially functions just as a power amp. I'm not 100% sure about whether the bass/treble trims will still be active when the input is fixed, but the volume will certainly be fixed on the NAD, with the calibration on the AVR taking that gain into account when setting the levels for the speakers.

    From the NAD manual:
    It's just how the Hegel I currently have is setup and this part of the system works simply and as expected. Where I have an issue with the setup is that if the sub is run only via the NAD then I can't cross the mains and sub from the AVR side, because the AVR essentially sees the NAD+sub as a pair of full range front speakers.
     
  10. flu!d

    flu!d Motoring and Intel forum admin

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    Well in that case it's no big deal re: The subwoofer, you just run it off the AVR and re run the calibration routine being sure to set the crossover level on the sub higher than the crossover level on the AVR. I used to run a separate power amp for the fronts no problem at all.

    The issue is you have to run the NAD in the above mode unless you want to risk clipping and possible amplifier damage due to the pre outs on the AVR going too high, so I see no way that you can purely use the NAD in some reference 2ch mode and completely bypass the volume on the AVR. You certainly won't be able to use the sub.
     
  11. OP
    OP
    srey

    srey Member

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    Yeah, but the complicating factor here is that I also want to use the NAD as a 2.1 system for music usage, which means its preouts need to run to the sub too, and as far as I can tell the pre-outs on the NAD remain active when the unit is in fixed volume mode.

    Sorry, not sure I understand the issue. The fixed gain on the NAD is a per-input option, so I just set it on whichever input the AVR is feeding, and as soon as I switch to that input we're operating basically as a power amp. If I want to play 2ch content I just switch to the optical input for my streamer, or the line input that's fed by the phono stage and the NAD is just working as a normal integrated, the AVR isn't in the signal chain at all.
     
  12. flu!d

    flu!d Motoring and Intel forum admin

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    Well your ability to do so is going to be determined by the crossover options on the NAD, unless your sub has speaker level inputs? Although using speaker level inputs isn't really ideal from a purity perspective.

    I can't imagine a 2ch amp intended for use regarding musical playback will go far below 100Hz as a crossover point? And even then it's going to mess with the AVR's calibration routines.
     
  13. OP
    OP
    srey

    srey Member

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    The sub does have speaker level inputs, but I intend to drive the sub from the NAD using the full range preouts, with the LPF on the sub set wherever I find it needs to be to blend the sub with the mains.
    The NAD does have a high pass filter option, but it's really high at 150Hz so I doubt I'm going to want to use that.

    The hypothetical is what happens if I do this:
    • NAD doing full range preouts to the sub (2 into 1 rca)
    • Sub low passed at say 90hz

      The above is the music setup, but for AV there's also the following:
    • AVR fronts crossed at 90hz
    • sub output from AVR direct into the other rca input from the sub
    It means that the NAD will see the 90hz crossed signal, so it'll send that to the mains (great) but it'll also send it to the sub, so there's going to be whatever signal is coming on that crossover slope into the sub input at the same time as the AVR is sending it the other half of the crossed signal vias its own sub-out.
    And there's the sub's own LPF running at the same frequency, so I figure I'm likely to get a whole bunch of weirdness going on in that a-bit-under-90hz range?

    Thinking about it, it'd probably just be really good if I could disable the preouts on the NAD on a per-input basis, but I don't think that's possible.


    EDIT: I guess the real question I'm asking is 'how bad is it to have these different x-overs operating on signals sent to the same sub at the same time?
     
    Last edited: Jun 27, 2022
  14. pezzy

    pezzy Member

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    i think in that scenario, both the avr and integrated amp will need to occupy the lfe input on the sub?
     
  15. Audionut

    Audionut Member

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    Fair enough. I would still use the NAD as a dumb power amp from the pre-outs of the AVR though, and let the AVR handle all of the routing.

    Correct. Subs tend to be inherently delayed, usually 6ms (half phase) or more. Phase controls on subs are technically delay controls and they can't negative delay, only add more delay.

    In every situation you describe, except for routing everything though the AVR, the timing of one sub will be tied to the NAD. This will make it difficult, at best, and most likely impossible, to get accurate timing between the mains and the sub/s, and you'll likely have all 3, that being mains/sub1/sub2, out of sync in the time domain. You can play around with phase dials to get things "in phase", but the subs will be 1 or more cycles behind the mains. And I'm envisioning a scenario where you have 1 sub a full cycle (12ms) out of sync, and the other sub another full cycle behind again. They might all be "in-phase" in the frequency domain, but you'll lose tightness and clarity if they are delayed in the time domain.

    What's the fear with using the Marantz pre-outs to drive the NAD in music mode?
     
    Last edited: Jun 27, 2022
  16. OP
    OP
    srey

    srey Member

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    Thanks for the reply, that is sufficiently dumbed down! :) I'd expected that there'd likely be an effective amplitude increase at certain frequencies below the crossover point due to the stacked signals, but was hopeful that the filters on the AVR side may be able to adequately compensate. I hadn't considered the timing issue though. I'm guessing where you talk about two subs you're referring to the two sub signals from the pair of amps? Because in my setup they'll both be running into the one physical sub.

    Mostly that it sounds pretty trash at the moment, and I'm not sure that an external power stage alone is going to give a noticable improvement. I figure that the preamp is likely to have much more effect on what I actually hear, so I should be using the NAD in that role.

    Yeah sort of: the sub has L/R RCA pair for low level inputs, the right channel serves as the LFE in a mono output, and I would intend to use a 2 into 1 RCA cable to get the dual preout from the NAD into the other low-level RCA on the sub. Both inputs are subject to the sub's LPF, but they also would both be active when I was using the AVR and I'd likely see the issues described above.


    I mean I haven't actually got this setup going yet, so maybe I'll fire it up and find that music from the NAD is actually fine without the sub, but I do listen to a fair bit of electronic music, and like it to kick something like it would in a club.

    What's the general consensus on introducing a RCA line switcher between both amps and the sub in order to toggle from the AVR to the NAD depending on whether I'm watching TV or listening to music?
     
  17. pezzy

    pezzy Member

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    ah i see. so something like this? i think this could work if the avr is switched off when using the amp for music. int l/r line out should be l/r sub out.

    edit: actually in this scenario, you will run into the problem where your avr and amp is on when watching movies? i imagine you will have to unplug the sub connection with the amp.
     

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    Last edited: Jun 27, 2022
  18. OP
    OP
    srey

    srey Member

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    I'd been thinking of just using the Y cable from the preouts on the NAD into the left input of the sub as the sub only needs mono, but actually, thinking about it I should probably just run a single RCA lead one of the preouts on the NAD anyway as I'm likely to get a level boost otherwise, right?
     
  19. flu!d

    flu!d Motoring and Intel forum admin

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    I just don't know how you're going to calibrate it? I know my AVR uses it's MCACC routines to calibrate the distance and levels automatically using the setup mic. You can do it manually using an SPL meter and measuring tape if you want - But there's also standing wave resonance adjustments that are difficult to manually (although not impossible by linking the AVR to a laptop and inspecting the waveform using the Pioneer supplied software).

    Personally, I'd be buying an AVR that sounds better in 2.1ch mode. By doing so you're avoiding a world of pain.
     
  20. OP
    OP
    srey

    srey Member

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    The calibration will work exactly the same way though? The NAD basicslly just functions as a power amp as far as the AVR is concerned.

    Obviously there won't be any DSP for music sources since they won't run through the AVR but that's typical of most stereo amps.
     

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