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From sub out to Line in on THX amp, is it still THX?

Discussion in 'AV Receivers & Amplifiers' started by Apocalypse, Sep 14, 2002.

  1. Apocalypse

    Apocalypse
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    Silly question I know but I'm not really sure on this one.

    If I wire my front speakers from the "Line Out" of the sub to the "Line In" of the THX power amp will the front channels still have THX processing?

    I ask because now that I'm finally getting a Servo 15 I'm going to use the B&W ASW 675 sub as a booster for the fronts to get better musical performance.

    So to clarify :

    Subwoofer = Line Out to Line in of Power amp
    Subwoofer = Line in to Line out of Processor

    Amp and Processor are both THX.
     
  2. Reiner

    Reiner
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    Possible that you confuse line level and high (speaker) level connections?

    And why would you want to connect any output from the subwoofer back to the amplifier/processor? What input do you intend to use?

    If the sub is wired via line level you cannot connect your speakers to the sub "speaker out". Well, you could but they wouldn't work. ;)

    Normally in an AV setup you will just use a line level connection from the amps/processors "Subwoofer out" to the "Line in" at the subwoofer. Set the x-over at the sub to MAX and adjust the cut-over frequency at the amp only (if applicable only, on some amps it's static, i.e. cannot be changed).


    For high (speaker) level connections there are two options:

    1. Connect speaker out from amp to speaker in at sub. Connect speakers to speaker out at sub.
    Now you can use the sub's x-over to cut bass. This type of connection is suitable for stereo amps which don't have a bassmanagement and/or subwoofer output. Can also be used with AV amps of course.

    2. Connect speakers and sub in parallel to the amp. Speakers and sub will now reproduce the same frequencies (i.e. bass is duplicated). You may still adjust the x-over at the sub but it will have no effect on the main speakers.

    Note that some subs are specifically designed to take both inputs (line and high level) at the same time, allowing individual settings per input. I think REL offers this for example.

    If you use the high-level connection only you will IMHO loose the bass when THX is engaged as it requires the use of an (active) subwoofer. Front/Main speakers must be declared as LARGE then.
     
  3. Apocalypse

    Apocalypse
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    I don't think my first post was very clear and I apologise, below is how I want to wire my front speakers to the sub (that's the sub I use btw). In that configuration it gives superior music playback because the B&W sub is excellent for music with it's tight bass whereas a Servo 15 is really only for movies.

    In the speaker setup I intend to set the fronts to "Large" but the centre and rear to "Small/THX" and of course the Servo 15 will handle the subwoofer duties.

    I hope that clarifies what I was trying to get across :blush:

    Sub Connections
     
  4. Reiner

    Reiner
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    OIC, you have a pre-power combo - now it all makes sense! :)

    If the sub passes through the signal without cutting off the higher frequencies (which I believe he won't) it shouldn't be a problem.
    Fronts/Mains must be set to LARGE as you said while others can be small.

    However I am not sure if your amp allows the combination of LARGE and THX ON, it may activate the x-over in the processor and cut all frequencies below 80Hz. What processor are you actually using, does it support THX Select or THX Ultra?
    Doesn't the processor have a "subwoofer out"?
     
  5. Apocalypse

    Apocalypse
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    Hi Reiner, my pre/power combo is the RMB-1075 power amp and Marantz AV9000 pictured here

    The processor allows a "Large" setting while the centre and rears are set to "Small/THX" and the sub set to THX. Both amp and processor are THX Ultra btw.
     
  6. Reiner

    Reiner
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    Then I see no issue.

    However why do you not just use the subwoofer out of the pre-amp!? I am sure it has one, doesn't it?
     
  7. Apocalypse

    Apocalypse
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    We're still on diff pages of the same book I think Reiner :)

    Yes the pre amp has a sub out and the Servo 15 will be connected to it. However I have another subwoofer in the form of the B&W ASW675 which I want to use with the front speakers for "Direct" music playback which normally cuts off the LFE channel.

    So you see I wanted to know if my front channels will still have the quality of the Rotel 1075 power amp if I connected them via the B&W sub at line level. I realise by not setting the front speakers to "Small/THX" that it's not how it "should be" but I'm willing to accept that for better music playback. If you or anyone else has a better idea for achieveing that with my setup by all means please tell me as I'm new to pre/power setups.
     
  8. Reiner

    Reiner
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    ... which I want to use with the front speakers for "Direct" music playback which normally cuts off the LFE channel.

    What do you mean by that? What has "direct" (music) to do with the LFE?

    Note that LFE is not the same as subwoofer (or "subwoofer channel")!

    I realise by not setting the front speakers to "Small/THX" that it's not how it "should be" but I'm willing to accept that for better music playback.

    I think that's perfectly allright as you would not engage THX for music playback, right? So indeed the fronts should run as LARGE.


    If you want to run the fronts as LARGE and use the subwoofers then you can of course connect the way you show in the picture, but keep in mind that the bass is then duplicated to font speakers and subwoofers.
     
  9. Jase

    Jase
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    Hi

    Just poking my nose in here. What does your processor do in Direct mode, does it send full range signals to the front channels regardless of speaker settings?? If so, just leave all speakers set to Small/THX, bass to sub. This will be fine for movies etc and the Paradigm will be handling bass & LFE duties. Then just wire your other sub in line with the front speakers and you should also have the option to turn OFF the SW (subwoofer) channel (the Paradigm) so you don´t double up on bass.

    This is what my Denon does. I assume that´s what you´re trying to do.:)
     
  10. Apocalypse

    Apocalypse
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    Hi Jase and Reiner

    The "Direct" mode on the Marantz AV9000 bypasses tone controls for better music playback, the drawback to this is that it cuts out the subwoofer completely so yes the music has better clarity but it lacks the oomph. By connecting a sub to the fronts at line level I can get the oomph back but still have the improved clarity so I get the best of both worlds.

    Here is the worry though, I've yet to try the Servo 15 for movies with all the speakers set to "Small/THX". If it is an improvement over setting the fronts to "Large" I might have the annoying task of constantly changing the fronts setting depending on music or movie material :mad: :)

    I don't think there is a solution to this problem as I'm trying to get the best of both worlds, better music and movie playback in one setup.
     
  11. Reiner

    Reiner
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    Well, I would just try it then - can't break anything ...
     

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