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Is using front channel pre outs better than using LFE output?

Discussion in 'Speakers' started by James Buhler, Mar 10, 2004.

  1. James Buhler

    James Buhler Stunt Coordinator

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    I was looking at some new subs yesterday and was told by the salesman that using the front channel pre outs on my reciever was a superior connection for subs than using the LFE out (single rca out.

    Does anyone have any thoughts on this?

    My current setup has the pre-outs running to a Yamaha amp then to a Paradigm passive sub. I am also using the LFE out to a Velodyne sub.

    Would I be better off running the pre outs to the Velodyne, then the lo pass line outs on the Velodyne to the Yamaha amp to power the Paradigm sub?
     
  2. Lee Carbray

    Lee Carbray Second Unit

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    What are your mains and how do you have then set up, large small? Do you listen to mostly music or movies?

    The easiest way to set it up would be to use the sub preout usa y adapter and send the signal to the Velo and the Yamy. All speakers set to small.
     
  3. ScottCHI

    ScottCHI Screenwriter

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    i'm not certain how your receiver/pre-amp works, but my denon will route the LFE signal to the front pre-outs if told that there is no sub. of course, this usually forces your fronts to LARGE and sends them the LFE signal, too. what is your front speaker set-up?
     
  4. James Buhler

    James Buhler Stunt Coordinator

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    My mains are Polk RT-800's, large tower speakers. Receiver is HK-AVR500 with fronts set to large. The HK will still route LFE channel to the sub with fronts set to large.

    My question was really more to the effect of, is the salesperson full of doody? He went as far as to say that B&W recomends not using the LFE outputs on recievers when using their subs and to use pre outs and the sub's crossover to handle the bottom end.
     
  5. ScottCHI

    ScottCHI Screenwriter

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    right, but it won't route the LFE to the front pre-outs unless you tell it you have no sub (unless your receiver/pre-amp has some feature that will allow this).

    if you use the front pre-outs for a sub connection instead of the LFE outs, and the speakers are set to LARGE, it will work fine for music, as the salesman described; the speakers will naturally roll-off and you can use the sub to "fill-in" the very low-end.

    HOWEVER, during 5.1 playback, the LFE signal should not normally be routed through the front pre-outs, unless, as i said, your receiver/pre-amp will do this. this will present a problem if you want your LFE channel reproduced.

    one option is to tell your receiver/pre-amp that you have no sub. then, the LFE signal (along with the low-end signal of any speakers set to SMALL) should go to the front pre-outs. HOWEVER, with this setup, the LFE signal plus the signal of any speakers set to SMALL will come out of your front speakers, as well. this may not be desirable to you.

    another option might be to experiment with connecting a sub via the front pre-outs AND the LFE out.
     
  6. James Buhler

    James Buhler Stunt Coordinator

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    Actually, the receiver does route the signal to the pre outs with sub set to "on". I am running my velodyne from the lfe out and using the front pre outs to the Yamaha amp powering my Paradigm sub.
     
  7. David Judah

    David Judah Screenwriter

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    It depends on the related equipment and application, but I think generally it would be better to have the main crossover done in the digital domain.

    DJ
     
  8. Wayne A. Pflughaupt

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    Superior?

    One word: Hogwash.

    Actually I see it as a potential problem since your only option then is to set the mains to large. Do this and you’ll probably have some bass overlapping, and that usually messes up the sub’s response.

    Regards,
    Wayne A. Pflughaupt
     
  9. ScottCHI

    ScottCHI Screenwriter

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    the LFE signal shouldn't go through the front pre-outs unless you're somehow forcing it to. with sub set to ON, the LFE signal shouldn't come out of the front pre-outs.

    how do you know that the LFE signal during 5.1 playback is coming out of the paradigm? are you certain? think about this, because the answer may not be as obvious as you think. it'd be very hard to distinguish the low frequency signal coming from the L+R MAIN channels from the low frequency signal coming from the LFE channel in that situation (sub connected to front pre-outs with LFE signal "mixed in") during movie playback. even with a calibration disc, like avia, it'd be difficult.

    btw, look at this thread for some recent discussion about pre-out versus LFE sub connection.
     
  10. James Buhler

    James Buhler Stunt Coordinator

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    I'm not saying that the LFE channel is coming from the pre outs. All that they send to the Yamaha amp to the Paradigm sub would be the full range program material from the front right and left channels.

    I have the LFE output on the receiver running to the Velodyne line in and both subs are producing sound. So can't I assume that the .1 (LFE) channel is coming from the Velodyne and the Paradigm is getting the front channel signal?
     
  11. ScottCHI

    ScottCHI Screenwriter

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    do you still have the same question? it seems there is a reason that you, personally, want separate subs for LFE versus L+R signal during dd/dts playback; this "piggyback" option you're describing will eliminate that possibility. if you run both subs in a chain like that from the pre-outs, AND FORCE THE LFE SIGNAL TO THE PRE-OUTS, you will have a mix of LFE+main in both subs. of course, if you don't do something to force the LFE signal into those front pre-outs, you'll miss the LFE signal completely with this piggybacked setup. usually the only way to get the LFE signal into the front pre-outs would be to tell your receiver that you have no sub (this is how mine works, anyway).

    it comes down to whether you want to keep the LFE and MAIN low end signals in separate subs or not, right?
     
  12. Edward J M

    Edward J M Cinematographer

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    I agree 100%. The RT800i performs far better set to small than large. And BM done in the digital domain is best.

    With a Y splitter, both the Yammy/Paradigm and the Velo can be individually calibrated from the same signal.

    One sub is probably capable of more clean output than the other. Determine that approximate difference in dB (for arguments sake, let's say it's 3 dB). When calibrating, set the weaker sub 3 dB below the level of the stronger sub.
     
  13. Kernel X

    Kernel X Extra

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    How' it going? If your receiver has a LFE output, then you should definitely use that, even if you have two subs you can connect them with a y-connector. Sometimes its better to run a single cable from your receiver's LFE and split the signal at the end of that cable using a Y-connector and another cable to the other sub. Try both ways to see which sounds best. I get a better signal when splitting from the first sub to the second. Using pre-amp ins and outs on a receiver is better for equalizers or if you are upgrading the power you can use the pre-outs to connect seperate amplifiers. Best of luck!
     
  14. dave alan

    dave alan Second Unit

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    I apologize for being a bit lost.

    I understand the SW output to the Velo.

    The FL/FR preamp outs go to "the Yamaha amp then to the Paradigm sub."

    The FL/FR preamp outs go where exactly, if you don't mind?
     
  15. ScottCHI

    ScottCHI Screenwriter

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    according to his post, they go to an amp which is connected to a passive sub. what's confusing you?
     
  16. dave alan

    dave alan Second Unit

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    ScottCHI,

    I appreciate the reply.

    I'll be more specific:

    1. How are the FL and FR Polks connected?

    2. How does the Yammie receive FL and FR signals and output 1 signal to the passive sub?

    3. How is the signal to the passive sub filtered?

    Thanks for your patience.
     
  17. ScottCHI

    ScottCHI Screenwriter

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    well, there's gotta be a crossover (or low-pass filter) somewhere. i'm assuming it's at the sub itself.
     
  18. Michael__M

    Michael__M Stunt Coordinator

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    There are times that running the subs off of the main outs is an advantage over the LFE. If your LFE out is fixed (which is usually is) at a very high frequency, this may not mate well with the sub/main combo you are using or maybe even the room you are in. I had my Yammie on my system for a while. It had a fixed 90hz LFE out. This was very hard to manage. Using the main outs and the adjustable crossover on the sub (spaekers to large and sub off) gave better results for me in that setup. You have to really find out where your mains roll off and bring the sub crossover in to blend well. It is more difficult to set up in a way, but the results could be better in some situations. Now for you, I think your LFE out is adjustable, isn't it?

    In that case you should use the LFE for both subs and bypass any crossovers on the sub. All speakers set to small ans sub on.
     
  19. ScottCHI

    ScottCHI Screenwriter

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    no. from the descriptions in his posts, it looks like he purposefully wants one sub to handle LFE and the other to handle the L+R low-end. he runs his front speakers as LARGE. he's using the passive sub to "fill-in" the low end where his fronts, set as LARGE, naturally roll-off.
     
  20. BruceD

    BruceD Screenwriter

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    I actually disagree with this "BM done in the digital domain is best", but it depends on the specific equipment used, and I don't have Polk RT800 speakers.

    I disagree because most of the high-pass digital xovers in receivers have a 12dB/octave slope for the main speakers, and it is almost impossible to get a good match with the receiver's 24dB/octave low-pass for the sub with tower mains set to small.

    This is because the main speakers do not have a 12dB/octave rolloff at the xover frequency (90Hz, 80Hz, whatever) to add to the receiver's high-pass 12dB/octave slope to get a full 24dB/octave slope for the high-pass. You generally want the high-pass and low-pass slope to be equal across the xover boundary. This is why THX certified speakers have a -3dB of 80Hz (with a rolloff of 12dB/octave).

    But, I do have main speakers that are towers and have a -3dB of 31Hz. I set them to large, say sub=no, and use an external active crossover between the L&R preouts and the main speaker's amp and the sub(s). You could also use the xover in a sub, but they are typically of lower quality.

    I use an active xover that has 24dB/octave slopes for both the high-pass and low-pass and then set the xover frequency for the mains (in my case 60Hz) about an octave above the main speaker's low frequency -3dB point of 31Hz.

    Setting the xover an octave above the main speaker's -3dB takes the main speaker's rolloff characteristics completely out of the picture.

    This works great for both 2-channel and HT 5.1 material.

    For a quick description you can check out my Equip List below.
     

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