Back Surround Speakers vs Overhead Channel

Discussion in 'TAG McLaren Audio Owners' Forum' started by ThomasBelgium, Jul 20, 2004.

  1. ThomasBelgium

    ThomasBelgium
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    Hi all,

    I want to use my TAG AV192 as the centerpiece in a reference quality HT I want to built. Until now I only used the Av192 as a 5.1 processor, because I do not have the place for a 6.1 or 7.1 system. What I wonder is this:

    1-Is it better to use 1 extra speaker for Dolby EX and DTS-Es or are two speakers better?

    2-Is it OK if I use one of the two back surround outputs of the Av192 and attach it to a Y-cable which then will be connected to two amplifier modules (could be a stereo power amp)? Doing this lets me use the other back surround output for a height channel... I believe that the two channels in a 7.1 system are identical but maybe I am wrong. Maybe THX Ultra 2 processes the two channels in a such a way that they are a bit different. If that would be true, using only one back surround output with the Y-cable would be compromise, wouldn't it?

    3-I also wonder if a height channel is really an added value? There is no content for this channel on a dvd, so why bother? Another problem is, that you should use identical speakers in a surround system or at least speakers with identical mids and heighs. If you add a height channel to your system, you need a special speakers that is meant to be built into a ceiling. Brand like KEF and B&W have some nive timbre matched ceiling speakers, but what if I more like speakers from Wilson or Avalon, just no name a few?
    :confused:

    4-And here is the final question: If I want to use a height channel, would'nt it be better to use another Y-cable and connect it to two amplifier modules and two ceiling speakers? I thought that could spread the sound a bit more...

    Thanks for your answers! :smashin:
     
  2. Stevesky

    Stevesky
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    Answered in the same sequence as your questions:

    1. With the introduction of technologies like PLIIx and THX UltraII Cinema I personally suguest going for 2 surround backs. In the early days the 6th channel was not that great as the Matrixes that steer the audio from SL, SR to SB had a habit of doing an all or nothing job. I prefer +PLIIx from THX Ultra 2 as it generates quite a nice natural surround effect. If you only have one surround back speaker then PLIIx can't really work at it's full potential as it's then doing EX decoding using the latest PLII matrixing algorithms.

    2. You would need to do the Y adapter on the SBR. Issue with this is that you need to reconfigure your AV in the menu system to tell it that you want ceiling support, not stereo surround backs. Also the time alignment, level and TMREQ settings will be different for the two different speakers.

    3. Some people love it, some don't! It can be a bit hit or miss on how well it works as the height channel is implemented by analysing the audio in the centre channel and surround back and deciding if it should really go to the height channel (or somewhere inbeween) or stay where it is. The scene in Pearl Harbour where the Americans get a good kicking at the end works really well with the height channel, with planes wizzing over and the voice on the tannoy in the bombed boat come from above ... cool!

    When a speaker is located on a different axis or fundamental position it will have not have the same timbre as say your left/right - just like a "matched" centre speaker of same brand/drive units normally have a different timbre due to the position of the speaker. A good dose of TMREQ can sort most of that out though.

    4. No harm in that - just recheck your levels afterwards.

    All I can suggest is try and bodge it together with existing speakers you have to see if you like it or not. Out of having a 7.1 system and a 6.1 + height I prefer 7.1, but every man to his own.

    In my home system I run 5.2 as I can't justify the space for the surround backs and my system is more used for music than movies.
     
  3. ThomasBelgium

    ThomasBelgium
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    Hi Stevesky,

    Thanks for your answers. However, it is still not quiete clear to me whether or not I lose something if I use one output (SBR) and splice it then with a Y-cable to two channels. Because doing this would result in two absolute identical surround back channels...

    If I use the two surround back outputs of the Av192R (with normal cables) are the two channels then in some cases (PLIIx, Dolby EX, THX Ultra 2) a different from each other or not?

    The point is that, before I consider using a height channel or not, I want to know whether or not that is a compromised situation for my back surrounds?
    Anyway, it is fine that the TAG allows different TMREQ settings and level/delay settings for the SBL and SBR channels.

    What exactly do you mean with: (quote:) I prefer +PLIIx from THX Ultra 2 as it generates quite a nice natural surround effect.

    Do you mean that you like using DTS or Dolby Digital together with PL2X and that you don't like it with THX Ultra 2?

    I remember that on the old TAG Forum there was quiete some information to be found of people who were using a height channel... Sad that I can't check it now that I nedd this information... :thumbsdow

    Could you tell me why you prefer the 7.1 over the 6.1 + height channel?

    Thanks!
     
  4. Stevesky

    Stevesky
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    With PLIIx and THX Ultra 2 Cinema the surrounds are stereo, not mono and the various techniques used to generate this information is far far superior than a mono signal spread across two channels. when doing the Dolby EX processing mode the surround backs are mono so it won't make any difference.

    On the AV192R and AV32DP we never got round to supporting DTS with PLIIx, but with multichannel Dolby Digital (eg. 5.1) it does a good job. As you have an AV192R have a listen and decide what format you prefer! hehe, I don't want THX sending me hate mail!!!! :)

    I prefer 7.1 over 6.1+height channel as there is sufficient information in the discrete surround channels to derive a sensible set of surround backs using systems like PLIIx. In the case of height channel it a hit and miss affair if the information steered to the ceiling was ever intended to go up there. The system can only work reliably if the original material was mixed so sounds that had a height aspect to it had a phase relationship between front centre and surround back. It's quite feasible for cars, boats etc. to go wizzing over your head!!!

    As I said best to experiment before you starting bolting things to your ceiling. I know several people posted on the old forum who have loved the height channel feature.
     
  5. ThomasBelgium

    ThomasBelgium
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    So, if I understand this right then the follwowing statements are true:

    1-The extra channel in a Dolby Digital EX datastream is matrixed from the 'normal' surround channels. If this extra channel is routed to two speakers (without any extra processing engaged) then the signal in these two back surround speakers is identical. In that case, a 7.1 system doesn't have any real advantages over a 6.1 system.

    2-The same statement is true for a DTS datastream, with the difference that sometimes the extra channel is totally discrete and sometimes it is matrixed. (I do not remember having seen on a dvd package the word 'Discrete' next to DTS, it just says 'DTS-ES' and then you can guess whether it's discrete or not...).

    3-If Dolby Pro Logic IIx is engaged, then the signal in the two back surround speakers is indeed different. So in this case information will be lost when the Y-splitted cable is used on the surround back channel of the TAG, in stead of connecting a cable both on the surround back left and surround back right outputs. It doesn't matter what kind of signal the source signal is: it could be plain stereo, Dolby Digital, DTS or even Dolby Digital EX or DTS ES.

    4-The same statement as in point 3 goes for THX Ultra 2 Cinema (what about THX Ultra 2 Music?).

    As a conclusion, it is fair to say that there is indeed a hard choice to be made whether you want a height channel or not. If you use one of the surround back outputs of the TAG for the height channel, then you have just one channel left for steering the surround back speakers. A Y-cable splitter can be used to steer two surround back channels, but of course those signals will be identical. That is no problem as long as you do not (want to) use DPLIIx or THX Ultra 2 Cinema, but if you do, information will be lost.

    And if even 'normal' Dolby Digital or DTS signals indeed sounds a their best in a 7.1 system when they are processed by DLPIIx or THX Ultra 2 Cinema, then withholding one of the surround back outputs in the Av32/192 for a height channel might be not a good idea after all...

    Comments are welcome!
    :clap:
     
  6. ThomasBelgium

    ThomasBelgium
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    I was thinking that it is sad that this kind of information (the fact that the two back surrounds are not the same signal in the case of Dolby PL2x & THX Ultra 2 Cinema) cannot be found on the websites of Dolby and THX... :nono:

    Even worse is the fact that on the old TAG Forum there was lots of info to be found on the Overhead Channel and now this beautiful Forum is closed!! :thumbsdow :thumbsdow :thumbsdow
     
  7. lenny

    lenny
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    You right for both statements. That's a pity! Thank you for this discussion : very useful indeed. I think I'll not use the 8th channel....
     
  8. Bogi

    Bogi
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    Thomas

    As I remember it we discussed an external switch that would make it possible to use both back speakers when using DPLIIx, THX Ultra 2 etc and then switch over to mono signal to both back speakers and the overhead speaker.

    I recall that Udo had such a switch which can be bought from well stocked audio shops. I ended up buying components for a DIY-job, however I never got around to it as the software in the AV32R DP didn't store the settings for the 7th back speaker (if you switched from 7.1 to 6.1+Overhead and then switched back, the latest setting was lost). So in the end I couldn't be bothered.

    Those with the overhead channel reported excellent results with Master and Commander (the Russel Crowe flic), but software that lends itself to the Overhead channel is so scarce that frankly I don't think it's worth the hassle.

    DPLIIx in it's different forms is really my standard setting for most material these days. I use a 7.1 monopole set up which works really nice. I think Dolby really did a terrific job with DPLIIx and it'll take some beating before DPLIIx is left in the dust by another format.

    I also find THX Ultra 2 Music useful, however I'm not too fond of THX Ultra 2 Cinema as the correction on the front speakers takes away some of the dynamics on most modern day DVDs, which are mostly post edited for use in the home environment nowadays.

    Cheers
    /Bogi
     
  9. Stevesky

    Stevesky
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    For info on PLIIx check out:
    http://dolbysearch.dolby.com/Consumer/Technologies/PLIIx/

    For basic operation of the PLII matrix (aka Dolby EX matrix) check out:
    http://dolbysearch.dolby.com/Consumer/Technologies/PLII/PLIIwhtppr.html

    Couldn't find much on the THX site, I think they've been too busy designing their THX trailer video download page!

    For clarification on the second round of questions the THX Ultra II Cinema and THX Ultra II Music are not possible on a 6.1 system so the AV doesn't offer them as a processing mode.
     
  10. ThomasBelgium

    ThomasBelgium
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    @ Bogi: Yes, I remember having seen discussions on the old TAG website regarding special switches and so on, but I do not remember what those switches exactly could do and where they could be bought..?
    Maybe Udo could clear this up.

    Such a switch might be the golden solution as, depending on the situation, both surround speakers could be used in stereo (for Dpl2X and THX Ultra 2 Cinema) or the height channel could be used together with mono back surrounds. If such a switch could be controllerd with a Pronto or by a 12 volts trigger, it would even be better...
    Too bad that the software in your Av32R DP didn't allow you to do what you wanted to. I hope the software in the AV192 does not have this problem...

    You said: (quote:) DPLIIx in it's different forms is really my standard setting for most material these days.

    I pressume you mean using DPLIIx on top of Dolby Digital/ DTS: Dolby Digital EX/DTS ES soundtrack? Whenever people are refering to DPL2X is never quiete clear to me whether they mean DPL2x in 7.1 system or in a 5.1 system. On the other hand, I believe that it is not possible to use DPL2X without a 7.1 or a 6.1 system...

    @ Stevesky: I had already checked the documents your links are refering to, but they never really say that the two extra channels are different from each other when DPL2X is engaged or have I missed something?

    I am afraid I do not quiete ubderstand this quote: For clarification on the second round of questions the THX Ultra II Cinema and THX Ultra II Music are not possible on a 6.1 system so the AV doesn't offer them as a processing mode. :confused:

    I will be out for a few days, but I am happy to find any more comments on this post! :clap:
     
  11. Stevesky

    Stevesky
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    The issues in the switch idea is that you would need a very easy way to reconfigure the unit between single back+height and two backs. Also the unit would need to have separate eeprom storage areas for height channel and surround back right for distance, level and TMREQ. At the moment it's shared to save space and for backwards compatibility and its easier said than done to separate it out.

    If you have a look in the PLIIx FAQ there is the question:
    >> Are they stereo Surrounds and stereo Backs?
    Answer: YES!
    It's also on the front PLIIx page next to the funky animated diagram where it states each signal is unique.

    As for the bit you are confused about, you asked:
    >> 4-The same statement as in point 3 goes for THX
    >> Ultra 2 Cinema (what about THX Ultra 2 Music?).
    THX Ultra II Music (and Movie) are inhererently stereo surround back formats, so don't exist in a 6.1 system where you only have a mono surround back. If you are using the height channel then you have a 6.1 config, so no THX Ultra II Music or Movie.
     
  12. ThomasBelgium

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    Hi Stevesky,

    I fought that people on the old TAG Forum came with a working switch solution (or even different solutions), but maybe it had some disadvantages that I am not aware of...

    For the PL2X FAQ: I stand corrected :blush:
    The THX Ultra 2 explanation also makes sense now.

    Thanks a lot for your information!

    It would be nice to get some reaction from people who are using the height channel.... And it might even be better if Udo (or someone else) could explain the external switch thing...
     
  13. Barry.NI

    Barry.NI
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    Thomas,

    I was wiring up my AV room, when the height channel came into being, I therefore put in two KEF ceiling speakers and two KEF surround back speakers. SBR is wired to a Tag 60p power amp, through a splitter, with one channel going to the RH ceiling speaker and one channel to the RH surround back speaker. Likewise SBL is wired to a similar amp on the LH side, feeding the LH ceiling speaker and the and the LH suround back. If you sketch this out, you will see that it is quite simple to manually feed the SBR channel through the splitter to the two ceiling speakers,using one channel of the L & R 60P., and the SBL through the splitter to the two surround back speakers, using the other channel of the L & R 60P. This as you say would result in the same signal going to the surround back speakers, and the height information going to the two ceiling speakers. When PL11x came out, I decided I would prefer the split information on the Back Surround speakers, as most of my viewing is SKY+ TV. There was some discussion on the TMA Forum, regarding a better method of being able to switch between these two modes. John Mulcahy, technical director of TMA, posted a reply to the effect that THX Ultra could not be selected with the height channel enabled, and that they would look into ways of incorporating a system that would switch between the height channel, and the split back surround speakers, one suggestion was to use the Zone Two outputs. Unfortunately events overcame this modification. Udo came with a switching system, which I looked at, but like Stevesky, I never really followed it up. I have the DVD 'Master and Commander', so I might try to reconfigure the system to restore the height channel, and advise on the results. Will have to wait till September till the projector is working again.
     
  14. ThomasBelgium

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    Thanks for the information, Barry.
    I would be pleased if you could tell me your experiences with your re-installed height channel with dvd's like Master and Commander as well as with other dvd's that have no Height Information on them (99,99% of all dvd's, I suppose...).

    If someone (maybe Dr Zucker?) could help me with the automated switch thing, it would even be better!
     
  15. Stevesky

    Stevesky
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    Hi Thomas,

    As mentioned in one of my posts the switch box idea had issues and would of required some software modications to make it work in practise. These would come down to:

    1. Ability to drive an action trigger based on switching height speaker on/off. Also make the system switch between 6.1 + height and 7.1 mode at the same time.

    2. Separating the storage space for SBR and height channel so they can have independant settings. As mentioned this is not an easy job.

    3. Adjust the SBL level to cope with it driving either 1 speaker or 2 speakers as inroom level will increase when driving two speakers from 1 channel.
     
  16. edward

    edward
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    Stevesky,
    You said you never got around to supporting DTS with PLIIx. Having experienced the difference that came to Dolby Digital with the PLIIx version of the software, I'm wondering what sort of improvement it might also have made to DTS. Presumably you had some notion about theoretical improvements. Care to share them with us?

    Has anyone had any indication of when we might see the next version of the software released?
     
  17. ThomasBelgium

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    Hi Stevesky,

    So, if I read this correct, the external switcher thing is just not possible because of software issues. In the heydays of TAG this problem could have been fixed, but I am afraid IAG won't care too much.

    I hope I am wrong on this and that IAG will indeed start to take over the real work in stead of just moving boxes around... :thumbsdow
     
  18. Stevesky

    Stevesky
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    Hi Thomas,

    Correct, for a simplistic switch box the idea won't really work properly without some software modifications.
     
  19. karlknurr

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    Hello, I like to try high channel speakers with my AV32R DP but I doesn't find this setting in the AV32R menu. Any ideas how to activate them?
     

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