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7.1 is a con

Discussion in 'AV Receivers & Amplifiers' started by mike_cummi, Aug 6, 2003.

  1. mike_cummi

    mike_cummi
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    7.1 has mono surround backs, therefore, it is nothing more than 6.1 through 7 speakers. I know 7.1 refers to the number of speakers and not the number of channels, but that flies in the face of traditional surround nomenclature. By the same logic DPL would be a 5.1 system - we all know it isn't.

    Anyway, what's to stop you having 7.1 off a 6.1 amp by buying a speaker switch from RS for about £13 and delivering the 6th channel to 2 speakers?. Okay, it wouldn't sound as good as a proper 7.1 amp and a 7.1 amp would doubtless have more advanced facilities and upgradeability, but you would save a whole lot of money which you could put towards more frequent amp upgrades as technology advances. Many 6.1 amps have 100w or thereabouts for the 6th channel and so I'm sure 50W per speaker would be enough for the 6th and 7th channels in a 7.1 system.

    Has anyone tried this?

    I realise that you can achieve the same thing by hooking the 6th and 7th channels from a 7.1 output up to a stereo power amp, but power amps tend to cost more than £13!
     
  2. HotblackDesiato

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    Couldn't you just wire the two rears in series...and thereby save 13quid!
     
  3. mike_cummi

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    In series? sorry, long time ago since i did physics. i remember circuits can run in parallel or series but can't remember which one's which.

    Is in series where you would run the speaker cable into one speaker and then the other? Would this create a delay in the soundstage?

    Or do you mean splitting the speaker cable and soldering two lengths of cable onto each end. You would then have 2 y-shaped cables with which you could run two speakers off one amp. Would that work?
     
  4. Dimmy

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    It'd simply mean running two sets of speaker cable to each speaker from the same power amp channel.
     
  5. mike_cummi

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    Doh! I see. Thanks.
     
  6. wilber

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    O level physics 25 years ago so don't trust me - check further.

    Surely its amp red to spk1 red spk1 black to spk2 red spk2 black to amp black
     
  7. owenw

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    Does anyone know is there a discrete (i.e. real) 7.1 surround system under development by the boffins at Dolby / dts?

    The cynic in me also thinks the current DD-EX / dts-ES systems
    are part of a scam to part people from their hard-earned! :thumbsdow:

    OwenW
     
  8. mike_cummi

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    I don't know if it's on it's way or not. I would imagine it probably is but not for a couple of years or so. Even when it is developed it may take a while for software to become available - 6.1 software is still not exactly everywhere!

    To be as future proof as possible I was considering getting either the Denon 2803/3803 or pioneer 1011/2011 which are 4 of a handful of reasonably priced receivers around at the mo which have 7.1 analogue inputs and outputs. Such connections will allow you to utilise discreet 7.1 from a source with an on board 7.1 decoder and 7.1 output when using 7.1 software if and when it ever arrives. Note, you will need an amp with 7.1 inputs and outputs for this! Not just one or the other. This is similar to how pro-logic amps with 5.1 inputs can be partnered with a suitable source with a 5.1 decoder and output to give 5.1 sound.

    However, by the time discreet 7.1 arrives there will probably be so many other bells and whistles developed that the amp will still be obsolete even if it has 7.1 inputs. We've seen the recent arrival of DPL II, DTS Neo 6 etc... Who knows what will be around in a few years!

    My advice would be to get a decent 6.1 amp with enough power in the sixth channel to drive two speakers in mono (80 watts or more should be more than enough and is commonly available on decent 6.1 amps. Just hook up two speakers to the sixth channel. The money you save can be put towards more frequent amp upgrades as technology progresses.
     
  9. pwiles1968

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    Dimmy not quite that is parallel and will put quite a large load on the amp, wilber is correct, this is how I am about to wire my new centre rear Solid’s as soon as they arrive, The Marantz will effectively see 16 Ohms (assuming 8 Ohm each speaker), which is OK according to the back of the reciever.

    The time difference should not be an issue as from memory I believe electricity travels at near the speed or light, which is quite a bit faster than the speed of sound.
     
  10. wilber

    wilber
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    pwiles thanks for reassuring me that i'm not senile after all - must tell the kids not to ready the old people's home just yet
     
  11. buns

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    Sorry to rain on the parade..... but although you may wire up so as the amp sees a higher impedence and it should work, you may well have volume issues. In doing what you are suggesting, each speaker will get exactly half the power that an individual will, so you may not be able to get the same level on any speakers which you run in this fashion. Suffice to say, you will have to run that channel at excess volume as compared to the other channels, so you will be potentiually overloading your amp even doing it this way. There is a famous phrase that im applies in these matters, 'there is no such thing as a free lunch'.

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  12. Reiner

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    There is no need for a switch to make a "7.1" system out of a 6.1 one. Else just use on back surround speaker (i.e. a 2nd center).

    Speakers should be connected in parallel (all red together, all blacks together) if their individual impedance is 8 Ohm or higher.
    For speakers with lower impedance, in particular 4 Ohm speakers, wire in series: red (amp) to red (sp1), black (sp1) to red (sp2), black (sp2) to black (amp).

    DTS can support more than 6.1 but of course it would require new hardware (encoders and decoders/AV amps with such a decoder). And someone needs to mix the soundtracks accordingly.
    MPEG-MC was also specified as 7.1 but it's pretty much dead now.
     
  13. EvilMudge

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    Get yourself a listen to something like a Lex MC12 or Meridian 568 with full 7.1 processing. Both these machines can steer rear sounds in ways that even THX Ultra2 can't quite manage. Even then Ultra2 processing is a cut above ordinary Ex/Es processing.
     
  14. roversd1

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    Its best to have two surround back speakers. If you just use a second centre speaker for the single surround back, the brain thinks its noise from the front.

    A. It does sound better, and with most processors you can matrix the two extra channels for normal 5.1 information

    B. Dolby Prologic was never marketed as '5.1' as it only generates two extra channels.

    C. Dolby Pro Logic II however, generates genuine stereo rears, a centre and the sub channels. You can even have 7.1 with some processors. Eastenders never sounded so good.

    D. Look carefully on the box and in the DVD menus. Many disks contain ES or EX material but without actually advertising it.

    E. Yes, it may appear to be a bit of a con with most recieivers only having 6.1 amplification. But heck, its a great hobby and keeps us off the streets.

    :devil:
     
  15. mike_cummi

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    Thanks for the input guys. Think I'm gonna go for the speaker switch. It's only £13 and was designed specifically for the purpose of running two sets of speakers off one amp without overload problems. I'm sure a 6.1 amp with 100WPC will be able to cope running tow speakers in mono. If I have to turn up the volume on the surround backs then so be it.

    Don't have enough dosh for a lexicon or meridian processor.
     
  16. eviljohn2

    eviljohn2
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    I think there IS talk of discrete 7.1, but rather than having 2 discrete surround backs the 7th channel is a height channel (ie. in the ceiling above you).

    This is obviously only going to be practical in cinemas and custom installs themselves but you'll not only get helicopters and the like flying around you, they can land and take off on you as well!
     
  17. Dave20

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    ^^ correct A+ ;)
     
  18. pwiles1968

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    Just got the second pair of solids and wired them in, I put them in series (16 Ohms) as my amp says 8-16 Ohms on the rear, the speakers have to go on the windowsill behind my sofa so I have pointed them in towards each other, a couple of feet either side of my seating position. and it works great, much better integrated than the makeshift Kenwood, I was stuck for speaker wire the local store closed earlier than they should so have used 2 core mains, can someone remind me to change it in 6 months because I just know I will forget.

    Have listened to about eight of my favourite movie sequences and am quite happy with the set-up (Is anyone ever totally happy), The Red Queen Q&A scene from Resident Evil was particularly good. I know it is not a 6.1 mix but if you turn EX on you still get centre rear and IMO sounds better than the plain 5.1 much more rear depth, and the Matrix well:cool:.

    By the way buns you are correct in pointing out that you have half the power or –3dB available but you overlooked the fact you have two speakers doubling the SPL adding +3bB so it evens itself out and in the end I only did a slight level change on the centre rear to match the sides this was probably due to the sensitivity differences between old and new speakers.

    I was also sad enough to work out the time difference between the sound coming out of the first speaker to the sound coming out of the second one when you wire them in series (I’m an engineer it was bugging me), I have 8 feet of cable between the speakers so for my set-up it will be 8 nanoseconds if you round up. I even worked out how much closer the second speaker had to be to compensate but could not find a tape that would measure that small (it was about 0.000001173 Feet if you were wondering).:rotfl:
     
  19. buns

    buns
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    Ah...... well i was considering having each speaker at the main setup level as opposed to having the composite being that level! if you are doing it like that it dont matter! :D

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  20. owenw

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    Mmm sounds interesting, what sort of money are you looking at for these amps? Do you know any dealers who might have them in stock?

    Owen
     
  21. buns

    buns
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    for the meridian......£4k for the lex......£lots more!

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  22. CarlB

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    ...and they aren't amps, so you'll be needing one of those as well!
     
  23. buns

    buns
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    and the power doesnt come cheap...... so you might need a loan into the bargain! :D

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  24. EvilMudge

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    Hence why I said listen, not buy...

    There is some demo material around from Dolby and DTS which features some properly mixed (as in phase as well as volume) rear panning effects. That can be really incredible even with a standard decoder.
     
  25. owenw

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    Right, so I need:

    a 7.1 ch processor - £4000
    a power amp (is one amp enough with all those speakers?) - £4000

    a load more high quality cable - £500

    another pair of surround speakers (in fact I better replace all the speakers to do justice to the processor / amp capabilities - £6000

    Probably should place the AV gear on some sork of rack which cancels out vibrations, interphasic radiation and neutrino showers too? - £500

    Might as well add a second sub woofer to improve bass dynamics. - £1000

    So I really need about £15,000 from my bank manager :D

    Have I overlooked anything?! Oh yes I better drill some holes in the ceiling for the vertical surround speaker upgrade! :D

    Will we also have to rip up the floor for the 8th channel speaker in years to come, for full 360 degree sound?!

    Who says 7.1 is a con?!

    OwenW

    PS: buns whats your "secret new stuff"? :)
     
  26. garmtz

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    Even if the Meridian and Lexicon processors can deliver different sound to 7 speakers and a sub, doesn't make them 7.1... The highest you can go is still 6.1 with DTS-ES Discrete. What you CAN say is that the 4 surround channels are steered independently, but that's not discrete.

    When fed 5.1 EX material, the Lex has a 3/3:2:4.1 matrix... :lesson:
     
  27. mike_cummi

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    OwenW,

    Why not just buy your local multiplex, would probably be cheaper and you could keep one screen for yourself and sell tickets for the other 11, so it would be a good investment too.
     
  28. Reiner

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    I can connect 3 subs to my amp and though it has only DD and DTS 5.1 processing I have two front effect channels, so that would make it 7.3? Nah .... it's 5.1 and that's it, so I am in total agreement with garmtz (i.e. real discrete is only up to 6.1).
     
  29. EvilMudge

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    So by your reckoning Dolby Pro-Logic and Pro-Logic 2 are still 2.0 ;)

    I don't even regard DTS Discrete as being remotely 6 true full range channels, because the surround back is still matrixed into the rears of the five channel mix and must be removed before the so called discrete rear channel comes into play.

    In terms of number of channels required to amplify different signals then 7.3 is a valid number, as in theory none of those channels should contain identical information, unless specifically intended in the mix (a la Donnie Darko). All I'll say is that with proper matrix encoding, 7 (or more) different channels can be derived from a 2 or 5 channel master.

    BTW DD5.1 isn't totally discrete anyway IIRC. Not as bad as MPEG multichannel though :p
     
  30. EvilMudge

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    That's not strictly true Garmtz. Only in THX Surround EX does that apply. Logic 7 or THX Ultra 2 are quite a bit more advanced than simple matrix systems.:cool: It would be more accurate to call them phase comparator DSP modes, but even then that's not accurate.
     

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