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7.1 Sound: Why?

Discussion in 'AV Receivers & Amplifiers' started by JamesL, Feb 25, 2005.

  1. JamesL

    JamesL
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    I notice many medium/upper end receivers offer 7.1 surround outputs. Other than multiroom setups (5.1 plus stereo in another rm) does this have any other application? Virtually all films have 5.1 sound, a few Dolby/DTS EX have 6.1. I haven't seen any that have 7.1. So what is the benefit of 7.1 on a receiver? Do the receivers offer some sort of audio 'upconversion' or is sound from 5.1 channelled to both surrounds and rear speakers?

    I would greatly appreciate it if someone could explain!

    James
     
  2. ahin4114

    ahin4114
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    Actually the 7.1 is a bit of a strange one, you only have 6.1 discrete channels, the two rear back channels are run off of the same source. I use 6.1 as it helps fill in the sound stage at the rear, and it makes a difference compared to 5.1

    I would imagine if your room was sufficiently large the extra rear channel would make a difference, in my case it would be overkill though.
     
  3. mhuk05

    mhuk05
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    can you run two speakes off a the rear channel? ie make a 7.1 from a 6.1 amp?
     
  4. JamesL

    JamesL
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    Thanks for the replies guys,

    So the receiver basically is 6.1 just outputting the centre rear twice? How about with 5.1 content, are the rear speakers silent or are the left/right surround simply duplicated by the extra speakers?
     
  5. Astaroth

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    No mhuk05 it wouldnt be advisable. Whilst a 7.1 amp only actually plays 6.1 channels it has seperate amplifier circutry for the 2 rear channels (though it plays the 2 in mono).

    with a 7.1 amp you really have a choice of 3:

    Use 7.1 surround sound (either matrixed or discreate for the rear 2 channels)
    Use 2 channels for multiroom uses
    Use the rear 2 channels to bi-amp the front L&R in a 5.1 setup - some amps have native support for this others you can do this by using the preouts and reinputing these as a new source and con the amp to think it is outputing in multiroom.
     
  6. tpc3416

    tpc3416
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    James,

    Another way to take advantage of the additional 2 channels would be audio vs dvd. If your room allows or is large enough, place your video surrounds to the sides of you, and your audio surrounds behind you. Some claim you get better sound from behind with audio and more realism with movies at the sides. So you can switch based on your listening preference. Some amps also have a 7.1 "stereo" mode feature which utilizes all 7 channels by basically reversing the stereo in the 6th and 7th rear speakers, making them true reverse stereo. I have that, but it seems there is so much going on you can't tell the separation as well with all the drivers. I think it's best used for either bi-amping or for a secondary room.
     
  7. MarkE19

    MarkE19
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    Apparently if useing a single rear speaker the sound confuses the human brain and it can't tell that the sound is coming from the rear. By adding a second rear speaker the brain works out that the sound is 'behind you'.

    Most modern receivers will have Dolby Pro Logic 2 & DTS Neo6 that can give a 6.1 surround 'effect' from a stereo source ie driving all the speakers and removing some sound from the L&R and outputting it from the surrounds.
    Some of the newest receivers have DPL2x that can do a similar effect as DPL2 but with any source from stereo up to 6.1 and give a 7.1 output, ie all 7 speakers are outputting an individual sound. Lexicon have something similar called 'Logic 7'.

    Mark.
     
  8. Diamond

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    H/K 335 also has Logic7.
     
  9. MarkE19

    MarkE19
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    Yes, they may well have Logic 7 but they licence it from Lexicon who wrote it in the first place.

    Mark.
     

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