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Dolby digital EX question.....

Discussion in 'AV Receivers & Amplifiers' started by Army Bloke2, May 13, 2002.

  1. Army Bloke2

    Army Bloke2
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    ....that has probably been asked a thousand time on these here forums, I'm afraid.:rolleyes: however, I have just spent the last 2 hours searching for the answer, but to no avail so any help would be appreciated.

    I have a marantz SR5200 amp which provides 1 output for the surround back channel. however, I would like to use 2 and am set up for this at the moment but am worried that I may be damaging my amp somewhat.

    I have a set of Boston VRS micro's (courtesy of Ian J) that I have wired in parallel from this one socket. (1 cable going to each speaker from the socket, rather that 1 cable to 1 speaker, then from 1 speaker to the next). The speakers are rated at 8 ohms. The question is, does wiring them up this way halve or double the load? The amp can handle 4 - 16 ohms on all terminals.

    Also, on my search, I read that you should reverse the phase on each speaker. I have actually reversed the speaker positions (left on the right and right on the left), does this do the same job or should I put them back and reverse the phase?

    Many thanks in advance.
     
  2. bob007

    bob007
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    Hope this helps for one of your questions raised.
     
  3. Jim Hudd

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    Wiring in series has a cumulative effect on the impedance, so in your case you'd end up with a 16ohm load. If I remember my physics correctly wiring in parallel produces an accumulation of the reciprocal impedances, so in your case you have 1/8 +1/8 = 2/8 ohms, or 1/4 of an ohm. I think you'd be safer wiring in series and adjusting the level up. I've seen quite a few speakers at parties destroyed by wiring in parallel and getting the volume too high!

    From what you've said you've done you've wired them up in parallel in both cases anyway. To wire in series you need to take the positive wire from the amp to the positive terminal on speaker A. Then wire the negative from speaker A to the positive of speaker B, then the negative of speaker B to the negative on the amp. If you wire positive and negative from the amp to speaker A and then just piggy back the wires form speaker A to B you've wired in parallel.
     
  4. baileych

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    That sum should result in 1/4 of an ohm^-1.

    You need to take the reciprocal of the sum of the reciprocals. i.e. 4 Ohms.
     
  5. Army Bloke2

    Army Bloke2
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    Thanks guys. I have now wired up in series, and, as expected, had to up the welly to the surround back by about 5db. However, how do I reverse the phase? I would expect this to be impossible as whatever way you look at it, the speakers will be wired the same. Will leaving the speakers reversed have the same effect? Any advice would help.
     
  6. bob007

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    Just swapping the position of the speakers will have no affect on the speakers phase, you have to swap the wires over on both speakers, you should be able to tell which of the two connections (in phase/out of phase) sounds better, speakers out of phase tend to have little/poor bass.

    bob
     
  7. Army Bloke2

    Army Bloke2
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    Cheers Bob. Do you have EX/ES? I was wondering, if you have, have you ever heard anything that made you turn around and wonder where the sound came from? I find that the EX?ES experience is more about ambience than spot effects.
     
  8. bob007

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    Have got the Denon 3801 and single SB for EX, not many 6.1 discrete soundtracks out, but the ones i have listened to really open out the rear soundstage, also has more accuracy for sounds that need to be to the left/right/rear of the rear soundstage.

    Find sometimes listening to a 5.1 soundtrack in 6.1 (matrix) doesn't always sound better, but when it does it sounds great.

    cheers bob
     
  9. Bonesy

    Bonesy
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    I thought you reversed the phase on bipoles/dipoles to stop a cancellation between the two rears. but perhaps I'm wrong.:confused:
     
  10. Jase

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    For Dipoles as Surround Backs (in an EX/ES system) you would swap Left for Right & Right for Left.

    Bipoles I think you´ll find you have to reverse the phase (wiring). I´m not 100% on this!!
     
  11. Jim Hudd

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    It's been 14 years since I last did any physics!!! This is why I'm not doing a job that involves any electronics beyond simply using a device!!!
     
  12. Army Bloke2

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    The THX website has no info on this whatsoever. Over to you Stuart M Robinson...;)
     
  13. Jase

    Jase
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  14. Army Bloke2

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    That's a great link and just about covers everything. It seems that i have everything wired up correctly - i.e, speakers in series and reversed left for right and right for left. Lovely.

    Thanks everyone.
     
  15. bob007

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    Army Bloke2,

    Glad you got it sorted, thought they were bi-poles, don't know why, but just as i were posting i had this vision of a couple of pole dancers.

    :D
     
  16. Army Bloke2

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  17. garmtz

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    Nothing there in the specs that says if they are di- or bi-polar... In both cases, wire them properly, so don't switch the polarity on one of the speakers.

    If the speakers are bi-polar, don't worry about anything. The two will be identical, so they are interchangeable.

    If they are di-polar and ONLY if you also use di-polar side surrounds, switch the position of the left and right back surround in respect to the side surrounds (there should be Left/Right indications on all 4 speakers). If you have monopole or bi-polar side surrounds, it doesn't make a difference which rear goes left or right.

    Hope this has made things more clear... :eek:
     
  18. Bonesy

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    Read Stuart's EX article in HCC from a few months ago, last night, whilst on the bog, too much info?

    Anyway, he reckons, if you fancy going the double rear centre route, you just need to use a y-splitter on the speaker cable, or run two wires from amp. (guess splitting them near the speakers would be cheaper, my rear run is 10ms).

    He then says NEVER wire them in series, only parallel.


    Now perhaps he says this because most people would work out the loadings incorrectly?
     
  19. garmtz

    garmtz
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    Wiring speakers in series is very bad for bass quality. When wiring speakers directly to an amplifier, the output impedance of the amplifier will be able to damp the back-EMF of the woofer very well. This is called damping factor and can be calculated by dividing the impedance of the speaker by the output impedance of the amplifier, resulting in a number of for example 8 Ohm/0.1 Ohm = 80. A number of at least 20 is desireable.

    When wiring speakers in series, the amplifier will have almost no control over the woofers of both speakers (8 Ohm/8 Ohm = 1, very bad).
     
  20. jon smith

    jon smith
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    What type of Y splitter would I need cos I plan to do this very soon.

    jon
     
  21. Army Bloke2

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    I have tried wiring them both in series and in parallel now and the only difference is series required a bit more volume in the set up.

    The main question is - will I damage my amp by wiring them in parallel?? This is the easiest route for me and by far the tidiest!:rolleyes:
     
  22. Bonesy

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    Sorry Jon, you've caught me out, I haven't ever done a y split in speaker cable, only interconnects. I was quoting as best as I could from SMR's article in HCC.

    call a local hifi shop and see what they say.

    armybloke, I'll search for the article, to see if it is on the net anywhere.
     
  23. Army Bloke2

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    Would appreciate it, thanks.
     

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