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Thread: Center Channel Help Needed

  1. #1
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    Question Center Channel Help Needed

    First, let me say what a great site this is, wish I found it sooner!! It's nice to know I'm not the only one obssed with the JBL sound.

    I'm setting up a 5.1 surround system and could use some advise with the center channel. My thoughts2) LE10, (1) LE175, (1) 075 crossed at 1500hz & 7000hz using a LX10 & N7000 network. Each LE10 would be in its own 1.25cu.ft. compartment.

    Most of the time I listen to music in 2channel format. For the most part Jazz is my game. My front channel is a pair of 4343B, (new arrivals).

    Am I going in the wrong direction Should I find a factory setup and adapt it? Any thoughts would be appreciated.

    Thanks much,
    Dave
    MRPO

  2. #2
    Administrator Robh3606's Avatar
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    Sounds like a good direction on the center. You should reasonable match the L/C/R and what you are proposing sounds like a good match. I would upgrade the 175 to a 2425 or 2426 though. Lot's of power in that front channel with HT.


    Rob

  3. #3
    Senior Member GordonW's Avatar
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    I dunno, Rob. An original (re-gaussed) LE175, an original 075 or 077 supertweeter (I'd use the 077/2405, it's what's in the 43XX monitors), and a pair of original LE10As would all be ALNICO POT magnet assemblies, and should be reasonably well SHIELDED, as a result. A 2425 or 2426 would be a CERAMIC magnet, and would NOT have NEARLY the degree of video shielding.

    If you DID want to use the bigger-magnet version of the driver, I'd use a 2420 or LE85. They're also alnico...

    My only crossover change, would be to use the N8000 rather than the N7000. The preponderance of experience here on the LH board says (and my own personal experience bears out, too) that the supertweeters sound better crossed over, the HIGHER the BETTER. The last system I did using one (a 2404H) paired up with a 2410 (same as a LE175) wound up with the crossover point being around 11KHz. Now, that was for an extremely "high-power" app (the guy was matching it up with 4560 Perkins horns with 2225H woofers and 2445/2382 horns, on mondo power)... so 8000 Hz should be just fine, especially with a good 077/2405 alnico...

  4. #4
    Administrator Robh3606's Avatar
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    "I dunno, Rob. An original (re-gaussed) LE175, an original 075 or 077 supertweeter (I'd use the 077/2405, it's what's in the 43XX monitors), and a pair of original LE10As would all be ALNICO POT magnet assemblies, and should be reasonably well SHIELDED, as a result. A 2425 or 2426 would be a CERAMIC magnet, and would NOT have NEARLY the degree of video shielding."

    I have used a Jubal Center and the 077 was a PITA because of the very resticted Vertical Dispersion like 20 degress up high. The 075 has twice that. I know it doesn't go as high but if you have it why not try??

    Opps correction the 075/2402 has the same almost at 15K!! Potentially the same problem got to be aimed at you.

    Good point on the shielding but if it's not direct view it doesn't matter. He doesn't say if they LE-10's are A's or H's. I guess we will find out!

    Rob

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    Robh/Gordon:

    I have a pair of LE10A baskets, (very bad surrond repair). They will need to be re-gaussed, cone kits as well. Should I have them reconed as 2121H.

    I also own a spare 075 driver. I'll try that first. If I use a LE85 (2420) what horn should I use, HL87 or HL91? There is also a shorter version of the HL87, (for 1500hz) don't know the # off hand. If I go with the HL91 I'll also need a lens.

    All opions welcome,
    Thanks
    Dave
    MRPO

  6. #6
    Administrator Robh3606's Avatar
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    You know Gordon does raises a good point. Since you are using 4343's why not set-up the center to follow suite. Figure the 2 10's can act as the 2231/2121 combo with the compression driver and 075 as the top. That said why not cross the 10's over to the compression driver at the same frequency use the same horn and lense and then cross the 075 again at the same point. I would be worried about 2 10's in a horizontal layout. How are you going to set things up on the baffle??? Do you have to worry about shielding??? As far as reconning with 2122 kits?? I really don't know. I would be inclined to use a standard Le-10 kit as you have real woofers there. I don't know how low and with how much power you can run the 2122's. I have only used them as midranges from 300 to 1.2K

    Rob

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    Getting Closer

    My original baffle plan was to lay things out horizontally. LE10 on each end, HL87 & 075 in center, (stacked with 075 on top). I was going to use the 1500hz crossover point because the LX10 seemed to be a good choice with the drivers I was using. It's also eaiser for me to purchase a crossover verses attempting to buid one. I chose the HL87 horn because it was not going to be positioned on top of the LF driver.

    1. What problems can be encountered using -2- drivers on a horz. plane?

    2. Please explain what video shielding I will need.

    Thanks again,
    Dave
    MRPO

  8. #8
    Administrator Robh3606's Avatar
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    1. What problems can be encountered using -2- drivers on a horz. plane?

    All center channels have issue using the arrangement. You get lobing and cancelation problems that end up in the horizontal plane. The idea is to get the crossover low enough so the driver spacing is not an issue. If you are on axis or not to far off center in may never be an issue.

    2. Please explain what video shielding I will need.

    Not video but magnetic shielding. A direct view TV as in your standard television does not like stray magnetic fields which is why all HT speakers have "shielding" which minimizes or cancels with a bucking magnet the stray magnetic field from you speaker drivers. If you want to see what it looks like very carefully approach your TV holding a driver. You will see the colors change. JBL Alnico drivers are shielded because they use magnetic structures that form a closed circuit so very little of the field escapes. By the way not all alnico just the ones with closed pots like JBL or Altec as an example. There are open pot alnico's which are not nearly as well shielded.

    Good idea on the HL87. With the 2307/2308 you are pushing the 10's further apart or?? Why not set them up like a Lancer L 77 and put the 075/077 where the Le20 would go and drop the horn on top right over the 075/077?? That way you can get the 10's real close and you can use any horn you want.





    Rob
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    Administrator Mr. Widget's Avatar
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    Is this the layout you have in mind?

    If you are using all alnico drivers, they are inherently magnetically shielded. If you use the newer "H" versions with ferrite magnets it will be a bit of a challenge to shield them.

    Widget
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    Baffle Layout

    I was planning to space the le10's further apart, dropping the HF drivers between them, (stacked).

    In a horizontal layout, is it best to have them close, (directly next to each other).

    Thanks,
    Dave
    MRPO

  11. #11
    Senior Member GordonW's Avatar
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    With an HL87 horn and a 1200 Hz crossover, it should be OK with the horn/tweeter "stack" to be between the 2 10" woofers. That's still a pretty close center-to-center distance. Heck, it's better phasing than most of the MTM center channels commercially sold... two 10" woofers with 1200 Hz crossover is LESS of a wavelength "alignment error" at crossover than 4.5" woofers at 3000 Hz (done on MANY center channel speakers)...

    Here's how I'd place the drivers. Put the tweeter in the very center, raise the mid a bit... that'll get the closest CTC spacing possible without making a tall cabinet...

    (oops, noted a typo... on the pic, where it says '077', it should say '075'...)
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  12. #12
    Administrator Mr. Widget's Avatar
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    I certainly agree that Gordon's layout looks nicer, though I would bet the layout I posted with the woofers closer together and the HF units stacked above would sound better.

    This drawing is to scale. It would be difficult to construct with separate chambers for each woofer. I realize you can use a common enclosure, but dual chambers usually sounds better. There is also the issue of not much wood around the closely spaced cutouts. This could be a structural problem.

    Widget
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  13. #13
    Senior Member GordonW's Avatar
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    Yeah, WRT the baffle, I'd DEFINITELY use birch plywood, marine ply or something REALLY STRONG for the baffle. Also, I'd support the back of the HL87 horn with a top-to-bottom brace, to make sure the horn doesn't "lever itself" and break the baffle board.

    As far as dividing the cabinet- personally, I've built lots of center channels with common cabinets- as long as the woofers are wired in PARALLEL, it shouldn't be a problem. This might require custom-reconing the LE10s, to use 16 ohm voice coils... but that shouldn't be too bad, for someone who does aftermarket recones. The coils in the LE10 are the same dimensionally as several other models, some of which are available in 'J' versions. I'd certainly think I could find a recone kit that would take care of this, if necessary...

    Regards,
    Gordon.

  14. #14
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by GordonW
    Yeah, WRT the baffle, I'd DEFINITELY use birch plywood, marine ply or something REALLY STRONG for the baffle. Also, I'd support the back of the HL87 horn with a top-to-bottom brace, to make sure the horn doesn't "lever itself" and break the baffle board.
    Exactly what I was thinking.

    Quote Originally Posted by GordonW
    This might require custom-reconing the LE10s, to use 16 ohm voice coils... but that shouldn't be too bad, for someone who does aftermarket recones.
    You and your custom jobs....

    I agree with you about wiring the woofers in parallel. I would definitely use stock woofers and do a custom network though.

    Widget

  15. #15
    Senior Member GordonW's Avatar
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    Well, if the amp is 4 (and preferably 2) ohm stable on the center channel, then the stock LE10As should work anyway. Just make sure that whoever does the crossover, compensates for the FOUR ohm load on the bass. Standard N1200 and such isn't going to work into 4 ohms... but you can probably just HALVE the inductor values and DOUBLE the cap values in the lowpass of an N1200, and have it work OK... that's the general effect of changing from 8 to 4 ohms, as far as crossover design is concerned...

    If this is done, I would have someone run an impedence sweep on the completed system before putting into service, though. Just to make sure, there aren't any nasty little "near short" surprises at any frequencies for the amp to choke on. Doubt there will be a problem, as the DCR on an LE10 isn't THAT low, compared to other "8 ohm rated" JBL drivers... but it would be good to make sure.

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