Couple of M8A questions

Discussion in 'Home Theater Projects' started by James W. Johnson, Sep 23, 2004.

  1. James W. Johnson

    James W. Johnson Screenwriter

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    I am about ready to try something else so unless Adire quickly throws something new together I think I am going to build some M8As (or whatever they are called. [​IMG])

    1. I have a smaller room and a subwoofer so I was considering an MTM in a 100 liter /32Hz enclosure, is there any reason I should consider larger?

    2. I'll probably just use the M8N driver, so do the 3 x-over pics floating around still apply to this?

    3. Parts: what is the most cost effective/easiest way to gather all the crossover parts? Id like to make all of my purchases in 2 or 3 moves.
     
  2. James W. Johnson

    James W. Johnson Screenwriter

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    One more question: how might these compare to my old Kit281s in terms of clean SPLs and overall SQ?
     
  3. Michael R Price

    Michael R Price Screenwriter

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    Hey James,

    I envy your ability to try out new speakers. 100 liters is probably fine for the MTM; the M8N and M8a drivers are compatible with the same crossover; and Thomas has recommended buying a bunch of 10uf capacitors from Madisound at a reduced rate, and paralleling them. The rest comes from PE, I think. Of course it probably won't be long until he shows up here and gives you the real answers. I bet the M8s can play almost as loud cleanly as the Kit281s. And I also bet they sound a lot better in the midrange and treble.

    BTW... I am perfectly content with my now active-crossover-ized Kit281s. [​IMG] (I am now attempting a lower, steeper crossover where the breakup mode is attenuated by some 34db electrically.)
     
  4. James W. Johnson

    James W. Johnson Screenwriter

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    Check my crossover list please, also what wattage should I make the resistor circuits?

    Woofer:
    900uH
    450uH
    72uF
    30uF
    100uF
    5 ohm
    Tweeter compensation? :
    700uH
    2uF
    136 uF
    4 ohm
    12ohm
    Tweeter:
    22uF
    23uF
    270uH
    68uF
    800uH
    1.2 ohm
    10 ohm





    So basically these are biampable right and the woofer circuit just gets connected straight to the dual input cup?
     
  5. James W. Johnson

    James W. Johnson Screenwriter

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    Also is it going to hurt anything if I am off say 4uF on the 136uF part or 2uF off on the 72uF part etc?
     
  6. ThomasW

    ThomasW Cinematographer

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    I think we covered most of the fundamental MTM questions in this thread
    http://www.htguide.com/forum/showthread.php4?t=3606

    You want to use 10-12 watt resistors except in the L-pad circuit. I suggest using a Phoenix Gold 4 ohm L-pad from PE. If you want make a fixed L-pad from individual resistors, you'll need to create a pretty high value since it's handling quite a bit of power. Note that a 8 ohm L-pad can't be subsituted.

    As long as you're within 5% of the cap value you're good to go.

    No offense to Dan and the gang at Adire, but the drivers used in the M8a-MTM are pretty much in a different league compared to those in the 281.

    Since PE has significantly lowered the price of the M8a, I suggest using it. All the front panel measurements are based on the M8a.

    If you don't mind building the big cluster caps, and living with the size of the XO, you'll save almost 50% using the GE caps
     
  7. James W. Johnson

    James W. Johnson Screenwriter

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    Ok, ill go over to that thread and try and get what I need.


    Ive never seen any mention of an L-pad, does this take place of the resistors in just the tweeter compensation circuit?


    Id like to see a picture of a crossover board with the L-pads, are there any around?
     
  8. ThomasW

    ThomasW Cinematographer

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    There's a passive L-pad shown in the circuit. People replace it with a 4 ohm variable L-pad so they can set the tweeeter level to fit their needs/wants.

    You usually won't see a picture of the variable L-pad because people don't mount them on the XO. Usually they're mounted then somewhere convenient for ease of adjustment.

    Here's one pic I found of Paul's XO the L-pad is the gold colored disc. He has the shaft sticking out the outer side of the perf board.

    http://www.htguide.com/forum/attachm...ttachmentid=50

    http://www.htguide.com/forum/attachm...ttachmentid=81
     
  9. Paul His

    Paul His Agent

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    They look strangely familiar... [​IMG]

    James, do read through that rather long thread on the other forum - I asked a lot of dumb and not so dumb questions and got good answers to all. If there's questions I didn't ask fire away and I might be able to help if the experts aren't around!

    These speakers are sweet.

    Paul
     
  10. Pete Mazz

    Pete Mazz Supporting Actor

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    I'm building a set right now for my brother. I'm using the M8ns and the Vifa ring tweeter. If you look in my thread at HTGuide, you'll see my list of caps that I purchased from Madisound. I have some of the smaller values left if you want some.

    Pete
     
  11. James W. Johnson

    James W. Johnson Screenwriter

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    Thanks Thomas, Pete & Paul! [​IMG]
     

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