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Crossover construction questions.

Discussion in 'Archived Threads 2001-2004' started by Brett DiMichele, Jan 22, 2003.

  1. Brett DiMichele

    Brett DiMichele Producer

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    Hey all,

    I just have some simple questions about replacing crossover
    components.

    If you have prebuilt crossovers and you want to replace a
    capacitor and you know the value and say it's a 40.0uf and
    all you can find is a 39.0uf and a 1.0uf you can use the
    pair together to make 40.0uf correct? The capacitance value
    comes out the same by using two to arrive at the figure.

    Next question...

    Can an Iron Core Inductor be replaced with a regular Air
    Core Inductor? Why would they use an I-Core and an Air core
    on the same side of a board, was this done to thwart magneto
    striction between two air core inductors?

    Third question...

    Say the Air Core Inductor you need is a 0.31mh and all you
    can locate is a 0.33mh, can you unwind some of the windings
    to get the 0.31mh figure? What do you need to test the inductor
    with to make sure you arrive at that precise value?

    And Fourth... Why in gods name is a 200.0uf Capacitor so
    danged expensive.. YEESH $90.00 for a pair of Solen 200.0uf's

    [​IMG]

    A rough shoppers list of components to rebuild my existing
    XO's comes out to $256.16 from PE!

    That's all Solen Caps, Dayton Non Inductive Resistors, Alpha
    Foil Inductors (where I could find them that matched the
    specs..)

    Crossovers get pretty expensive it looks like [​IMG]
     
  2. Patrick Sun

    Patrick Sun Moderator
    Moderator

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    1. Just parallel caps together to arrive at the value (additively).

    2. Iron Core is used for space considerations (smaller for larger inductance values vs. air core of the same wire gauge). Iron core, rule of thumb, should only be used in the lower frequencies due to saturation effects as frequency increases into the midrange region. Some people dig the clean sound you get from foil inductors, but those are very very expensive in relation to air core and iron core inductors.

    The 2 easiest way to minimize magnetic fields between inductors is to space them apart as far as possible (3" or more), and/or keep the inductors at right angles from each other.

    3. Sure, you could unwind a larger value inductor to get a smaller value inductor. But you need a LCR meter to correctly measure the newly unwound inductor. A 0.33mH inductor won't make all that much difference from a 0.31mH inductor.

    4. This is why companies use the cheap electrolytic caps when large values are needed for the crossover, at the expense of using caps whose values can change as a function of frequency.
     
  3. Brett DiMichele

    Brett DiMichele Producer

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    Pat,

    Thanks for the info!

    Well I don't have an LCR Meter but I am friends with an EE
    and he probably has one, I am going to have to ask him
    before I order something that I can't figure out without
    the appropriate test equip.

    I was fairly certain just paralelling the Caps with additive
    values would give me what I needed.

    I understand that the higher quality caps will be more
    expensive it's just a fact that quality costs more. But
    what I don't understand is how a 1.0 Farad Cap can be had
    for as little as $70.00 but this dinky 250uf deal costs
    $45.00 each!

    The 1.0Farad's used in car audio are most likely low quality
    inside since all they need to handle is incoming voltage
    and not a signal with constant changing frequencies.

    Again MANY thanks for the information!

    (Now I need to think about whether it's worth it to spend
    $250.00 on parts for the crossovers in a pair of speakers
    that I only paid $580.00 for....) I am thinking nah!

    I would be just better off to save that money to spend on
    the Line Arrays...

    Besides they don't sound bad at all, I am just in this Tweak
    everything ta hell mood untill I can start on my projects!
    [​IMG]
     
  4. Mark_E_Smith

    Mark_E_Smith Second Unit

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    The 200 uF is used in the woofer section to roll in the 5" speakers around 150 Hz. You don't need a high quality one there, but in the tweeter circuit you bet. You can also use a small uF "bypass" cap that will greatly improve a lower quality large cap. IE 30 uF and a 1 uF in parallel will sound very close to a 31 uf expensive cap. use foil core inductor in the tweeter. Be advised that the gage of the inductors makes a difference in the x-over as it changes the resistance of the circuit. So try to stay with the same gage inductors. Foil inductors usually have a little lower resistance than air cores. ONLY use iron core inductors in the woofer circuit and in your application I wouldn't use them if you are not going to use the 10" woofer.

    What are the values in your x-over?
    Is it a 3 way or a 2 way?
     
  5. ThomasW

    ThomasW Cinematographer

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    Brett

    You certainly don't need the high priced foil inductors. The Solen Perfect-Lay are fine for your speakers

    My experience with the Dayton non-inductive resistors is that they don't meet the advertized tolerance. So go with the Mills.

    Madisound has some GE film caps that are really quite good. The largests value is 10mfd. You could make a fairly inexpensive 200mfd cap with a cluster of these. The down side of course would be the size of the cluster.
     
  6. Brett DiMichele

    Brett DiMichele Producer

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    Mark,

    Here are all the values (not including the polyester caps
    they have on the board (I didn't check the value on those)

    Front of Crossover:

    Capacitors:

    Capacitor F 4.3J MT100V
    Capacitor F 40.0K MT 100V
    Capacitor F 12.0j MT 100V
    Capacitor 60 Uf 150v

    Non Inductive Resistors:

    Resistor 10w 4Rj
    Resistor 10w 4Rj
    Resistor 10w 25Rj

    I-Core Inductor:

    4.0mH

    Back of Crossover:

    Capacitors:

    250 uf 100v

    Non Inductive Resistors:

    10w 30rj

    I-Core Inductor:

    0.73mH

    Standard Inductor:

    0.31mH
    -----------------------------------------------------------

    Tom,

    I was thinking the same thing about the Dayton vs. Mills
    Resistors, the Dayton resistors don't look any better than
    the one's that are on the board now.
     
  7. Mark_E_Smith

    Mark_E_Smith Second Unit

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    My sugestion,

    Leave all the resistors alone
    Change the 4 mH iron inductor to a 14 gage air core same value, leave the 250 uF alone. these are in the woofer section an seem to cross at about 150HZ, cant be exact because I don't have the driver info.

    Change the .73 mH and the .31 mH to 16 gage foil inductors, replace the 40 and 60 uF caps with metalized not high dollar film and foil, replace the 4.3 and the 12 uF with film and foil caps or replace the 12 uF with a 10 uf metalized and parallel a 2 uF film and foil cap with it. I would try one speaker and see how it sounds compared to the other.
     
  8. Scott Simonian

    Scott Simonian Screenwriter

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  9. Brett DiMichele

    Brett DiMichele Producer

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  10. Brett DiMichele

    Brett DiMichele Producer

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    HOLY COW...

    I just got both speakers done (no I didn't touch the XO's
    yet..)

    I just replaced all the wire with 12Awg OFC with 4% Soldered
    connections.. I stuffed the Midrange Enclosures with 50%
    Polly-Fill and did the same for the SubWoofer Enclosure..

    I can NOT believe the difference.. The Bass is Tight I mean
    REALLY tight now... Kick Drums smack you in the chest and
    almost knock you over, but they don't boom.. They are fast
    and clean sounding..

    The mids, Brass Instruments are smoother (silky) vocals are
    even better.. Better Instrument Seperation...

    I am very skeptical about everything and I rarely hear any
    differences.. But I sure as hell am now!

    I think I am going to go ahead and order all the parts to
    rework the HF side of the XO's with top quality Caps and
    Alpha Foil Inductors..

    *shakes head* Unbelieveable!
     
  11. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    Scott :

    I'll take a stab at your question. With the 2 caps in parallel, the current has 2 options, 2 paths to choose from. At high frequencies, a cap is essentially a short. The concept is that the better cap is a more perfect short to let the current flow to the tweeter a little cleaner.
     

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