Results 1 to 8 of 8

Thread: Inductor Lead Length in Crossover Networks - Does it Matter?

  1. #1
    Junior Member
    Join Date
    Apr 2016
    Location
    Portland, OR
    Posts
    14

    Inductor Lead Length in Crossover Networks - Does it Matter?

    How critical is inductor lead length in a crossover network? I've only seen three pairs of JBL crossovers (L36 Decades, 4301B Control Monitors and L19s) in the flesh and all had what appeared to be excessively long leads on the inductors. Certainly much longer than necessary to make the connections to the other components and terminal strips.

    I'm currently recapping the crossover networks for my 4301B Control Monitors with new caps, but borrowing the inductors and L-pads from a pair of L19 crossovers. My first instinct was to trim the leads to tidy things up. This would shave about an inch and a half off the leads of the inductor in the tweeter circuit and 2.5" - 3" off the leads of the inductor in the woofer circuit.

    But, before doing so, I thought I'd ask. Will shortening these leads have any negative impact on the performance? It seems weird to me that they were all so excessively long. Any conductor with current flowing through it acts as both a radiator and an antenna. I've always been told it's best to keep lead wires as short as possible to keep them from generating/picking up noise. But, will shortening them alter the DCR or inductance of the inductor enough to audibly impact performance?

    I measured the length of all of the inductor leads in my L19 and 4301B crossovers and all (8 inductors = 16 lead wires) were between 6" and 6 1/4". Knowing that JBL used the same components in many different designs, it makes me wonder if they just speced all inductor lead wires as 6" so they would be long enough for all their different models. In other words, for assembly/cost reasons, not electrical performance.

    I look forward to the responses. I'm a little OCD when it comes to clean looking crossovers. So, as said, my impulse is to trim the leads, but sound quality always comes first. Once they are re-installed in the cabinets, no one else will see them. So I'm ultimately more concerned about the potential for pickingup noise vs. changing the DCR of the inductors.

    What say you? Trim them or leave them long? Why/why not?

  2. #2
    Junior Member
    Join Date
    Apr 2016
    Location
    Portland, OR
    Posts
    14
    BTW, here's why I am borrowing the inductors and L-pads from the L19 crossovers to use in my 4301Bs.

    Original 4301B crossover showing obvious damage from improper storage (excessive heat and humidity):





    These were stored under conditions hot enough to melt the wax in the capacitors, cause the glue holding the inductors to fail and humid enough for the outside of the L-pads to be covered with corrosion/mildew.

    You can't really tell how long the inductor leads are in these photos. So, here's a photo of the L19 crossovers, that are physically over twice as large as the 4301B crossovers:



    Mounted on this much larger board, you can kind of see why woofer inductor leads (green on the board on the left, blue on the board on the right) are 6" long. But, you can also see that the tweeter inductor leads are about twice as long as they need to be. Same for the purple capacitor lead wires - much longer than necessary.

    In fact, in my limited experience with JBL crossovers, most capacitor and inductor leads are longer than necessary. This creates a real rats nest of wires in the more compact crossover networks. Here's what my L36 Decade original crossovers looked like:



    Here's what they look like after I recapped them (and shortened the inductor leads):


  3. #3
    Senior Member
    Join Date
    May 2007
    Location
    Ingolstadt in Germany
    Posts
    430

    Inductance of a straight wire

    See https://www.allaboutcircuits.com/too...ce-calculator/

    A pice of wire, 1mm diameter, 1cm length, has an inductance of 6 nH

    Inductors in crossovers have typical values in the order of mH which is a million times larger.

    So the inductor lead length is irrelevant.

    Ruediger

  4. #4
    Senior Member
    Join Date
    May 2007
    Location
    Ingolstadt in Germany
    Posts
    430

    Capacitive and Inductive Coupling ...

    ... both require that wires are close to each other and run in parallel. The excessive leads in the old JBL xovers don't do that.

    Neither of these two kinds of couplings is involved here.

    Ruediger

  5. #5
    Senior Member Ian Mackenzie's Avatar
    Join Date
    Apr 2003
    Location
    The Tardis
    Posts
    6,399
    Lead length is not relevant

    Location of the inductor is relevant.

    Use suitable hook up wire (don't unwind the inductee to make the leads longer)

  6. #6
    Junior Member
    Join Date
    Apr 2016
    Location
    Portland, OR
    Posts
    14
    Quote Originally Posted by Ruediger View Post
    ... both require that wires are close to each other and run in parallel. The excessive leads in the old JBL xovers don't do that.

    Neither of these two kinds of couplings is involved here.

    Ruediger
    True, but the placement of the inductors could be better. On the L19 crossover board the two inductors are physically parallel to each other. Simply rotating one of them by 90 degrees would reduce any mutual inductance. Better still, move the tweeter inductor to the same side as the tweeter cap and move the woofer inductor to the bottom tight area of the board, closer to the woofer cap, and rotate it by 90 degrees.

    You can't see the inductor placement in the 4301B crossover photos I provided (they had fallen off one of the boards and are hidden behind the capacitors in the photo of the other board), but it's even worse than the L19 placement. Both inductors are placed standing upright right next to each other (physically touching) and arranged in parallel. Space was tight, but simply rotating one of the inductors 90 degrees would help reduce mutual inductance due to coupling of their parallel magnetic fields.

    I'm not really sure how much impact there is due to this placement, but general best practice is to place inductors as physically far apart as possible, and orient them so their magnetic fields are orthogonal to minimize mutual inductance due to coupling.

    On my rebuilt 4301B crossovers, the inductors will still be close together (but not physically touching). The board is so small, it's simply not possible to get much in the way of physical separation between the inductors, but I will orient them at 90 degrees to minimize coupling. I'll post a photo once I finish assembling the first crossover.

  7. #7
    Junior Member
    Join Date
    Apr 2016
    Location
    Portland, OR
    Posts
    14
    Quote Originally Posted by Ian Mackenzie View Post
    Lead length is not relevant

    Location of the inductor is relevant.
    Agreed, and in my reply above, I mentioned how the placement of the inductors, especially in the stock 4301B crossovers is less than ideal.

    Quote Originally Posted by Ian Mackenzie View Post
    Use suitable hook up wire (don't unwind the inductee to make the leads longer)
    No hookup wire (or unwinding) needed in this case. The original lead wires are more than long enough. They will simply be trimmed, the ends stripped and soldered in place.

  8. #8
    Junior Member
    Join Date
    Apr 2016
    Location
    Portland, OR
    Posts
    14
    I just refinished rebuilding the first 4301B crossover network. Here's what it looks like:



    As mentioned in my earlier post, I oriented the inductors at 90 degrees to minimize field coupling and mutual inductance.

    As you can see, I trimmed the inductor lead length to clean things up a bit. Thanks to all who responded for your input. I appreciate your assistance.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. LX5 Crossover Rebuild; Mismatched Autoformer and Inductor part numbers??
    By mbeards in forum Lansing Product Technical Help
    Replies: 0
    Last Post: 05-13-2014, 11:58 AM
  2. L100T3 Crossover Inductor DCR Values and General Inductor Advice
    By Wayniac in forum Lansing Product DIY Forum
    Replies: 4
    Last Post: 12-10-2012, 11:15 AM
  3. Urei 809 Crossover inductor values
    By eso in forum Lansing Product Technical Help
    Replies: 13
    Last Post: 04-27-2010, 10:16 AM
  4. L65 Crossover rebuild .3mh Inductor
    By jwor in forum Lansing Product Technical Help
    Replies: 9
    Last Post: 06-24-2007, 05:23 PM
  5. Crossover networks 101
    By penguin in forum Lansing Product Technical Help
    Replies: 15
    Last Post: 04-05-2005, 08:32 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •