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Thread: How to choose rossover coils?

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    How to choose rossover coils?

    Hello everyone! My name is Ari and I have finally taken steps to build 4344 inspired speakers. I've been roaming the forums and thinking of this project for over 15 years! I don't have room for 4345s and these will probably take up the entire living room. Since 2122H are difficult to source I am using 2123Hs and the 4344MKII charge coupled crossover below.

    As I am acquiring parts, I ordered coils from Jantzen via HiFi collective in the UK. My question is how does DCR of a coil affect the crossover? According to the list below L2 is a .6mH with a DCR< 0.5 ohms. When I ordered this exact part the coil wires are 24 AWG gauge which seems very small. Is it better to use a coil with larger wires which will lessen the DCR? How will this change the crossover if at all? How do you guys best match coil specs?

    Also how much would I benefit from air coils vs iron cored coils in different parts of the crossover?

    Thanks for your help!
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    Senior Member RMC's Avatar
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    Hi Ari,

    I have some info for you but i don't have time right now, i'll be back later tonight with the info.

    Richard

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    Quote Originally Posted by RMC View Post
    Hi Ari,

    I have some info for you but i don't have time right now, i'll be back later tonight with the info.

    Richard

    That would be super and much appreciated!

  4. #4
    Senior Member RMC's Avatar
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    Ari,

    I don't have precise answers to all of your questions but the following should help.

    Here's some guidelines for crossover coils. Most is from David B. Weems, Designing, building and testing your own speaker system, 4th edition.

    Air-core coils are the preferred ones, however if of large value they can get sizeable and add a fair amout of resistance in the circuit. Ferrite-bobbin core coils provide lower resistance for identical inductance value.

    In a woofer circuit, coil wire ought to be smaller gauge (larger size) to get lower resistance. But in a tweeter circuit coil wire may be smaller size (higher gauge). So there's also an energy aspect related to power level sent to each driver in a system. As you probably already know there is usually more sent to the LF than to HF devices. Coil wire size may depend on specific application, i.e. need "heavy duty" or not?

    Weems' hi-fi speaker building book and projects don't normally target high power pro gear folks, nonetheless his coil wire recommendations are larger than the 24 ga you got on the coils purchased:

    For inductances from .1 to .32 mH, use 24 ga wire. For .33 to .51 mH, use 22 ga wire. For .60 to 1.28 mH, use 20 ga wire. For 1.4 to 4.3 mH, use 18 ga wire.

    That means for your L2 .6 mH coil, Weems recommends two sizes larger wire. Plus he has a note about this: "Avoid using wire of smaller diameter than that listed for a choke if possible." (p. 175).

    I note on your parts list JBL uses Air Core for small values, but switch to Iron Core for 1.0 mH and more. Might be because of the size and/or resistance aspects mentioned above.

    While writing this i'm having a quick look at a parts supplier catalog for inductors. Their standard Air Core inductor coils .1 to 2.0 mH use 20 ga wire and are rated 180 Watts; then from 3.0 to 10 mH they use Ferrite Core, rated 250 Watts and have 18 ga wire. Their high power inductors use 15 ga wire, high grade transformer steel laminate cores, these are rated 600 Watts, but are available 5 to 15 mH, unless special order.

    I hope the above can be of some help to you.

    Richard

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    Senior Member Ian Mackenzie's Avatar
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    Hi Ari,

    I have built a number of these particular crossover for various JBL users.

    The DCR of the inductor coils can have influence on the Q magnitude or Peak of the resonance of the filter. In the case of the midrange band pass filter this is important and in the UHF filter. This can have a marked effect on the voltage drive in the crossover region.

    In all the 4344mk11 crossovers l assembled l have used air core inductors as the ferrite or iron core inductors do not document the current rating accurately before saturation. For a modest cost increase an air core inductor is a more ideal inductor without the effects of hysteresis as the dynamic signal increases.

    If you cannot obtain a close Dcr value then add a small value power resistor in series with the inductor with a lower Dcr value to obtain the correct total Dcr.

    I recommend you mount the parts on a non ferris material such plywood or acrylic sheet and hot melt glue with zip ties to attach the parts. Keep all inductors well clear of each other by two inches. An example of such construction is shown below l prepared earlier this year.

    I used WAGO terminal connectors, adhesive zip tie pads and 7.5 amp pvc insulated flying leads soldered and wire wrapped from the components. All the terminations are also hot melt glued to prevent vibration and fatigue which may impact on reliability. These WAGO terminals have excellent electrical characteristics. This allows flexibility in changing out parts should trim adjustments be required. I prefer stranded flying leads to prevent fatigue of solid wire solder joints in loudspeaker crossover assembly. Each filter had its own star ground connection taken from a 15 amp rated ground spur from the input connection to the amplifier output ground terminal. This approach minimises the influence of ground potential variations from associated filters and IMD distortion.

    There are other approaches to construction and this is just one example.

    Unfortunately a good crossover implementation is never a cheap exercise.
    Good luck with your project.
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    Quote Originally Posted by RMC View Post
    Ari,

    I don't have precise answers to all of your questions but the following should help.

    Here's some guidelines for crossover coils. Most is from David B. Weems, Designing, building and testing your own speaker system, 4th edition.

    Air-core coils are the preferred ones, however if of large value they can get sizeable and add a fair amout of resistance in the circuit. Ferrite-bobbin core coils provide lower resistance for identical inductance value.

    In a woofer circuit, coil wire ought to be smaller gauge (larger size) to get lower resistance. But in a tweeter circuit coil wire may be smaller size (higher gauge). So there's also an energy aspect related to power level sent to each driver in a system. As you probably already know there is usually more sent to the LF than to HF devices. Coil wire size may depend on specific application, i.e. need "heavy duty" or not?

    Weems' hi-fi speaker building book and projects don't normally target high power pro gear folks, nonetheless his coil wire recommendations are larger than the 24 ga you got on the coils purchased:

    For inductances from .1 to .32 mH, use 24 ga wire. For .33 to .51 mH, use 22 ga wire. For .60 to 1.28 mH, use 20 ga wire. For 1.4 to 4.3 mH, use 18 ga wire.

    That means for your L2 .6 mH coil, Weems recommends two sizes larger wire. Plus he has a note about this: "Avoid using wire of smaller diameter than that listed for a choke if possible." (p. 175).

    I note on your parts list JBL uses Air Core for small values, but switch to Iron Core for 1.0 mH and more. Might be because of the size and/or resistance aspects mentioned above.

    While writing this i'm having a quick look at a parts supplier catalog for inductors. Their standard Air Core inductor coils .1 to 2.0 mH use 20 ga wire and are rated 180 Watts; then from 3.0 to 10 mH they use Ferrite Core, rated 250 Watts and have 18 ga wire. Their high power inductors use 15 ga wire, high grade transformer steel laminate cores, these are rated 600 Watts, but are available 5 to 15 mH, unless special order.

    I hope the above can be of some help to you.

    Richard
    Richard,

    This information is very helpful! Thank you for taking the time and effort to help me and anyone else that has these questions.

    I read somewhere that it isn't necessary to use air cored coils if it is a shunt or used in parallel with the driver. Is this correct?

    I will review my list and size the coils accordingly.

  7. #7
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    Quote Originally Posted by Ian Mackenzie View Post
    Hi Ari,

    I have built a number of these particular crossover for various JBL users.

    The DCR of the inductor coils can have influence on the Q magnitude or Peak of the resonance of the filter. In the case of the midrange band pass filter this is important and in the UHF filter. This can have a marked effect on the voltage drive in the crossover region.

    In all the 4344mk11 crossovers l assembled l have used air core inductors as the ferrite or iron core inductors do not document the current rating accurately before saturation. For a modest cost increase an air core inductor is a more ideal inductor without the effects of hysteresis as the dynamic signal increases.

    If you cannot obtain a close Dcr value then add a small value power resistor in series with the inductor with a lower Dcr value to obtain the correct total Dcr.

    I recommend you mount the parts on a non ferris material such plywood or acrylic sheet and hot melt glue with zip ties to attach the parts. Keep all inductors well clear of each other by two inches. An example of such construction is shown below l prepared earlier this year.

    I used WAGO terminal connectors, adhesive zip tie pads and 7.5 amp pvc insulated flying leads soldered and wire wrapped from the components. All the terminations are also hot melt glued to prevent vibration and fatigue which may impact on reliability. These WAGO terminals have excellent electrical characteristics. This allows flexibility in changing out parts should trim adjustments be required. I prefer stranded flying leads to prevent fatigue of solid wire solder joints in loudspeaker crossover assembly. Each filter had its own star ground connection taken from a 15 amp rated ground spur from the input connection to the amplifier output ground terminal. This approach minimises the influence of ground potential variations from associated filters and IMD distortion.

    There are other approaches to construction and this is just one example.

    Unfortunately a good crossover implementation is never a cheap exercise.
    Good luck with your project.
    Hi Ian,

    I've been following yours and Richard's posts for over a decade! I feel like you guys are pioneers on the 43xx subject.

    These crossovers are absolutely beautiful and quite refined when compared to the past. I mean that in a practical sense, that they have been worked out and thoughtfully improved through your "natural selection" an evolution of parts.

    Somehow I feel charge coupling is no longer the way to go, but I am committed now since I have all the solen caps.

    Where do you source your coils from?

  8. #8
    Administrator Robh3606's Avatar
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    If you don't have access to a good simulation program like LEAP just stay close to the DCR values that JBL published for the crossover. You could go to all air wound coils but the cost and size can be prohibitive for the same DCR values.

    I tend to go with minimum values for the woofer inductors to minimize sensitivity loss and for the shunts I will sometimes use a higher gage and use the inductors DCR instead of adding a low value resistor. Smaller part count same network response.

    Rob
    "I could be arguing in my spare time"

  9. #9
    Senior Member RMC's Avatar
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    Ari,

    Thanks for your good word.

    However i'm not a pioneer on 43xx, in fact the 43 series isn't really my thing, i intervene in 43xx related threads occasionaly, not much more. Many such threads are about cloning existing designs, but i never cloned anyone's design and might never do so. I do my own design/engineering work for my DIY boxes, then i know the what, why and how for each choice, preference and compromise made.

    I don't design boxes nor crossovers for members, other than showing sometime few speaker software modelings in order to support a point, indicate what is feasible re cab size/tuning or an expected response curve (good/bad).

    I replied to help you since nobody else did at the time, and i usually try to help the orphans or newcomers getting no reply to their question(s). Now that you have additional company i'm confident even more crossover guys here will make your mouth dripping.

    Btw you mention having Solen caps, this is where i get most of my crossover parts, though i have also bought some stuff from qcomponents.ca

    Good luck with the project.

    Richard

  10. #10
    Senior Member Ian Mackenzie's Avatar
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    Quote Originally Posted by scombridae View Post
    Hi Ian,

    I've been following yours and Richard's posts for over a decade! I feel like you guys are pioneers on the 43xx subject.

    These crossovers are absolutely beautiful and quite refined when compared to the past. I mean that in a practical sense, that they have been worked out and thoughtfully improved through your "natural selection" an evolution of parts.

    Somehow I feel charge coupling is no longer the way to go, but I am committed now since I have all the solen caps.

    Where do you source your coils from?
    These coils are made by Jantzen and l source them from a local supplier.

    Edit.

    One thing to mention is that aspiring 43xx builders don’t always the the originally specified drivers. For example they might have a 2121 mid or a LE85 compression driver. No problem. I can measure these drivers and obtain the impedance and acoustic response and modify the network to accommodate these drivers until the user can obtain the other originally specified drivers.

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    Quote Originally Posted by Ian Mackenzie View Post
    These coils are made by Jantzen and l source them from a local supplier.

    Edit.

    One thing to mention is that aspiring 43xx builders donÂ’t always the the originally specified drivers. For example they might have a 2121 mid or a LE85 compression driver. No problem. I can measure these drivers and obtain the impedance and acoustic response and modify the network to accommodate these drivers until the user can obtain the other originally specified drivers.

    Thanks Ian! I am lucky enough to get very close to the 4344 MkII drivers. I have original 2235H, 2123h, 2426H Aquaplas coated by Upland Loudspeaker and the 2405 slot tweeter. I will be bi-amping with an Ashley XR1001. The thing I'm most confused about is the crossover slope for the woofer but I figured I would play around with the "response" knob until it sounded best.,,, the monkey test Thanks to your earlier posts, you have given me the confidence to live a dream!

  12. #12
    Senior Member RMC's Avatar
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    I have the XR-1001.

    Shortly. The filter slope is fixed at 24 db. The response knob is more about tuning of that filter, like making it act as a Butterworth type filter curve or a Linkwitz Riley for example. In other words how the filters combine at the crossover frequency.

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    Senior Member Ian Mackenzie's Avatar
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    Quote Originally Posted by scombridae View Post
    Thanks Ian! I am lucky enough to get very close to the 4344 MkII drivers. I have original 2235H, 2123h, 2426H Aquaplas coated by Upland Loudspeaker and the 2405 slot tweeter. I will be bi-amping with an Ashley XR1001. The thing I'm most confused about is the crossover slope for the woofer but I figured I would play around with the "response" knob until it sounded best.,,, the monkey test Thanks to your earlier posts, you have given me the confidence to live a dream!
    Hi Ari,

    I understand your situation.

    Your Ashley crossover will give a competent crossover region with some trial and and error adjustments.

    To replicate the actual passive crossover using the 2335/2245 as me the 2123 mid driver is somewhat more of a customised active solution with specific crossover slopes that are outside a universal like the Ashely. I recommend you tweak the Ashley crossover for best subjective performance for now,

    Subject to our current Covid situation l will make available a tailored active crossover specific to each jbl design using SOA circuitry.


    The thing is you have a loudspeaker with incredible performance potential.

    On dcr of inductor try to keep the woofer coil the lowest possible dcr. The other dcr value should be adhered to closely in order to keep the filter slopes

    J suggest you keep to air cores with the exception of the woofer filters which can be an iron core.

    Ian

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    Quote Originally Posted by Ian Mackenzie View Post
    Hi Ari,

    I understand your situation.

    Your Ashley crossover will give a competent crossover region with some trial and and error adjustments.

    To replicate the actual passive crossover using the 2335/2245 as me the 2123 mid driver is somewhat more of a customised active solution with specific crossover slopes that are outside a universal like the Ashely. I recommend you tweak the Ashley crossover for best subjective performance for now,

    Subject to our current Covid situation l will make available a tailored active crossover specific to each jbl design using SOA circuitry.


    The thing is you have a loudspeaker with incredible performance potential.

    On dcr of inductor try to keep the woofer coil the lowest possible dcr. The other dcr value should be adhered to closely in order to keep the filter slopes

    J suggest you keep to air cores with the exception of the woofer filters which can be an iron core.

    Ian
    Ian,

    Please correct me if I am wrong but the woofer can be wired directly to the amp because I'm using an active crossover right? The only crossover I am building is for the MF, HF and UHF.

    What is SOA circuitry?

    Thanks,
    Ari

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    Quote Originally Posted by RMC View Post
    I have the XR-1001.

    Shortly. The filter slope is fixed at 24 db. The response knob is more about tuning of that filter, like making it act as a Butterworth type filter curve or a Linkwitz Riley for example. In other words how the filters combine at the crossover frequency.

    Name:  IMG_2638.jpg
Views: 191
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    Richard,

    I understand without correct measuring setup and software it is virtually impossible to adjust much effectively. That said, theoretically, when would it be desirable to have more attention at the crossover point versus less? Are there certain circumstances/environments that would create these conditions? Is the 43** four way systems known to need steeper crossover slopes between the 15" and 21** drivers? I noticed it's common to have the polarity reversed only for the woofer. I'm thinking this also has something to do with particular blending at that crossover point.

    Thanks,
    Ari

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