Crossover Inductor Coils

Discussion in 'Audio Hardware' started by FrostEOne, Jul 27, 2018.

  1. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Looking for information regarding crossover coils, I can't find an air coil with the right specs.
    Looking to match this iron core with an air core, Jantzen 000-5143 Iron Core Coil With Discs 5,000mH +/-3% 0,420Ω wire 1,00=18AWG OD45/46
    Thanks in advance
     
  2. Davey

    Davey very clever with maracas

    Location:
    SF Bay Area, USA
    You can't make an air core inductor with the same specs, it will have to use a lot more windings, so if the same wire gauge, will probably have 3x the resistance and be much bigger. If it's in a woofer circuit, and you need to match the resistance because of the box alignment, and you need air core, you will need to go with much larger gauge wire, probably 12AWG. If you have the money and they are special speakers that warrant the expense, companies like Goertz make copper foil inductors in 12AWG. Looks like they have 4.7mH, so just as an example, it has .348 ohms resistance, about right, you just need to find one for 5.0mH...

    [​IMG]

    Goertz CF4.7 (12 AWG) Copper Foil Inductor
     
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  3. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Thanks for the reply, I'll check into the foil coils.
    This inductor below is closest to the iron core, slightly different ohms rating though.
    I don't know enough about these to know if the difference in ohms 0,420 vs 0,534 is an issue.
    000-0138 5,000mH +/-3% 0,534Ω wire 1,80mm=13AWG OD-82 / 60mm
    Yes indeed, it's big and more costly. I've read that an iron core inductor is not as linear as an air core.
    Yamaha NS1000M speakers I originally purchased in 1975 15,xxx serial number
     
  4. Davey

    Davey very clever with maracas

    Location:
    SF Bay Area, USA
    Yea, those should be close enough, you'd lose just a tiny bit of power and the alignment would be a touch different, but the NS1000 had a fairly slow rolloff anyway, using a second order closed box design, so probably wouldn't notice. Those are very nice speakers, be careful what you do because they are still quite valuable. Definitely change out the electrolytics on the woofer for some high quality film caps, maybe paper in oil if you can to match the others. That would be my priority. The powdered iron core inductors will be less linear than air-core, but it won't show up too much until higher power levels. You've probably seen the thread at Yamaha NS1000M - Tweaks - Page 2 .. for others, this is the capacitor section of the crossover, inductors are below, won't see anything like that again in a modern speaker from a big company like Yamaha, all those paper film caps in parallel feeding the beryllium midrange, very expensive ...

    [​IMG]

    [​IMG]
     
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  5. allied333

    allied333 TUBE AMPLIFIER REBUILDER - inquire

    Location:
    MI
    Buy a large gauge wire coil (not foil type) with slightly higher inductance than you need. Buy an inductance meter and remove tue=rns off of coil until you get same inductance spec you need. Then, re-shellac coil to keep windings tight.
     
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  6. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    I have a Chokes Unlimited 6.0mH coil, which measures at 0.7 ohms. At 17.5 oz., it appears to use about 18 AWG, although the diameter is 1.1-1.2mm so maybe closer to 17 gauge. Average coil diameter seems about 3.5cm, and length is 5.5cm. It is wound on an iron tube, but is air-core otherwise, so I guiess this is what they call a "hollow core iron core". Since it seems to use about twice the wire as OP's iron core, I would guess it is closer to hollow. So it seems like the specified coil is doable with ~14-16AWG without it being the size of a power supply toroid. Edgewound rectangular wire might make for less wire and less impedance.
     
  7. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Thanks again for responding,
    I have 2 sets of Yamaha NS1000M, set from 1975 and another set from 1976. New crossovers are to be external, I don't want to modify anything original, instead I intend to remove original crossovers and put away in a safe place. Here's my external crossover design and speaker input plate. All caps are Mundorf Supreme, except the Monacor 47uf 250V 5% Bipolar MKP Polypropylene in woofer section

    [​IMG]

    [​IMG]
     
    Last edited: Jul 27, 2018
  8. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Thanks for your response.
    Not sure I want to do that with an inductor that costs $61.50 each, won't removing coils change the mH as well as Ohms?
     
  9. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Thanks for your suggestion.
    Air coil I have located is 13 AWG and likely looks like a small toroidal transformer 82mm OD x 60mm height, but it will fit in my enclosure.
     
  10. MusicNBeer

    MusicNBeer Forum Resident

    Location:
    Florida
  11. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Thanks for your suggestion, I will look into this, 112mm diameter though, don't think is going to fit in current enclosure. Oh, and very pricey these are.
     
  12. Davey

    Davey very clever with maracas

    Location:
    SF Bay Area, USA
    Cool that will be a nice setup, it's a good idea to preserve the stock crossovers. I made a similar external crossover board for a 3-way speaker set with Focal drivers, it's a very nice sounding system. I went slightly different route and chose large steel laminate core inductors, paralleled for very low resistance to the woofer and to keep them very linear. In my case, the other inductors are air-core, and capacitors are vacuum epoxy impregnated paper film on the tweeter, with polypropylene film wrapped in silicone/lead sheet on the midrange and woofer... good luck with the design and I'd love to see the final results, and hear some about the sound. From experience modding a couple commercial speakers with better parts, It will definitely be a huge difference, but always a bit of a gamble too if you like the current sound.

    [​IMG]


    I my case, I chose to make a stereo set of crossovers that was vry close to the amplifier, then have individual wires from there to the drivers. Make sure the returns from the drivers are separate for best results.
     
    Last edited: Jul 27, 2018
  13. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Thanks Davey, you've touched on something I don't understand. Paralleling inductors - does the mH stay the same and ohms is added together or how does this work?
     
  14. Davey

    Davey very clever with maracas

    Location:
    SF Bay Area, USA
    Inductance and resistance is cut in half, so I have two 12.5 mH inductors in the picture on each side to get around 6mH, but very low resistance. They were easily obtainable inductors at the time.
     
  15. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    It may be preferable to use the manufacturer's provided option for biamp but with an active crossover instead of stuffing more copper in the box. This will be even more linear and give you later tuning options.

    From the "speaker review" page where that Yamaha diagram you posted is from, there is also Thiele-Small measurements of the woofer and box volume.

    This allows us to calculate the response of the driver alone (white), and with the passive crossover network and inductor resistance in place (orange):

    [​IMG]

    The reason my big coil is not in service is because of the large phase shifts it makes in the crossover region - you can see this in the last plot. The review says the total speaker response has a mid-bass hump - we can see the coil itself adds a mid-bass hump to the woofer, yet the total output below 50Hz is less. Going active two-way may get you a better system after removing both ~150Hz passive crossover filters.

    Anyway, the coil resistance doesn't affect much between 0.4-0.8 ohms, worse values just reduce the woofer output more.

    PS: adding a 2" port 6" long to this same box and driver (red) extends the frequency response flat much lower:

    [​IMG]
     
    Last edited: Jul 27, 2018
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  16. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Many thanks Davey, I'm going to see what I can come up with for a parallel option, like to check all my options before committing. This is an interesting option.
     
  17. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Woah harby, way too much information I'm not familiar with. Let me think and see if I can make some sense of this. (to be continued)
     
  18. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    I think I should explain, I originally was looking at just recapping the original crossover, there's a lot of information on an Aussie forum regarding recapping options.
    Next I found the Yamaha NS1000M - Tweaks by Qwin, interesting read that evolves into an active crossover.
    Next is How to Make Your Own Yamaha NS-1000M Crossovers by YNWaN, really nice looking and well thought out project. This inspired me to go external and save original crossovers.
    These people deserve a lot of credit for what they've done and both have shared information with me to get me where I am now.
    Credit where credit is due I say.
     
    Last edited: Jul 28, 2018
  19. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    It seems consensus is that a slight ohms difference in this low range isn't a big issue for woofer inductor coil as it's effect would be a tiny bit of power loss and the alignment would be a touch different than original Yamaha design. Here's drawing with all 4 inductors being air coils.

    Comments, critique and suggestions openly welcomed, thanks in advance.

    [​IMG]
     
    Last edited: Jul 28, 2018
  20. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    The original coils aren't going to go bad or out of spec like capacitors might. It seems like a lot to invest just to experiment with coils, although I'm surprised if the original speakers came with iron core inductors, except to achieve a reasonable price point even with the 1975 price of copper, as they are known to behave non-linearly.
     
  21. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    All the original Yamaha coils are iron core w/discs, I think they were used due to size constraints.
    I'm using a 12" x 8" enclosure to get this all in, original crossover is 4½" x 6½".
    This isn't only about the inductors, Mundorf Supreme capacitors I've chosen won't fit in original space and I don't want to modify the original crossovers.
    [​IMG]
     
    Last edited: Jul 28, 2018
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  22. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Modified layout, moved large inductors for woofer and mid-range farther away from each other as they sit in the same orientation due to their diameter being bigger than my enclosure is tall.
    [​IMG]
     
  23. Davey

    Davey very clever with maracas

    Location:
    SF Bay Area, USA
    I'm curious why you are using so many smaller Mundorfs on the series midrange instead of bigger ones since they would be more economical? I know they did with the original paper in oil caps, but I think that was because bigger values weren't easily available back then. Based on my experience, I'd probably do the same because the smaller caps in parallel generally sound better, they are wound tighter and have less delayed resonances in the core. But most people would just pick bigger ones and save some money, in fact you could just use the 22uF, not quite the 21uF in original, but within 5%, and half the price of your 6 capacitors. There are some who believe parallel caps should all be the same size and don't like using bypasses either, which may also be the path you are on. But I like the way you are going :)
     
    Last edited: Jul 28, 2018
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  24. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA
    Hi Davey, You've just given all the reasons I have as to why I'm using the 6 smaller caps vs other cheaper combinations.

    1. they did with the original paper in oil caps,
    2. smaller caps in parallel generally sound better,
    3. they are wound tighter and have less delayed resonances in the core,
    4. There are some who believe parallel caps should all be the same size
    5. don't like using bypasses either

    That about sums it up, couldn't have said it better myself. Thanks for complimenting my plan.

    I actually have 2 - 22uF Mundorfs sitting here that I was originally going to use, decided against it for reasons just stated. HUGE they are for sure!
     
    Last edited: Jul 28, 2018
  25. FrostEOne

    FrostEOne Likes it cold! Thread Starter

    Location:
    Iowa, USA

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