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Thread: Speaker coil winding

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    Speaker coil winding

    I hope this is the right place to put this. I figure winding magnet wire is winding magnet wire so there shouldn't be much difference skill wise. Is it worth it to repair speaker coils?

    Note: This thread was originally posted in the 'Tools and Coil Winding Gear' sub-forum of the 'Pickup Makers' forum.

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    Last edited by Boss; 12-02-2018 at 08:41 AM. Reason: added note about location change

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    Old Timer Leo_Gnardo's Avatar
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    I would expect, with the need to keep the coil & former perfectly circular, and the coil firmly glued in place, the skill set is much more demanding. And that's with round wire. How about winding JBL-style, flat wire, edge-on? Yikes! But - somebody's doing it somewhere, recone kits are being made & that's proof enough. I'm looking forward to what our pickup winding brain trust has to say.

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    How often does the brain trust check in?

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    Quote Originally Posted by anchor View Post
    How often does the brain trust check in?
    Why don't you try it and report back?
    How much does a new speaker cost vs what you have to buy to repair one speaker and learn how to do it.
    Do the math.
    nosaj

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    At this stage of my understanding, I don't think it would be worth it for me. I've never worked with magnet wire. I probably don't have the tools and materials to make it worthwhile. That may not be the case for people already familiar with winding. It's why I posted here. Are you a member of the brain trust?

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    ToneOholic! big_teee's Avatar
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    How about this.
    English not great, but the pictures are good.


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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by anchor View Post
    I hope this is the right place to put this. I figure winding magnet wire is winding magnet wire so there shouldn't be much difference skill wise. Is it worth it to repair speaker coils?
    It can be done, but thereīs some important differences.

    FWIW I do wind my own voice coils, but I reserve that for custom jobs, such as cloning old Jensen voice coils, using old style synthetic enamelled wire, wound on paper formers, and glued with solvent based Nitro adhesives.

    For bulk production speakers, I pay around $1 for a Chinese ready to use round copper on kapton former one, glued with high temperature epoxy and with leads precut and pretinned ... why worry?
    You can get those in the usual sizes for $2 to $5 from Ted Weber, as well as suitable cones, suspensions, and everything else.

    The few times where I was forced to rewind a voice coil still attached to the cone was wehere it was irreplaceable and removing voice coil (which to boot was odd sized) would destroy it, so ....
    And itīs not a job for the faint hearted.

    You also need to have a lathe available, better if on the same premises, because you need to make an exact size core to hold former (which is weak and flexible, paper thin) in the proper position against wire pressure , which is high because you want it tight.

    A big difference with pickup winding is that these can be (and usually are) scatter wound, with one turn mounting on others not a big deal, while voice coils are two perfect layers, period, with each turn perfectly parallel and touching those on its sides.

    And wire must be glued , of course, since itīs designed to vibrate back and forth, and push/pull a load 20 to 40 times larger than its own weight.

    Car engines and most machines are *designed* to be disassembled and reassembled, thatīs why they use bolts, pins, clamps, click together, etc. so you can half disassemble a car engine, take 200 parts out, replace some component deep inside and reassemble using all of the old parts.

    Speakers on the contrary, and because of extreme weight and space considerations, are *glued* together, and are made of weak paper , cloth, foam, etc. so standard speaker repair procedure is to grab an X Acto knife, cut everything away (and junk it) , scratch old glue and reassemble with all new parts, except magnet and frame.

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    Thanks for the helpful posts. It looks like the choice of adhesives and glues are critical here. Where do you guys source yours? In my case, I have an 8" driver that froze. I considered using some de-oxit in the coil gap but that would leave the residue in there. Looking further, the ohm value is still in spec so the coil is probably not damaged. How would you guys approach this repair?

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    Old Timer J M Fahey's Avatar
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    Search any Industrial Epoxy supplier.
    I use Araldit but canīt tell you the original name since my supplier buys the 55 gallon drums and repacks it into 250 gram and 1 kilo cans, with his own brand.
    But itīs the one which is thick as honey at room temperature, mixed about 1:1 which makes measurement easier, one component is honey yellowish transparent, the other is whitish translucid, and takes some 6 to 8 hours to cure at room temperatuire.
    It cures faster at higher temperatute, say 15 minutes at 100C and you must not go over 120C or it bubbles.
    Any knowledgeable supplier willl find it with that data (which is pretty common) or give you another brand equivalent.
    Toluene you get in small amounts (itīs a controlled substance) from your friendly Industrial Chemist,.
    Enamelled wire from usual suppliers, with the caveat it **MUST** be the high temperature enamel type, Class F or H or better , guaranteed 160 or 180C operation, typically used to rewind electric motors.
    The currently popular "self soldering" type, with atoms thin enamel which evaporates at low temperatures has no place inside a speaker.
    The polished metal cores such as shown in the (very accurate) video are custom made on a lathe.
    I suggest using small stiff brushes to apply epoxy instead of fingertip, I am half expecting the video guy to grow a tumor there, not kidding, uncured epoxy is very aggressive, as well as Toluene (and the impurities it carries which are left behind under your skin).

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by anchor View Post
    Thanks for the helpful posts. It looks like the choice of adhesives and glues are critical here. Where do you guys source yours? In my case, I have an 8" driver that froze. I considered using some de-oxit in the coil gap but that would leave the residue in there. Looking further, the ohm value is still in spec so the coil is probably not damaged. How would you guys approach this repair?
    What driver is it? If it's nothing special just replace it and be done with it. Hate to think your asking all this for a cheap chinese speaker.

    nosaj

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    Quote Originally Posted by nosaj View Post
    What driver is it? If it's nothing special just replace it and be done with it. Hate to think your asking all this for a cheap chinese speaker.

    nosaj
    Jeez, lighten up.

    I do stuff like this all the time with cheap, junk, crap stuff that is broken or non functional.

    I got nuttin to lose and I find out how stuff is put together, and how it works.

    If I'm successful in the "repair"... then great! plus I learned something.

    If I'm not successful then... no big loss, it was broken anyway...
    BUT, I still LEARNED something, and may be better prepared to tackle working on something of value.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by galaxiex View Post
    Jeez, lighten up.

    I do stuff like this all the time with cheap, junk, crap stuff that is broken or non functional.

    I got nuttin to lose and I find out how stuff is put together, and how it works.

    If I'm successful in the "repair"... then great! plus I learned something.

    If I'm not successful then... no big loss, it was broken anyway...
    BUT, I still LEARNED something, and may be better prepared to tackle working on something of value.
    He has a reason

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    I don't know that it is special but it seems well made. There is only a cryptic stamp of 220B. The magnet is ~135mm diameter and very strong. The basket structure is very rigid, it has tarred cloth, accordian surrounds, etc. It weighs 5 kilo. I don't think I could get similar quality for less than 100. I didn't pay for it so I don't know its origin. To get all the chemicals required will cost me ~60. A cheap replacement coil that fits might tempt me to try the repair. I'm still on the fence about it.

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    ToneOholic! big_teee's Avatar
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    Let's hope he winds it.
    I would like to see what he comes up with.
    Of Course we need documented play by play & pictures, along the way!
    GL,
    T

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    Quote Originally Posted by anchor View Post
    I don't know that it is special but it seems well made. There is only a cryptic stamp of 220B. The magnet is ~135mm diameter and very strong. The basket structure is very rigid, it has tarred cloth, accordian surrounds, etc. It weighs 5 kilo. I don't think I could get similar quality for less than 100. I didn't pay for it so I don't know its origin. To get all the chemicals required will cost me ~60. A cheap replacement coil that fits might tempt me to try the repair. I'm still on the fence about it.
    Where is your location, someone could suggest something close to you since your not in the US. Show us a picture, what did it come out of.
    nosaj

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    Old Timer J M Fahey's Avatar
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    Start by showing a couple speaker pictures, front , back, sideways (so we see the magnet).
    How do you know itīs chinese?
    Cut suspension and edge all around, cut tinsel wires, remove cone and voice coil carefully and post its pictures, looking at the coil, whether itīs complete or disassembled, charred, where are the toasted areas, I can reasonably "read" what happened to it.
    Try not to leave bobbin pieces in the gap, youīll need to clean it well anyway.
    You will need to measure coil diameter, height, winding length exactly; replacements wrong by a couple thousandths of an inch will "scratch inside" or "scratch outside" or plain noit fit in the gap, tolerance is that close.

    Are you in or near any large city?
    If you have to mail order everything it may be problematic, itīs not easy to mail Toluene or Acetone.

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    I am fairly close to industry in Frankfurt but the chemicals are still expensive.

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    Last edited by nosaj; 12-03-2018 at 12:22 AM.

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    Master Destroyer nosaj's Avatar
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    How about some pics of the said speaker?

    nosaj

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by anchor View Post
    I am fairly close to industry in Frankfurt but the chemicals are still expensive. I have an unrelated question about this website. I have clicked on links in recent posts and have been unable to access them. The dialog states I have insufficient priviliges. If this is a feature of the website and not a problem with my browser, how or when will my privilges be elevated to access these links?
    Please post a detailed full list showing *all* links you canīt connect to.
    Maybe itīs a problem about Member "being outside USA" ... which I also am.
    So with your list I may try to access it from here.
    Happened to me some times too, here and in other Forums, so I am not surprised.

    As of the speaker, please post some pictures, *specially* one showing the gap, if possible close up sharp and well illuminated pictures showing what kind of debris is clogging it.
    And some of the removed voice coil, to see how it burnt and how much it crumbled, show the burnt wire and from the inside of the former, to check whether it bubbled, melt, cracked or distorted.

    IF you want to clone it, youīll need an aluminum, brass or iron core turned to exact dimensions, the one in "Video Rockola" will give you an idea about how itīs made and mounted.

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    I notice that in the video he may be confusing the DC resistance with the impedance. A voice coil DC resistance of somewhere around 6.5 ohms is typical for an 8 ohm speaker.

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    Quote Originally Posted by nickb View Post
    I notice that in the video he may be confusing the DC resistance with the impedance. A voice coil DC resistance of somewhere around 6.5 ohms is typical for an 8 ohm speaker.
    I agree. I have the same thought. I'd also like to know just how you would design a voice coil for a specific impedance other than matching and old damaged voice coil turn for turn with the same size wire. For instance, when you send a speaker for recone you can ask for an impedance change. That is if it was an 8 ohm speaker you can ask for the reconer to install a 4-ohm voice coil when the speaker is rebuilt. How exactly do they do that?

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    Fur Reader:
    I think going from 8R to 4R is only a matter of using fewer turns.

    I will post some photos but there is not much to see. Even with a light, I cannot get a good shot of the voice coil. I was able to locate only one of the links I spoke of. Here it is below:
    https://music-electronics-forum.com/...l=1#post514504

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by anchor View Post
    Fur Reader:
    I think going from 8R to 4R is only a matter of using fewer turns.

    I will post some photos but there is not much to see. Even with a light, I cannot get a good shot of the voice coil. I was able to locate only one of the links I spoke of. Here it is below:
    https://music-electronics-forum.com/...l=1#post514504
    Pics will help so please show the basket and everything. Less turns possibly means different wire gauge also. Same gauge fewer turns means less power handling.

    Where did you find the link? Cause you said " I have clicked on links in recent posts and have been unable to access them" So curious where you found the link.

    nosaj

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by nickb View Post
    I notice that in the video he may be confusing the DC resistance with the impedance. A voice coil DC resistance of somewhere around 6.5 ohms is typical for an 8 ohm speaker.
    Well, yes ... "Rockola" is a quite crude site (technologically) but I praise them for rolling up their sleeves and doing it, and even more for providing all the data, PCBs, etc. plus tons of stepby step pictures and videos.
    And they do not sell kits or transformers, do not ask for paid membership, anything $$$ , so they are quite altruistic in their area.

    Yes, that winding "formula" applies just to *one* voice coil type and model, is useless for other diameters, winding lengths or impedances ... but at least cover 8 ohm 2" voice coil woofers, and is reasonably close for 2.5" ones, which cover most of the generic woofers they will ever meet.

    "Build your own rockola" site in practice covers typical small town DJ needs, or Tropical Music dance bands PA, I bet both regularly burn a fair amount of woofers which to them are expensive to replace.

    Of course 8 ohm DCR is high, but since he did not discount 1 ohm or so parasitic meter resistance, in the end both sort of compensate ; REAL DCR must be somewhat less than 7 ohm which is fine
    Often, Ignorance is bliss

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Well, yes ... "Rockola" is a quite crude site (technologically) but I praise them for rolling up their sleeves and doing it, and even more for providing all the data, PCBs, etc. plus tons of stepby step pictures and videos.
    And they do not sell kits or transformers, do not ask for paid membership, anything $$$ , so they are quite altruistic in their area.

    Yes, that winding "formula" applies just to *one* voice coil type and model, is useless for other diameters, winding lengths or impedances ... but at least cover 8 ohm 2" voice coil woofers, and is reasonably close for 2.5" ones, which cover most of the generic woofers they will ever meet.

    "Build your own rockola" site in practice covers typical small town DJ needs, or Tropical Music dance bands PA, I bet both regularly burn a fair amount of woofers which to them are expensive to replace.

    Of course 8 ohm DCR is high, but since he did not discount 1 ohm or so parasitic meter resistance, in the end both sort of compensate ; REAL DCR must be somewhat less than 7 ohm which is fine
    Often, Ignorance is bliss
    i am not the OP is really with us. To get a shot of the voice coil means the speaker will have been dissected at this point , no?

    nosaj

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    Quote Originally Posted by nosaj
    Same gauge fewer turns means less power handling.
    What makes you believe this? A lower ohm rating should not change the amount of amps going through the wire if is the same gauge. You are correct observing that I have not removed the voice coil. I left it as I found it as I have not decided to fix it.

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    Quote Originally Posted by anchor View Post
    What makes you believe this? A lower ohm rating should not change the amount of amps going through the wire if is the same gauge. You are correct observing that I have not removed the voice coil. I left it as I found it as I have not decided to fix it.
    You are exactly right. Same current but fewer Ohms. Power = I^2 * R so fewer Ohms for the same current means lower power rating.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by eschertron View Post
    You are exactly right. Same current but fewer Ohms. Power = I^2 * R so fewer Ohms for the same current means lower power rating.
    Well isn't that what I said?
    Quote Originally Posted by nosaj
    Same gauge fewer turns means less power handling.

    nosaj

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by anchor View Post
    I will post some photos but there is not much to see. Even with a light, I cannot get a good shot of the voice coil. I was able to locate only one of the links I spoke of. Here it is below:
    https://music-electronics-forum.com/...l=1#post514504
    That makes two of us
    I can not even see a link there, let alone open it.
    I wouldnīt worry about that anyway, old stuff.

    Fur Reader:
    I think going from 8R to 4R is only a matter of using fewer turns.
    Thereīs more parameters involved:
    * coil diameter
    * winding length
    * actual wire diameter (which may or may not match what raw Gauge # indicates)
    * number of turns
    * insulation thickness
    * copper or aluminum
    * number of layers.
    Usually 2 but some dome tweeters use only 1 (and made out of aluminum).
    Some subwoofers use 4 layers.
    * high performance PA speakers and horn drivers use a single layer of *edgewound* aluminum or copper ribbon.

    That said, 99% speakers use 2 layers copper roundwire because all other options are orders of magnitude more difficult to make.

    * Guitar speakers generally have short coils, same or 1mm longer than gap height, woofers generally are up to 2X as long, and some special high excursion subwoofers *up to* 4X gap length.

    * Some supertweeters have coils *shorter* than gap length.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by anchor View Post
    What makes you believe this? A lower ohm rating should not change the amount of amps going through the wire if is the same gauge. You are correct observing that I have not removed the voice coil. I left it as I found it as I have not decided to fix it.
    Then how did you expect to take a picture of it? Are you sure you know where the voice coil is? You'll have to remove the cone and the spider.

    nosaj

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    Quote Originally Posted by Reader View Post
    I agree. I have the same thought. I'd also like to know just how you would design a voice coil for a specific impedance other than matching and old damaged voice coil turn for turn with the same size wire. For instance, when you send a speaker for recone you can ask for an impedance change. That is if it was an 8 ohm speaker you can ask for the reconer to install a 4-ohm voice coil when the speaker is rebuilt. How exactly do they do that?
    I'd keep the coil length the same and use sqrt(4/8) = 0.707 time the original number of turns. The wire would have to be thicker to keep the winding tight but that could be estimated: wire dia = coil length/ number of turns in on one layer.

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    Quote Originally Posted by escherton
    Same current but fewer Ohms. Power = I^2 * R so fewer Ohms for the same current means lower power rating.
    The power dissipated also has a voltage perspective where it does not change. If the amp used with the original voice coil is 100W rated at 4R, reducing the voice coil resistance does not change its power rating. Note p=v2/r, when you halve the resistance, more power is dissipated. The post by nosaj seems only half true and does not tell the whole story.



    Thereīs more parameters involved:
    * coil diameter
    * winding length
    * actual wire diameter (which may or may not match what raw Gauge # indicates)
    * number of turns
    * insulation thickness
    * copper or aluminum
    * number of layers.
    Of all those listed above, the "winding length" appears to be the only factor relevant to the case above. The number of turns only changes the impedance, not the resistance.

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    Quote Originally Posted by anchor View Post
    The power dissipated also has a voltage perspective where it does not change. If the amp used with the original voice coil is 100W rated at 4R, reducing the voice coil resistance does not change its power rating. Note p=v2/r, when you halve the resistance, more power is dissipated. The post by nosaj seems only half true and does not tell the whole story.



    Of all those listed above, the "winding length" appears to be the only factor relevant to the case above. The number of turns only changes the impedance, not the resistance.
    If wire diameters are the same the 8ohm coil will have more wire to dissapate more heat than the 4 ohm which will be shorter. Shorter wire of same value means more heat in my book.
    nosaj

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    Quote Originally Posted by anchor View Post
    The number of turns only changes the impedance, not the resistance.
    If wire didn't have resistance. But it does and the number of turns around a fixed size of coil changes the length and therefor the resistance and since the resistance is in parallel with the impedance @ frequency imposed by inductance there has to be an affect on impedance due to wire length if the same gauge is used. Further, the inductance affect on the impedance will be largely affected by the coils capacitance and that related to a large degree on insulation thickness and number of layers. You can see where this is going... Juan is a smart guy and probably the only person posting on any diy amp forum that makes his own speakers. If he says something is relevant then it probably is.

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    My layman's approach would be like this:

    Speaker power rating is determined by its max. voice coil temperature. The voice coil gets heated by the power dissipated in its DCR and is cooled via heat radiation to the surrounding structure and by convection.

    An example: An 8 Ohm/50W speaker can take 20Vrms. This means a current of 2.5Arms. It DCR is typically 6.4 Ohm (80% of 8 Ohm), so the max. dissipated thermal power is 40W.
    Everything else being equal, the 4 Ohm version of the speaker needs to have a DCR of 3.2 Ohm for a thermal power of 40W and a rated apparent power of 50W.

    Everything else being equal means that both voice coils should have the same surface area and (thermal) mass. Realization (including achieving the necessary inductance to get a Z of 4 Ohm) will require a heavier wire as well as less turns for the 4 Ohm version. The optimization process probably requires some iteration.

    I am aware that I ignored radiated acoustical power, but this is assumed to be the same for both versions.

    Surely JMF knows better.

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