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Thread: About to re-cone JBL 2225 to 2234/5 need advice

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    Senior Member turnitdown's Avatar
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    About to re-cone JBL 2225 to 2234/5 need advice

    As the title says, that's my current project. I have re-coned speakers, like for like, before.This is different.Going from 2225 to 2235 my question is:How much of the voice coil should be showing above the pole piece? Is there a measurement or an eyeball test to be sure it sits in the gap correctly before I attach the spider?Thanks in advance.Denny

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    Administrator Robh3606's Avatar
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    Quote Originally Posted by turnitdown View Post
    As the title says, that's my current project. I have re-coned speakers, like for like, before.This is different.Going from 2225 to 2235 my question is:How much of the voice coil should be showing above the pole piece? Is there a measurement or an eyeball test to be sure it sits in the gap correctly before I attach the spider?Thanks in advance.Denny
    Shouldn't it be centered?? You should be able to measure the top plate thickness, the voice coil winding depth and pencil mark the spot on the inside/outside of the coil form that you can line up with the top of the pole piece. Say mid coil plus 1/2 pole piece.

    Just a thought.

    Rob
    "I could be arguing in my spare time"

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    Senior Member turnitdown's Avatar
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    Quote Originally Posted by Robh3606 View Post
    Shouldn't it be centered?? You should be able to measure the top plate thickness, the voice coil winding depth and pencil mark the spot on the inside/outside of the coil form that you can line up with the top of the pole piece. Say mid coil plus 1/2 pole piece. Just a thought.Rob
    I need to be dead sure about this. If I bottom out the new voice coil and make a pencil mark, then divide that distance in half - will that put me in the ballpark? I can't afford/don't want to have to do it twice.

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    Administrator Robh3606's Avatar
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    Bottom it out?? That doesn't make sense to me. The coil should never bottom out with in the spec. X-max. Maybe under extreme excursions at the limit of mechanical X. Then you have a mass ring that does smack the pole piece at the extremes.

    I am not a a speaker tech. But common sense says the coil at rest is centered in the gap. To center the coil you can do basic measurements to determine how much of the coil should be visible above the top of the pole piece.

    If you have any doubts don't. All I am saying that's how I would do it as a novice WRT speaker repair. I have never done a re-cone without a spider pre-installed to the coil. Like a typical JBL stock re-cone kit.

    Did you look on You Tube for videos?

    Rob
    "I could be arguing in my spare time"

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    Senior Member turnitdown's Avatar
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    Quote Originally Posted by Robh3606 View Post
    Bottom it out?? That doesn't make sense to me. The coil should never bottom out with in the spec. X-max. Maybe under extreme excursions at the limit of mechanical X. Then you have a mass ring that does smack the pole piece at the extremes. I am not a a speaker tech. But common sense says the coil at rest is centered in the gap. To center the coil you can do basic measurements to determine how much of the coil should be visible above the top of the pole piece. If you have any doubts don't. All I am saying that's how I would do it as a novice WRT speaker repair. I have never done a re-cone without a spider pre-installed to the coil. Like a typical JBL stock re-cone kit.Did you look on You Tube for videos?Rob
    I would bottom the coil, make a mark on the coil at the top, then divide the distance by two which would, theoretically give me the halfway point.

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    Administrator Robh3606's Avatar
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    Does the Voice Coil extend to the bottom of the form? Take a look at the attached pictures Alnico and Ferrite.

    The key is the center the coil in the gap. There should be clearance under the coil at X-Max built into the magnetic return structure.

    So as an example 1" coil and 1/4 inch pole piece. You would make a mark at 5/8 from the bottom of the voice coil. That should line up with the top of the pole piece at rest.

    So 1/2 the coil where the center of the pole piece should be then add 1/2 the pole piece to line up with the mark on the top where you can see it. .

    If this doesn't make sense to you simply don't.

    Rob
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    "I could be arguing in my spare time"

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    Administrator Robh3606's Avatar
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    This is a picture of a 129H JBL re-cone kit. You can see the VC form extends below the coil. You would take any offset between the form and the coil into account when making calculations to center the coil if you were measuring from the bottom of the form to center the coil.

    Best of luck! If you find another way or a hard number somewhere please post it.

    Can we have a re-conner chime in?

    Rob
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    "I could be arguing in my spare time"

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    Quote Originally Posted by turnitdown View Post
    As the title says, that's my current project. I have re-coned speakers, like for like, before.This is different.Going from 2225 to 2235 my question is:How much of the voice coil should be showing above the pole piece? Is there a measurement or an eyeball test to be sure it sits in the gap correctly before I attach the spider?Thanks in advance.Denny
    See if you're able to glean the info you need from this conversation between GordonW + myself.

    2234/2235 Voice Coil Former Length




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    Administrator Robh3606's Avatar
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    Quote Originally Posted by Earl K View Post
    See if you're able to glean the info you need from this conversation between GordonW + myself.


    Oh good a picture should help.

    Rob
    "I could be arguing in my spare time"

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    Senior Member turnitdown's Avatar
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    You're all so helpful. It's not rocket surgery, I guess, so I'll dry fit everything and take a picture of it later today.

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    Quote Originally Posted by turnitdown View Post
    You're all so helpful. It's not rocket surgery, I guess, so I'll dry fit everything and take a picture of it later today.
    What's the length ( height ) of your kit's Kapton former ( that the Voice-Coil is wound onto ) ??

    OEM JBL ( from around year 2000 ) was @ 1.25" ( with about 1/8" sticking above the glue-line > of the paper-cone and the former ).

    Also, ( in the spirit of sharing ) what's the total weight of that recone kit ( including all parts minus the "Mass-Ring" >> OEM JBL is 137grams, including the mass ring ) ??

    Thanks <> EarlK

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    Senior Member turnitdown's Avatar
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    Quote Originally Posted by Earl K View Post
    What's the length ( height ) of your kit's Kapton former ( that the Voice-Coil is wound onto ) ??OEM JBL ( from around year 2000 ) was @ 4.25" ( with about 1/8" sticking above the glue-line > of the paper-cone and the former ).Also, ( in the spirit of sharing ) what's the total weight of that recone kit ( including all parts minus the "Mass-Ring" >> OEM JBL is 137grams, including the mass ring ) ??Thanks EarlK
    Kapton former is 1.25 inches tall. Weight of all parts minus mass ring is 102 grams. Add the 35 grams mass ring for 137 grams total.

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    Thanks for that.

    Those kits seem to be real close to OEM JBL then , a good thing.

    I notice I had a senior moment and changed a 1.25" measurement into a 4.25" measurement.

    I'm going to correct that now.

    Thanks!

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    Senior Member turnitdown's Avatar
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    Here, I hope, is a picture with the voice coil in the gap centered with a shim. I dry fit the spider on top of its perch. What's left is about 1/8-3/16 above the spider. This gives plenty of purchase for the cone and cap and it looks as though the coil itself is halfway in/halfway out of the gap. Thoughts?
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    Thoughts??

    If one looks at my pic of the OEM kit ( posted above ) the "collar" of the spider is pointing towards the voice-coil >> suggesting that you may have your spider flipped upside-down

    Rob's pic shows similar ( and is clearer ).






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