Crazy 2108 4" question

[bldozier]

Firstly is it possible just to trip back to top cone
Use a 2108 surround

Would it work.
Crazy yes just looking at options

[mech986]

could you rephrase the question, I'm not making any sense of what you wrote. :confused:

[Allanvh5150]

Apart from the typo the question seemed quite straight forward, although I have no answer and not sure I would want to try.

[mech986]

Ok help me out then, I am not making sense of the question.

[BMWCCA]

Ok help me out then, I am not making sense of the question.
FWIW, it's not just you who can't figure out what the hell Dozier is talking about or asking. :banghead:

[kelossus]

I think I can translate.

He wants to know if he can get a 4" recone kit like the 2235H trim the cone down to the correct size and retrofit it in a 2108/112 basket?

I think thats what he is getting at......And if so no.....its not possible for multiple reasons.

[speakerdave]

I think I can translate.

He wants to know if he can get a 4" recone kit like the 2235H trim the cone down to the correct size and retrofit it in a 2108/112 basket?

I think thats what he is getting at......And if so no.....its not possible for multiple reasons.

If the OP is willing to try something like that, and actually has the cores, why not just have Orange County Speaker install their after market recone?

[mech986]

I think I can translate.

He wants to know if he can get a 4" recone kit like the 2235H trim the cone down to the correct size and retrofit it in a 2108/112 basket?

I think thats what he is getting at......And if so no.....its not possible for multiple reasons.

Ok, so he wants to know if 2108 can be created when there is no OEM cone kit left?
Well the 2108 is the 8" midrange and only has a 3" voice coil. The 2235H uses a 4" voice coil so I don't see how those would be compatible.
The 2214H uses a 3 inch voice coil, but woofer voice coils are likely way too deep for use in a midrange application, magnetic circuit speaking. That and the cone is very deeply angled so wouldn't likely fit well with the needs of a shallow cone/shallow frame like the 2108.

The 2203A/H 12 inch woofer also uses a 4 inch voice coil, and as such, might be considered spiritually like a 2235H cut down to fit a 12" 2204 type frame.

Now if he's taking a 2108 frame and putting a 4" Voice coil gap magnetic system on it, well, then a Frankendriver is being thought of. It would pack a heck of a wallop but again, most of the 2235 type cones are deep dish concave so not sure they would fit in a 2108 frame. A lot of engineering, trial and error would have to be done. Probably at that point, try getting an unassembled 2235H aftermarket kit to see about how fitment might work. Doubt though it would be much of a midrange driver due to weight of coil and 2235 cone type. You probably would need something like a LE8 or maybe LE10 type and cut that cone down.

The big problems with trying to "design" a replacement 2018 is getting all the elements correct - voice coil diameter / winding length, magnetic gap and length, underhung/overhung, cone weight, cone rib/damping, spider softness, etc.

If he is trying to replicate a 4315 or get parts for that, and has the 2108 frames already, yes, I'd say that the aftermarket recone is probably the most straightforward way to do it. Or to contact GordonW or Edgewound for possibly a more customized solution.

[bldozier]

Sorry, it was could I recreate a 2108, for a 4315s. I have le8t & pr8 baskets. I have had to procure le10a baskets to do a magnet swap. Looks like I may have hit the wall however bcd on the frames are different... the le8t being something like 130mm the space between screws is larger on the le10a, 3 1/4 vs 3" on the le8t. The frames for the 2108 seem to be a different cast then le8s to accommodate the larger magnet.
Bummed, dont know what iam going to do.

75088

[Aaron]

I have a 2108H that I just refoamed. PM me If you're in the market.

[bldozier]

Thank you sir. I needed a pair. I know how it is looking for the unobtanium. My luck another single will feather, I will remain pat, thanks for your offer.

[mech986]

I have a 2108H that I just refoamed. PM me If you're in the market.

Do you have pics front and rear of this driver? Did you shim or use the tone method for centering?

[bldozier]

Didn't do either I don't have a 2108. Trying to build them. ☺

Has anyone tried or can attest to the difference in baskets between the 2108/112a & le8t baskets.( which I have )
I have bought le8s thinking they could be tunrnt into ( turnt ) into the elusive 2108/112a. An also have pr8 baskets which I was going to use for, L212s,

im still excited for this baby project, but this is a hurdle hopefully not a tall one.

[bldozier]

75090 75092

The second photo being the 112a, the seat to me looks extend closer to the basket outward ring, I guess if I needed to absolutely have one with older le8 frames, I could machine the basket to allow the use of the larger magnet, so le8 as of now from my knowledge dont seem compatible, the 2108 frames however, for any reason ypu wanted seem to be able to use bother a 2&3 inch magnet.
im wondering if inwould hqve better luck with a 221x basket

I managed to free the le10 motor. Here is a look.
75093

[bldozier]

Here is the le8th I had with the magnet also removed, I have zero idea what the recessed area is being used for or if its necessary as the motor sits atop on the plate, an rest againt the shoulder


7509475095

[Aaron]

I followed Rock Cobbs instructions and used the tone.

Also, I pulled out every last vestige of the foam filter on top of the pole piece using an MEK dipped rag wrapped around my finger...I'm gonna die of cancer aren't I?

http://i278.photobucket.com/albums/kk87/666csi/Sales/112h%201.jpg (http://s278.photobucket.com/user/666csi/media/Sales/112h%201.jpg.html)

http://i278.photobucket.com/albums/kk87/666csi/Sales/112h%202108h.jpg (http://s278.photobucket.com/user/666csi/media/Sales/112h%202108h.jpg.html)

[quindecima]

Probably

[speakerdave]

No, but if you're made of glue you'll have only nine fingers.

[Flodstroem]

One idea could be to move a 2123H magnet to a LE8T basket. The important thing when doing that is to reach the same hight over the magnet pole piece in relation of the spider mounting face so you get the same hight over the magnet as in a 2108 motor or same hight as in the 2123H motor. Then one idea could be to use a 2123H cone kit (or an old parted cone from 2123H) and cut the diameter down for the 8" foam surround (for 2108/112A type surround) I dont know if its possible, it depends on the 2123Hś cone angel but that is a simple thing to measure. Then you will get a smaller copy of a 2123H and as a midrange I think its at least as good as an old 2108/112 or maybe better due to the longer voice coil and the Aluminum ribbon equipped voice coil :D

[bldozier]

As I mentioned earlier the magnet is a different bcd.
if the baskets could be machined I wouldmbe incline to think a transfer would be possible. I took photos of all components on the 1st page.
Brian.

[Flodstroem]

Yes it has to be machined for a new 2123 bolt circle pattern and you have to reuse the LE8T spider because the 2123 spider have a to large diameter :D
If you could make some type of drill template this machining would be a simple job ;)

[bldozier]

The baskets would need to be widened for the larger magnet, and four screw holes added along with the pin mounting hole. I dont think its to difficult of a job. The rear plate as shown in the photo has the recessed area for the magnet sit.
The area needs to be wider I think a shop could do this work. Then the 3" motor would fit, the 2" motors has some play in the fitting its not super snug. Btw.

75188

[Flodstroem]

The baskets would need to be widened for the larger magnet, and four screw holes added along with the pin mounting hole.


Why does it need to be widened? if the outer rim surface is flat and you have the two pin mounting holes fixed (drilled) then the magnet will sit exactly where it should
What I suggested in my earlier post was the main important thing is: the spiders outer mounting surface hight over the magnet,it has to be checked out (if you choose to use the 2123 cone assembly) It also could be the case that you have to mount some shims for to get the right hight for the spider........
The LE8Tś spider hight (mounting surface) over the magnet seems to be 9.4 mm (or 0.3701") I imaging the 2123 spider sit higher than that?

Now, this is valid only if you choose to use the 2123 cone assembly for to get an 8" substitute for the 2108/112 ;)

[bldozier]

Why does it need to be widened? if the outer rim surface is flat and you have the two pin mounting holes fixed (drilled) then the magnet will sit exactly where it should
What I suggested in my earlier post was the main important thing is: the spiders outer mounting surface hight over the magnet,it has to be checked out (if you choose to use the 2123 cone assembly) It also could be the case that you have to mount some shims for to get the right hight for the spider........
The LE8Tś spider hight (mounting surface) over the magnet seems to be 9.4 mm (or 0.3701") I imaging the 2123 spider sit higher than that?

Now, this is valid only if you choose to use the 2123 cone assembly for to get an 8" substitute for the 2108/112 ;)

I see, but if the le8t is 9.4mm from magnet to spider, mounting directly to the outter ring would enlarge that number. To use the larger motor the ring diameter needs to be widened and pin holes added, to keep the figure at 9.4mm.

[bldozier]

here is the le10a basket w/ ap motor & the le8t basket w/ the same motor an no seat. See how it sit further off the frame. Is the proximity of the motor height on the frame to the spider not of any importance?

75201
75202

[Flodstroem]

Is the proximity of the motor height on the frame to the spider not of any importance?

Its the most important thing.
If you are going to use the LE10/2123 magnet motor and voice coil with cone you have to check what height there is on the LE10 motor and LE10 spider and apply that to the new 8" basket ;)

The important thing with hight of spider is to have the voice coil in the right position in the magnet gap and not disowned down or upwards..... :blink:

[FE3T]

I am looking at the same project but have the type of LE8T basket where the terminals are on one of the spokes, wich sadly enough makes the use of my LE10H motors (the ferrite motor are to large too clear the terminals) impossible without a lot of modifications to the basket. So there is where I am stuck. if I had the version you have I could succeeded. :crying:

[bldozier]

Its the most important thing.
If you are going to use the LE10/2123 magnet motor and voice coil with cone you have to check what height there is on the LE10 motor and LE10 spider and apply that to the new 8" basket ;)

The important thing with hight of spider is to have the voice coil in the right position in the magnet gap and not disowned down or upwards..... :blink:

Ahhh, I understand now. The le10 baskets do have a slightly taller spider height, with that and the height of the le8t frame without modification it maybe closer to the le10 spider height, true, if we are using the le10 as our measurement in height. The height of the le8 frames 112&2108 included seem to be the same fro. The photos I've seen lower the the relationship to le10a

Fe3t, did you try mounting directly to the frame of the basket with the le10h magnet. Can you tell me the height of the le10h magnet from the spider, the difference...

[FE3T]

If I measure the height from the spider landing to the magnet on the LE8T basket i get 9.25mm or 0.364"

If I just place the LE8T frame on top of the Le10H magnet the height up to the spider landing are 10.9mm or 0.429"

If I measure the height from the spider landing to the magnet on a Le10H basket i get 15.7mm or 0.618"

Measured with some cheap old calipers, so minor faults can occur.

[Earl K]

Can I suggest a redirect ( for both of your energies ).

I understand the desire to create a killer midbass driver / I really do .

The problem here is the 122/2108 magnetic structure uses a .35" thick top plate with a .17" voice-coil centered within it .
- This defines an under-hung voice-coil topology .

The kicker is that these (3" vc style thick ) top-plates were unique to the 122/2108 drivers.

What you're currently struggling to adapt ( the le10 mag-structure ) has only a .28" thick top-plate.
- (IMHO) you won't be able to create an effective ( useful ) underhung vc topology that has enough travel ( Xmax ).

I'd suggest using the complete le8t structure ( basket & magnet ) and utilizing it's super deep top-plate as is ( @ .47" I think ) to create an under-hung mid-bass with a .2 - .25" ( generic 2" ) coil and a generic 8" paper cone.

I think you have a higher likely-hood of creating something worth using going this route ( as well as getting a pro-reconer interested in your project / since you're going to need an infinitely patient professional to supply you with all the "soft parts" )

:)

[Flodstroem]

Thanks Earl K for clarifying some fundamental JBL construction details.
But if one could use the 2123 magnet including the 2123 voice coil what do you thing will happened if scaling the cone down to an 8" driver?
After all the 2123 uses the Aluminum ribbon wire and the 112 or 2108 uses the copper ribbon wire. That could be some beneficial aspects in the thoughts?
Yes Im aware of the overhung voice coil in the 2123 motor but is it possible it could match the 112A or 2108 driver in the mid band frequencies? :blink:
But I can imaging that the answer is hard to tell, one had to do a conversion/construct one driver and then take measurement, thats the only possible way to go I guess....... :D

[Earl K]

One of the main reasons I suggested keeping the le8t intact is to attract the participation of pro-reconers .

Only they have access to the needed catalogue of soft parts ( generic ) that are needed to make a project like this work.

If the project is successful ( their motivation ) could be to sell ( via eBay for instance ) a mid-bass kit ( for le8t cores ) for any-one interested in a high-performance mid-bass 8" driver.

The ratio of cone weight to VC weight helps determine efficiency of the moving system.
- It's a balance that must be finely tweaked to achieve the stated goals ( which are just what here ?? ).

I've read that a ratio of 1 to 1 ( cone to coil; weight ) is a good place to start .

I use 2123 mids and have great respect for them ( therefore, I guess one must ask themselves why they want/feel the need for an underhung vc system ).

The 2012 10" has a very deep magnetic gap / it would be a better magnet ( mule ) if one feels compelled to keep on this ( underhung ) road.

FYI, the 202x family of twelves have the same 3" wide VC and deep-gap topology as the 2012 ( &, there are a lot more of these 12's available on eBay when compared to orphan 2012's ).

:)

[toddalin]

What about the feisability of using a 2169 cone found in the JBL STX835?

http://i.ebayimg.com/images/g/cjwAAOxy039TKz0l/s-l300.jpg

[bldozier]

If I measure the height from the spider landing to the magnet on the LE8T basket i get 9.25mm or 0.364"

If I just place the LE8T frame on top of the Le10H magnet the height up to the spider landing are 10.9mm or 0.429"

If I measure the height from the spider landing to the magnet on a Le10H basket i get 15.7mm or 0.618"

Measured with some cheap old calipers, so minor faults can occur.

Thank you, .15mm difference, maybe a range for these?

[bldozier]

Excuses the clamoring rhetoric supplied by me here, it is all in pace wit trying to recreate that driver with no one really having the soft forms to bring it toghter, nor a spec sheet to back up any one combination of parts, with the thicker top plate, I'm asuming travel is going to be greater ( xmax ) in the 2108, to a specific fs range. Correct. Compared to a uhf.
I dont have all the data from the char available to me but could you please explain the 2108 & le8t here to me. Andwhy I would want one over the other in this specific application
75205

[FE3T]

The kicker is that these (3" vc style thick ) top-plates were unique to the 122/2108 drivers.

What you're currently struggling to adapt ( the le10 mag-structure ) has only a .28" thick top-plate.
- (IMHO) you won't be able to create an effective ( useful ) underhung vc topology that has enough travel ( Xmax ).

I'd suggest using the complete le8t structure ( basket & magnet ) and utilizing it's super deep top-plate as is ( @ .47" I think ) to create an under-hung mid-bass with a .2 - .25" ( generic 2" ) coil and a generic 8" paper cone.

Just got an horrifying thought. Do you happen to know the thickness of the top plate on the 2122H? according to the driver specs on this site they use the same voice coil as the 2108

[Earl K]

Excuses the clamoring rhetoric supplied by me here, it is all in pace wit trying to recreate that driver with no one really having the soft forms to bring it toghter, nor a spec sheet to back up any one combination of parts, with the thicker top plate, I'm asuming travel is going to be greater ( xmax ) in the 2108, to a specific fs range. Correct. Compared to a uhf.
I dont have all the data from the char available to me but could you please explain the 2108 & le8t here to me. Andwhy I would want one over the other in this specific application
75205

In my opinion, you should buy some surplus 2118H(s) from eBay, coat them with some aquaplas standin ( to create the 108H wannabee used in the 250t series of speakers ) and use them as your metric ( as to what's achievable when transforming a Sound Reinforcement driver into a HiFi driver ).

No-one will ever have ( or post ) the complete data as to why JBL created it's multiplicity of 8" transducers.

If you don't know ( at this point ) what the benefits ( of the 2" le8t vs the 3" 2108 drivers ) are, then you need to study transducer design some more before proceeding any further.

ie; You're currently over-reaching yourself .

:)

[Earl K]

Just got an horrifying thought. Do you happen to know the thickness of the top plate on the 2122H? according to the driver specs on this site they use the same voice coil as the 2108

No, I don't know ( or have references for ) the 2122s top-plate thickness.

The people you want to search out for an answer to that question are RobH3606 and SpeakerDave & SubWoof ( GT & 4313b if they are around ).

Here's the most important 122a thread on this site, re top-plate. (http://www.audioheritage.org/vbulletin/showthread.php?24917-4315s-midlows-travel&p=250649&highlight=108h#post250649)

:)

[bldozier]

I can only assume the windings on the vc allow the cone to resonate frequency. From one band to the other from clean wattage,

with a underhung vc and .17" of turn its going to play into a specific frequency. Not over or under its desired band.

ok

These are studio monitors smaller ones at that, not tyying to handle 1000 watts ona dance floor.
no need for a overhung vc

the deeper motor on a 2108 being underhung shall play to its band cleanly, I guess. As opposes to the le8t which has a shorter top plate and more winds on the vc ie full range mid bass.

Im just looking for a motor to accommodate the 4315s midbass curve the le8t baskets are my choice for a few reasons, the motor im chosing alnico over the ferrite motors, although a le8t a or h may supply peaky performance ideally id like to shorten allowed amount of vc travel.

[bldozier]

No, I don't know ( or have references for ) the 2122s top-plate thickness.

The people you want to search out for an answer to that question are RobH3606 and SpeakerDave & SubWoof ( GT & 4313b if they are around ).

Here's the most important 122a thread on this site, re top-plate. (http://www.audioheritage.org/vbulletin/showthread.php?24917-4315s-midlows-travel&p=250649&highlight=108h#post250649)

:)

I think the spider helps with the re leveling of the vc in the downward travel, trying to make it back from center, lowering distortion.

[FE3T]

No, I don't know ( or have references for ) the 2122s top-plate thickness.

The people you want to search out for an answer to that question are RobH3606 and SpeakerDave & SubWoof ( GT & 4313b if they are around ).

Here's the most important 122a thread on this site, re top-plate. (http://www.audioheritage.org/vbulletin/showthread.php?24917-4315s-midlows-travel&p=250649&highlight=108h#post250649)

:)

Well I guess my 2122`s are ok then. It was 4313B that gave the LE111H baskets I had the thumbs up for reconing with genuine 2122H kits. (he basically said that the LE111H baskets and magnet where identical those for the 2122H)

BUT that opens a new can of worms in this tread.

If the 2108 needed a 0.35" gap to reach 1.52mm xmax
how can the 2122H reach 3mm xmax with a 0.28 gap? after all. the specs on these drivers specify basically the same voice coil (0.170" ww)

Have JBL speced the 2108 with +/- 1.5mm xmax and the 2122H with 3mm total xmax?


Some math

0.28" gap with 0.17" voice coil = +/- 1.39mm linear xmax (probably +/- 1.5mm if a small drop in BL are allowed)
0.35" gap with 0.17" voice coil = +/- 2.29mm linear xmax (wich dosent really match either +/- 1.5mm = 3mm total Xmax or +/- 3mm xmax.

Conclusion: I am confused.:dont-know:

Edit. some sources do also spec the Xmax for the 2122H as 1.6mm wich are still probable for a 0.170" coil in a 0.28" gap

[bldozier]

Me 2
xmax = vcL - gap/2 correct.
2.3 ~ 2.5mm either direction. Idk :dont-know:
bananas

[bldozier]

between the 400 ~ 100hz where the 3114 crosses over to the 2105, the le8t according to the graph seems to be slightly more musical.
i have both now, le8t & 2108 i will compare them soon.