Crazy 2108 4" question

[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?
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.......

[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?

[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

[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

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.

[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.

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.

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.

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
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.