View Full Version : Gaps and Depths

Mr. Widget
08-15-2003, 06:27 PM
Earl K made a post on a general thread that got me thinking...:o

I know I've put K140 kits sans the aluminum dome into 2220A frames to produce a sort of super 2205A and many of us have run into these into those situations.

I would really appreciate it if those with lists, and those that currently have opened up frames could post their list or lists of the various JBL motor sizes, both the classic alnicos and the current and not so current ferrites as well. I think it would be very useful to compile a list of all of the top plate depths and gap widths. I know that JBL has not been very consistent with some models, the D130s for instance, so in some cases we may find differing data. In these cases perhaps we can reference a date or serial number.

Earl K, Giskard, anyone else with pertinent data if you could post it here I know I would appreciate it, and I bet it would clear up a few things for others as well.

Mr. Widget

08-15-2003, 08:35 PM
OK - time for the first posting...

I have a sheet of paper on the wall in the shop with measurements of a LOT of jbl magnets taken over the decades and notes on what combinations are possible.

I will attempt to compile it and post next week???? it is however limited to the 12-15-18 older magnet types.

I've created many "oddballs" over the years and the one thing that is common to any variance is the magnets with the deeper gaps ( 2220, E145/2215/LE15 ) will never work right with any other kit, unless you actually mill DOWN a frame 1/2 the difference in mag gap depth.

However this will weaken it to the point of instability.

The problem is voicecoil offset which prevents linear use and some of the overhang/underhang issues result in very high efficiency but limited linear travel.


Earl K
08-16-2003, 11:42 AM
Mr Widget

Yes , that would be beneficial.

- Also helpful is a measurement of the depth of the gap "well". This, among other things will limit the maximum allowable excursion before mechanical damage occurs. I'm speculating the non-vented magnet types like the le15a might be somewhat shallow in this regard .

- Funny you should bring up your 2220a/K140 matchup. I have a pair of 2225h kits in 2220a baskets that even after close to 2 decades of use - retain an Fs of 40 hz ( just about spot-on ). These are "tight" powerful drivers - and ( of-course ) well-seasoned by now. I wish I knew what their starting Fs was - .

I can easily get 2220h measurements since I just bought an empty assembly for an experiment . :spin:

regards <>Earl K:)

08-18-2003, 08:27 PM
Welcome subwoof! Nice to have you on this board. Been reading it for awhile?
I still have the E130's that your buddy coned with 2225 paper; also the clone 4725A crossover you did for my 4560 boxes; unfortunately I parted out the 2370A horns and 2420 drivers; stupid!!!
We seem to have lost, at least temporarily, our JBL knowledge guru in the person of Giskard; perhaps you can help fill the gap!! (Did you know of Giskard??)
Have any other goodies lurking out there??!! Many of us on here keep watching the tent sale in the event that something nutty transpires again on there. I think it has been two years since the really insane deals................
what's new in your woods??
Mike Baker

08-18-2003, 09:02 PM
Hey there one and all - been 2 busy with 2 ( now ) teenage daughters to do much surfing / reading / posting / etc.....

Been selling on ebay for awhile but that gets kinda old paying FOUR TIMES to ebay ( listing, ending, paypal and CC ) so perhaps offering to the REALLY dedicated JBL crowd should be an improvement over the occasional ebay wannabe.

Remember, you grandad might of said that "what doesn't fit in your mouth is waste" wasn't referring to speakers / livingrooms / spouses ..:o)


08-19-2003, 03:18 AM
Welcome Mike (subwoof)!

I like your idea of posting this table with magnet measurements. this would be very very helpful.

I'm looking forward to have this information. Thanks in advance!

08-19-2003, 09:49 AM
Hello Subwoof glad you decided to drop by. Thanks for the info on the frame mill down. I asked a local JBL reconner if they had any E145 kits. Response was too hard to get, I will take off the extension frame and use a 2225 kit and you get the same speaker?????!!!!!:eek: Didn't make sense because of the pole piece depth and Flux Density mass all wrong. Sounded real odd to me so I went elsewhere for the correct kit. Didn't want to deal with the guy after that.

Rob :)

08-19-2003, 11:39 AM
"I asked a local JBL reconner if they had any E145 kits. Response was too hard to get"


Currently in stock and pretty damn cheap too compared with other kits.


Have your favorite reconer check both Pro and Home kit prices.

08-19-2003, 12:49 PM
Hey guys - the idea of plopping a 2225H kit into a "ring removed" E145 won't work correctly....

The E145 magnetic gap depth is MUCH MUCH deeper than the 2225 and the "center" of the gap will *not* be centered on the coil windings ( this the offset problem ).

This would make it very non-linear at anything above 50 watts or so.

Unfortunately it's not possible to mill down the frame enough - the mounting plate is too thin....

BUT you CAN put the LE15H kit into that frame and it would become a LE15H-1 NOTE: the LE15A kit will NOT work due to different frame depth!


08-19-2003, 09:48 PM
OK guys - here is the accumulated info...A few caveats:

(1) measurements were made in a dusty woodshop with an old set of ( now magnetized ) calipers
(2) Some variations of magnet structures ( bolt thru vs plate screws ) *might* be found.
(3) MOST magnets have a casting number that may or may not match others?? I'd bet JBL would know...:)
(4) JBL has a "goes into" checklist that applies to 10% of their items so use with a grain of salt...
(5) Some magnet structures use a thicker ring of ferrite - these WILL allow longer excursion ( wow - a whole 1/16 in.... )
(6) The earlier Alnico magnetic gap depths are the same as the ferrite if the model number is the same.
(7) Some variations of magnetic intensity are found in the published JBL literature - no attempt was made to confirm.
(8) The vented gap types are in a different league - NOT interchangeable.
(9) There are TOO MANY variations of magnets + cones on the smaller / consumer sizes so little info was compiled
(10) The 18 ferrite magnet structures are larger in diameter than the others
(110 Yeah I probably missed a bunch but I needs da sleep...:)


E120 / 130 / 140 9 / 32 7 / 8
E145 19 / 32 7 / 8
E155 / 2240 / 2245 11 / 32 7 / 8
2220 11 / 32 3 / 4

2205 / 2230 / 2231
2135 / 2202 / 2130
2203 / 2204 / 2234
2235 / LE14H / etc 9 / 32 3 / 4
( most common type by far )


Earl K
08-22-2003, 08:25 AM
JBL published ( fairly accurate ) gap widths on their pre 1990 Alnico and Ferrite magnet types. This was relevant for those older model types until the introduction of the vented gap style of woofers.

- Does anyone have the gap width for the 1990s type of "Vented Gap & SFG 4" voice coil woofers ?
ie ; 1400 pro, 2206, 2217, 2226, 2227, 2241, 2242

- And how about the gap width for the later 90s' - 2000 series of 3" voice coil woofers ? - ie; the 2012, 2020, 2022/3/5/, 2032, 2035, etc. ( the cut sheets are quite clear for the 2012 & 2020 about top-plate and voice coil winding depths - but I've never seen those other models speced. )

regards <> Earl K :)

08-22-2003, 10:05 AM
Hello Earl

Well I have a 2035 out of the box and the top plate is 1/2 inch the magnet is 3/4 and the backplate is maybe a 32nd less than the top plate. The back plate is a bump back to give a little more throw space for the coil.

Rob :)

08-22-2003, 10:23 AM
You might want to look at the consumer techsheets. They have the gaps for the drivers listed in some cases. I putting up the L250TI as an example. Problem is I don't think there are to many crossover products for the drivers you are interested in. At least it can give us the gaps on some of the consumer drivers if anyone is interested.