Voice Coil Position relative to pole Plate

[ivica]

Does any members have an idea about the voice coil position relative to pole plate?
On some drives it is obvious that the coil is not position geometrically "in the middle" of the pole plate. It seems to me that the coil is "more deepen in the gap" then expect-able, even the divers are of SFG (symmetrical field gap) construction.
From that point of view it seems that the magnetic field under the pole palte is even stronger than over the plate. Is there any technical info about the coil position for 2202H, 2235H, 2245H, 2123H, E120H and E110H, relative to the top plate.:confused:

[Eaulive]

I can tell you the E140 has an offset, but I don't know about the others. I would be tempted to say they are centered... :dont-know:

[subwoof]

The design goal is to have the center of the coil match the center of the gap. The differences in depth will determine the performance but NO designer deliberately offsets a coil.

sub

[Eaulive]

The design goal is to have the center of the coil match the center of the gap. The differences in depth will determine the performance but NO designer deliberately offsets a coil.

sub

According to JBL, the E140 has an offset to create the characteristic tone and "kick".
That's the only one I'm aware of, of course it's a "sound producer", not a "sound reproducer" 53094

After reading I'm not sure if it's only a matter of compliance and spider, one fact is, on the E140, the spider and the outside compliance are not aligned, meaning that when surround looks flat, the spider looks pushed down towards the magnet, and whe the cone is pulled outwards to have the spider look "flat", the outer compliance looks like it's pushing out too much... that's why I doubt the coil is exactly centered at rest position.

I don't know if I'm clear :o:

[subwoof]

(dynamic)
If you read carefully, you will see that the "offset" is created when the *moving* coil has a temporary DC "bias" that allows non-linearity motion.

(static)
It does not mean that the coil is not centered at rest..:)

A speaker that is (A) not loaded / tuned in a cabinet correctly, (B) is powered by a significantly non-linear signal / amplifier with a DC bias or (C) actually designed to "burp" will eventually cause the spider to stretch and relax with age. And they invariably go *in*

I have owned hundreds of 15" JBL's of every variety imaginable and the D/K/E 140's were always the most problematic with the "sunken" spider. Once it stretches the whole alignment goes and would explain your observations.

sub

[ivica]

According to JBL, the E140 has an offset to create the characteristic tone and "kick".
That's the only one I'm aware of, of course it's a "sound producer", not a "sound reproducer" 53094

After reading I'm not sure if it's only a matter of compliance and spider, one fact is, on the E140, the spider and the outside compliance are not aligned, meaning that when surround looks flat, the spider looks pushed down towards the magnet, and whe the cone is pulled outwards to have the spider look "flat", the outer compliance looks like it's pushing out too much... that's why I doubt the coil is exactly centered at rest position.

I don't know if I'm clear :o:

It is expect-able that some amount of magnet flux is not passing only through plate as can be seen in technical info for 2023
http://www.audioheritage.org/vbulletin/showthread.php?21756-2023h,
so, there about 20% of flux is 'passing around' and that would introduce some shift of 'flux center' off the geometrical center of the plate, but what is the value of that center "offset" is known to JBL, and I think that was starting point for coil center position (if spider and cone surround has symmetrical compliance), but at the end experiments with 2nd and 3rd harmonic distortions would give optimum static position of the voice coil. For many of JBL LF and MF drivers data about the coil length and radius are known, but unfortunately I have no success to find what would be the coil statical position relative to top plate. This info is of great importance (as seen in http://www.audioheritage.org/vbulletin/showthread.php?31836-Voice-Coil-Position-relative-to-pole-Plate&p=321184&viewfull=1#post321184 ) if it is needed to exchange the voice coil.
Interesting reading can be find in:
http://www.klippel.de/fileadmin/klippel/Files/Know_How/Application_Notes/AN1-Optimal_Voice_Coil_Rest_Position.pdf
http://www.klippel.de/fileadmin/klippel/Files/Know_How/Application_Notes/AN2-Separating_spider_and_surround_.pdf

but that is just general info.

[Eaulive]

I have owned hundreds of 15" JBL's of every variety imaginable and the D/K/E 140's were always the most problematic with the "sunken" spider. Once it stretches the whole alignment goes and would explain your observations.

sub

Interesting... I never had a new one or an original recone in the hands so I never could compare, but all of the E140 I've seen, _and I've my share_ all had this aspect.
I have the impression they are made like that, as if there was more space allowed on the former between the cone and the spider, creating that "push in".

I would be curious to compare the relative height of the spider and cone between a E140 and a 2225, which are basically identical besides VCs and this possible mounting configuration.

When a spider sunks in, the cone and outer suspension follows and it's visible, but on all the beaten up E140 I've seen, the outer suspension looks OK :blink:

I'll dig more into this :D

[ivica]

Interesting... I never had a new one or an original recone in the hands so I never could compare, but all of the E140 I've seen, _and I've my share_ all had this aspect.
I have the impression they are made like that, as if there was more space allowed on the former between the cone and the spider, creating that "push in".

I would be curious to compare the relative height of the spider and cone between a E140 and a 2225, which are basically identical besides VCs and this possible mounting configuration.

When a spider sunks in, the cone and outer suspension follows and it's visible, but on all the beaten up E140 I've seen, the outer suspension looks OK :blink:

I'll dig more into this :D
From my measurements for E140, total length from spider to the coil end is about 19mm, and the voice length is about 12mm, so from spider to the voice coil start is about 7mm. If the distance from frame plate (where spider has to me glued) is about 11mm, it seems that for E140 the 'beginning" is about 4mm away from top plate, and the end of the voice coil is about at the same 'level' as end of the top plate. May be that is the reason why E140 coil 'had a tendency' to sink deeper in to the gap, and after hours of operation under high power a "spider sunk", stiffness of the spider and surround become deformed.
Concerning that E140 has to PRODUCE some kind of distortion (I believe mostly 2-ND harmonic - for larger power), I believe that such non-linear behavior is
is produced by nonlinear movements of voice coil - spider stiffness had a tendency to 'take the coil OUT OF GAP, while magnetic force had tendency to keep IN)

On the contrary, as example, 2231A (REPRODUCER type driver) voice coil length is about 16mm (about 4mm longer then VC in E140, while starting position of VC is about 7mm from spider), and the coil center and top plate flux center are about the same place if the same basket are used.
I do not have 2235H cone kit to see where starting position of the coil is. Its VC, alone, has to be about 19mm long(wires only).

All these things are reasons why I have been asking for other members help, to find out what are the real voice coil starting offset from top plate.
That would be helpful for members who have to change voice coil.....

[Robh3606]

More food for thought

Rob:)

[subwoof]

I just looked in the storage room and I have (4) original E140 woofers from Cabaret cabinets and none have the "sunken" spider although they have been stored face down for about 2 years. When I purchased them I had the filters/dustcaps replaced and the cones given the WR coating.

I have seen a tendency for any of the heavier, ribbed paper ( COPPER COIL ) woofer cones to sink in when stored face up but that usually corrects itself in a short time when they are mounted on a baffle.

I might have an odd E140 recone kit in the stash - if I find it I will post the measurements.

FYI: I have NEVER seen a JBL 15 ( or any cone for that matter ) come from the factory with a sunken spider. I have never had one *reconed* and the result was a sunken spider. I HAVE had them come back from total abuse from glam band bass players and *sometimes* I saw a sunken spider but it was hard to tell untill the smoke cleared and the rest of the burnt cone fell away...

:cheers:

sub

[ivica]

I just looked in the storage room and I have (4) original E140 woofers from Cabaret cabinets and none have the "sunken" spider although they have been stored face down for about 2 years. When I purchased them I had the filters/dustcaps replaced and the cones given the WR coating.

I have seen a tendency for any of the heavier, ribbed paper ( COPPER COIL ) woofer cones to sink in when stored face up but that usually corrects itself in a short time when they are mounted on a baffle.

I might have an odd E140 recone kit in the stash - if I find it I will post the measurements.

FYI: I have NEVER seen a JBL 15 ( or any cone for that matter ) come from the factory with a sunken spider. I have never had one *reconed* and the result was a sunken spider. I HAVE had them come back from total abuse from glam band bass players and *sometimes* I saw a sunken spider but it was hard to tell untill the smoke cleared and the rest of the burnt cone fell away...

:cheers:

sub

Concerning the spider it seems to me that original one was much softer the 'aftermarket'. I have realized that on original E140 recone kit.
But here I would try to get (from the members) what is the distance of the voice coil
start from the spider level, so after it would be possible to do some kind of repair of blown coil, with new one. In literature, it is said that such position is of great importance concerning distorsion

[Allanvh5150]

As the E140 coil is supposed to sit in the gap, exactly, it should be a pretty easy calculation to figure out where the spider would need to sit.

Allan.

[Robh3606]

But here I would try to get (from the members) what is the distance of the voice coil start from the spider level, so after it would be possible to do some kind of repair of blown coil, with new one.

Why don't you just use the one you all ready have, the one with the blown coil, to get the measurement?? Unless you are starting from an empty basket trying to figure out what would fit you already have everything you need.

Rob:)

[ivica]

As the E140 coil is supposed to sit in the gap, exactly, it should be a pretty easy calculation to figure out where the spider would need to sit.

Allan.
Well, it seems to be easy, but if you measure it seems to me that about 0.5mm or something is offset. Rough measure are known, but I ma looking for exact ones.

[ivica]

Why don't you just use the one you all ready have, the one with the blown coil, to get the measurement?? Unless you are starting from an empty basket trying to figure out what would fit you already have everything you need.

Rob:)
Sometime, the driver came, had previous 'operation', so no reference, or reference is not reliable, some time destruction was too large to trust measurements.....in any case correct data is the best solution.
What surprise me is that, about such important data is almost unavailable at all. Here on the site I could not fine anything about.

[ivica]

As the E140 coil is supposed to sit in the gap, exactly, it should be a pretty easy calculation to figure out where the spider would need to sit.

Allan.
For E140 top plate is (I think) 7.112mm [0.28"], and voice coil is about 11mm~12mm [0.4"~0.45"], so where is exact coil "rest position" ref. to top plate ??
Firs expectation is about 2mm (out of the gap), really is it 1mm or 3mm ??
Even the measurements from re-cone kit can be referenced only to the spider connection to the former body, no to the top plate....

[Allanvh5150]

Not 100% sure but the centre of the voice coil should be in the centre of the top plate. I have handled these a lot over the years but I have not paid that close attention to it.

Allan.

[edgewound]

The E140 is slightly over hung...which is far better than under hung with a hangover... which means that equal parts of the voice coil would be protruding for the top and bottom of the top-plate. This would also indicate that the centerline of the voice coil should match the centerline of the top-plate gap depth.

The spider should sit perfectly flat at rest. If the spider is pushed down when the whole cone assembly is installed, the cone body is too deep for the frame....unless the suspension is soft enough to to sink in when the speaker is sitting face up...which shouldn't happen with a properly reconed E140. The depth of the cone should meet the spider without pushing it down....You want equal travel in each direction.

[ivica]

The E140 is slightly over hung...which is far better than under hung with a hangover... which means that equal parts of the voice coil would be protruding for the top and bottom of the top-plate. This would also indicate that the centerline of the voice coil should match the centerline of the top-plate gap depth.

The spider should sit perfectly flat at rest. If the spider is pushed down when the whole cone assembly is installed, the cone body is too deep for the frame....unless the suspension is soft enough to to sink in when the speaker is sitting face up...which shouldn't happen with a properly reconed E140. The depth of the cone should meet the spider without pushing it down....You want equal travel in each direction.
Theoretically I totally agree with you, and my expectation is that the "center line" of the voice coil should match center line of the top plate, especially for SFG drivers, but I am not sure what is the facts in "reality", and that is why I have started this thread,i order to find out the real data.
For E140 it seems to me that center of the voice is not in the "top plate center". It seems to me that the coil center is 1~2mm nearer the top plate surface.

[ivica]

Not 100% sure but the centre of the voice coil should be in the centre of the top plate. I have handled these a lot over the years but I have not paid that close attention to it.

Allan.

May be, next time try to measure the data and, please, send to us

[grumpy]

Is there an urgency or specific need to understand this further? or general curiosity...
I.e., are you attempting to build or reconstruct a unit from piece parts rather than from
a recone kit? Apologies if this rationale was already stated.

[ivica]

Is there an urgency or specific need to understand this further? or general curiosity...
I.e., are you attempting to build or reconstruct a unit from piece parts rather than from
a recone kit? Apologies if this rationale was already stated.
At the moment I am trying to "keep alive" two pairs of 2202, that are in K120 and E120 baskets. Concerning that, when removed the cones I realized that all coils were not original, so I have to get something appropriate (edge wound coils).....but I know that the rest position of the coils would become problem.
From MWA I realized that they can offer the coils that can fit (MWA 1830-8, 0.46" coil length)...
Generally speaking I think that info about mentioned, and the other well known, drivers would be helpful for all members.

[edgewound]

At the moment I am trying to "keep alive" two pairs of 2202, that are in K120 and E120 baskets. Concerning that, when removed the cones I realized that all coils were not original, so I have to get something appropriate (edge wound coils).....but I know that the rest position of the coils would become problem.
From MWA I realized that they can offer the coils that can fit (MWA 1830-8, 0.46" coil length)...
Generally speaking I think that info about mentioned, and the other well known, drivers would be helpful for all members.

The gap depth on the 2202 is .28" (7.1mm)
The voice coil winding length is listed as .435" (11mm)
The amount of coil overhang protruding above and below the gap will be 1.95mm for the coil to be properly positioned at rest.

If the spider is pushed down after installing the assembly, it's not gonna be right.

Good luck with your project.

[ivica]

The gap depth on the 2202 is .28" (7.1mm)
The voice coil winding length is listed as .435" (11mm)
The amount of coil overhang protruding above and below the gap will be 1.95mm for the coil to be properly positioned at rest.

If the spider is pushed down after installing the assembly, it's not gonna be right.

Good luck with your project.

Many thanks for the data. It seems to me that geometrical center of the voice coil and top plate center are exactly "overlapped".

One more question, is it the same case with 2235H, too??

[Allanvh5150]

One would expect to find that under perfect conditions, i.e. straight off the production line, the center of the voice coil will align with the center of the top plate.

Allan.

[Eaulive]

The gap depth on the 2202 is .28" (7.1mm)
The voice coil winding length is listed as .435" (11mm)
The amount of coil overhang protruding above and below the gap will be 1.95mm for the coil to be properly positioned at rest.

If the spider is pushed down after installing the assembly, it's not gonna be right.

Good luck with your project.

Ken, I don't want to doubt your expertise, but about two years ago a customer wanted to recone 24 E140, the job was never completed, I only stripped and clean the 24 cores and he then backed off when it was time to purchase the cones.

Anyways, some of the speakers were in bad shape but still working, particularely one wich I was able to salvage, carefully removing the entire cone/spider assembly without a rip.
I cleaned the gap, remove the inner foam goo and reglued it and to my surprise, it felt exactly like if the basket was too short for the assembly, meaning, when the spider rested perfectly flat, there was about 1/8" gap between the outer compliance and the frame.
Also I noticed that on the former, I think there was also a space between the spider and the cone, of about the same distance, where usually on a "normal" assembly, the cone and the spider meet.
Unless I'm mistaken, all the cones I had at the time were like this, they look saggy but when out of the frame, they are flat.

I whish I could go back in time to ascertain this, I didn't put too much tought in it at the time, even if it looked odd.

Yes, they were original cones.

[edgewound]

Ken, I don't want to doubt your expertise, but about two years ago a customer wanted to recone 24 E140, the job was never completed, I only stripped and clean the 24 cores and he then backed off when it was time to purchase the cones.

Anyways, some of the speakers were in bad shape but still working, particularely one wich I was able to salvage, carefully removing the entire cone/spider assembly without a rip.
I cleaned the gap, remove the inner foam goo and reglued it and to my surprise, it felt exactly like if the basket was too short for the assembly, meaning, when the spider rested perfectly flat, there was about 1/8" gap between the outer compliance and the frame.
Also I noticed that on the former, I think there was also a space between the spider and the cone, of about the same distance, where usually on a "normal" assembly, the cone and the spider meet.
Unless I'm mistaken, all the cones I had at the time were like this, they look saggy but when out of the frame, they are flat.

I whish I could go back in time to ascertain this, I didn't put too much tought in it at the time, even if it looked odd.

Yes, they were original cones.

The space you might have seen could have been a bead of epoxy that bonds the cone to the spider.

Ever since I was authorized in 1988, cyanoacrylate adhesive on the spider landing has been used on the assembly line and is virtually impossible to soften and remove without damage. Even debonding the Bostik glue on the surround/cone compliance will end up either stretched or warped.

E140s that were run hard with suspension fatigue can be succesfully rebuilt with a fresh spider but it's pretty tedious work to get it right.

I can't really comment on your situation since there's no evidence.....But the bottom line is, proper production AND reconed speakers have voice coils that are centered both axially and radially in the gap and the spider is perfectly flat at rest when mounted as intended.

[Eaulive]

Ever since I was authorized in 1988, cyanoacrylate adhesive on the spider landing has been used on the assembly line and is virtually impossible to soften and remove without damage. Even debonding the Bostik glue on the surround/cone compliance will end up either stretched or warped.

I know those had been reconed before, the spider was easily removeable, it didn't have that brisk hard glue like the factory cones.

Oh well, since I can't go back in time, I'll take your words to the bank :D

[ivica]

.....
....But the bottom line is, proper production AND reconed speakers have voice coils that are centered both axially and radially in the gap and the spider is perfectly flat at rest when mounted as intended.

I think that would be the easiest solution for coil mounting,
"middle of the coil" has to be "in the middle" of the top plate
(especially for SFG construction).
In such situation calculation is very easy:

coil overhang protruding above top plate = 0.5*(coil length - top plate thickness)

May be such "simple solution" is the reason why it is almost 'impossible' to
get such data in public data.
Many thanks for the information and suggestions.