K140: dual vs triple roll surrounds (and possibly a DIY C8RK140)

[lfh]

Hi all,

it's been a while since my last period of frequent visits and posts -- good to see so many familiar names and that this place is cooking as usual with creativity, nice projects and fun!

Anyway, I need some expert help on K140:s. Actually I've never seen one IRL (only D:s and E:s), but I've studied some pics lately, and apparently it came with two different types of surrounds.

First, to check if I have the terminology right, here's a pic of a 2216/LE15B with what I think is called a "triple-roll" (or "accordion") surround, since (as best can be seen about 3 o'clock) there are three peaks in the cloth cross section between the cone edge and the frame rim :



Is this understanding correct, to begin with?

Now here are two pics of supposedly NOS K140:s, both with what to my eyes appear to be the same fundamental kind of surround as above:





However, in various factory pics of the K140:s in the library, the surrounds look more like that of the E140 shown below, i.e. a common (large) dual-roll design:



See e.g. the 1978 Pro Catalog:



Hence my questions number two and three are:

Was the K140 made in two versions over time?
If so, which version surround was used in the C8RK140 kit (discontinued in the 80:s)?

(If the dual roll version depicted in the catalog is the only proper factory version, the two K:s above are either after all equipped with aftermarket kits or hybrid recones.)

My final question is about the possibility of putting together a K140 cone kit, since the C8RE140 is not equivalent in many aspects (lighter cone, shorter VC and more), and may not cut it for purists.

Looking at TS parameters, it looks like one could get close e.g. by using a 2225 cone and VC, spider from a 2205 or other driver in the group below, and an aluminum dome from a E140.

Mms = 105 // K140, 2205, 2225, 2234
Vas = 297 // K140, D130, K130, E130, E140, 2205, 2220
Xmax = 5.08 // K140, 2225, 2231, (2203)
Re = 5.5 // K140 only!
Le = 1.3 // K140 only!

What are your thoughts on this?

Finally, I'd say (not based on real world observations, though) that a K140 frame with a C8RE140 in essence sounds and behaves like an E140, at least much more so then a K140, since the E140 cone assembly would be the "sonically dominating factor" (by means of the TS parameters of course, but also less easily quantified aspects) rather than the slight difference between the AlNiCo and Ferrite engines. Would you agree (based on testing or theory)?

Optional question (bass players input especially welcomed): Which is your preferred driver (sound wise) of D140F, K140, and E140, and why?

TIA.

[lfh]

Here are some more pics I've found on the Net:

This one is claimed to be a straight out of the box NOS K140. Clearly it has the E-style surround found in the catalog picture above:




Here's a nice and clear shot of a unit with the other type of surround:

[Eaulive]

I would agree that a K140 reconed with a C8RE140 will behave more like a E140, but the flux is lower in the K version so it would not be a real E140 either.

For the rest, I don't know, this accordeon surround is obviously not very common on those drivers.

[lfh]

I would agree that a K140 reconed with a C8RE140 will behave more like a E140, but the flux is lower in the K version so it would not be a real E140 either.

For the rest, I don't know, this accordeon surround is obviously not very common on those drivers.

Ah, thanks! Actually I forgot that the E:s have 1.35 T magnets (gap depth is the same, though), and was only thinking about the thermal differences and possibly small differences w.r.t. non-linearities at peak excursions. Yeah, like you say it'd not be a real E140 either.

On a sidenote: I wonder why the designers decreased Xmax when going from K140 (a decent 5.08 mm) to E140 (only 3.56 mm).

[Earl K]

The triple pleated surround ( found in those ancient 2216s, D140f, 2205, K140, & D140R(s) ) allowed an Fs of 30hz ( when coupled with a softer spider ) .

JBL recognized that raising the Fs to 40 hz would save them a lot of warranty returns ( from the growing music industry types ) , so they migrated their SR & MI product lines in that general direction in the early 70s .

FYI; The original 2202a prototype also had a triple pleated accordian surround ( for about a year, until sometime in 1972 ).

I'll post some pics tomorrow of the older triple pleated offerings .

<>

[lfh]

The triple pleated surround ( found in those ancient 2216s, D140f, 2205, K140, & D140R(s) ) allowed an Fs of 30hz ( when coupled with a softer spider ) .

JBL recognized that raising the Fs to 40 hz would save them a lot of warranty returns ( from the growing music industry types ) , so they migrated their SR & MI product lines in that general direction in the early 70s .

FYI; The original 2202a prototype also had a triple pleated accordian surround ( for about a year, until sometime in 1972 ).

I'll post some pics tomorrow of the older triple pleated offerings .

<>

Wonderful info! I'm looking forward to the pics.

Ok, so for the ultimate DIY cone kit, we also need a soft triple pleated surround...

[Earl K]

As promised ;

Here's the 2202a ( in the prototype stage , I believe ) .

> ( I photo-shopped in some of the front page to establish the date for this pic )

> Note the triple pleated accordion surround and the 40hz (Fs) .
> This increased to 50hz when JBL changed the surround to the double M-Roll type .



> A year and a half later , JBL was in full swing, changing over their "legacy" surrounds to the types we recognize today .

> See here ;



<>

[Eaulive]

Wow, this is amazing to realize the 4350 was also used as a sound reinforcement speaker!

Thanks for sharing this

[lfh]

Wow, indeed! Factory documentation, dates and explicit mentioning of the design modification for the K120 and K130 was way more than I could ever hope for. The mystery is solved! Many thanks, Earl K!



While being at it: Does anyone know precisely when the K-series replaced the D1xxF-series? The latest factory reference to D:s in production I've seen is a brochure in the library dated 3/70 (lower right corner):




The earliest reference to the K:s I've found is at an Australian PA company named JPJ Audio, in reference to the 1971 Elton John tour (lots of cool old school systems are shown at their site!):

RCA W-bins w/ K140:s

If that info is correct, they were running K:s "down under" already in October 1971.

[Eaulive]

The earliest reference to the K:s I've found is at an Australian PA company named JPJ Audio, in reference to the 1971 Elton John tour (lots of cool old school systems are shown at their site!):

RCA W-bins w/ K140:s

If that info is correct, they were running K:s "down under" already in October 1971.

2 x RCA W Bin with 2 x 15″ JBL K140
4 x Jands U Bin with 2 x 15″ JBL K130
2 x RCA Multi-cell Horns with Altec drivers
8 x JBL 075 high frequency drivers
10 x Jands 150w Power Amplifiers
1 x 16 Channel Jands Mixing Console

Amazing, an Elton John concert in a small stadium with 16 inputs and 1500W

Today to do this they would use a layered 64 inputs minimum and at least 50 000W in a line array