Deductive Reasoning Required

[10 Watt Street]

Expert opinion needed, what driver is this from? D130?

http://cgi.ebay.com/ws/eBayISAPI.dll...713332884&rd=1

[Mr. Widget]

Does anyone know how many woofer models were produced before the cast magnet pots were introduced?

My guess would be that they have a D130 or 130A. The preceeding model, the D 101 had a taller magnet pot I believe.

Widget

[Don McRitchie]

The 12" D131 was also of that vintage and used the same magnet structure. I agree that it does not look like the pot from the D101 since, as you say, it is too short for that. Not to mention that the D101 used a 3" coil and the auction motor sure looks like it has a 4" gap. The only other cone driver in production before the cast pots were employed was the 8" D208.

Getting back to the driver in question, the Ebay pictures are intriguing. This is the first time I have seen the pole piece and top plate from a JBL driver of that vintage up close. They appear to be about the same thickness as that of an LE15 or Altec 515. In other words, it would appear that Jim Lansing designed all of his drivers using underhung motors and that the conversion to overhung designs must have happened sometime later during the Thomas years.

[Mr. Widget]

Originally posted by Don McRitchie
This is the first time I have seen the pole piece and top plate from a JBL driver of that vintage up close. They appear to be about the same thickness as that of an LE15 or Altec 515. In other words, it would appear that Jim Lansing designed all of his drivers using underhung motors and that the conversion to overhung designs must have happened sometime later during the Thomas years.

I wondered about that too as all of the later JBLs including D130s have a top plate that is the thickness of the gap. Looking at this exploded view you see that the earlier designs were different and that the thick plate we are seeing is not a top plate like those of later models. This early D130 would have a thin top plate and gap just as the subsequent models did.

http://lansingheritage.org/images/jb...1948/page4.jpg

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[Don McRitchie]

This early D130 would have a thin top plate and gap just as the subsequent models did.

It's hard to tell. I went to that page as soon as the first post was made to try and identify the motor. Since it contains a low resolution, not-to-scale drawing, it's hard to say just what the thickness of the pole piece is. I tend to think it is the same as that illustrated in the auction motor for the following reasons:

1) All of Jim Lansing's "D13X" series of drivers used the same motor for economy of production. This is indicated in the Arnold Engineering correspondence.
2) The pot in question (and the drivers illustrated in the 1948 catalog) were only in production for one year. By 1949, Jim was venting the rear of all of his pot magnets. I don't see him changing the basic pole piece design of his drivers in the very short time prior to that.
3) Jim was known to have drawn on his Altec experience in designing the first JBL drivers. The Alnico Altec 604 and 515 that he designed appear to use the same underhung topology and gap depth. It would not be surprising that he would carry this same gap depth design into his first JBL drivers.

[scott fitlin]

When I spoke to Bill at GPA about Altec speakers, he once said to me part of the reason they sound the way they do is the underhung design!

To me, it seems very logical for early JBL designs to be very much like Altec,s because both James B. lansing and Altec worked together prior to Lansing Mfg being formed, and because Jim lansing had alot to do with what Altec made in those early years!


I have a question, since I never really knew about coils and how they are hung. Is an underhung coil a better sounding way of doing things?

[Don McRitchie]

The properties and advantages of an underhung design are explained here:

http://www.audioheritage.org/html/pr...ogy/1500al.htm

[scott fitlin]

That was informative reading, and tells me the same thing my ears tell me. They had stuff right long ago!

Its cool to see JBL making one driver the traditional way. Even though they say they have come up with improvements over what was made twenty five years ago, the 1500AL, to me, represents a little return back to making things that sound great!

How about a NEW super premium Alnico JBL compression driver? Or am I asking for too much?

[Steve Schell]

That sure looks like a D130 or 130A motor to me too, although a 131 pot of the same period would have looked the same. I turned down the opportunity to buy a 131 with that label one time and have always regretted it.

It is an early Venice piece, which probably dates it to sometime in 1947. The reason I say early is the later Venice drivers have a clear water decal, with a border with half circles on the ends and straight horizontal lines between. The label on this piece is barely changed from those on the earlier San Marcos drivers that started it all. This is what I would call a "flat back, no hole" driver, as it predates Jim's inspiration to vent the pot with a hole in the rear.

10 Watt Street, are you going to snag this one? If not, I'd like to add it to my collection of about 10 various early flat backs. I'd sure like to put them all in a museum someday...

[Don McRitchie]

It is an early Venice piece, which probably dates it to sometime in 1947.

Hi Steve

I've never been able to nail this down definitively, but my best assessment is that Jim Lansing did not introduce the D13X drivers until early 1948. There is a copy of a letter from Jim to Arnold Engineering asking them to develop a prototype magnet for a new 4" coil driver dated August 18, 1947 here:

http://www.audioheritage.org/images/...130-magnet.jpg

I've attached the reply to that letter below. As is stated therein, Arnold was not able to respond until November 29, 1947 and only sent out a few sample magnets that Jim likely didn't receive until early December. Therefore, I don't see how production could have started before January 1948.

Don

[10 Watt Street]

Steve Schell, go right ahead, it needs a good home with its own kind.

[Steve Schell]

Thank you, 10 Watt Street- I snagged it!

Don, at some point we need to drag out all the materials we have which would provide clues and try and establish a timeline. About a year ago, Joe Knight provided me with photocopies of single page flyers on D101, D130, D130A, D131, and D175 with H1000 horn. These are all formatted something like the D101 flyer photocopy we got from the JBL archives. In the block at the bottom they say "James B. Lansing Sound Inc., Office: 510 South Spring St. Los Angeles 13, Factory: San Marcos, Calif." Differences from the earlier D101 flyer include the addition of "James B." to the company name, and removal of the "Iconic" logo. Jim must have had his little talk with the Altec folks by the time these were published. These flyers seem to indicate that these items were all in production in San Marcos, before Jim made the financial arrangements with Roy Marquardt in November 1947 and moved his operation to Venice.

I may have forgotten to scan and send these flyers to you...yikes... please let me know if this is the case.

My theory for the moment is that the "new magnet" under discussion in the correspondence is not the original magnet for the D13xx series, but an improved version, with different shape and / or material than that supplied until that time.

[Don McRitchie]

My theory for the moment is that the "new magnet" under discussion in the correspondence is not the original magnet for the D13xx series, but an improved version, with different shape and / or material than that supplied until that time.

I think you might be right. The letters above refer to a magnet structure with a .281 gap depth. This is the the gap depth that would become the most common standard for JBL's drivers up until recently. It is too shallow to acommodate a truly underhung design and seems shallower than the top plate illustrated in the auction. You'll have to measure the top plate on that motor as soon as you get it. If it is in the .5" range that it appears to be, then this could be an original D13X motor that was modified in 1948.

Don

PS. I don't have a record of receiving the flyers you mentioned.

[Steve Schell]

The flat back magnet assembly arrived the other day. It looks good; thanks again, 10 Watt Street. I compared it to a couple of later, cast pot assemblies retrieved from the shed, a D130 and a 130A. Here are the results:

The early flat back has a gap width of about .050", difficult to establish because it is no longer quite concentric. The top plate is .390" thick. The flux density measures between 12.8 and 14.5 kilogauss at various points around the gap, and the flux seems consistent over a large range of depth.

The oval label D130 has a much thinner .280" thick top plate. The gap measures .050" wide. The flux density measures between 14.1 and 14.5 kilogauss.

The oval label 130A has a .375" thick top plate. The gap is wider than the others, possibly as wide as .060". Flux density measured between 11.2 and 11.8 kilogauss.

I dug into my pile of boxed flat backs to check for top plate thickness, but the results were inconclusive. The top plates in all these drivers drop into a recess in the basket casting, which might or might not be the same thickness on different vintages. Sooo, I won't be able to determine top plate thickness on the early ones until I have a reason to take them apart.

My suspicion is that the top plate may have always been thinner on the D130, and that this flat back pot is from an early 130A. If that is the case, the gaps were widened on the later ones.

One interesting factoid I discovered a while back is that there is quite a history to aspects of these drivers' design. The D13XX pots are 6.5" in diameter, same as the large format Altec compression drivers and their Lansing Mfg. Co. ancestors. Six screws hold the basket and top plate to the pot. The bolt circle diameter and thread size are identical to those used in the large format Altec compression drivers, Altec 15" woofers (515, 803, and on), and the Altec 15" Duplex drivers, including the original field coil 601. It seems that Jim Lansing found dimensions that worked well and stayed with them.

[GordonW]

The 6-hole mounting for the motor/basket interface on the D130s... would anyone know if this is the same dimensions as the mounting for the motor on later model JBL units? I just had a 2240H basket apart the other day, and it too, has 6 bolt holes in what look to be the same pattern...

If this is true, it could lead to some interesting potential combinations, interchanging magnet motor assemblies and baskets ... how about a theoretical 2245A?

Regards,
Gordon.