Interchangability of 1,75" diaphragms Altec/JBL

[reVintage]

Googled for new dias for my 808´s. Noticed the same replacements where sold for Altec and for example LE175 and 2425.

As I have never heard of this before I doubt it will work. Or will it? If so it would be interesting to try some of the later JBL in the Altec.

[Earl K]

Googled for new dias for my 808´s. Noticed the same replacements where sold for Altec and for example LE175 and 2425.

As I have never heard of this before I doubt it will work. Or will it? If so it would be interesting to try some of the later JBL in the Altec.

IME, yes the diaphragms are somewhat interchangeable within the gaps / but JBL & Altec use different mounting holes ( in relation to the location pins ). Therefore, you would be forced to drill out some new holes .

Are you talking about buying real JBL & Altec diaphragms or buying counterfeits ?

GPAs price on replacement diaphragms makes it a no-brainer for those on this continent to use OEM diaphragms .

<> cheers

[tomee]

IME, yes the diaphragms are somewhat interchangeable within the gaps / but JBL & Altec use different mounting holes ( in relation to the location pins ). Therefore, you would be forced to drill out some new holes .

Are you talking about buying real JBL & Altec diaphragms or buying counterfeits ?

GPAs price on replacement diaphragms makes it a no-brainer for those on this continent to use OEM diaphragms .

<> cheers

If an Altec diaphragm can fit into a JBL 2410 I'd be willing to give it a try. If it's just a few mounting holes I wonder if GPA would consider selling JBL-compatible diaphragms (although that would be servicing the competition, and he's probably better off selling a new 902 than getting your old 2420s back in service....)

GPA is selling NEW 902-8As on eBay for $202 +shipping. Not sure what replacement diaphragms sell for but that sure seems like a nice price for a complete driver.

[Steve Schell]

Just a little background... Jim Lansing designed the user replaceable diaphragm assemblies for the Altec Lansing large and small format drivers in 1944, as the drivers were being converted from field coil to permanent magnet operation and the top plates would no longer be removable for diaphragm assembly swaps. The driver families were also converted from half roll to tangential compliances at this time. Jim developed a method for hydraulically forming these new diaphragm shapes, which could no longer be formed with a spinning process as had been the case with the earlier diaphragms.

In the first picture below, you can see some radial puckering around the edge of the dome. This is an early Altec 288 diaphragm pressing, found in Jim's workshop in San Marcos by his family after his death. As can be seen he was not quite there with the process, though he worked it out as the production 288 diaphragms looked perfect right from the start.

Jim left Altec in August 1946 and soon developed his own small format driver, the Lansing Sound 175. The second picture shows a pressing of a 175 diaphragm. Note that the tangent at the bottom of the picture, slightly to the right, has a flaw, a little raised bump. This bump can be seen on all (I think) original 175 diaphragms until some time in the mid 1950s, so they were evidently produced until that point using Jim's original tooling.

One more thing... one difference between the Altec and the JBL diaphragms is that the tangents spin in opposite directions. Jim may have done this to differentiate his product from that of Altec.

[scott fitlin]

AMAZING INFORMATION, Steve! Where do YOU find all this stuff?

[Progneta]

Just a little background... Jim Lansing designed the user replaceable diaphragm assemblies for the Altec Lansing large and small format drivers in 1944, as the drivers were being converted from field coil to permanent magnet operation and the top plates would no longer be removable for diaphragm assembly swaps. The driver families were also converted from half roll to tangential compliances at this time. Jim developed a method for hydraulically forming these new diaphragm shapes, which could no longer be formed with a spinning process as had been the case with the earlier diaphragms.

In the first picture below, you can see some radial puckering around the edge of the dome. This is an early Altec 288 diaphragm pressing, found in Jim's workshop in San Marcos by his family after his death. As can be seen he was not quite there with the process, though he worked it out as the production 288 diaphragms looked perfect right from the start.

Jim left Altec in August 1946 and soon developed his own small format driver, the Lansing Sound 175. The second picture shows a pressing of a 175 diaphragm. Note that the tangent at the bottom of the picture, slightly to the right, has a flaw, a little raised bump. This bump can be seen on all (I think) original 175 diaphragms until some time in the mid 1950s, so they were evidently produced until that point using Jim's original tooling.

One more thing... one difference between the Altec and the JBL diaphragms is that the tangents spin in opposite directions. Jim may have done this to differentiate his product from that of Altec.

Those pictures are the most beautiful things I have seen all day!

[Mike Caldwell]

AMAZING INFORMATION, Steve! Where do YOU find all this stuff?

Agreed!!!! Things like that I'll never forget.

[scott fitlin]

Agreed!!!! Things like that I'll never forget.

For real, Mike! Forget that Steve has pics of Jim Lansings original work and prototyping. He has the really tiny details of everything, too. To narrow something of this age, down to that JBL probably used Jims original tooling due to a little nib on one of the tangents, talk about a needle in the haystack!

And, I never even knew the tangents for the JBL spun in the opposite direction of the ALTECS!

Steve Schell, YOU are ONE INCREDIBLE INDIVIDUAL, and certainly one of the best LIVING ENCYCLOPEDIAS OF AUDIO I KNOW OF!

[reVintage]

Thanks,

Great info!

different mounting holes ( in relation to the location pins ).

So if I understand this right, the location(centering) pins are in the right place? In that case it should be a walk in the park(almost).

My idea was to try one of the later JBL´s to, if possible, get more top end. But maybe the nice sound from the Altec 1" lies in the old alu diaphragm.....

[reVintage]

OK, checked some pics and on these aftermarket dia´s we can see that the bolt-pattern is mirror-imaged.

[grumpy]

turn one around 180º

[robertbartsch]

The Jim Lansing prototype diaphragms are true treasures.

Do we know, after leaving Altec, how many tooling dies Jim Lansing used to manufacture the first 175 diaphragms? I'm assuming it was only a few or perhaps only one or two tooling dies.

...just interested since my grandfather was a tool and die maker in Newark NJ about this time. Apparently, he did a lot of work for Bell Labs and others at the time. The name of his shop was Enterprise Tool and Die Co. He employed about 20 machinists.

[Steve Schell]

Thanks for the comments guys. I was given several of each type of diaphragm pressing by a member of the Lansing family a few years ago.

I am working on the assumption that there was only one 175 diaphragm tool for the first few years, as all the early diaphragms I've seen have that little flaw. It represents a small chip on the tool, as the diaphragms were pressed using a one part female tool. As I understand the process, a piece of foil is placed over the tool, then a rubber bladder filled with liquid is forced into the mold by either a press or a hammer blow. The D130 center domes were made this way in the early days with the hammer blow technique.

Robertbartsch, that is really interesting about your grandfather's machine shop. It is still routine in the speaker business for the engineer to make a drawing (CAD these days), then have a machine shop build the piece. JBL does a fair amount of prototyping with a couple of in-house rapid prototyping machines. Jim Lansing's ability to design something and immediately build the tooling himself and turn out examples had a lot to do with his tremendous output.

I am not sure of the differences between the Altec and JBL 1.75" diaphragm mounting. I do know that the positions and diameter of the locating pins are the same for the Lansing 801 field coil driver and the later Altec 802/804/806 etc.

Here are a couple of pictures of a 175 from ebay last year. I have seen many more like this. Notice anything unusual about the tangent down around 5 o'clock? The driver serial number indicates (I think) a manufacturing date of March 1953, which means that the chipped tool had been in use for at least six years by then.

[Steve Schell]

Here we go with the oversize pics again folks... sorry. This is an early 175 diaphragm I obtained from Hal Cox years ago. It was probably part of the load of memorabilia he obtained from William Thomas. I used to think that this diaphragm was a prototype due to the lathe turned bakelite and fabric ring, but later found that these were used until the mid 1950s. Imagine what it would cost to do that now! Anyway, we see the same tooling flaw, only this time someone has taken a small blunt object and pushed the flaw somewhat inside out in three spots. Note the lead out dress along the tangents, like the early W.E. 555W diaphragms. Also check out that beautiful edgewound aluminum voice coil, so perfect it looks like a single band of metal. The carefully made wooden box the diaphragm came in is typical of 1940s/1950s JBL diaphragm boxes according to Hal.

[Altec Best]

For real, Mike! Forget that Steve has pics of Jim Lansing's original work and prototyping. He has the really tiny details of everything, too. To narrow something of this age, down to that JBL probably used Jim's original tooling due to a little nib on one of the tangents, talk about a needle in the haystack!

And, I never even knew the tangents for the JBL spun in the opposite direction of the ALTECS!

Steve Schell, YOU are ONE INCREDIBLE INDIVIDUAL, and certainly one of the best LIVING ENCYCLOPEDIAS OF AUDIO I KNOW OF!

Where in the world do you find all this stuff Steve ?? I just absolutely love reading your posts this is a prime example of WHY !!! Super informative. And why Jim's suicide was a tragedy for everyone as he was one of the top genius's in the audio world at that time.Who knows what other innovations he could have brought to the audio world had he lived a full life.I just love the sound of any of the audio devices he thought of or improved upon and as why my favorite speakers have always been Altec & JBL .I hope you don't mind if I copy those pictures. Thank You for the info once again Kind Regards ~ John