New Diaphragms

In answer to a PM asking if all a person had to do was put the new diaphragm on the pins and bolt it all back together.

I always run the requisite frequency sweep to ensure there are no unwanted characteristics. Before re-assembly I hit the gap with 120 psi of air followed by a carboard digger with masking tape wrapped around it followed by a cardboard digger with cloth dampened MEK. I inspect the gap with a light and a magnifier. I check the voice coil for any gunk and remove it before using the new diaphragm.

Reconers feel free to add whatever. Reconers should be using gap gauges and the gauges from JBL are expensive.

BTW - On recones always check the VC with an ohm meter before doing anything. I did a beautiful recone job about 30 years ago on a 2121A that had an open VC right out of the box. :rotfl: :applaud: I naively believed JBL never made mistakes.

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In answer to a PM asking if all a person had to do was put the new diaphragm on the pins and bolt it all back together.

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Hello Giskard

Great post!

If your lucky and they have alignment pins! There are a few that don't like 2425/2426/2445. You also have to watch the alignment very carefully on the compression drivers. They have channels cut into the top plates to accomodate the voice coil wire where it is bonded against the side of the coil. If you try to rotate the diaphram on the gap you will jam and damage the coil. You need to line it up carefully before you drop it into the gap. The 2425/2446/2445 have JBL embossed into the top plate as a visual aid to get the alingment correct along with the mounting holes. The terminal with the polarity marking green for 8 ohms and red for 16 ohms should be aligned with the JBL marking on the top plate.

Rob:)

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Originally Posted by Giskard

In answer to a PM asking if all a person had to do was put the new diaphragm on the pins and bolt it all back together.

I always run the requisite frequency sweep to ensure there are no unwanted characteristics. Before re-assembly I hit the gap with 120 psi of air followed by a carboard digger with masking tape wrapped around it followed by a cardboard digger with cloth dampened MEK. I inspect the gap with a light and a magnifier. I check the voice coil for any gunk and remove it before using the new diaphragm.

Reconers feel free to add whatever. Reconers should be using gap gauges and the gauges from JBL are expensive.

BTW - On recones always check the VC with an ohm meter before doing anything. I did a beautiful recone job about 30 years ago on a 2121A that had an open VC right out of the box. :rotfl: :applaud: I naively believed JBL never made mistakes.

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Yes...that's a very good synopsis. That's the way we are trained at the factory.

While I am not a reconer, I like to read these little technical tidbits!

Ron

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Originally Posted by edgewound

That's the way we are trained at the factory.

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I've been referring the pm's I've received on this very topic your direction. Lemme know if that is not cool...

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Originally Posted by boputnam

I've been referring the pm's I've received on this very topic your direction. Lemme know if that is not cool...

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That's cool...I don't mind.

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Originally Posted by edgewound

That's cool...I don't mind.

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Recone's too, I'm guessing? :hmm:

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Originally Posted by boputnam

Recone's too, I'm guessing? :hmm:

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No guessing required , Bo. You know.;)

Cool. I just wasn't sure where you source from, and whether shipping is OK.

I know members here are plenty resourceful in finding solutions to their needs - pm's work! :thmbsup:
But it's nice to know more about you.

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Originally Posted by boputnam

Cool. I just wasn't sure where you source from, and whether shipping is OK.

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Source is JBL Professional, shipping is fine. I have in the past and I am currently doing business with forum members.

I do complete factory recones as well as refoams when requested, and can replace the complete suspension on cone assemblys that are NLA, but the cone and voice coil are still good.

I have a limited number of rebuildable take-out assemblies available for the thrift minded. I don't currently have a website, but that is on my to-do list. Listed on JBL Pro customer service.

Thank you, Bo.

As requested - Here's a link to a Test Tone Generator.

Test Tone Generator (TTG)

I checked out a previous version several years ago and it worked well.
This one has a volume licensing discount I see.
I'm sure there are plenty of software packages out there these days.

Just to underline the importance of good alignment of the diaphragm.

The following measurements were taken on the same 2425/tractrix horn combo.

The Winairr software was set up with 5 sample averaging, no other smoothing, back-cap off.

Thanks!
Graphical illustrations are good. :)