Sunday, August 07, 2011

Let's cut some stuff open. Here's a pair of blown Sunn Magna 158A 15 inch transducers; the later 200 watt variety, not to be confused with the square magnet CTS 80 watt drivers. Neither are operable, and the likelihood of a model specific recone kit to surface is practically non-existent.

It would be a shame to let that cast aluminum basket and massive magnet assembly be melted down and reformed into useless junk.

First step is easy, it involved a knife. I did sever the gasket as uniformly as I could prior to digging the cone out, because I can ALWAYS use 15 inch gaskets. For the record, there are two 15 inch folded horns that are awaiting drivers, and four 2x15 cabinets. I expect a slough of recone posts in the future, as time and money allow.

Anyway, back to the 158A. A friend shoulder tapped me to assist in reconing a torn up JBL D130, and it occurred to me that I've got a small collection of JBLs awaiting recone too, and before performing work that I am not 100% familiar with, I may as well work through some of my own before taking on his.

Then, as lateral pondering tends to do, I remembered the Sunn speakers rotting away in storage. It certainly seems reasonable to check fitment of the JBL cone kit with the Sunn basket, worse it can do is not fit before being installed in the frame it was built for. Hopefully in the same era 4 inch voice coils were made more or less the same, 4 inches..

This particular shot isn't inherently clear, it is the nominal measurement of the depth of the coil former from inside edge to spider, an Xmech variable. The D140 recone kit specifies a former height of 0.860 inches, which is very close to what I have here.

I should stress that all of the measurements pictured are pretty rough, pictured are fast and dirty field measurements more for proof of concept than anything else. I have JBL D130, JBL D140 and JBL 2226 up for recone, and each of these will be mocked up on the Sunn 158A basket, and I will certainly opt for the best fit if any actually seem to work in the first place. Make no mistake, I'm not measuring this out to order a kit based on measurements alone.

Internal diameter of coil gap, fairly accurate, though I cannot be certain my pinch point is the widest point in the gap I can be certain the caliper is seated within the gap itself. The caliper is also built out of ferrous material, so magnetism was applicable.

Outer diameter is, however, a total crapshoot. I couldn't physically get the caliper to seat within the gap due to caliper readout chassis, and above disclaimers also apply...

I feel pretty good about this particular measurement though.

Something the recone kit provider does not supply is the cone depth, so I'll have to see if I can dig up this measurement on that dimension at the JBL library at, just, you know, to appease my sense of curiosity.

Subtracting this amount naturally. And yes, I might just directly measure the cleaned out basket of the JBL drivers instead of attempting to reverse engineer this cryptic (though very important) dimension. I came up with 2.9440 inches after subtracting one from the other.

The two baskets now sit gutted, masking tape shielding the gap, awaiting some sort of progress. Progress is good, it's probably going to be a bumpy couple months here (relocation is afoot). In the event of success I will indeed link the source of the recone kit I am going to use.


krivx said...

When doing this kind of "subtraction" measurements I just zero the calipers on the first measurement. Anything you measure from then will use that as a zero reference so the subtraction is done for you.

Rob Francis said...

Well now its June of 2017 and I am curious if you ever successfully reconed this speaker. I too have one I have used for a number of years,,,,as in back in the day. It's in a Leslie and still works. I am curious is this speaker was originally built by Cerwin Vega, it sure looks like it. I live in Tucson and just east of us is the small town of Vail Arizona. There is a MWA speaker part factory there that splintered off the original company in L.A. They manufacture parts for companies all over the world. I am pretty sure they could rebuild this speaker, or perhaps supply the parts. If anybody has info on this speaker please contact me @ I would be most appreciative.

crochambeau said...

I have not made any progress on this project, been busy with builds that are not quite blog material.

The Cerwin Vega is an interesting angle, I'll have to explore the CV data I can find to see if anything clicks. If I find anything promising I'll let you know. I should probably post here more often too, thanks for the nudge!

Rob Francis said...

Thanks for the quick response. I too will dig in a little deeper. I have two possible resources, one is a gal that re-cones for me. She has been at it for the better part of 35 years now and is very knowledgeable. And besides her knowledge her network has to be huge. The other is about 29 years of keyboard magazines in my attic going back to when they were known as "Contemporary Keyboard". I have a vague recollection of an add showing a 15" speaker sitting on an entirely white back drop which has an electrical outlet on it. From the speaker is a wire lead with a electrical plug just waiting for somebody to plug it into the wall. The caption reads, "We dare you to do this with any other speaker". Hopefully I will get back to you. But first I must I would bet that if nothing else she could build the repair cone from materials they have or could create.