The Re-coned 416-8C's

[RonSSS]

Hey AMH,
Yes, the cones were from GPA.
I have 3 examples of untouched 15" drivers. One is the mentioned 416-8B and the other 2 are my 904-8A duplexes. On all 3 of these, the outer surround is perfectly flat. No inward angle at all.

The cone kits have the VC/Spider assembly pre-assembled. The cone itself is seperate. Once the VC/Spider assembly is centered and glued in place, the cone is then dropped over the VC former and glued to it. So there are 2 things that can be messed up. The height of the VC assembly, and the height of the cone.

Like I stated in an earlier post, I bet Altec had assembly fixturing for this. But someone here said no, they probably eyeballed them just like the re-coners do. Sorry, but I doubt it.

Anyway, I hope your 515's sound good and work fine. I bet they are ok.

I measure mine electrically because I can, and to be honest, I think it should be a requirement for a re-coned speaker. At least within 20%. 50% off is not even close.

I plan to see if they will re-do the one they messed up at their cost. But since it doesn't rub, I doubt it. Never know though, I've done business with them for years......on and off....sort of. I have 2 more cones......

Ron

[joyspring]

Ron:

Sorry to hear about that second 416 being so far off spec... and definitely sorry to hear about the `sunken' cones. I was especially hoping I wouldn't hear about _that_ particular problem...

The local reconer in my area offers both GPA (`OEM') cone kits (at a premium) and `ground-up' recones (assembling from separate Waldom parts: cone, surround, spider and voice coil former) for lesser cost.

To tell you the truth, every GPA cone kit that I've encountered (604-8G, 604E, 604-8K and my personal 605As) has suffered from the `sunken cone' syndrome. Strangely enough, the 604s built from third-party parts seem to look fine (appearance-wise).

I don't expect either to have Thiele-Small parameters anywhere close to the originals, however...

Someone here suggested that fixturing is not required to do this work, and that eyeballing it ought to be good enough. Problem is, this doesn't take into account skill and experience.

<font size="2" face="Verdana, Helvetica, sans-serif">That would be me and I stand by that statement.

OEM Altec (and UREI) recone kits had cone, surround, spider and voice coil former preassembled, and those were definitely aligned in a fixture.

The reconer was simply responsible for centring the voice coil former by shimming, gluing the lot and then removing the shims once the glue has cured.

I've personally done this on many 604Es, 604-8Gs and 604-8Ks as most studios did this work in-house in the 1980s.

I repeat: the shims must remain in place until the adhesive on the spider and surround completely set.

I did not realise that the GPA kits do not have the cone attached to the spider and voice coil... now that is nearly (but not quite) a ground-up rebuild...

Even so, a good reconer can do this by eyeball IF (and that's a big IF) the parts provided are to spec.

From the examples I've seen, my personal experience (out-of-spec 605As with sunken cones) and your experience as well, I'll (tentatively) stick to GPA HF diaphragms but will have my very experienced local reconer do `ground-up' LF rebuilds from third-party parts.

I'll let you infer what I intend to state from that...

BobR

[RonSSS]

Hi Bob,

The spider on the really sunken unit is sunken as well.

It seems to me that if you do the VC/Spider first, let the glue dry, and remove the shims, the spider should set the height of the voice coil. You could then measure the distance from the pole piece to the top of the VC former with calipers. Next, re shim it, at the proper height, so the cone insertion doesn't move the VC, and put the cone in.
Establish the height of the cone.....even it's eyeballed....it's not too hard to see if the surround is flat....then glue the cone to the VC, and the outer surround to the frame. This "should" keep the outer surround flat, and the VC at the correct height.

Now wouldn't this eliminate the sunken cone?

When I recieved the cone kits, I set the VC assembly into the gap and indeed, the spider set the height, and it didn't appear to be sunken. Putting the shims in W/O moving the assembly is tough to do. Friction ya know. But if the VC height was measured before inserting the shims with calipers, or set up with a simple fixture, the height would be correct after gluing.

Maybe I'm just a fixture nut, but in my world of precision GHz RF components, fixturing assures that even meatheads can do the job correctly. I can picture a simple fixture that would not only center the VC in the gap, but would set the correct height.

Anyway, didn't mean to slam you, I'm frustrated.
So I apologize for any inference.

Maybe the sunken cone isn't totaly to blame for the messed up T/S parameters, but I just bet it is, because the VC is not in the proper location. Makes for non-linear travel. Even though these drivers had rubbing VC's before I had them re-done, the T/S specs were pretty close.

Wanna form an Altec re-coning buiseness?

BTW......I appreciate your insight, I really do.

Ron

[Russellc]

RonSS:
Could you explain to me what to look for with the "sunken" cone thing? My 5158G have been reconed once by GPA, and then one had to be reconed again after a targic accident. My 416 8C have the original cones. What do I look for to be sunk? Also, how and what do you use to measure the driver's specs? Or did your reconer measure them? I would love to know how to measure them my self, and any info would be greatly appreciated.


Thanks, Russellc

[RonSSS]

Well,
I got em back today. Right away I noticed that the cones seemed to be sunk into the frames more than a stock driver. I have one stock 416-8B to compare to that has never been re-coned, I bought it new in 77.
Anyway, I don't know why, but I figured this would happen. Arrgh! One looked worse than the other.
So I bring them home and hook em up to an amp and run them at 8watts @ 10hz for 3 hours to break them in. Then sat down to measure the T/S parameters.

I measure the one that looks the best and come up with the following numbers:

Driver #1
Qes_____.30_____Spec__.26
Qms_____5.39____Spec__6.1
Qts_____.28_____Spec__.25

Pretty dang close, within about 15%

Driver # 2 (seemed to look worse)
Qes_____.49____Spec__.26
Qms_____11.4___Spec__6.1
Qts_____.47____Spec__.25

This is what I get for trusting my local re-coner. I saved $50 in shipping to lose a $76 cone.......
This is so typical for me. Make the wrong decision.

Someone here suggested that fixturing is not required to do this work, and that eyeballing it ought to be good enough. Problem is, this doesn't take into account skill and experience.

Cr*p!

I could have done it better myself I'm sure, and from now on, I'll be doing the work myself.

Here is what they did wrong. They centered the VC and spider with the shims, glued it, but didn't remove the shims to let the spider return the VC to center height wise. They left the spider sunk, then glued the cone to the VC and Wha-La, sunk assembly. And messed up specs.

I have no idea if GPA does them any better.

I should have freakin told them what I expected, and how they should have looked when done.
Instead, I'm left holding the ****** -bag.

I'm tired of incompetent people. Just plain tired.

Ron

[amh]

Really sorry Ron.

Seems like everything from McDonalds to Medicine has ****** service and incompetent employees these days.

You got the cones from GPA didn't you? After my last post I noticed that the cones on my new 515-8Gs are ever so slightly depressed. The surround angles down just a touch. I don't have originals to compare to so not sure what "normal" is. I wonder if Bill got a batch of out of spec cones?

[RonSSS]

Russell,
The 515 cones might be different than the 416 cones. I don't know, I've never seen a 515.
The area I'm looking at to tell the cone is sunk it the outer surround. On an original driver, the accordian is flat.
To get mine to look flat, I have to lift the cone upward about 1/8".

Go to : http://sound.westhost.com/tsp.htm

for a good procedure on how to measure the T/S parameters. They have a nice spreadsheet that takes the data you input and does the calcylations.
Ron

[amh]

Hi again Ron,

BOTH the spider and surround are depressed? It seems between the two it would just lift the VC in it's gap. I'd wager the spider or something has improper shape to begin with.

If you are giving 20% tolerance you're being generous. On JBL drivers more than 10% off is out of spec, that's according to their spec sheets and service manuals. A few re-coners I talked to about my JBL 2245Hs said you can live with it, but you may want to start thinking about re-cones if close matching is important. Remember, 20% one way on one driver, and 20% the other way on another is 40% mis-match.

Any thoughts on my cab plans, I answered your question in "new 515" post. I'd value your input.

Thanks

[joyspring]

Ron:

The spider on the really sunken unit is sunken as well.

<font size="2" face="Verdana, Helvetica, sans-serif">Yup, my 605As and 604s outfitted with GPA recone kits suffer from that as well.

It seems to me that if you do the VC/Spider first, let the glue dry, and remove the shims, the spider should set the height of the voice coil. You could then measure the distance from the pole piece to the top of the VC former with calipers. Next, re shim it, at the proper height, so the cone insertion doesn't move the VC, and put the cone in.
Establish the height of the cone.....even it's eyeballed....it's not too hard to see if the surround is flat....then glue the cone to the VC, and the outer surround to the frame. This "should" keep the outer surround flat, and the VC at the correct height.

Now wouldn't this eliminate the sunken cone?

<font size="2" face="Verdana, Helvetica, sans-serif">Firstly, you don't want to remove the shims until BOTH the spider AND surround are glued in place... this is to make absolutely certain that the voice coil former is so parallel as possible to the pole piece and top ring; otherwise, you risk `rub' as the moving assembly eventually sags (with gravity over time).

Any very-high-compliance/high-efficiency LF driver is vulnerable to `cone sag' as the spider and surround are intended to be flexible enough to lower cone resonance, ensure linear excursion, etc. You'll note that Altec LF drivers stored on their backs for extended periods also suffer from the `sunken cone' malady as well.

Even so, the spider is a phenolic resin-impregnated linen cloth and is essentially thermoset; that is, it ought to hold its shape, even when stretched over a 48 hour period (for an adhesive to set).

Maybe I'm just a fixture nut, but in my world of precision GHz RF components, fixturing assures that even meatheads can do the job correctly. I can picture a simple fixture that would not only center the VC in the gap, but would set the correct height.

<font size="2" face="Verdana, Helvetica, sans-serif">I agree, but the parts have to be serviceable to begin with... and I'll leave it at that :-/

Anyway, didn't mean to slam you, I'm frustrated.
So I apologize for any inference.

<font size="2" face="Verdana, Helvetica, sans-serif">No offence taken; I tend to p*ss people off on this forum... I like to think of it as reality vs. advocacy.

Wanna form an Altec re-coning buiseness?

<font size="2" face="Verdana, Helvetica, sans-serif">Far too much time and capital necessary for what is really a *very* tiny market.

And what's necessary isn't the actual reconing which even monkeys like myself can handle, but the consistent and custom production of unavailable parts: particularly cones of the same composition, geometry and mass as the original Altec cones, spiders built to OEM spec., even the purportedly now-unavailable surround damping dope, etc. These things even Altec in their heyday did not do in-house.

Considering the amount of capital and time necessary, what Bill at GPA and Todd do provide is admirable despite some of the technical glitches.

I wish the best for Iconic and GPA but everyone should realise that they service an extremely small, admittedly nostalgia-centred market.

BobR

[Russellc]

Well, GPA reconed mine and turned them around at incredible speed. less than a week total turnaround last time. My accordians appear flat, with only the exception of the edge on the GPA 515 cone. And like ron said, the 515 cone may be different in that regard to the 416 8C cone I was comparing it to. I am happy to have a resource like GPA, and short of original cones is as close as it gets.

Russellc