ROCK CONCERTS

[417 - Alnico]

I do not have the whole Alnico brew ha-ha down; I would think it would take quite a long period of time & considerable output to generate enough heat or any other factor to have an impact on a large A5 magnet like the 417's have.

"While I've read lots of opinions touting the 'power compression/Alnico magic', I've yet to see any supporting test data. Even if there's some truth to those statements, musical instrument applications would be the only legit uses to take advantage of such"

[bfish]

"I would think it would take quite a long period of time & considerable output to generate enough heat or any other factor to have an impact on a large A5 magnet like the 417's have."

It would, and until such a point is reached, there should be no difference in performance assuming magnets of equivalent strength. IF such compression exists, and IF you drove the Alnicos to such a point, the resulting compression would be undesireable for HIFI listening, but could be useful for a musician trying to acheive a particular sound (at the risk of permanent driver damage).

[417 - Alnico]

The only way I can think of in a MI situation is..old 15 - 20 watt Utah..CTS..Jensen Alnico speakers w/ Cherrio (sp?) sized magnets driven by 100 watt Marshall or fender amps..not the same as a 417 or D120's tank-like structure. The paper cone would be torn before..that

[Art J.]

I've been enjoying this discussion. Don McRitchie wrote a
nice article about Alnico on his site.

http://audioheritage.csdco.com/vbull...ead.php?t=4031

.

[amh]

Very interesting thread guys. Here's a couple more links to aid this discussion.


http://www.lansingheritage.org/html/...s/tech1-3a.htm

http://www.audioasylum.com/forums/hu...ges/95945.html

[417 - Alnico]

[quote]Originally posted by 417 - Alnico:
[b]I have a hard time getting this question answered..so here goes another try w/o as many words to clutter.

The term is "Rim-Resonance Dip" problems.

What does this mean & does the heavy doping on that type of surround negate this entirely?
Here is that info on accordian 4 roll surround.



http://www.lansingheritage.org/images/jbl/reference/notes/tech1-3a/page06.jpg

[bfish]

Originally posted by 417 - Alnico:

Speaking of paper cone speakers...
BobR or anyone. I was hoping to get a defination of a term that an Altec competitor used in the 70's when they mentioned Altec's almost exclusive use of the 4-fold "Accordian" Cloth Surround.
The term is "Rim-Resonance Dip" problems.
What does this mean & does the heavy doping on that type of surround negate this entirely

<font size="2" face="Verdana, Helvetica, sans-serif">Thanks for the link! I assume you're referring to "Figure 3D. Multiple-roll accordian pleat", which mentions the the "rim-resonance dip" you refer to. I think we've been talking apples and oranges;

First of all, the difference between a roll (half-round), and a pleat (fold). Doesn't seem like a big thing, but tiny details in speaker design can make huge differences. Also, no mention is made of the material used, or if treated or not. Look closely at your 417 surround, and you'll see sharp folds or pleats, completely unlike the rolls shown in Fig. 3D. After reading all 8 pages of the tech note, I could find no reference to Altec design whatsoever, as the entire tech note is detailing JBL design strategy. Although there's some good design theory there, I see no way to apply any of it to your Altec 417s' surround. (nor would I try.)

In no way am I endorsing one brand over another (I'm moderately crazy, not stupid!), as I believe there are gems and duds in both lines.

[bfish]

For posterity, here's the straight dope on doping Altecs. To make the counterfieters and
info-resellers work for a living, I'll leave it buried in this rambling thread. Note the absense of several drivers, notably the 414 and 416 series. The procedure for them was on a separate bulletin that I've been unable to find. Will update with that info if I still have and can find it.


From Altec doc. #42-02-109554, rev. 6, 1086-5M (assuming 1086 to be Oct., 1986)

For Altec 21640, 23713, 406A, 406-8C, 406-8Y, 408A, 412, 412C, 412-8A, 415C, 417A, 417B, 417-8C, 417-8D, 417-8H, 417-8H series II, 417-16H (and series II), 418B, 418-8H (and series II), 418-16A, 419C, 419-8A, 420A, 420-8B, 422A, 422Z, 422-8Z, 423-8Z, 425-8A, 425-8H (and series II), and 600B;

Apply two or three coats of solvent-based surround dope (#54007 or 54007/15). Apply one coat of water-based dope (#124078). (Note, as-written, this could be interpreted 2 ways; use BOTH the solvent and water-based dope, or, Use one or the other. My experience says one or the other)


For Altec 515-8G, 515-16G, 515-8GHP, 3184, 3156, 3127, ER-15, G-15, ER-12, G-12, ER-10, and G-10;

Apply surround dope 510 Airflex on these models only. (Airflex is NLA, but as it was a solvent
based dope, one assumes the 2 or 3 coat application as before. No personal experience doping any of these to say for sure).

[417 - Alnico]

[quote]Originally posted by bfish:
[b][QUOTE]Originally posted by 417 - Alnico:
[QB]Thank you for that insight..That leads me to questions about dampening."

Ah, the next logical question.....BTDT


"Theoretically, if you use a thinner, lighter; yet stiffer sealant for Doping.. Just enough to close or fill the gaps in the cloth surround..to prevent the air from passing thru..how will that effect the sound."


Only to the extent that the altered surround deviates the force/deflection characteristics from design. Could be a little or a lot. My first experimentation along these lines was a real flop, and reminded me that others with far more smarts than myself had already spent lots of time to determine the best way to do it. The doping concoction I made up (being out of Airflex, which you can't get anymore...), was as you describe, thinner, lighter, and stiffer, as it did dry, though it had the wet, shiny, appearance of the real McCoy. Satisfied that I was a genius, I proudly stuffed the 421-8HII back in its' cab, and ran a sweep.....ooops....all thoughts of patents vanished......LF response dived at 240hz, was off the scale (nonexistant) at 180. I meekly cut out my work (and a $65 kit), recleaned the frame, and set it aside to redo when I had the right materials.

The lesson? If you're reconing/repairing a speaker and want it to sound like it was designed to, use identical methods and materials as the factory....period. If you want to experiment with design, use your frame of choice, and have a large quantity of software at your disposal, so you can build, test, record, rebuild, retest, etc....to your hearts content.


" Altec & GPA use a heavy..thick..rubbery dope. Does this effect the dampening?"

[i]Yes. Intentionally. The current product has the appearance and consistency of honey...or STP, and seems to perform as Airflex used to. Don't expect to learn the exact method other than by experimentation and experience, as this is one of the few bits of proprietary information a builder can keep to himself, as most other parameters can be easily reverse-engineered.

TIP; for those of you with Altec doped surrounds as described, which exhibit drips or localized puddling. Don't try to remove or redistribute the doping by brushing, solvents, etc., except in extreme cases. Instead, rotate the drivers mounting a quarter or half turn in the cabinet, to allow heat and gravity to slowly do the job. For old drivers that have been mounted in the same position for 20 years or more, a half turn can have other benefits, too. In the old days, it wasn't uncommon to open a cab and find a penciled schedule, with the dates and initials of the driver rotations!
I thought this was interesting

[LICORNE]

Hi,

You all watched the grammy's last night.

Good performance .Broadcast sound was good to excellent. Some artists manage latency better than others. Of course Sir Paul Mcartney with the Helter skelter song gave evry one goose bumps . Notice he and is musicians had no in ear monitors ,wedge
all the way.

A true Professional .

Enough of this psycho acoustic stuff I'll let you go back to your drivers and speakers.

.......................................