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starlifter f/e
05-12-2010, 10:02 PM
Soft, but obvious rattle on any deep bass, from moderate volume to full power on an Onkyo AVR3805, the rattle stays the same. I've swapped speakers left to right (its definitely the speaker), removed the grilles, removed all rattle prone objects from the area, inspected the cone(no obvious defects on cone or surround), and compared the compliance with the good woofer(moves easily, feels the same). What now??? I welcome ANY and ALL suggestions, because I simply cannot afford to ship the woofer to Great Plains anytime soon:(:(:((snif)

John
05-13-2010, 02:16 AM
Try rotating the woofer 180 degee's. :spin:

By the way is it a 416B or 416C ? :hmm:

robertbartsch
05-13-2010, 02:45 AM
I recently bought a pair of dead Altec 416-8cs (ferrite motor) for re-coning.

One woofer had a quarter size piece of metal that had become loose, presumably from the top plate, and you could hear it rattle around when you picked up the woofer and shook it.

The guys at Gabriel Sound in NJ removed the cone and VC to see if the motor had shifted and it had not so they used GPA kits to retore them.

You might want to shake the woofer to see if you might have a similar issue. If yes, and your woofers still play, it might be "repaired" by removing and replacing the dust cover and not reconing it.

...not sure thou...

Earl K
05-13-2010, 05:11 AM
Hopefully ( just like Robert mentioned ) you've got a 416-8C with a loose vent-blocker .

A remedy is to remove the dustcap and reglue the loose metal slug , then reglue the dustcap ( just like Robert has speculated ) .

Here's a picture of one such patient owned by Wardsweb ( the king of AudioKarma :p ) .

http://wardsweb.org/audio/altec_images/4168c_cap.jpg


The thread this pic came from is here (http://www.audioheritage.org/vbulletin/showthread.php?12698-Repairable-or-trash&highlight=) .


<> cheers Earl K

robertbartsch
05-14-2010, 01:39 PM
That is an interesting picture Earl. - Thx!

...So the design of a 416-c is that the voice coil is vented [cooled] through the dust cap; right? I wonder why the pole piece needs a hole in the center for this model? Is this related to getting the moter to perform correctly or perhaps it is there for ease of manufacturing.

Anyway, I know the reconer said the units were a pain to recone since the VC gap is very tiny and it required a lot patience and skill to get correct. I'm guessing the small gap design helps increase the drivers' sensativity.

Earl K
05-14-2010, 02:00 PM
,,,,snip,,,,...So the design of a 416-c is that the voice coil is vented [cooled] through the dust cap; right? I wonder why the pole piece needs a hole in the center for this model? ,,,,snip,,,,,,,or perhaps it is there for ease of manufacturing. ,,,,snip

I think the vent hole to the back was there for" ease of manufacture" ( so that Altec could use the same ferrite pancake magnet for different model woofers such as their M.I. types ) .

I think this whole generation of 416C will suffer this problem if/when the glue lets go of the disk .

<> cheers EarlK

Don McRitchie
05-14-2010, 09:57 PM
...So the design of a 416-c is that the voice coil is vented [cooled] through the dust cap; right? I wonder why the pole piece needs a hole in the center for this model? Is this related to getting the motor to perform correctly or perhaps it is there for ease of manufacturing.

The hole in the dust cap on the original 416 and 515 is not for cooling but rather to relieve the back pressure from the air that would otherwise be trapped between the dust cap and the pole piece. The very first dynamic drivers did not use dust caps for this very reason.

This was not a big issue when voice coils were nominally 1" or so in diameter. However, as Altec pioneered the widespread adoption of large diameter voice coils, the lack of a dust cap would be a limiting factor in performance. The now large area inside of the voice coil becomes unavailable to radiate sound.

Altec's design was a compromise. They incorpoated a dust cap, but one with a hole in its centre to relieve the back pressure. The more effective solution is to back vent the motor so that the cone and dust cap form a contiguous surface with no holes. However, I suspect that a combination of reluctance to re-engineer a good selling design and manufacturing economics kept Altec with this design for decades after most others had moved on. It's cheaper to punch a hole in a paper dust cap than a metal pole piece and metal pot structure.

When Altec converted their motors from Alnico to ferrite, they standardized on a new geometry that included back venting. This was likely done to allow flexibility in applying the new motor to more advanced designs that began showing up around the same time and used the superior back venting. However, I'm guessing that the visual identity of the 416 and 515 with holes in their dust caps was so strong with their customers that Altec was reluctant to abandon this look. Thus Altec kept the dust cap hole on the ferrite 416C even though it was entirely unnecessary and arguably detrimental.

herki the cat
05-15-2010, 01:41 AM
Hopefully ( just like Robert mentioned ) you've got a 416-8C with a loose vent-blocker . A remedy is to remove the dustcap and reglue the loose metal slug , then reglue the dustcap ( just like Robert has speculated ) .

http://wardsweb.org/audio/altec_images/4168c_cap.jpg
<> cheers Earl K

herki the cat:
Eark K, you did a fine job of removing the dust cap. How did you remove the dust cap so skillfully? I have qty(4) of 416-8C with the rattle problem, & I would like to use your technique.

Earl K
05-15-2010, 04:49 AM
Herki,

The skilled removal of the pictured dust cap was accomplished by Wardsweb ( alas ) not I .

His thread about it , is here (http://www.audioheritage.org/vbulletin/showthread.php?12698-Repairable-or-trash&highlight=) .


FWIW, I need to develop this skill myself for my JBL woofers .

I need to replace quite a few rotting foam air-filters ( on 2225Hs ) which are hidden from view just behind the one-piece dust cap ( glued across the interior entrance of the vent ) .

From the perspective of longevity. this is a design flaw that's non too enduring ( towards JBL ) for those of us who care about avoiding planned obsolescence.

<> cheers :)

ps ; Another alarming picture ;

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=14508&stc=1&d=1143961353

starlifter f/e
05-17-2010, 09:44 PM
Well, I removed the woofer and shook it as hard as I could, reorienting it several times, but it made no rattling sound at all. I could easily see the round metal disc through the vent hole from the back of the magnet. It is securely fastened to the front of the magnet. I couldn't find any thing identifying this woofer as a 416-8b or 8c, but I bought these Model 19s new at Pacific Stereo (San Mateo, CA) in 1981 if that helps. I remounted the woofer upside down (rotated 180 degrees) to reposition the wires, in the off chance the cone was contacting them during long excursions.

If I were to operate the woofer in free air for a test, say a slow sweep or warble between 20-60 Hz at one watt, would a healthy, undamaged woofer make rattling or flapping noises?

robertbartsch
05-18-2010, 01:19 AM
I assume if the metal slug is not loose and the woofer rattles you looking at reconing the pair, hopefully, with GPA kits.

I believe the 416-cs are front or rear mounted designed frame and the 416 As and 416 bs are back mounted only frames. The 416-cs also usually have a 16" not 15" frame. 416-cs also have ferrite not Alnico motors....

Don McRitchie
05-18-2010, 07:00 AM
That's not quite accurate. Altec switched to the 16" frame late in the "A" series production and a number of Model 19's were built with factory installed 16" "A" drivers that were front mounted. The "B" series always had the 16" frame and is distinguished by the switch to a cast pot instead of the previously machined pot over the Alnico magnet. This is the most common driver in the 19. The later "C" series used the same frame but introduced the ferrite motor.

I believe that the 15" "A" series could also be front mounted if desired. Early Altec drivers had reinforcing ridges that extended back from the driver lip that prevented front mounting. However, these were removed at some point (I don't know when) to allow front mounting. For example, the 411-8A with a similar 15" frame was front mounted on some Altec factory systems.