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Old 18th September 2002, 05:06 AM   #11
navin is offline navin  India
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i copied the plug from a Audax HM170Z0 driver. it is solid. so i figured one can make them out of epoxy resin moulded in shape too right?
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Old 18th September 2002, 06:07 AM   #12
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Quote:
Originally posted by navin
i copied the plug from a Audax HM170Z0 driver. it is solid. so i figured one can make them out of epoxy resin moulded in shape too right?
Sure, why not? Or Ceramic (get the potter's wheel out boys), or leggs "boxes" filled with X, a 35mm film canister filled with "X", lipstick caps, wood, metal, foam, felt, plastic, cement ...

Each material will have a set of resoncance/absorption/reflection/transmission characteristics which may or may not be beneficial to the performance of a particular driver. And then there is the shape ... With such a large space to explore we might as well dive in with what we have and establish some data points.

dave
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Old 19th September 2002, 05:11 AM   #13
navin is offline navin  India
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tip toes?
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Old 19th September 2002, 06:03 AM   #14
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Not to forget those Estes and other nosecones on the "speaker company" thread
Also: how come Pinoccio's nose isn't animated?
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Old 19th September 2002, 09:39 PM   #15
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Question surgery

Aquired two vintage Eton (German variety) Hexacone (Kevlar honeycomb membrane) 8-480/32 drivers through ebay. One of them was a free extra to the other because it scratched. Clearly, it was manufactured at a different time (differnt color of membrane, different basket, diffent magnet, though all the same size).

Turns out the scratching is evident if I push down one side of the membrane by only 1 mm (the other one will exhibit no scratching even if I move the membrane by as much as 6 mm).If I distrubute the force more evenly, i.e. push down on the center of the dustcap or move up on four points on the rear, I can get +/- 3-4 mm without scratching noises.

- Is this dirt in the gap (the magnet hole is not covered by a sieve) or rather too tight tolerances?
- If dirt, what is the most promising way of opening the thing:

a: unglue the magne from the basket? how?
b: unglue surround (rubber) and spider from the basket? how?
c: demagnetize the magnet? how? why at all?

Eric
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Old 20th September 2002, 01:24 AM   #16
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Slide a strip of cellotape down the gap and run it around the polepiece - this will usually grab any bits of debris in the gap.

Eric.
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Old 20th September 2002, 01:28 AM   #17
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Also by selecting the right thickness paper or cardboard, you can slide a sleeve down into the gap to centralise the voicecoil.
Heat the cone/voicecoil glue joint carefully with a hot air blower until it eases a bit, let it cool fully and remove the sleeve and you might fix it.
Do not heat the spider because this will make it go loose and alter the characteristics.

Eric.
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Old 20th September 2002, 07:27 AM   #18
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Very good tips, thank you very much. Before I can try, I'd have to know how to gain access to the gap.
Remove dustcap? Will only give me access to the inner side which is already something.

Remove magnet? how? If I heat the magnet-basket joint, I will probably demagnetize the ferrite and ruin the spider.

Also, I have the impression that scratching occurs no matter which side of the membrane I press down. So either they got the tolerances (uniformly) wrong or there is dirt in all directions.

Eric from the other side
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Old 20th September 2002, 05:39 PM   #19
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Quote:
Originally posted by capslock
Very good tips, thank you very much. Before I can try, I'd have to know how to gain access to the gap.
Remove dustcap? Will only give me access to the inner side which is already something.

Remove magnet? how? If I heat the magnet-basket joint, I will probably demagnetize the ferrite and ruin the spider.

Also, I have the impression that scratching occurs no matter which side of the membrane I press down. So either they got the tolerances (uniformly) wrong or there is dirt in all directions.

Eric from the other side
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Yes, remove the dustcap with a hot air source to weaken the glue, and with an exacto (scalpel blade or stitch cutter blade) knife both lift the cap and carefully slice/seperate the glue web without damaging the cone or dome.
Typical glues go soft with heat and become much easier to work.
Now you have access to the pole-piece.
If the magnet is fixed by screws, by all means do so carefully, if not do not attempt it.
Some drivers run very fine tolerances and will scrape if not pushed or pulled perfectly evenly.
Other reasons for diminished gap is white powder corrosion of zinc plating of the pole-pieces, or the end of the voicecoil former having mushroomed by mechanical bottoming, or the voice-coil having 'sprung/shifted' due to thermal overload.
A thin stiff blade (a broken retracting tape measure is good) can be slid down the gap and used to scrape any corroded zinc, or ream the former back to shape.
After this, use a fine strong jet of compressed air and sticky tape to remove any smeg.
Then if needed, fit an appropriate thickness sleeve down the gap and cook the VC/Cone glue joint and allow it to self align and let it cool for a long period. (hours).
Practice on a junked old driver FIRST before you try any of this on a valuable treasure.
A very carefully used paint-stripper hot air gun is an appropriate tool, or a hairdresser dryer that gets HOT.

If you need more help, just ask.

Eric Von Downunder.

A low frequency high excursion drive free air test will tell you of any dynamic operating scraping.
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Old 30th September 2002, 05:04 PM   #20
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Default partial success

Hi Eric,

tried your tips. Wrapped the speaker in aluminum foil except for dustcap and used hot air gun in low setting. Could remove dustcap easily with knife.

VC former was surprisingly modern, i.e. coil wrapped on paper that had an inner liner of this stiff brown, semi-transparent plastic.
It had also 4 mm holes to let the air trapped by the spider escape into the 10 mm hole in the center of the magnet. The inner slit was very narrow, could not even slide in a piece of very thin cardboard (file card).

Found thick paper that worked. Afterwards, scratching was gone but slight ticking sound remained when using 20 Hz for test.

Inserted a whole sheet of paper slightly less long than the inner circumference of the VC former. Then added three additional strips of the same paper 120 apart.

Rewrapped the speaker, heated and cooled. Clicking sound was gone but cone had sagged by about 5 mm. Redid the paper trick with a little extra paper and fixed cone in nominal position. Heated only rubber surround and spider. Assume spider is the problem as it still looks slightly deformed. Clicking back, but only at large amplitude.

Eric
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