Refoaming AR3 woofer, technic question...

[Guest Danlaet]

Hi,

I'm refoaming a AR3 woofer, and I'm in front of a "problem" of fiber ring : it is not centered. Look at the photo to understand :

http://www.classicspeakerpages.net/dc/user_files/2409.jpg

I have to say that this woofer had been refoamed yet, but when playing it has a problem whith loud or violent bass : vibrations. As the foam as two holes, I deceided to change it and hoped that that work could resolve the vibration problem (perhaps a bad centring in the coil I thought). And then, this strange uncentered fiber ring.

I take a look at the other hp, all is perfectly center and it works fine.

Do you think I must replace the fiber ring before continue whith the refoam operation ?

Thanks.

Daniel

[dynaco_dan]

Hi Daniel;

Normally the woofer you show in the photo, Alnico magnet and aluminum cast frame version, has a clothe surround, not a foam one.

Do not attempt to remove the damping ring, contains unobtainium, you would in all likelyhood, damage the cone material, irrepairably.

It has seen better days but should not affect the outcome.

The spider and cone may need to be removed from the frame to diagnose the voice coils condition.

More detailed assistance to follow.

[Guest Danlaet]

A clothe surround, not a foam surround. Yes. But I've found only foam kits.

I finally don't touch anything. Just put the new surround.

I've make a little movie of the bass driver in action, alone, with tweeter and medium pots turn to zéro. If you want to hear the phenomena : http://fr.youtube.com/watch?v=YfeFNirfaEg

Nice, isn't it ??

Daniel

[dynaco_dan]

Hi again;

I love this computer technology.

This video saves more than a thousand words. YEH!

I heard the buzz in your woofer.

Have you already done the re-foam?

It appears that you have in the video.

I did see that you had 3 voice coil paper shims before proceeding with your repair.

Did you do anything to clean out the gap prior to repairing?

It may be possible that the voice coil has been bottomed and is deformed and rubbing in the magnetic gap.

Another possiblity is, the voice coil has bubbles formed or the voice coil is detached from the form.

I would wait for others to advise you, it appears that you may need to remove the cone and inspect the voice coil form.

This is another procedure that you will need to follow some technical advice to do that job without any problems.

Please wait for further help.

[Guest Danlaet]

Yes, I've done the re-foam.

I had 3 shims sold whith the foam kit (they are invisible on the photo, but are in place), plus 3 paper hand made ones.

I didn't do anything to clean out the gap. Don't know what to do and don't want to worsen the things.

" It may be possible that the voice coil has been bottomed and is deformed and rubbing in the magnetic gap.

Another possiblity is, the voice coil has bubbles formed or the voice coil is detached from the form. "

Yes, I think so. But don't know if I'll know do the work (remove the cone). I noticed there are 3 (new) nuts behind the magnet, but don't know if it's possible to remove them whitout risk.

Pffffff !.....

Daniel

[tysontom]

>I didn't do anything to clean out the gap. Don't know what to

>do and don't want to worsen the things.

>

Daniel, there shouldn't be a problem with anything in the gap unless you got metal filings or steel-wool dust or something in there. Paper in the gap will fall down inside the magnet area and do no harm. Shimming the cone is unnecessary and usually not recommended, but since you have already done that, you should be okay from that standpoint. The dust cover should be replaced, which isn't shown in the video you provided.

>" It may be possible that the voice coil has been

>bottomed and is deformed and rubbing in the magnetic gap.

>

The voice coil on the alnico woofer (AR-1, AR-1W, AR-3, early AR-3a) does not "bottom," as such, since the back plate is much further back in the assembly. The cone, where it attaches to the voice coil area, can come in contact with the "top" plate, making a loud "blat" sound, and this can break the bond if driven hard enough. This will result in raucus distortion, very noticeable. This could be part of the problem, but I would almost bet money that the problem with your woofer is the masonite ring to which the *spider* (inner suspension) is attached. This inner ring frequently becomes unglued from the cast-aluminum frame. It will vibrate much like your YouTube demonstration, but remember that the microphones in camcorders -- unless you have one of the pro-level Sonys, Panasonics or Canons -- cannot reproduce any bass much below 50-60 Hz. Anything below that comes across as a rattling, feeble sound. Mega-dollar pro camcorders usually have wide-bandwidth ribbon microphones with appropriate amplification, and can reproduce deep bass without much distortion.

Anyway, you can verify the loose skiver attachment by (1) removing the woofer once again, (2) removing or slitting part of the nylon protective screen and (3) going along the edge of the ring with a knife or screwdriver to see if it is loose. If loose, it will rattle up and down with long excursions, making a rattling sound.

>Another possiblity is, the voice coil has bubbles formed or

>the voice coil is detached from the form. "

>

If the voice coil has bubbles, it would have become very hot and likely melted the varnish on the bell wire used for the voice coil, thus shorting some of the coils. In such a case, the resistance of the coil will change dramatically. You can measure the resistance to see if your woofer to see where it falls.

--Tom Tyson

[Guest Danlaet]

" you can verify the loose skiver attachment "

Do you mean the spider ? Because I just took a look and yes, it's completely unglued !!!! My little screwdriver passed under it whithout any resistance !! I will try to glue it !

I tell you soon !!

Ps : I forgot something : meter tell me 3.8 ohms.

[Guest Danlaet]

I removed the nylon, the spi_der is half not glued (?). How can I glue it again ?

[tysontom]

>I removed the nylon, the spi_der is half not glued (?). How

>can I glue it again ?

Ah, I'm relieved! Now is the time you should use the shims again to be sure the voice coil stays centered. You can then use something like 2-part epoxy glue to do the job, but be careful: if you clamp it to not let it slip around. You could also use something like "Goop" glue, a really versatile all-around glue. It dries quickly and is tenacious, and you may be able to hold it down with your fingers long enough for it to "form up." If the spider is loose only on part of it, do *not* pry up the remaining portion; leave it attached, but add glue to the part that has become loose. You could put a bead of the glue around the outside edge of the masonite ring that is still attached, to help prevent it from popping loose, but probably it never will once you get the loose part repaired.

You can do it; let us know how it works when you finish.

--Tom Tyson

[tysontom]

>" you can verify the loose skiver attachment "

>Do you mean the spider ? Because I just took a look and yes,

>it's completely unglued !!!! My little screwdriver passed

>under it whithout any resistance !! I will try to glue it !

>

>I tell you soon !!

>

>

>Ps : I forgot something : meter tell me 3.8 ohms.

>

Yes, I definitely meant "loose spider." The resistance seems normal, so I doubt that you have a voice-coil problem. That coil is pretty robust, and the former is bronze, so heat is dissipated well.

--Tom Tyson

[Guest Danlaet]

YES : that works. Not perfectly, but a million times better. I think I have now to do the second half, to consolidate it.

I will tell you more tomorrow, and don't be worry, I have other questions to ask you !!

Thanks for your kindness, it's a really nice forum !!

Daniel

[Guest Danlaet]

Bad new for me : in definitive it makes always the buzz. However not absolutely the same way, but it makes it.

[Guest Danlaet]

I have removed everything. There seem to have rubbing traces in the inner cylinder.

http://www.classicspeakerpages.net/dc/user_files/2447.jpg

The coil seem to be ok.

[Guest Danlaet]

It finally seem to be a centrage problem that comes only sometimes, depending on the force experienced by the surround.

I will try to be clearer as possible : the foam surround that comes in replacement of the original one have not exactly the size required to exactly correspond at the "wood circle" on which it must be glued.

So the roll doesn't come exactly where it must do.

Difficult to explain...

So, where to find perfect surround for AR3 woofers ??

Daniel

[Guest Danlaet]

In fact, the replacement foam surrounds just have too small rolls.