Speaker rattle caused by small debris hidden somewhere

[slidincharlie (Carlo P)]

I have a vintage C12Q Jensen speaker that used to work just fine.
Now I made some tests using three different Jensen speakers, including this one, in an amp of mine.
All of a sudden the C12Q developed a very clear, definite rattle while playing low- and medium- frequency notes with the guitar. It is definitely a ratller, not a buzz or other kind of noise.
I am almost sure that some small debris (maybe a small tin solder remain) fell inside the speaker somewhere. Actually if I rotate and move the cone around a little bit I can hear the noise of some tiny part rolling somewhere inside the cone.
I have tried to inspect the gap between the basket and the back of the paper cone but I couldn't find anything.
I am very upset because a perfectly working speaker is now unusable due to this silly yet serious problem.
Do you guys have any tip or advice to solve this issue?
EDIT: is there a non-destructive way to disassemble a speaker, or at least to open the dust cap?

[J M Fahey]

Yes, it can be solved.

1) shake it well to make *certain* that it's actually some kind of loose debris jumping around.

2) we have to determine *where* it is.

a) might be between back of cone and frame.
Shake/move/tap speaker , including balled fist, while looking inside the speaker with a *good* light; the all-around crevice where cone edge and frame meet is narrow and dark, debris may easily hide there.
If you see it, you can pull it out with tweezers or a small amount of tape at the end of a skewer stick.

b) might be under the dust cap, inside the voice coil and above the pole piece.
You can cut an inverted V slap in the dustcap piece (which on a vintage one should basically be just a felt disk) , you open that thumbnail sized window and fish the drbris piece, then you reglue the V flap back in place.
The V has the pointed angle towards dustca center and flat side is where it's glued to cone and voice coil top

c) it might be between spider and frame, outside of the voice coil.
Now you can cut a small window in the suspension, not touchingb the edge which is glued to frame, let/vacuum debris out and reglue it.

Both cuts I suggested do not compromise the speaker function or durability.

Plan B: if I had it on my bench, I'd fully unglue spider and speaker edge, and pull the full cone/coil/spider undamaged ,BUT it's slow, boring, takes practice and glue solvents are either pure acetone or toluene/xylene (depending on adhesive used) ... al 3 known brain cell killers, not recommended.

EDIT:
you have 3 places where that debris may be:

Unfortunately frame is not shown, I guess you can imagine it; if not (mentally) draw a lone connecting the blue dot labelled surround to the front plate to which the spider is glued.
a) is the space between back of the cone and frame.
Easy access through 4 large windows cut in the frame, some speakers use loits of narrow slots, the idea is the same.
One common place for debris to hide is where cone edge meets frame , near the blue dot called surround.
b) is the cylindrical space inside the voice coil, its floor is the center cylindrical polepiece, its roof is the dustcap.
c) is the annular space *outside* the voice coil, its floor is the front plate, its roof is the spider, hope now you see it.

Note: you might also have a partially unglued (old glue dries and cracks) dustcap, lightly pry it with a thin knife tip, if there is any space opening between dustcap and cone, that will rattle.

Old glue was nitrocellulose lacqer but you can use a little Loctite *gel* or similar, the normal runny one is too liquid and will be absorbed by paper before it hardens.

[slidincharlie (Carlo P)]

Thanks. I will try again a), then pass to b).
I am not sure that I fully understand point c), will ask more if a) and b) don't work.
What kind of glue should I use to reglue the small windows?

[J M Fahey]

Added speaker image.

[Jazz P Bass]

Rattle on a low bass note?

The coil former is not securely glued to the cone.

If that is the case, then I would get it reconed.


Speaker Diagram - Bing images

[slidincharlie (Carlo P)]

Rattle on a low bass note?
The coil former is not securely glued to the cone.
If that is the case, then I would get it reconed.

Speaker Diagram - Bing images

What makes me think it is debris hidden somewhere is that until the day before the speaker worked just fine. Maybe soldering/unsoldering caused a little dab of solder to fall somewhere...
I played it at low volume during my test, just a few notes. Am I so unlucky that the coil former got unglued all of a sudden during the test?
I will post again after my investigation is complete.

[olddawg]

I've had a similar issue before. Since the alternative was a recone, I removed the dust cover and stuck a shop vac hose over the hole. It was a piece of decades old glue. But... More often than not, a problem like you describe is a damaged voice coil rubbing at low frequency if you can't hear debris moving around.

[J M Fahey]

I also thought about a loose turn or voice coil but:

Actually if I rotate and move the cone around a little bit I can hear the noise of some tiny part rolling somewhere inside the cone.

[slidincharlie (Carlo P)]

Yes, it can be solved.
1) shake it well to make *certain* that it's actually some kind of loose debris jumping around.
2) we have to determine *where* it is.
a) might be between back of cone and frame.
(...)
b) might be under the dust cap, inside the voice coil and above the pole piece.
(...)
c) it might be between spider and frame, outside of the voice coil.
Now you can cut a small window in the suspension, not touchingb the edge which is glued to frame, let/vacuum debris out and reglue it.

I searched in (a) and (b)... nothing.
One more detail: I can hear the rattling noise ONLY if I put the speaker in a specified position and shake it. In other different positions no noise can be heard. It's like if a tiny piece of something is hanging loose somewhere inside the cone, apparently in the central part (but there wasn't anything below the dust cap).
I'm still not sure about (c). Where should I cut a window? Along the external suspension seems useless to me, so...?

[J M Fahey]

What do you call external suspension?
I mean the spider which in my book is quite inside.
I mean cut the small window (to let any small debris come out) about where the blue dot is at the edge of the spider, look at the image I posted.

I assume there is a small piece of something (solder/dried glue are expected) jumping around, imagine a grain of sand or 1/4 of an apple seed; if there is something at the end of sime kind of stump it will NOT come out .

I suggest you drive your unmounted speaker with about 1VAC 50Hz , may use a 6.3VAC winding but with 50/100 ohms in series, experiment with the value, the idea is to have the cone vibrate but not self destroy, and move the speaker in your hand all over the place, point up/down/to the sides/rotate it , what you hear will give you an idea about the debris and where it's located.
Try slightly pressing different points around the cone, put your finger inside the frame, tring to find if something stops it once heard.

One demonstration I often do to customers is to take a perfectly good speaker , put it up on the table, feed it 50Hz and then drop a tiny piece of (cold) solder on the cone, I just clip the end of the solder wiire roll ... it becomes unusable

IF you have any oscillator app or software, sweep the speaker about 1W power, so you'll damage nothing, between 20 and 200 Hz ... this will catch any rattle (loose/unglued coil wires/dust cap/suspension/tinsel wire rattle) in all its ugly splendor ... quite different sounding than some loose "grain of sand" in there.

If some kind of buzz/rattle is clearly audible, record and post it here.

Almost forgot: are we sure it's not voice coil scratch?

Try to *evenly* push cone up/down (speaker facing up) ... any scratching noise?

Lightly thump the cone: clean thump like a drum skin or ugly noise mixed in?

Apply the Enzo whack: with speaker held in the air by one edge, hit the magnet with a balled fist or a rubber mallet if you have one, it should cleanly thump, nothing else.

I guess we are leaving no stone unturned here.

Absolute worst case, we apply


meaning we try to safely unglue cone and spider from frame.

Not for the faint hearted though.

Just in case: can you buy technically pure acetone in Italy?
Or ethyl/amyl ether?

Don't want to get you in trouble with DEA, which lately decided *everything* can be used to "make drugs"

Check with your friendly Industrial Chemist (not the neighbourhood Pharmacy where you buy aspirin)

Worst case we can use regular car paint thinner, but since composition is not standard, YMMV .

[slidincharlie (Carlo P)]

What do you call external suspension?
I mean the spider which in my book is quite inside.

I meant what is called the surround in your drawing. But of course a cut made there will bring to nothing useful.

I mean cut the small window (to let any small debris come out) about where the blue dot is at the edge of the spider, look at the image I posted.

In this speaker it would be very hard to cut a window in the spider suspension, and it would be certainly impossible to repair/reglue. Also, if the debris is really hanging at the end of something (a tiny old glue filament?) it would be very very hard to take it out from there.

I suggest you drive your unmounted speaker with about 1VAC 50Hz , may use a 6.3VAC winding but with 50/100 ohms in series, experiment with the value, the idea is to have the cone vibrate but not self destroy, and move the speaker in your hand all over the place, point up/down/to the sides/rotate it , what you hear will give you an idea about the debris and where it's located.
Try slightly pressing different points around the cone, put your finger inside the frame, tring to find if something stops it once heard.

Do you mean just running a two-wire electric cord from a 6.3VAC source (like the heater filament in a tube amp) to the speaker lugs with one 50/100 ohms in series along one of the wires? (Apologies for my dumb questions, I am not technically trained).

Almost forgot: are we sure it's not voice coil scratch? Try to *evenly* push cone up/down (speaker facing up) ... any scratching noise?

Done: no such scratching noise.

Lightly thump the cone: clean thump like a drum skin or ugly noise mixed in?

Done: sounds clean to me

Apply the Enzo whack: with speaker held in the air by one edge, hit the magnet with a balled fist or a rubber mallet if you have one, it should cleanly thump, nothing else.

Done: sounds clean and metallic, no rattles.

Just in case: can you buy technically pure acetone in Italy? Or ethyl/amyl ether?

Why are you asking? Do I need it in case of total ungluing of cone and spider?

[slidincharlie (Carlo P)]

THIS attached here is the rattling noise inside my speaker. It sounds rather loud because it has been recorded from a very close distance, but that's it:
Rattling noise in speaker.mp3

[olddawg]

Have you lifted or cut into the center voice coil cover as suggested before? Then stucked it with a vaccum cleaner nozzle. It isn't a big deal to reseal it with some thinned contact cement. If you don't like the way it looks afterward a little flat black spray paint will mask the repair, especially behind a grill cloth. Speaker surgery is common with poor musicians used gear stores.

[slidincharlie (Carlo P)]

Have you lifted or cut into the center voice coil cover as suggested before? Then stucked it with a vaccum cleaner nozzle. It isn't a big deal to reseal it with some thinned contact cement. If you don't like the way it looks afterward a little flat black spray paint will mask the repair, especially behind a grill cloth. Speaker surgery is common with poor musicians used gear stores.

Yes I did search under the dust cap - look at the scars in the attached picture . There was nothing inside, I've used a small wooden stick and my pinky to search inside, no vacuum cleaner though.

[Jazz P Bass]

Have you tried it now that the dust cap is off?