035Ti Tweeter Repair

[Drugolf]

I am working on restoring my L80T speakers and one sounds a bit weaker than the other in the highs. I swap the 035Ti tweeters and sure enough it follows the tweeter. I measure 4.0 ohm on the weak one and 4.5 on the other. Is this evidence enough of a bad tweeter? The magnet is loose on it as well and can pivot when pushed.

I this repairable or do replace it? There is a functional one available but it has a dented dome and no cage. Could I use my bad one to replace those aspects? (In other words, can the domes on these be changed out?)

Thanks!

[kelossus]

If the magnet is loose it sounds like that could be the cause of the issue.

If you can get the replacement tweeter with the dented dome for cheap enough that might be a viable option.

Once you remove the tweeter cage and the 4 screws underneath, the plastic face of the tweeter containing the diaphragm comes off. If you are going to all this trouble you might wanna replace the piece of dampening foam underneath the dome and clean the voice coil gap as sometimes the degraded foam can fall inside. I would replace the foam in both tweeters.

[Ed Kreamer]

Hi Drugolf,

If you do this be very careful when you remove the magnet from the diaphragm, as it is very easy to sever the speaker leads I know because I've done it.

[kelossus]

Hi Drugolf,

If you do this be very careful when you remove the magnet from the diaphragm, as it is very easy to sever the speaker leads I know because I've done it.

Good point, this is something to be careful of. Also they are grooves in the back of plastic face to accommodate the lead wires. Make sure you line this up when assembling again.

[Drugolf]

I did get the tweeter with the dented dome. Where can I get the dampening foam?

[kelossus]

I did get the tweeter with the dented dome. Where can I get the dampening foam?

Hi Mate

As per a thread I read ages ago its best to use soft open cell foam. You will have to improvise as there is no genuine replacement.

Best to buy a sheet of it and cut the foam plugs to size.

[Earl K]

I did get the tweeter with the dented dome. Where can I get the dampening foam?

The "damping foam" is there to stop spurious sounds from being created by the titanium dome .

As such, it needs to lightly touch the dome ( from inside the dome ) .

The foam deteriorates with age & turns into a crumbly mess / eventually pulling away from the dome ( & no longer fulfilling its original design function ).
- The foam "crumble" can also get into the voice-coil gap, causing ugly distortion type problems .


The ( now ) under damped titanium will become brighter, a bit louder ( if the foams not in the gap ) & a bit more brittle sounding ( to those with well developed listening powers ) .

You need to remove the diaphragm ( try googling for directions ) , & then remove all traces of the foam ( including any bits found within the magnetic gap ), & then fit the unit with a new piece of acoustic foam ( use some glue to hold the foam plug in place / it goes without saying , you'll need to find some foam glue / 3M stuff works well ) .

Here's a thread that you need to read .

[Drugolf]

Fantastic! Thanks Earl.

[Drugolf]

I have taken apart the weak tweeter and this is what I have. The gap is not even. I assume these are 2 magnets?


The foam isn't too bad but starting to get a little dry.
the replacement tweeter with the dented dome and no cage sounds good so I want to use parts from this one I guess. in the least I can use the cage only. What is teh process for taking this one apart to get to just the dome? Or should I try just using the entire portion shown in the first photo with the magnets of the other?

[NickH]

Looks like you've got a shifted magnet.

[4343]

Looks like you've got a shifted magnet.

Yep.

I was able to repair one like that using some copper sheet cut into strips and formed to the circle. I put one strip int the wider side of the gap, then slid the pieces till I pinched it in, which allowed another strip to go in. Repeat till the gap is even, then epoxy the pieces together.

In this case, with a good magnet, you may be able to transfer the undented dome into it, assuming the voice coil was not deformed by the shifted magnet.

It is also possible that the dented dome will press out well enough to work, although hat is unlikely. Ti tends to break...

[Drugolf]

Mike, your strategy to realign the magnets sounds like a great plan. I will try that and hopefully end up with a nice even gap all the way around. Do you just put some epoxy around the outer edges of the smaller top magnet so it does not move?

You can see the voice coil in the first photo and it does not appear to be pinched or damaged, but I guess I wont know until I try it. Will a multimeter measurement tell me anything once it is back together?

[Wagner]

I have successfully realigned the magnets on separated tweeters like yours using a "carefully selected" and sanded down plastic medicine bottle (pill bottle) as a 360 degree "shim" and machine crews from the hardware store to align the assembly mounting holes (fortunately on the Peerless tweeters I have most recently repaired these passed all the way through both plates)

Difficult to hold everything where it needs to be, align those (screw) holes precisely AND easy not make a glue mess once those metal pieces come close! You want to have a nice straight "set down" the first time and avoid having to twist the assembly once the film of adhesive makes it's initial contact

Even if the screw holes don't continue into the back plate (easiest, and would possibly even negate the need for a shim) you still use bolts (machine screws) through the center section that does have through holes, in order to give you a controlled descent into the film of waiting adhesive and not a quick grab; your shim keeping things lined up obviously

If the JBL tweeter you are working on has holes in the slab which stop mid section then I would definitely encourage you to find something like the pill bottle that would afford you 360 degree control; those two pieces will pull like crazy once anywhere near one another! You will not get it done cleanly bare handed unless you've got some amazing hands!

From what I can tell from your photos, you are GOOD to go using the controlled descent method (machine screws)

I would suggest a dry run/fit BEFORE you whip out the glue!

For adhesion I used this:
http://www.bsi-inc.com/hobby/ic_gel.html

Although this product gets a "best" mark for metals on their little chart:
http://www.bsi-inc.com/hobby/slow_cure.html

Both are fine products and bond metal well; I went with the cyanoacrylate as it afforded me greater control and the bonded surfaces were aided by the magnetism (squeezes out 99% of whet you put in there anyway)

[Drugolf]

So someone please educate me. Are both metal plates magnets? Is there any special orientation to "aligning" the two other than getting the gap even? There are the holes for the screws but I cant tell if they are supposed to line up with anything.

[grumpy]

Just the dark gray ceramic/ferrite (flat donut) bit between the shiny parts. Even the donut hole is not a permanent magnet. The steel parts help get the magnetic flux lines concentrated where they need to be (in that gap you want to be concentric)