What to do about this?

[lasse]

Hello,



I finally have come around to use my DATS impedance tool on some of my drivers.



Now, I thought that I had a small fortune in the workshop, consisting of three Dynaudio D28AF tweeters but their impedance curves are like the one attached.



Are my drivers repairable, perhaps by replacing the magnetic fluid inside of them, or are they ready for the garbage bin?



Regards//lasse

Stockholm, Sweden

[Chris Roemer]

Do they make "sound"?
Is your DATS working (do a Z-sweep on your last project)?
They look like a very small value inductor...

[1100xxben]

The resonant spike comes from mechanical resonance, which these do not appear to have. As Chris said, they measure like small inductors, which means the coil is likely intact but the cone is not moving. If they have (maybe had) ferrofluid, maybe the fluid has dried out and left all the solids, effectively gluing the coil in place. Assuming those are service-able, you could open one up, gently, and have a look-see.

[lasse]

Hi,

The attached DATS-scan of one of my AUDAX domes was taken at the same time so the system seems to work.



Does anyone know how bad ferrofluid show up in a impedance measurement?

[lasse]

The resonant spike comes from mechanical resonance, which these do not appear to have. As Chris said, they measure like small inductors, which means the coil is likely intact but the cone is not moving. If they have (maybe had) ferrofluid, maybe the fluid has dried out and left all the solids, effectively gluing the coil in place. Assuming those are service-able, you could open one up, gently, and have a look-see.

Hi,

yes a "autopsy" is probably the next logical move….

Regards//lasse

[billfitzmaurice]

Your images are very hard to see. Try changing the Application Look to Light in the DATS View menu.

[badman]

I'm not a big fan of ferrofluid, but when you remove it, you have a different tweeter. I agree that the coil's likely frozen. Time for careful dissection and cleaning, but you definitely need to measure thoroughly thereafter. The stock response will change, particularly at the extremes of response (1khz, 12khz)

[lasse]

I'm not a big fan of ferrofluid, but when you remove it, you have a different tweeter. I agree that the coil's likely frozen. Time for careful dissection and cleaning, but you definitely need to measure thoroughly thereafter. The stock response will change, particularly at the extremes of response (1khz, 12khz)

But isn´t it possible to pour in new ferrofluid?

[devnull]

But isn´t it possible to pour in new ferrofluid?

Yup. Parts Express sells a general purpose replacement. The stuff that's sold for science experiments will not work.

[AEIOU]

But isn´t it possible to pour in new ferrofluid?

You have to clean out the old ferrofluid first, then you can add fresh ferrofluid. I have plenty of experience with adding ferrofluid to tweeters.

[lasse]

OK,

last question from me on this subject:

Has anyone replaced the ferrofluid on a Dynaudio tweeter with good results?

Regards//lasse

[Chris Roemer]

So... your DATS is working fine.

DO they make ANY sound? 'cause (as was said) if they can't move, they won't have a resonance.
If they HAD FF, it seems to have evaporated leaving the solids to glue everything up !

[lasse]

So... your DATS is working fine.

DO they make ANY sound? 'cause (as was said) if they can't move, they won't have a resonance.
If they HAD FF, it seems to have evaporated leaving the solids to glue everything up !

So, in theory, the same "symptome" (=no resonance peak) could be seen after a over-heat situation with a damaged coil?

Regards//lasse

[1100xxben]

So, in theory, the same "symptome" (=no resonance peak) could be seen after a over-heat situation with a damaged coil?

Regards//lasse

Most likely, an overheat that actually damaged the coil would result in an open circuit.

[lasse]

Is the more probable failure-mode for tweeters to have an open circuit than a overheated and misaligned/stuck voicecoil?