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Ohm Walsh F Hope of Resurrection

Now I have F's with rotten surrounds, but rest look nice, perfect even. Cones, spiders look great. 

One surround is done, decimated.  Other is intact, perhaps replacement as is not identical. 

Perhaps I try replacing surround? 
Any new and improved surround options? Willing to replace/ get repaired more, if necessary.  

Cursory search doesn't reveal any drop in replacement.  Or, am I wrong? I see the Ohm return/upgrade to newer version options. 

Experienced and insider opinions sought. I'm not cheap, and I'll spend the money to obtain the exceptional if needed. So, what are the likely and less likely options   TIA
What is that one "clone", HHR? Need to check...  i heard it at a show years ago. 
douglas_schroeder
douglas_schroeder OP
3,281 posts
 
So, one possibility is that it is ferrofluid? This is a very experienced tech, and I think that he would have known that possibility and would have recognized it.

It seems some grease may have been used on these old drivers, perhaps for heat dissipation? It sure does not seem intuitive, especially since the one does not seem to have it.

Looking at the images and discussion of ferrofluid, it appears that may be the substance. Does it get gooey and hard enough with time to lock a driver? 
douglas_schroeder OP
3,281 posts
 
More research... Look at this from this site:
https://ferrofluid.ferrotec.com/products/ferrofluid-audio/audioselect/

Spider removal: Voice Coil Centering With Ferrofluid

The presence of ferrofluid exerts a uniform radial centering force upon the voice coil in the air gap. The magnitude of this force is dependent upon the strength of the permanent magnetic field and saturation magnetization of the ferrofluid. The greater these values, the stronger the centering force. Reduced scrap rates on the production line, reduced field returns and reduced distortion (due to the suppression of radial and rocking modes of the voice coil) are some of the well-known benefits of this centering force.

In recent years, the availability of high saturation magnetization ferrofluids have allowed designers to completely remove the spider, relying on the ferrofluid to center the voice coil in the air gap. This technique not only yields lower cost and a simplified production process; it also removes the well-documented nonlinearities present in all spiders, resulting in lower distortion. In general terms, the saturation magnetization values of ferrofluids used in spiderless designs should not be lower than 33 mT.


I now if the tech used ferrofluid to center the voice coil because of the difficulty of doing so with the Model F driver. Then, because the wrong fluid was used, it got gooey and froze. So, perhaps the incompetence theory is most accurate. 
douglas_schroeder OP
3,281 posts
 
No one has any knowledge or insight about this? If so, that might underscore how unusual the situation. 
pryso
1,956 posts
 
Doug, is the black crap finding now a question for Ohm factory?  Even though they may no longer repair them they may know about the driver.
douglas_schroeder OP
3,281 posts
 
I may ask the Ohm factory about it. I'm grateful that the drivers appear to be in good shape to recondition. 
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