Ohm Walsh F Hope of Resurrection

BLACK CRAP in the coil/magnet gap? HUH?! 

The speakers are at a repair facility; not discussing particulars at this time. 

The tech finds some black goo that is like a tar, that has gummed up the driver to the point it was frozen in the coil. He said he has never seen anything like it with these speakers. I sure had not seen anything like it. It seems so improbably wrong that it makes me wonder if it could have been sabotage (especially since inside the speaker there sat a smaller (wrong sized) spider that had soaked up some sort of oil substance), or perhaps someone so inept that they can't deduce that the part had to move freely or it would seriously compromise the sound. Seriously, who puts black, sticky, gooey crap in the gap? Did some kind of lubricant at one time age so badly that it froze the coil unit it was worked loose again? It seems counter-intuitive to proper treatment of a driver. 

Could it be that there was rubbing of the voice coil after a repair - there is evidence it likely was repaired - and someone sought to cover it up by using a lubricant? Perhaps; I wouldn't put it past some people. That may make sense, given how hard it is to redo these cones. Perhaps someone screwed up, and tried to cover it up, caring less about the longevity of the speaker than not being discovered. Perhaps I have solved my own mystery... 

It's also not as if this would normally fall into the driver, as they are typically inverted, with the coil and magnet structure higher than the spider and cone. 

Has anyone ever encountered such a thing? I am willing to be educated on all this if there is a reason for such things to be done. 

The fabulous news... it has been removed, and it appears the drivers are well on their way to restoration! I was VERY wise to solicit the help of experienced persons on this.  :) 

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? 

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. 

No one has any knowledge or insight about this? If so, that might underscore how unusual the situation. 

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.