Old Ferrofluid, new tweeter?

My wonderful Hyperion HPS-938 speakers are almost 12 years old and perhaps would benefit from ferrofluid replacement.  It applies to both midrange and the tweeter.  Midrange uses ferrofluid for damping and doesn't have spider suspension.  It would be easy to remove it from the basket, but tweeter might be a problem.  It is inexpensive looking 1" soft dome snapped into short horn.  It was likely designed that way to reduce distortions (reduce required power) or to vertically align all speakers.


Membrane edge and wires are under glue and would be hard to remove and re-glue (risk of damage).  Xover is potted in the black epoxy, but I can see 2.5 ohm large white square resistor near tweeter wires.  That's possibly L-pad attenuator (whole speaker is rated 90dB sensitivity).   I've never removed membrane in any speaker, so I can find somebody who does it, or replace whole tweeter.  Morel makes short horn CAT 378 that has identical dimensions and great reviews.  I can measure voice coil inductance at 1kHz, DC resistance, impedance at 1kHz etc.  It is 3-way with 2.2 kHz crossover point - way above CAT 378 resonance (1kHz).  I have calibrated microphone to compare output at different frequencies.  Morel is 93dB sensitive, but if it is a little bit more I don't mind.  The whole point is to make it a little bit more vivid.  Speakers were always soft/warm sounding with great integration between tweeter and midrange, but now I would like a little more highs.  It might be dry ferrofluid, but it might be my hearing as well.   Advantage of CAT 378 is that voice coil is easily removable (3 screws) without even unsoldering and also spare coils are available.  Below is picture of Morel tweeter.  What do you think?


(I cannot get any help from Hyperion - they don't exist anymore)
A4cbbf0f e24a 481b bac9 8318cf2147eekijanki
Modern ferrofluid will likely remain stable for longer than 12 years.

If you can access the voice coil, it will be easy to assess whether the fluid has dried out. 
helomech, Most likely it is not completely dry or very thick, but just dried a little - changed viscosity.   Parts Express sells ferrofluid that is Ferrotec APGL11 - good for both tweeter and midrange, but they sell different fluids with different viscosities.  Is there a way of judging viscosity of the fluid inside of the magnet by eyeballing?

Hi @kijanki 

I have some 938s and noticed one of the tweeters in a touch lower in volume than the other.

I was wondering how you went with your fluid/tweeter replacement?

Thank you

For the tweeter doing a good cleaning is usually a good idea.  Requires being able to remove the dome though.  The old ferrofluid would gunk up on the coil, changing the mass and increasing friction.

Erik - I think that is already well known. It'd be nice to hear how @kijanki went, if he was able to get to the coil or had to replce the entire tweeter and learned any 'gotchas' along the way.

Hyperions are not well known for their repairability.