Bear,
In a gap like that with a short focused gap and equal length voicecoil you would hardly notice the ferrofluid, it would be stuck in the gap on the surfaces and you would have to put something that would show the stain from the liquid to know it was there. The problem with just putting ferrofluid in most gaps is that unless the magnetic assembly is vented correctly the ferrofluid is usually pushed out of the gap over time. It could end up on the outside or down below the gap. And as you say matching the fluid viscosity to the device is another problem in itself.
In a gap like that with a short focused gap and equal length voicecoil you would hardly notice the ferrofluid, it would be stuck in the gap on the surfaces and you would have to put something that would show the stain from the liquid to know it was there. The problem with just putting ferrofluid in most gaps is that unless the magnetic assembly is vented correctly the ferrofluid is usually pushed out of the gap over time. It could end up on the outside or down below the gap. And as you say matching the fluid viscosity to the device is another problem in itself.
I took a closer look at the Focal diaphragm assembly and I now see that they in fact bonded the foam to the underside of the rubber surround. They also put some tar like substance on the center pole piece I assume to dampen the rear reflective wave. It is still soft and gooey after many years of sitting, it could just be some type of tar, very thin coating. Looking at the front plate I now notice how thin it is, can't be much more than 3mm thickness, wonder about saturation on that piece of steel, perhaps 1/2 the thickness of the back plate.
having some of these tweets around, could you please comment further on this measurement procedure and ferofluid installation? Much appreciated!
Russellc
Ferrofluid is "self installing"!
Quite magical... you just put drop down (for a tweeter it is very little stuff) and it magically finds it's own position around the gap! With a Qtip you can remove any overage...
Kindhornman, I know the ferrofluid could be pushed out, if there is a good seal on one side and not the other and enough pressure. But on the Focals that I did, it has remained in the gap for many many years... even if it migrates slightly, the flux tends to pull it right back. If it gets blown out and atomized more or less, then NG for sure.
The effect was well worth it. Quite surprising, as I expected a *reduction* in the HF extension, but got extension instead!
Focal apparently has modified their design and construction approach over the years. Back when I did this, there was nothing much holding the front plate on the T120 series or the T90 other than the screws. I don't recall double stick tape or any adhesives. I merely centered the VC and lowered it carefully. Then put a random recording mic and preamp hanging about 6-12" above the center and monitored probably a ~2-3khz tone at not too loud a volume - watching the scope for best sinewave and max amplitude. Carefully tightening the allen socket screws slowly around the circle making sure the faceplate did not "walk" as the screws went in - watch the scope for that.
Btw, I doubt the pole piece plate saturates, since it is beveled in to form a wedge shape as it meets the VC... to focus the gap and meet the VC height... so it is thinner there than coming off the magnet. Ain't much space there since the VC height is minimal.
Hello All
I would just suggest you have a look on this thread ...
Le forum Audio Vintage • Afficher le sujet - tweeter focal TC120 remenbraner
It's in French but pictures are rather explicit. By the way, it's quite easy to center the coil with a wobulator and - yes - just the srews !
Hope it can help
None very cheap
The TC120TD5 is still available NOS. I think this is the last version made. Some think it is the worst sounding and the TC120K the best.
At least in my setup I think the 120TD5 sounds better. But I am comparing a "new" set of drivers to some TC120K with deteriorated foam surrounds. That is why I spent the money to get the new ones from Zalytron.
BTW, I have read about using a series inductor to smooth the highs and maybe damp resonance. What is good starting value, 1 uH or larger?
George
The TC120TD5 is still available NOS. I think this is the last version made. Some think it is the worst sounding and the TC120K the best.
At least in my setup I think the 120TD5 sounds better. But I am comparing a "new" set of drivers to some TC120K with deteriorated foam surrounds. That is why I spent the money to get the new ones from Zalytron.
BTW, I have read about using a series inductor to smooth the highs and maybe damp resonance. What is good starting value, 1 uH or larger?
George
There are foam surrounds for these Focal T120/T121 tweeters...
With original thickness and sizes.
Best regards, Fred
An externally hosted image should be here but it was not working when we last tested it.
With original thickness and sizes.
Best regards, Fred
Just another question re; Focal tweeters.
I have a pair of Ti90's. They are over 20yrs old and the rubber surrounds have lifted off the plastic face plate. They achieved this all by themselves! They have never been used and it must be just time, temperature extremes and humidity (periods of sub-zero for the first 5yrs and sub-tropical where I have lived for the last 17.). I am now in a position to use them and would like to repair them...........any thoughts re adhesive etc?
Just re-read the thread and mine are DEFINITELY the rubber surrounds referred to by Bear in #15.
Cheers, Jonathan
I have a pair of Ti90's. They are over 20yrs old and the rubber surrounds have lifted off the plastic face plate. They achieved this all by themselves! They have never been used and it must be just time, temperature extremes and humidity (periods of sub-zero for the first 5yrs and sub-tropical where I have lived for the last 17.). I am now in a position to use them and would like to repair them...........any thoughts re adhesive etc?
Just re-read the thread and mine are DEFINITELY the rubber surrounds referred to by Bear in #15.
Cheers, Jonathan
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Maybe an idea:
2"FO Sizes:
±42,5mm. Outer diameter
±27mm. Inner diamter
±1,5mm. thickness
Best regards, Fred
An externally hosted image should be here but it was not working when we last tested it.
2"FO Sizes:
±42,5mm. Outer diameter
±27mm. Inner diamter
±1,5mm. thickness
Best regards, Fred
Dear Jonathan,
Most glues suppliers sell are a kind of PVA-glue, hobby-glue and wood-glue belong to these series. However hobby-glue often stays flexible, wood-glue not (and shrinks a lot). I have tested some other glues. I took the glue that was the strongest (stronger than foam), and stays the most flexible / dries up clear. It's not available in a normal shop. But.... I have to say that people often use PVA hobby-glue with success. It's water based, and can often be made some thinner by put a drop water to it. I prefer some thick glue, because you can make the water based glue thinner, but not thicker
. Best regards, Fred
Which companies provide the wanted results after replace the surround.
I have look on the video from this supplier:
https://www.repairyourspeakers.com/...-reparatursatz-schaumst-ringe/a-1900-20000045
Fo find the right position for the center point of the cone incl. voice coil the user from the video don't use any equipment for measuring to check out the thiele-small parameter:
On Wilson Audio's tweeter (also from Focal) there is an additional carrier part (as usual with re-cone kits) to get automatically the correct center position:
An ebay member recommend for Focal tweeter this company in Poland for this surround replacement procedure - as long the voice coil isn't burning:
https://acoustic-24.pl
P.S.: several information to Focal's tweeter:
https://forums.melaudia.net/showthread.php?tid=6978
P.S-II.: this forum don't goes open in the meantime:
https://webcache.googleusercontent.com/search?q=cache:Ss8OTuSsAC8J:https://www.audiovintage.fr/leforum/viewtopic.php?t=8541&start=50&hl=de&gl=de&client=opera
maybe one of the members here are also member there.
I have look on the video from this supplier:
https://www.repairyourspeakers.com/...-reparatursatz-schaumst-ringe/a-1900-20000045
Fo find the right position for the center point of the cone incl. voice coil the user from the video don't use any equipment for measuring to check out the thiele-small parameter:
https://acoustic-24.pl
P.S.: several information to Focal's tweeter:
https://forums.melaudia.net/showthread.php?tid=6978
P.S-II.: this forum don't goes open in the meantime:
https://webcache.googleusercontent.com/search?q=cache:Ss8OTuSsAC8J:https://www.audiovintage.fr/leforum/viewtopic.php?t=8541&start=50&hl=de&gl=de&client=opera
maybe one of the members here are also member there.
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