Focal Tweeter Repair

[Kindhornman]

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.

[Kindhornman]

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.

[Russellc]

Originally Posted by bear

Department of free and unsolicited advice:

To make these tweeters sound MUCH better:

- run with a small series inductor, set so that the inflection point is just above ~10kHz. This flattens the slightly rising response of the tweeter and makes it sound *much* nicer

- add ferrofluid to the gap. You need the *right* ferrofluid, the stuff for woofers is NG. This does not drop the high end! In fact it extends the high end, and lowers the IMD and THD by an audible amount.

Now that these tweeters are somewhat passe I don't mind spilling the beans. Please credit me if this gets used and dredged up at some future time - please don't claim it. Not that it's that important.

(Dave Wilson - don't you dare claim this.)

_-_-bear

having some of these tweets around, could you please comment further on this measurement procedure and ferofluid installation? Much appreciated!

Russellc

[bear]

Originally Posted by Russellc

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.

[zepolo]

Originally Posted by JMFahey

Interesting.
You say the dome "floats", its edge is not glued to the front plate (or a rigid ring attached to it) but is held in its position only by a foam ring and nothing else?
I'd love to see that.
Since you pulled the dome , would you please be so kind as to post a couple of pictures, both from the front and from the back?
Thanks.

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

[rgrickerson]

Hi Guys,
I have enjoyed reading all the posts on the T120-TI.
For anyone that is unhappy with the sound of these tweeters I will be pleased to take them off your hands for working units in good condition.
I will be happy to pay the postage and give $30.00 each for them.

Just let me know.

RG

[rgrickerson]

Any Focal T120's for sale?

rgrickerson

[Panelhead]

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