Ferrite 604 high FS HF diaphragm?

[GM]

In preparation to post my 604's for sale, I've DATS tested the 'free air parameters' (*with loading cap, on the matnray horn) of both HF sections.
One looks normal (fs ~410hz), the other comes in at fs=1420hz!
Re and Le are comparatively the same.

Looking at the impedance plots, they track similarly in both areas:​
broad peak around 400hz
sharp peak around 1450 hz

...so not sure why DATS has decided the blue one has such a high fs. Am I looking at a diaphragm problem, or is DATS wacky?

I figured the 1500hz was the horn loading up (?).

pic attached fingers x'd

What broad peak around 400 Hz? If you mean ~1400 Hz, it's the driver's sealed box tuning frequency [Fc] after being loaded by the horn, i.e. should be higher with no horn.

The 410 Hz isn't 'normal': look at its nonsensical Qm, Qe, Qt specs while the other looks typical for this app.

Considering the high pressure the loading cap puts on the diaphragm when coupled to a horn combined with a lower impedance peak it could be a spec of dust/whatever keeping the cap from completely sealing or more likely a pinhole crack in one of the surround's sharp bends like I've super glued a number of on my late/great ultralites and since they tend to be tiny and close up when not in motion can be a pain to find if you don't have a regulated air supply, though I guess the spray cans sold nowadays to clean electronics can work if you don't shake like I do.

All I can think of ATM, good luck!

GM

[gearfreak]

Thanks to you both for the input.

What broad peak around 400 Hz? ... The 410 Hz isn't 'normal' ...
GM

Yes, 'small hill' would put it better I suppose.

Ahah! So I had it backwards. Ok, now that gives me an idea to go try out. Thanks!

[gearfreak]

Well, I though may have rotated the gaskets in an undersirable way, but no that's not the case.

To answer Louder's question - they've always sounded fine to me, I've never checked them in this way until now.

... if you don't have a regulated air supply...GM

So, how would I use the air supply to hunt for it? Is the idea to shoot it at the diaphragm, pushing it out, whilst looking closely at the surround pleats? (perhaps augmented by shining a light from behind it?)

If the point is to get the pleats 'stretched' in one direction, I could do the same with low voltage DC while it sits in the gap on the driver - unless that'd be detrimental?

[Earl K]

Well, I though may have rotated the gaskets in an undersirable way, but no that's not the case.

To answer Louder's question - they've always sounded fine to me, I've never checked them in this way until now.



So, how would I use the air supply to hunt for it? Is the idea to shoot it at the diaphragm, pushing it out, whilst looking closely at the surround pleats? (perhaps augmented by shining a light from behind it?)

If the point is to get the pleats 'stretched' in one direction, I could do the same with low voltage DC while it sits in the gap on the driver - unless that'd be detrimental?

Wow!

You are about to destroy those precious diaphragms.

You don't want to use compressed air to clean out parts of the driver if your diaphragms are still installed ( frankly I'm astounded you could even think that was somehow appropriate ).

[gearfreak]

Wow! ...

oh no, I'd imagined putting them in a panavise or such, but we'll see what GM says about the process first.

Ultimately they're not too precious, they're 26420's (909).

[LOUDER]

I understand what GM is saying about a REGULATED air supply to move the diaphragm but I like your idea better. And if you could
shine some bright led light in the mouth/throat of the horn, I bet you could see the tiny cracks he's talking about. Is the voice coil gap clean ? It doesn't take much. I hope you get this figured out because now it starting to drive me nuts. LOL

[gearfreak]

...Is the voice coil gap clean ? It doesn't take much. I hope you get this figured out because now it starting to drive me nuts. LOL

Thanks and good question. Seemingly 'yes', these are nominally pristine in that regard - that said, I've never had to/bothered to clean the gap(s), so will probably give that a try when next we open them up.

There is some 'birth marking', 'staining' (?) on the milled stainless steel in and out of where the 'phragm mates to it. Oxidized fingerprints from the original tech? Dunno.
In any case, despite these marks, I can't feel them when I run my fingers over them, so never bothered to attempt to clean anything. I could try some polishing compound, tape off the gap etc first, but to date have preferred to leave them 'factory' One mark is the reverse of the phragm's QC stamp's ink. The other 'interior' marks may be from the other stamps, but same/similar marks exist outside as well, e.g. on the milled edges down by the woofer, so not the result of ink transfer/leaching there.

will try to get a pic up shortly, and to decode what format would allow highest res here.

[GM]

So, how would I use the air supply to hunt for it? Is the idea to shoot it at the diaphragm, pushing it out, whilst looking closely at the surround pleats? (perhaps augmented by shining a light from behind it?)

If the point is to get the pleats 'stretched' in one direction, I could do the same with low voltage DC while it sits in the gap on the driver - unless that'd be detrimental?

Right, I've used an airbrush [touch-up gun for large drivers] with a rag wrapped around it to plug it into the driver throat. Between the main line regulator/filter/water trap to set max pressure and mini regulator/filter/water trap it I've had no problems I'm aware of.

While the drivers easily handle a 9V Dc 'hit' to find acoustic polarity, I doubt it can handle hardly any continuously, so with such tiny wire I'll leave that test to others.

GM

[gearfreak]

Thanks GM. The air approach probably would let you feel for the flaw as well. It'd be a little ungainly with the duplex structure, and the bug screen so close in the short mantaray 'throat'.

I was thinking 1.5v...

but first I think I will just pull it out and see what can be gleaned with a strong flashlight.

[gearfreak]

So if the image loads at proper res, despite the severe JPG compression required to get below 97.5 kb...
(The terminal you see is on the diaphragm).

Your task is to spot the flaw responsible.

Of course those who know what they are looking at will probably be able to make the correct educated guess. :-)

- - - Updated - - -

* and (second pic) I did look with a strong flashlight. Did not find anything of course.

...but for some reason, I have a sudden urge to pile all my mashed potatoes into a mound in the middle of the table. hmm.