435BE vs 2435HPL

[pos]

Sorry to refresh this old thread.

I just received two 2435HPL from an ebay auction, and I decieded to open them to check if they diphragms were correct.

As I understood it, if I simply open them but do not remove the diaphragm then I should be safe: no need to clean the gap or refill ferrofluid.

So I just removed the 4 bolts and gently pull the backcap.
I was surpised to see that the diaphragm is fixed to the backcap. I though it would be like the old 1" drivers. What I had was two independant parts.
So I don't understand the second photo in the first post of this thread, because it seems to show a diaphragm fixed to the front of the driver, the backcap being removed?
Have I done something wrong?
I also don't really understand were the ferrofluid is supposed to lay.

Could somebody explain this?

EDIT: and yes, the diaphragms were beryllium

[Robh3606]

That's how those drivers come apart. The screws hold down both the diaphram ring and the cover. There is a pair of spring clips that make the electrical contact between the diaphram contacts and the outside terminals. The tension of the clips is on the high side so when you open the driver it lifts the diaphram out of the gap.

Rob

[pos]

Ok I understand
So I would have to remove the 5th bolt to actually separate the diaphragm from the backcap.

So I guess I have opened it the wrong way, And now I should clean the gap (I haven't seen any ferrofluid by the way) ?
Also, am I supposed to play some tones while tightening the bolts, to make sure the coil is not rubbing in the gap now?

[Robh3606]

There is no 5th bolt.

You can easilly pry out the diaphram from the back cap.

Don't do a thing if it's operating OK. I would run a sweep to make sure the diaphrams back in place.

You won't see the Ferro Fluid. It's viscous and stays mostly in the gap when the diaphram is removed. The charge is only 100ul so it's not alot by any means. You may see a dark brown line at the bottom edge of the coil. That's the fluid base of the ferro.

This is what you get when you open one up. The diaphram in the cover. You can use the allen wrench to gently pry it out of the cover. When it all goes back together you use the key notch to line up the spring clips so you have the correct orientation with the slots in the gap so the voice coil doesn't bind in the gap. You can see the Ferro Fluid on the bottom of the coil.

Rob

[Zilch]

I posit that the purpose of the ferrofluid (high viscosity, small charge) is to create a seal between the front and rear of the diaphragm, i.e., to perfect the compression chamber between the diaphragm and phase plug.

I've never studied the construction in detail. Does that make sense?

[Robh3606]

I've never studied the construction in detail. Does that make sense?

Hello Zilch

Yes, but I think it's both for a 2435. Figure heat is a killer and anything to get rid of it is good. That Ferro is high viscosity at room temperature might change when it's hot. Here are some phase plug shots.

Rob

[Mr. Widget]

Hi Rob,

Thanks for that thorough exploration/explanation... I'll add that even though the 435Be back cap is much larger it clamps onto the diaphragm in the same manner.

I have never seen one of these phase plugs sans their protective wire mesh. Is that a damaged phase plug or are the chips along the razor thin edges "normal"?


Widget

[Earl K]

Zilch,

I posit that the purpose of the ferrofluid (high viscosity, small charge) is to create a seal between the front and rear of the diaphragm, i.e., to perfect the compression chamber between the diaphragm and phase plug.

- You're describing a partially vented voice-coil gap ( exiting into the phase plug ) which has been patented by JBL .

- I thought only JBLs' most recent, 4" diaphragmed drivers used this newer phase plug topology ( just an assumption ) .
- Can you see light in the gap when it's shone into the phase plug on these 3" dia. drivers / or / can you poke a thin wire all the way through ?






JBL Patent, as a pdf

PATENT # 5117462 at Google

[4313B]

Doug mentioned that he used the ferrofluid to get rid of a response anomally. Both he and Greg have said to either use the correct 100 ul or none at all. Some of these 2435's I've been going through were way overloaded with the stuff. Some had the double stick tape creep, perhaps due to heat, which forced me to carefully remove any that was directly touching the diaphragm.

They really are pretty decent little units.

They look absolutely rediculous bolted onto the H4338 or H9800 horns. Something like a 2441 might look alot better.

They sound really good though so whatever...

[pos]

They look absolutely rediculous bolted onto the H4338 or H9800 horns. Something like a 2441 might look alot better.

Do you think this is the reason the larger back cap of the 435?

Widget, Zilch, have you carried on new tests regarding distortion of the 2435 ?

In your last published tests the 2435 showed very high third harmonic distortion compared to the 435be, and also greater than the 2431 :
http://audioheritage.org/vbulletin/showthread.php?t=6050&page=2#28

[Robh3606]

Hello Widget

I would have to say they normally would not be chipped. That driver had the screen all disturbed. Here is what I got my 2435's distortion wise. The red is 2nd and the green is 3rd. The last 2 are composites from the pairs Giskard had to Aquaplas. First is 2nd and last is 3rd. I can wait to get them back to see what happens to the distortion levels after the coating.

Rob

[Robh3606]

Hello Earl

From the cross section it's clear that the 2435 voice coil is not vented into phase plug.

Rob

[pos]

Rob, your mesurements are similars to Widget's ones (distortion raised 30db, blue second, green third)

2435 :


435Be :


Widget and Zilch didn't knwo at that time if the difference was due to a bad driver, but your results seems to confirm that it was normal.

So the three last factors that could explain the superiority of the 435Be are :

• absence of ferrofluid
• aquaplas
• large back cap

I can't wait to see your mesurements when you get back your aquaplased 2435 !

[4313B]

Do you think this is the reason the larger back cap of the 435?

Well it was definitely meant to look like a finished Consumer product. That was a design goal. Same for the 045Be.

So the three last factors that could explain the superiority of the 435Be are :

• absence of ferrofluid
• aquaplas
• large back cap

The 435Be also uses ferrofluid. The aquaplas reduces spurious resonances of the diaphragm material. I've not directly measured the volume of either back cap so I honestly don't know if one is larger than the other. Early comments from JBL suggested that it was larger to allow a lower crossover point, later comments from JBL were that it wasn't.

I think I have seven more 2435's left to do; Maybe if I have time I will post some graphs. I had planned to early on but frankly, the 2435's I had for the "before" snapshot were sufficiently jacked up to negate any meaningful measurements. These 2435's have also varied wildly with the amount of ferrofluid they've containted.

I think both subwoof and RobH were going to provide various information with respect to distortion analysis. It's good to get data from multiple sources.

[Earl K]

Hi

They (2435H ) really are pretty decent little units.

I agree, JBL ( Pro ) really hit a home run when they designed up this series of 3 inchers for their Vertec line .

Doug mentioned that he used the ferrofluid to get rid of a response anomally. Both he and Greg have said to either use the correct 100 ul or none at all. Some of these 2435's I've been going through were way overloaded with the stuff. Some had the double stick tape creep, perhaps due to heat, which forced me to carefully remove any that was directly touching the diaphragm.

Thanks for mentioning the "tape creep" ( it's new information for most of us here ).

- A year ago I bought 8 used 2431H drivers ( now used in SR work ). Most measured noticeably different from each other . They all seemed to have "cooked ferrofluid" splattered about, under the dome.
- I cleaned them up and currently I'm running a few with dry gaps.
- The cleaning, restored 6 maybe 7 back to respectable response curves.
- Perhaps the other(s) have this tape creep that you mention. If not, new diaphragms will be in order / they're inexpensive enough .

So again , thankyou for bringing this information forward .