Difference between JBL coated diaphragms

[Niklas Nord]

Hi

In some horn -drivers, coated diaphragms are used.

JBL 2450SL used in the DMS-1

Does the coated diaphragms extend as high in frequency
as the non-coated diaphragms ?

Why is the coated diaphragm used in the DMS-1 ?
and not in the PA drivers? What is the advantage
of coated diaphragms..

Would the coated diaphragms used in 2450SL fit
in the 2446, 2451, 2450 drivers? What would be
the main difference between this and the regular
diaphragm?


is this a diaphragm for JBL 2441/2445/2446/2450

http://www.centralfloridaspeaker.com/skit1.jpg

Dont look like the membrane in 2450, no "rib" structure..

In my K2, i think i have the 2450 diaphragm instead of the
coated version used in DMS-1 and s9500

http://pal.pp.se/~nord/K2/K2_04.jpg

Would it be very wrong to use this diaphragm instead
of the K2 original version diaphragm?

The originating owner put it there to gain some more
high frequency ower the coated diapgragm.

is the 475nd the same driver as the 2450 ? etc etc..

[4313B]

Originally posted by Niklas Nord
Would it be very wrong to use this diaphragm instead
of the K2 original version diaphragm?As far as I know, JBL has never officially endorsed swapping drivers, cone kits, diaphragms, network components, etc. in their production systems. Something tells me JBL wouldn't bother dusting a diaphragm for a specific application if that application didn't call for it. I think people keep forgetting that JBL has very specific intent for the various systems they design and manufacture.

[Niklas Nord]

Any thoughts about the high frequency
cotated vs non coated

[4313B]

I'll have to go back over my notes. It's about time I finished my "diaphragm matrix" anyway. I've got to get several other people involved and that could take a little while. I could spew some preliminary stuff out but I want to avoid any potential misinformation.

[Niklas Nord]

And regardning the 475nd used in the K2 s9500,
dod you know if this is the same driver as the 2450 ? or
is it the same as some other model..

[4313B]

It rings a bell but don't hold me to it just yet.

[Niklas Nord]

Okay, thankt you, I´l whait for the answer :D
I think this would be interesting for other readers,
not just me.. Some info about various drivers..

[4313B]

Agreed.

[Maron Horonzakz]

The 475nd is not the same as the 2450. But they are close. Both have the coherent phase plug design. But the magnet structure is placed on the inside on 475nd & 2450 magnet ring is placed on the out side . I dont know what the nd weight of 475 or 2450 is. Nore the flux density difference in gap of both drivers.

[Niklas Nord]

Can we use the diaphragm for each one in the other?
No acousticaly difference in the driver?

[Maron Horonzakz]

Acousticly different? I dont think so. But why JBL moved the magnet in that structure but kept the coherent phase plug & diapram position the same. might have been easier to mass produce. Some say they hear adifference between embossed diaphram & smooth diaphram or smooth diaphram with aquaplas coating. Ide like to see some distortion charts proving the findings. But I guess you cant put these kind of sonic findings on paper. And if JBL has they aint publishing them.

[Niklas Nord]

Why dont they use coated diaphragms in all JBL drivers?
Do they lack high frequency ?

[Maron Horonzakz]

Well JBL does like to slather that aquaplas on alot of their speakers. I suppose it does smooth out any frequency anomolies. I havent seen a side by side result of cones and diaphrams tested with & without coated speakers. I guess the next design breakthrough will be diaphrams and cones coated with HEMP.

[Niklas Nord]

Giskard, dod you find something about this matter?

[Don McRitchie]

Here is all that I know on the matter. The coating material is aquaplas and it was originally intended to damp resonances in titanium diaphragms. Titanium has poorer internal damping than aluminum and it became more critical with that material when used for home speakers. The objective of the coating was to reduce distortion cuased by otherwise spurious resonances.

According to JBL, the aquaplas coating has minimal effect on HF response. I think this is due in part to reliance on parasitic resonance in determining the limits of HF extension. Further, the horn compensation designed for individual speaker systems very likely takes into account any output effects of the higher mass.

I found it interesting that during my first tour of JBL's Northridge plant in 2000, the line making 2445 diaphrams was using aquaplas coating. They seem to have subsequently dropped this for reasons that I am unaware. However, the new aluminum 2430 and berylium 2435 all receive aquaplas coatings when intended for home or monitor use.

Regarding the 2450 and 475nd, both drivers were developed at the same time by Francher Murray. The 475Nd used an internal magnet so that home speakers using it would be shielded (the 1400Nd woofer also had an internal magnet and was thus shielded). This resulted in marginally higher manufacturing costs. Since shielding is generally not an issue in pro applications, the pro 2450 used the simpler and cheaper external magnet configuration.

To address the original issue raised in this thread, I would not recommend replacing the 475Nd diaphragm with the 2450 diaphragm. The result will be higher distortion and a frequency response that is likely worse than what you are trying to fix.

[Alex Lancaster]

Hi There:

I have some D8R2450´s, radial ribbed, the diaph looks darker than a 2445, what can I expect if I use them in 2441´s and 45´s?

Thanks, Alex.