Different 4" SL diaphragms?

[sebackman]

Hi,

There seem to exist at least two different 4" SL diaphragms. The one is for 2450SL with the diamond pattern not coated with Aquaplas and the other for the 476Nd with the edge coated. Both are available.

Does anyone on this execelent forum have a view if there is a sonic difference? -Or just a preference.

They are going into a pair of 2447 behind some M2 guides.


Kind regards and thank you
// RoB

[sebackman]

Dear all,

I found some new D8R475Nd diaphragms. Does anybody here know if they are fully compatible with a 2450SL core?

The reason for asking is that 2450SL does have an external Neodym magnet but the 475Nd has an internal Neodym magnet. I have no idea if it maters.

They look different. Both are un-ribbed and coated but the 2450SL has a coated dome but the 475Nd dia also has the diamond pattern coated.

Kind regards
//RoB

[sebackman]

I did take the plunge and bough some diaphragms. For future reference I thought I would post my findings here. Maybe there is information on the Forum before, but here goes anyway.

I did get some new D8R475Nd diaphragms and they are indeed the same as the other JBL 4” diaphragms. We have mounted and measured them in 2451 and 2450 cores and they appear to work just fine. Hence I do believe that they are fully interchangeable with any 4” JBL Ti diaphragms.





However, some odd things to observe.

They turned out to be 16ohm and NOT 8ohm regardless of their designation (D8R475Nd). They also have a red blobb.



They do not have coating on the diamond pattern surround as can be seen in some pictures. The original JBL exploded view of the old K2 series does not show coated edge either. I have no clue as to why, but there seem to exist a smooth coated diaphragm with coated surround but I cannot find a part number or where they were used. It was not in the 475Nd at least.

Also the build quality was not really perfect. The voice coil is covered by some clear coating and that was not entirely smooth so I had to “sand” some of them very gently to get them to work in my 2450 cores.



Kind regards
//RoB

[Don C]

Thanks for posting this information. I was pretty sure that they were all interchangeable, but couldn't find any proof.

[JeffW]

I had a NOS pair of 2450SL diaphragms, I posted a pic Here. Coated, smooth dome, diamond surround that wasn't coated.

[ivica]

Dear all,

I found some new D8R475Nd diaphragms. Does anybody here know if they are fully compatible with a 2450SL core?

The reason for asking is that 2450SL does have an external Neodym magnet but the 475Nd has an internal Neodym magnet. I have no idea if it maters.

They look different. Both are un-ribbed and coated but the 2450SL has a coated dome but the 475Nd dia also has the diamond pattern coated.

Kind regards
//RhoB

Hi RhoB,

I would not expect almost any differences between suspension coated vs not suspension coated, even that some audio Authority has sugested that ONLY the diamond shaped suspension has to be coated ONLY, as that suspension has an influence in the UHF ferq.response., but I think that large diaphragm dome breaks over 10kHz, and its coating would absorb dome unwanted vibration.
Regards
Ivica

[gibber]

Hi all,

given what we've seen as to production abberations from our most favourite supplier, i'd suggest considering this to be a simple mfg sheet inaccurracy. The people on the line propably just were free to interpret the prod spec this or the other way.

Real differences may exist, though. As Ivica rightly pointed out, quite a significant portion of HF output is to be expected from the outer phase plug ring available in these ND cores. Which are mostly fed from that very suspension area damped by the extra AQ treatment.

Ralph

[sebackman]

Agreed.

I have not been able to locate a partnumber or "goes into list" that covers a version with coated diamonds. I thought the D8R475Nd would be, but they are not.

The only difference between them an D8R250SL seem to be that the SL's are 8ohms and the Nd's are 16ohms...

I do have a few original D8R2450SL's also and to the naked eye the look the same.

Kind regards
//RoB

[wrager]

Would the 2447h with SL phragms be equal to the 2450-SL? I realize the differences in mag types.

[1audiohack]

It should be.

Barry.

[wrager]

It should be.

Barry.

Ohhh, thanks for responding Barry! I was actually considering a PM to you directly. You're the best!

I did find some good condition 2435HPLs, but think the 4" SL CDs sound better. Am I crazy?

[JeffW]

I don't think you're crazy, I have 1.75" , 3" (435AL, close to the 2435 I think), and various 4" and I like the 4s the best.

I'd bet a new hat that I know what Barry's answer will be

Didn't you get some of the 2450-SLs the guy in Canada was selling? I have some of those and 2452s in the flat 4", and some 2450s in snouted 4"

I don't think the mounting bolt circle is the same on the 2447, but I'm not certain. The 435/2452/2450-SL all have the smal 3 1/4" circle.

[wrager]

Thanks for your thoughts Jeff. I am using the 2384 horn which is drilled for both bolt circles. Lucky me!
I just wonder if the Be diaphragm in the 2435 trumps the advantage of the 4" SL CD. From my reading, the 3" Be CD should play higher, better, while the 4" should play lower better. I am running my 4622s active (DSi 1000) which I think sets the x-over at 630hz vs. 750 for passive. I like to listen to music, so I want the best sound possible.

[speakerdave]

At those crossover frequencies the inherently lower distortion of the 4" diaphragm makes a difference that matters. The 435Be at 750 I would not recommend. The JBL2450 with an SL diaphragm gave the TAD 2001 a run for its money at 1200Hz, though I finally settled on the TAD. I'm not sure at 750 Hz I could pick out the TAD 4003 vs the 476BE in the Everest. For the music, as you say, experience suggests large format JBL with the dusted diaphragm, and down the road consider a Truextent Be splurge, if you can hear it somewhere first. It would be hard to spend that money without knowing.

[JeffW]

All my 4s have Be 'phragms now, so it's hard for me to offer much there. Barry will chime in directly, I think I recall him having a soft spot for the coated Ti 'phragms - I'm pretty sure that's where the ones in my pic above ended up - for upper extension. And the 4" Al 'phragms are so close to Be prices these days, but I'd like to try some one day just because. The little 435Al is no slouch, those 3" drivers ain't bad.