4" (JBL clone) diaphragm identification

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As far as I know:

-original JBL 2445 diaphragms were smooth.
-JBL 2446 diaphragms were ribbed.
-ribbed diaphragms can be used in a 2445, for slightly better HF.
-that hybrid is what it looks like I have got

Every pic I can find of a ribbed diagram looks the same - i.e. the clones are very faithful to the original.

I have 2nd hand 2445Js and diaphragms of unknown origin. One has a normal-looking rib pattern, and measures normally. One has an odd looking rib pattern. It measures better. I'd like to know where I can get more of these! Does anyone know what it is / who makes it?

Visually, the difference is that the radial ribs are much fainter in the centre, and there seems to be some intentional asymmetry. They are difficult objects to photograph, but I gave it a crack.

The attached graph is mic in morn mouth, with most factors the same: horn, eq (a low Q shelf to flatten the 1-8kHz range), and the the two old 2445J cores have consecutive serial numbers.

I shifted the graph of the unusual dia by +5dB to make it less visually confusing.

With the normal looking dia, I measured it when I first got it, then after cleaning out the gap, then removed and replaced the dia multiple times (going slowly, while playing test tones to avoid buzzes / rubbing) - and I never got it to measure any better than this.
 

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Thanks, Frangus.

This illustrates diminishing returns pretty well.

I started with a longer horn, then spent a lot of time extending it ...and it only gives ~100Hz more extension.

Ditto the HF. My mystery diaphragm measures well, particularly in the top octave... but after eq, yours also measure well.

+++

Question: if you remove the smoothing you used in REW, does the extra resolution show a single bump at ~13kHz, or does it show multiple spikes? I wonder if the real effect of the ribbing (on later diaphragms) was to smear a single resonance into many.
 
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I'll change the resolution and post it for you.

Do you notice the breakup? Playing full range I most definitely do. It is sounding very nice with my ribbon crossed at 6k though as has every compression driver I have used.

I am considering trying the radian PB950 diaphragm. It is supposedly smoother at the expense of some loss of verve.

Another option on the cards is to keep the Ti diaphragm and upgrade the ribbon with an AMT
 
Do you notice the breakup? Playing full range I most definitely do. It is sounding very nice with my ribbon crossed at 6k though as has every compression driver I have used.

Nope, nor does Melanie (whose ears are a bit younger and female-er than mine so she is a bit more HF acute). Maybe this is because the diaphragm I'm using is better (I'm testing in mono, so I've only listened to the one that arrived first / measures best). It could also be about expectations - I'm used to hearing horn treble (my living room system is six*15" drivers, the tops being coaxials), or you might be a keener listener.

Today I cannibalised my main system to test the JBLs in a 3.5-way:

dual 15" for midbass
2" on big horn
1" on small horn (the HF driver from my coaxials*)

I set it up so I could flip dsp configurations to either have the 2" play all the treble, or to cross the upper treble to the 1" (using DSP & REW to get the on-axis response near identical).

Crossing at 6kHz, the 3.5-way sounded very slightly clearer, but a little bit artificial - I was aware that a tweeter was in the mix. Crossed at 8kHz, I could still hear a difference - but only just. If I did blind tests 5 minutes apart, I doubt I'd be able to tell these two configurations apart.

This is a good thing - it means I can just add a channel if I never manage to get a match for my mystery diaphragm. The extra channel can only get better with optimisation, such as a proper HF driver that allows closer centre-to-centre spacing.

I am considering trying the radian PB950 diaphragm. It is supposedly smoother at the expense of some loss of verve.

Yeah, I've also considering that one, or even phenolic, for pure mid duty. It seems like JBL only switched to Ti for to get extension (parasitic resonance from the diamond surround) without a loss to durability, as described here:

interview about the 435BE and history of JBL horns

Ti was not selected for sound quality. If you don't need the extension (cos you have a separate HF channel) or the durability (because your home is not a stadium), then there's no reason to stick with it, that I can see.

If I do add 1" drivers, I may go with a Dayton or Faital unit for this reason (they have marketable names for the diaphragm materials - Polyimide and Ketone Polymer - but they are just different types of plastic).

I don't like descriptors like "verve" without context. "Verve" to some listeners may mean a big HF peak that lets them hear (part of) the treble like when they were young.

Another option on the cards is to keep the Ti diaphragm and upgrade the ribbon with an AMT

How is this an upgrade - is it because the AMT can be crossed lower?

*I have a Foster/Fostex super tweeter somewhere, but can't remember where I packed it!
 
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Update: I found where I'd left a super tweeter: it's a Plessey/Foster OEM version of the Fostex FT17H Horn Super Tweeter. It only took a couple of minutes to dial it in (needed a few dB more gain).

It integrates well. Hard to tell the difference - on some music, I have to put my ear up to the super tweeter to tell which configuration is active.

Simple vocal pop (e.g. Mavis Staples) is very marginally better with the good 2" doing all the HF, implying I haven't got the integration just right.

Raucous rock (e.g. Blood Brothers) is better with the super tweeter configuration. When there's a lot going on, more channels = more clarity.
 
"I am considering trying the radian PB950 diaphragm."

Big resonance at 16Khz, not bad otherwise.

I've had problems with these in the past, they may be better now (or worse).

Problems? First ive heard of it...

I'll be crossing before 8k so the resonance should be a non-issue.

I once owned a set of Radian 465Pb and they are still my favourite 1" compression driver though I have only tried 4 or 5 others from B&C, 18 sound, eminence etc
 
"Problems? First ive heard of it..."

In the past Radian had issues with the soldering flux they used, causing joint failures. Also short lead-out wires, causing lead fractures.

The peak is easy to measure with any kind of analyzer.

Under hard use they blew a hole in the apex of the domes, of course the JBL 2445's were developing pin-holes in the diamond surrounds too.

I have not tried them lately, and am not willing to do so (I sent back the 850 samples they sent, and made some JBL 2446 with 2441 diaphragms instead).

Meyer used to buy the 2450, sell the diaphragms, and replace with 2441 diaphragms. They kept records, and the 2441 lasted longer than the 2450 in leased systems.

The SL versions of the JBL 4" diaphragms sound quite good, as do the Be versions.
 
"Problems? First ive heard of it..."

In the past Radian had issues with the soldering flux they used, causing joint failures. Also short lead-out wires, causing lead fractures.

The peak is easy to measure with any kind of analyzer.

Under hard use they blew a hole in the apex of the domes, of course the JBL 2445's were developing pin-holes in the diamond surrounds too.

I have not tried them lately, and am not willing to do so (I sent back the 850 samples they sent, and made some JBL 2446 with 2441 diaphragms instead).

Meyer used to buy the 2450, sell the diaphragms, and replace with 2441 diaphragms. They kept records, and the 2441 lasted longer than the 2450 in leased systems.

The SL versions of the JBL 4" diaphragms sound quite good, as do the Be versions.

Fair enough, professional applications are far more demanding though. With domestic use I hopefully won't run into these issues and am yet to hear about anyone that has
 
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