Beryllium upgrade for JBL compression

[Guido]

Guido, I hope this information will help you at that meeting and I look forward to reading your impressions, Steve G

Yep! It helps me a lot.
We will easily see from the response graphs what they are doing.

I have the promise from my carpenter that my 4435 will be finished in April. So I'm set up to do listening tests with
2426 JBL Ti
2426 JBL Alu
2426 Aftermarket Ti
2426 Aftermarket Alu
2426 Be
2435 JBL Ti
At least this taiwanese company manage to get the DCR right (3.2 Ohms). Any other Aftermarket dia I measured was in the 4 to 5 Ohm area.

Additionally I will get Be's for my 2441. But I'm still waiting for my Westlake Clones from Matthias.

[Guido]

Back from the music fair in Frankfurt I brought some samples from XKonkord/Taiwan.

Unfortunately the 44mm Be dia was damaged when touching it during presentation so I got a dia with wrong surround. Other will come.
The DCR's also do not match bt I have the promise that my main order will be right DCR. Well we'll see.
Testing need to wait as I'll be in China whole next week (the trip has nothing to do with speakers ). So far they fit perfect which I tested yesterday.

"D16R2425Be" should be 6.9 ohms but is 5.9 ohms

See the 44mm VC pics here.
I'll start another thread called "asian dias" with pics of the other samples I've got.
http://www.audioheritage.org/vbullet...ad.php?t=10180

[Guido]

See pics

"D16R2441Be" should be 7.9 Ohms but is 6.8 Ohms

[Zilch]

"Dimple" surround, apparently....

[jimd]

I guess I must disagree with your desired voice coil DCR.

Impedance of a driver needs to be expressed in MINIMUM impedance, NOT average or peak. To say a 3.2 ohm DCR voice coil is 8 ohm is simply not true, it will be about a 4.5 ohm load.

The impedance "conversion" ratio reflects the magnetic flux in the gap. The higher the flux, the greater the ratio. 22 KilloGauss is the maximum that can be acheived and at that point, the maximum conversion ratio for minimum impedance is 1.45-1.5. HF Drivers with lower flux density, like most with 1.75" voice coils can have conversion ratios as low as 1.3-4.

Sure, those drivers with lower DCRs appear louder, they are simply drawing more power, can possibly endanger amplifiers and will upset crossover frequencies.

Proper DCRs for minimum impedance are 5.5-6.5 ohms for 8 ohms, 11-12.5 ohms for 16 ohms, depending on the flux desity in the gap. In the 1970s this was quite controversity in the Pro Audio spectrum and resulted in manufacturers, including ALTEC and JBL changing their voice coils. In the later's case, several 16 ohm units were relabeled as 8 ohm. Seems to me, that right now no one appears to be watching.

I like the idea of a possible source for Be diaphragms, just want the DCRs to be right to properly work in vintage drivers, many of us won't buy any that aren't.

By the way, I am told, the JBL Berrylium diaphragms are Be/Al alloy, which seems to work fine.

My 2 cents, JIM

[Guido]

Thanks for input Jim. Before I answer you should know that I'm an electrotechnical engineer and into JBL for more than 20 years. I'm well aware of the differences between DCR and impedance.

The older 8 ohm rated JBL Drivers have an DCR of 3.2 ohms doesn't matter what you mean.
The older 16 ohm rated JBL drivers have an DCR of 8 ohm. Some very old 16 ohm drivers have an DCR of 10-11 ohms

Hope that helps to clear things up.

[Guido]

By the way, I am told, the JBL Berrylium diaphragms are Be/Al alloy, which seems to work fine.

A lot of rumours are circling about this. I also do not believe in "pure" Be. The samples I got are an alloy also.

[northwood]

[jimd]

Again, I repeat, there is no possible way a 3.2 ohm VC can have a 8 ohm MINIMUM impedance, same as an eight ohm DCR cannot be a minimum 16 ohms in a driver. Just because someone says it is, does not make it true.

In the 1970s drivers with voice coils that were below their rated impedances resulted in a lot of the early direct coupled solid state amplifiers expiring prematurely. The fragile nature of these amplifiers simply would not tolerate overloads, especially when driven to close to rated output. Previous tube amps and current solid state amps were/are able to tolerate greater overloads.

Two good examples of this are the ALTEC 802D and the JBL LE 85.
The "16" ohm VC of the 802D was 9 ohms DCR. When ALTEC redesigned the VC to minimum 16 ohms, it came out about twelve ohms DCR.
The LE 85, whch was labeled 16 ohms has a VC DCR of about 6.7 ohms. In the 70s they relabeled the driver, with the same Diaphragm/VC, at 8 ohms, just about right.
Further the 802D and the LE85 are very similar in construction, same voice coil size, diaphragm suspension, diaphragm radius, same phasing plug, same acoustic length, nearly identical and in some cases, identical magnet. The LE85 does have a larger and more efficient magnet return structure, however this could never amount to much difference in rated impedance. I used these two drivers as examples as I have both. A LE 175 would have been a better comparison as it is magnetically identical to the 802, but I don't have one.
Later drivers with different magnet types and topology operate under the same laws of physics these drivers do so ratings will be similar.

I personally do not care what someone says something ought to be, merely that the driver is as it is rated, an honest 8 or 16 minimum ohms impedance. Anything else is patently missleading. Jim

[Guido]

REAL DCR=8.0 Ohms.
Testing will start this weekend.

Quality of new Kapton Voice Coil looks excellent

[Guido]

REAL DCR=3.2 Ohms.
Testing will start this weekend.

Quality of new Kapton Voice Coil looks excellent, now diamond surround

[JBLnsince1959]

Looks GREAT!!!

Can't wait to hear how they sound

[Maron Horonzakz]

The variation in diamond pattern size is interesting. also the beaded pattern to extend hf response. This will effect compairison between authentic JBL and clone units.

[Guido]

The 44m (2426) Beryllium Dias are fakes!
Original D8R2425 measures better.

Testing of the 100m types in 2441 core will follow when my Westlake clones are finished.

[Zilch]

Fake in what respect, Guido?

Are they not Be?

What difference were you expecting to see?

The FR plots don't reveal much definitive, from what we saw comparing 2431 and 2435:

http://audioheritage.org/vbulletin/s...4&postcount=69

The difference would be in the sonic quality, I would think....