JBL 2450 with Truextent vs TAD 4001?

[pos]

Truextent should do a recall for such a problem.

I think Guido told me once that diaphragms with serial number below 700 might have the problem.

[Mr. Widget]

Truextent should do a recall for such a problem

The way they explained it to me was that it was only a problem in certain drivers. Ultimately they made a change in production so that their diaphragms would fit more drivers, but I believe, that for those who bought the very early diaphragms, if the diaphragm fit your driver, you are good to go.

Guido, do you have any more info on this?


Widget

[ivica]

I had some bad experience buying old and (ab)used Alnico drivers.
Unfortunately there is no recharge service in my country
Maybe is better and safer to go with neodymium magnet.

I think that 2446 -"motor" would be cheaper and appropriated solution, while the diaphragms would be another "story". At the end I think that desired horns would be of great influence to the total sound experience. Old 2311 with 2308 would be a good starting point if the speakers are intended for "home listening" but, with some kind of mid-bass support (such as: 2122, 2123, 2202,....).

http://audioroundtable.com/forum/pdf.php?th=16472
Upper link very interesting for reading.


Using 2405 (or something the same) would be "a must" in any case

[4313B]

The way they explained it to me was that it was only a problem in certain drivers. Ultimately they made a change in production so that their diaphragms would fit more drivers, but I believe, that for those who bought the very early diaphragms, if the diaphragm fit your driver, you are good to go.

I had one pair that absolutely would not fit into some 2441 cores. They fit just fine into some 2445 and 2446 cores.

[edgewound]

I had one pair that absolutely would not fit into some 2441 cores. They fit just fine into some 2445 and 2446 cores.

That's probably due to the later ceramic units having a relief machined into the top plate where the voice coil leads rise up the terminals.

The alnico drivers don't have that feature....which makes fitting new diaphragms more of a challenge.

[1audiohack]

The first ones of these I got my hands on, serial numbers in the 300's would not run rub free in the 2441's I had either, noway, nohow. Having carefully measured half a dozen of these I can tell you that the concentricity is much better on the later assemblies and as hard as it is to measure something so fragile and flimsy as a voice coil the later ones are about 0.010" smaller overall. There should be no problem if they don't rub, either they do or don't. The early ones went, measured, run and sound fine in the 2450's.

[Mr. Widget]

The first ones of these I got my hands on, serial numbers in the 300's would not run rub free in the 2441's I had either, noway, nohow. Having carefully measured half a dozen of these I can tell you that the concentricity is much better on the later assemblies and as hard as it is to measure something so fragile and flimsy as a voice coil the later ones are about 0.010" smaller overall. There should be no problem if they don't rub, either they do or don't. The early ones went, measured, run and sound fine in the 2450's.

Good God man... How many Be diaphragms do you need!



Widget

[Guido]

That's probably due to the later ceramic units having a relief machined into the top plate where the voice coil leads rise up the terminals.

The alnico drivers don't have that feature....which makes fitting new diaphragms more of a challenge.

That exactly WAS the problem with Alnico core JBL's and Radian 950PB. The newer ones fit fine.

[pos]

But the graph with high distortion in the article is with a 2450 driver which has the machined ribs for the VC leads!

[Mr. Widget]

But the graph with high distortion in the article is with a 2450 driver which has the machined ribs for the VC leads!

Good point... could be a less than stellar diaphragm or installation.


Widget

[Guido]

could be a less than stellar diaphragm

Yep, this was one of the first dias. In fact a beta version. See the lower impedance. It was also fixed later.

[Elac310]

I do happen to have the magzine article/test mentioned earlier, with the comparison JBL original vs JBL with Truextent Dia.
I also do happen to be fluent in German.

What was interesting was that the test concluded that the JBL driver with Truextent was better in all respects, DHT-wise, frequency response extension and linearity-wise etc. Not quite obvious to me, but I'm not an engineer.
I don't dare imagining what the conclusion would have been with a proper diaph mounted...

[ivica]

I do happen to have the magzine article/test mentioned earlier, with the comparison JBL original vs JBL with Truextent Dia.
I also do happen to be fluent in German.

What was interesting was that the test concluded that the JBL driver with Truextent was better in all respects, DHT-wise, frequency response extension and linearity-wise etc. Not quite obvious to me, but I'm not an engineer.
I don't dare imagining what the conclusion would have been with a proper diaph mounted...

Here are my measurements with JBL 2450SL (1.5 inch) driver with its original Ti-SL diaphragm, and Be ( truextent) diaphragm, with JBL 2332 horn (1.5 inch).
It is 'visible' that over 10kHz Ti diaphragm has become more 'nervous'..
But over 12kHz either Be diaphragms has started to 'shake', it is visible in non-smoothed blue curve.

Non-smoothed curves are windowed with 8ms long window in order to eliminate first reflection from the sealing.
Smoothed curves are 1/3 octave 'averaging'.

In my opinions UHF driver used over about 10kHz would be good suggestion.
( JBL 2405, or Beyma TPL150, or Beyma CP21/F).

Measuring THD (distortion) up to 10kHz did not make too many differences between them.

[speakerdave]

I used the 2450 in my stock 4345. Mounted on the 2311 the wide part of it fell just aft of the dog box. I was using a factory dusted diaphragm. I thought it sounded really good. With the truberyl there should be additional refinement. Used 2450's have been available steadily on eBay for quite a while, now for $449. If you are planning on new diaphragms anyway, that might be a good way to go, but the total investment would be over $2k. The 2450 has a more recent phase plug and throat design than the 2445.

[Champster]

Here are my measurements with JBL 2450SL (1.5 inch) driver with its original Ti-SL diaphragm, and Be ( truextent) diaphragm, with JBL 2332 horn (1.5 inch).
It is 'visible' that over 10kHz Ti diaphragm has become more 'nervous'..
But over 12kHz either Be diaphragms has started to 'shake', it is visible in non-smoothed blue curve.

Non-smoothed curves are windowed with 8ms long window in order to eliminate first reflection from the sealing.
Smoothed curves are 1/3 octave 'averaging'.

In my opinions UHF driver used over about 10kHz would be good suggestion.
( JBL 2405, or Beyma TPL150, or Beyma CP21/F).

Measuring THD (distortion) up to 10kHz did not make too many differences between them.

This is an interesting thread, but it strikes me as odd that there seems to be a reluctance to accept Ivica's several posts that adding a 2405 resolves the breakup issues in all of these 'phrams. Especially when a pair of 2405's costs less than 1 Truextent 'phram.

Can someone explain please explain this?