Does Ti Increase UHF Response?

[Mr. Widget]

Zilch had dropped off a few horns from his immense collection of JBL bits, pieces and complete systems and asked me if I might be interested in doing a bit of response testing... well, yeah!

I titled this thread Does Ti Increase UHF Response? because the most surprising thing for me from this exploration was the response of an old aluminum "red wax seals intact" LE85. This plot compares a titanium JBL 2425 and 2426, and an aluminum LE85 all mounted to a JBL 2370 measured on axis at 1 meter. You can see the 2425 and 2426 have different response curves, but the LE85 to my mind was the real shiner here. Imagine what the 2421 diaphragm's response would look like!

Now, these drivers are all used, so this is not a definitive test. With a sample lot of one each I wouldn't claim that this is definitive, but it is certainly intriguing.

2425 is in Green
2426 is in Red
LE85 is in Blue

[Mr. Widget]

This plot and the next two show the off axis response of the 2344 and the 2370. They both show why these horns are called constant directivity. I did not do a complete polar response as I don't have a motorized turntable and doing it manually would be a real pain. These plots show on axis, 15 degrees off axis, 30 degrees off axis, and 45 degrees off axis. This covers a 90 degree arc in front of the horns. On both the 2344 and the 2370 I was amazed at the control and excellent off axis response.

This plot shows the 2426 driver on the 2370 horn with no network.

Red on axis
Blue 15 degrees off axis
Green 30 degrees off axis
Purple 45 degrees off axis

[Mr. Widget]

This plot shows the 2425 driver on the 2344 horn with no network.

Red on axis
Blue 15 degrees off axis
Green 30 degrees off axis
Purple 45 degrees off axis

[Mr. Widget]

This plot shows the 2425 driver on the 2344 horn with 3135 (4430) network set to the position to create the flattest response.

Red on axis
Blue 15 degrees off axis
Green 30 degrees off axis
Purple 45 degrees off axis

[GordonW]

My only concern, is that the LE85 appears to have a rather strong resonance peak near 20KHz, in the first graph. This could make it sound "zingy", as those resonances tend to 'overhang' beyond the normal duration of a transient in that frequency range.

I would wonder, if a new aluminum diaphragm would have such a pronounced resonance, or if that's because of metal fatigue?

Regards,
Gordon.

[Mr. Widget]

I do not know if that VHF resonance is true of the LE85/2420 or if it is an anomaly unique to this unit. Unfortunately JBL has been rather shy about posting specific driver curves in the past. From the JBL Technical Notes Volume 1, Number 8, page 3 in their description of mass break up they do show the resonance peak at 9KHz for the 375/2440 and the 18KHz peak for the TAD 4001. In my measurements of the TAD 4001 I have measured a similar peak. In the case of the 18KHz peak, it doesn't bother me but that may be due to age. I am currently topping off about 16KHz. For this LE85 with a peak at 21KHz, I doubt many of us older JBL fans would ever hear it.

[Zilch]

In all of the technology here, there's few items that qualify as "Magical" in my mind and experience. Mr. Widget documents two of them above:

1) Biradial horns really work as claimed. I don't have a listening room set up with a "sweet spot" chair. Most often I'm all over the place listening, working, whatever, sometimes even in other rooms. When there's several of us listening from different positions, we can all enjoy the same experience. I don't pad the walls or give a whit about controlling the reverberant field. I don't tweak EQ, either. Biradial fits perfectly here.

2) The 4430 (N3134) "Quasi-three-way" crossover topology really works, too. That clever scheme of bypassing VHF around attenuated MF to the same driver is also seen in N200B, 3110A, 3115A, 3120A, N3124, and elsewhere I've yet to discover, most likely. HF boost, indeed, it makes two-ways actually WORK! "How'd they DO that?"

I'll be tearing into a pair of L200's here soon, and swapping the LE85 diaphragms out for Ti's. Perhaps Mr. Widget will test those before and after as well when the time comes. We'll see if that 21K peak is an anomaly or not then, and whether it's even necessary to upgrade LE85's (Mr. Widget's initial findings argue "NOT") in making an L200 to Quasi-4430 conversion....

[Ian Mackenzie]

Nice Curves Widget.

Would be good to see a 2421 curve..and even a dusted curve.

Those curves are spot on with the 4430/35 White paper.
(a useful read on the whys and why not's of horns for monitoring).

Rob and I have been playing around with the 2344 for yonks, it sounds as good as it looks..

I am not sure about the audibility of the resonances but the mass roll off of all compression drivers kind of tells the way they behaviour as they attempt to reach towards the top end...they just run out of steam and seem to lack that sparkle that a dedicated UHF driver (low mass) can bring into the picture.

Does any one have A 2307/2308 and a 2405 they can offer The Widget for test.


Ian

[Mr. Widget]

Would be good to see a 2421 curve..and even a dusted curve.

Does any one have A 2307/2308 and a 2405 they can offer The Widget for test.

I'll talk to Infredible. He has the 2421s in his 4343s. We were discussing my running over to his house to shoot them. I'll grab a plot of his 2421 with 2405s.

Widget

[Ian Mackenzie]

We'll have to start calling you doctor Widget with those day visits

Just remember the Postman always rings twice..LOL

Ian