PT-F95HF Compact Progressive Transition Waveguide

[Zilch]

I waited nearly three years for them to become available, PT-F95HF, the "Compact" version of the 90° x 50° Progressive Transition waveguide, JBL Pro part# 338650-001, ~$100 apiece, now used in this product with 2452H-SL drivers:

http://www.jblpro.com/installedsound...7212MDP.v5.pdf

1) Certainly beefier than the $10 version for 1" thread-on drivers (338800-001), and seems like it will independently support Nd drivers.

2) Front view. Same size as the other PT-Fs, with dispersion pattern embossed.

3) The bad news, there's a "problem" with 243x drivers at ~14 kHz. Four samples each 2431H, top (+10 db) and 2435HPL, both using the same compensation filter. Too bad, they look damn good, otherwise.

4) It's not the waveguide, inherently, as they work fine with 2452H-SL. Filter needs less "boost" in UHF with these drivers, obviously.

5) Also fine using BMS 4555, here with compensated Altec 846B filter. Sorry, I forgot to put a legend on the plot. It's four drivers, which virtually superimpose. Be nice if they made a Nd version....

[Robh3606]

Hello Zilch

I wonder what the notch is?? Do you move the microphone around at all?? Is it that there both on and off axis as well?? If it was the waveguide I would expect to see it with the other drivers as well. Strange???? Did you run them without the filters?? Still see it then??

Rob

[johnaec]

The 2452 has the same larger bolt mounting diameter as the 2447, correct? Is that what's standard on these new horns? I wonder what 2447's would sound like, seeing that rising HF response with the 2452's...

John

[Zilch]

The 2452 has the same larger bolt mounting diameter as the 2447, correct? Is that what's standard on these new horns? I wonder what 2447's would sound like, seeing that rising HF response with the 2452's....

2452H has the larger bolt pattern of 2447, but the "SL" version uses the smaller pattern of the 243x family. Same deal with 2451H versus 2451H-SL, as I recall.

In my experience thus far, a major benefit of the "Next Generation" 2452H-SL is its smooth, extended HF response. I've never opened one up, but there's apparently more than just an "SL" Aquaplas-damped diaphragm involved in accomplishing that.

[johnaec]

2452H has the larger bolt pattern of 2447, but the "SL" version uses the smaller pattern of the 243x family. Same deal with 2451H versus 2451H-SL, as I recall.

OK - 'looks like I'm back to using the 2426J driver with the original PT-F95 (? - nomenclature) for stage monitors... ('Gotta' sell those 2447J's with new dias. here, but damn - they're nice drivers for what I have into them...)

John

[Zilch]

('Gotta' sell those 2447J's with new dias. here, but damn - they're nice drivers for what I have into them...)

There's no knowing 'til we try it, John. An adapter plate would be easy, but it looks like there's enough flange on these to simply drill the requisite mounting holes. I had to do that to use the BMS drivers with them, which have a 4" diameter bolt circle.

I'm also seeing 2452H (not "SL") and throatless 2450s (2450H-SL?) showing up on eBay recently. For stage monitors, I think I'd be looking at Nd drivers like those for their lighter weight....

[Zilch]

This is my second try with these, Rob, with the same result. I need to investigate and report more, and these findings should be independently verified before concluding anything. I tried shimming the driver back in 1/8" increments without apparent benefit.

I believe we already know there is an anomaly with 2431H at that frequency on other horns. 2435HPL uses the same two-stage phase plug, and it appears this particular waveguide has a problem with both of them, which may be a reason it was not used in any products in combination with members of that 3" driver family.

[blackwell]

I waited nearly three years for them to become available, PT-F95HF, the "Compact" version of the 90° x 50° Progressive Transition waveguide, JBL Pro part# 338650-001,....

Why did they opt not to use a CD design on these? I assume it was to keep the depth at a minimum, but is there any other reason?

[blackwell]

Excerpt from pdf link below:

"Compared to JBL’s previous generation of horns, the PT series offers dramatically improved constant-coverage response, and improved frequency response, while keeping distortion low."

http://www.jblpro.com/PD5000/PDF/PT_WaveGuide.pdf

Very interesting. You can see from the plots that it loads the driver less than the 2383, but I guess that's why they call it a waveguide not a horn. The overall responses look really good. Thanks for the link.

[Thom]

Isn't the overall gain of the horn a product of it's directivity? (I did read the literature although possibly not enough times) Also I didn't catch, when you were through, is there still a problem with this horn in combination with the 4435 or was there a problem with your driver?

[Zilch]

Yes. The HF compensation is different for each dispersion pattern among PTs of genrally the same design.

PT-F95HF has a notch in the VHF with 243x drivers. The other PTs I've tried, which is most all of them, don't exhibit that anomaly. Other members are using those combinations successfully, as well.

I haven't pursued it further. They're fine with BMS 4555 or 2452H-SL, as shown in the measurements. Somebody at JBL knows the answer, but I don't have access to them, even if they are willing to disclose it.

They sound fine, actually, but I'm a curve junkie, and just can't rationalize using them that way. Maybe I'll send RobH a pair to verify....

[blackwell]

Isn't the overall gain of the horn a product of it's directivity? (I did read the literature although possibly not enough times) Also I didn't catch, when you were through, is there still a problem with this horn in combination with the 4435 or was there a problem with your driver?

Yes, but what I was refering to is the impedance plot. A horn acts as an impedance matching device and a waveguide is just a patern controlling device. In the plots I saw there is a little ripple in the impedance plot that also shows up in the frequency response. I hope that clears it up.

Cheers.