Filter for 2426H on (PF-F64HF) 338800-001 waveguide

[sebackman]

Dear all,

I have two 1" screw on JBL waveguides 338800-001 in the shop. I think they are the PT-F64HF.

There seem to be some confusion of the numbers of the 1" vs 1,5" waveguides when reading various forum posts. Please correct if wrong.

Anyway, I remember someone posting a filter (or a link) for the above combo a while ago, but I can't find it. It mayhave been a modified AM34 filter? If anyone has a filter for this combo to share, it would be much appreciated.

I will use the horn/driver in a small PA two way with a 2226H or a 2206H.

All the best
//RoB

[4313B]

I will use the horn/driver in a small PA two way with a 2226H or a 2206H.

http://www.minidsp.com/applications/digital-crossovers/stereo-2-way-xover

I'm going to be trying one of these in a couple weeks when it arrives.

http://www.minidsp.com/onlinestore/detail/15-minidsp-in-a-box/flypage/63-minidsp-2x4-revb?sef=hcfp

You can try some 48 dB per octave filters along with any kind of EQ you wish to dial in if you get the Advanced Plug-In.

http://www.minidsp.com/products/plugins

[ivica]

Dear all,

I have two 1" screw on JBL waveguides 338800-001 in the shop. I think they are the PT-F64HF.

There seem to be some confusion of the numbers of the 1" vs 1,5" waveguides when reading various forum posts. Please correct if wrong.

Anyway, I remember someone posting a filter (or a link) for the above combo a while ago, but I can't find it. It mayhave been a modified AM34 filter? If anyone has a filter for this combo to share, it would be much appreciated.

I will use the horn/driver in a small PA two way with a 2226H or a 2206H.

All the best
//RoB



May be:
http://www.jblproservice.com/pdf/AE Series/AC2215,64-WH.pdf

can help, as crossover is shown

and JBL Technical Notes vol.1 no 31 (tn_v1n31.pdf)

http://www.jblpro.com/catalog/support/getfile.aspx?docid=277&doctype=3

Regards
Ivica

[sebackman]

Hi,

Thank you.

I want to go passive I think... The the filter curves between the 2412 and 2426 are quite different. I have a pair of 2412 and they are really not to compare with the 2426's. I will have to do some math I guess.

In the JBL white paper it is not clear what driver they used with the F64 in the graphs... Do you know?

All the best

//RoB

[badman]

If you want passive:

You can do a filter with notches to manage ripple from the impedance spikes..... http://www.enjoythemusic.com/diy/0311/crossover.htm

The horn example with notches is pre-figured for you- the PT wg with 2426h will have a very similar profile with the same spikes to be addressed.

Or parallel a resistor (10-20 ohms) and accept the dropped impedance overall. L-Pads will also do this.

You need a shelving curve as you'll get a response, with ripple down at cutoff (1.5-1.8k) and falling sensitivity above about 3k, in addition to a "normal" highpass. If you want 20kHz out of it (I wouldn't suggest) you'll need to work in that eq as well.

Or, you could do it with DSP (mo bedda unless you need LPs or other analog sources, in which case, it gets dicier).

[Robh3606]

In the JBL white paper it is not clear what driver they used with the F64 in the graphs... Do you know?


The only way you can do this right is to measure a 2426 on the PT mounted to your baffle. Anything else is just guess work and will not be optimal. You might want to search through 4430 quick and dirty. Zilch may have a 2426/25 on that PT somewhere just to get an idea.



Rob:)

[badman]

Can't upload impedance sweeps but I've got the PT WG free-air with 2426h, ping me if you want them emailed as a starting point.

[4313B]

Technically the PT waveguides won't support a low frequency transducer larger than twelve inches so the 2206 should work out great.

The lowest recommended crossover frequency for any of them is ~ 1.3 kHz.

At a 1.3 kHz crossover frequency you might want to round the top and side edges of the waveguide baffle by ~ 2.6" to mitigate diffraction and mount the waveguide and 2206 flush with the baffle.

For SR work this is arguably unnecessary but for hi-fi use one might find it beneficial. Note how JBL uses waveguides for SR versus monitoring applications.


The only way you can do this right is to measure a 2426 on the PT mounted to your baffle. Anything else is just guess work and will not be optimal.+1

[Earl K]

That " 338800-001 " part number belongs to the PT-F95 ( the waveguide that Zilch took to the masses ) .

Do a site search using that part number ( & Zilch as the poster ) to see what I'm talking about .

Here is the first "raw" measurement of that waveguide coupled to a 2426H driver ( the red trace ) .

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=7979&stc=1&d=1117357728
- To the best of my knowledge, Zilch never developed a separate HF Hipass network for the 2426 and this wavequide ( he preferred to work with much less expensive drivers ) .

- If it were my project, I would lash up a few of his ( Zilchs ) simplistic Hipass networks ( meant for either the Selenium driver or the B&C 250 driver ) .
- Check them out to see how they sound and measure up .
- Portions of his "Z-19" network could also be made to work ( though I'd likely leave out the Tannoy-inspired, HF roll-off ).

:)

[4313B]

JBL AM6212/95-WH SCHEMA TIC - Jblproservice.com (http://www.jblproservice.com/pdf/AE Series/AM6212,95-WH.pdf)

This might work if one is simply going to copy something. At least it has the correct crossover point for a twelve-inch driver. The PT falls apart below ~ 1300 Hz and the 2206H falls apart above ~ 1300 Hz so there you have it. ;)

[subwoof]

And I seem to remember way back when a special card for the 5234 was 1250hz...and it worked the best in the 12/horn wedge monitors we built that used the (now) ancient 2340 horn and a 2202. Small box on stage but nothing could touch it for volume and clarity.

ended up using a pair of those for home stereo for a long time until I had a house that accommodate the bigger stuff. But then the S.A.F. factor became an issue but that's another story...

:cheers:

[badman]

And I seem to remember way back when a special card for the 5234 was 1250hz...and it worked the best in the 12/horn wedge monitors we built that used the (now) ancient 2340 horn and a 2202. Small box on stage but nothing could touch it for volume and clarity.

ended up using a pair of those for home stereo for a long time until I had a house that accommodate the bigger stuff. But then the S.A.F. factor became an issue but that's another story...

:cheers:

You know what they say: "There's guys with big speakers then there's guys with too much estrogen in their lives."

Okay, they don't... but I just did :p

[badman]

At a 1.3 kHz crossover frequency you might want to round the top and side edges of the waveguide baffle by ~ 2.6" to mitigate diffraction and mount the waveguide and 2206 flush with the baffle.

For SR work this is arguably unnecessary but for hi-fi use one might find it beneficial. Note how JBL uses waveguides for SR versus monitoring applications.


While bigger is better for roundovers, (and this is especially true for roundovers to the sides of rectangular waveguides like the one under discussion), one should definitely NOT skip roundovers for want of a bigger size as the difficulty implementing this- even little ones can make a surprising difference.

I realize you're not advocating NO roundovers, but some folk see 2.6" and say "whoah, I can't do that...." and skip working on edge termination altogether.

The reason that smaller roundovers work is that if a ray from the acoustic source (assume point sources) encounters the baffle roundover at anything other than a right angle, the roundover "acts" bigger than it is because the wave has further to travel around the roundover before it's fully transitioned to 4pi.

http://www.enjoythemusic.com/diy/0412/foaming_at_the_mouth.htm

Foam around the mouth of the waveguide can be really useful as well- think Urei coax horns, but on a larger scale. This tends to make a modest difference on-axis, but a dramatic difference in off-axis performance and in polar consistency (helps with Constant Directivity).

[4313B]

It looks like they are using a fifteen to 1.5 kHz with theirs. I personally wouldn't, but to each their own. Nice link with some additional info. Thanks!