Fixed L-Pads

[Robh3606]

No free lunch. You want horizontal, you pay with vertical.

Not so look at the conical lense. The serpentine and slat lense have minimal effect in that plane. You essentially go back to the horns directivity. Look at the directivity curve for the horn and horizontal pattern they mirror each other. They didn't plot the verticle but it would follow as the other plot does. That 22 degree and less wedge works in well with Jack quoted post.

http://www.lansingheritage.org/html/...nical/lens.htm

Well, I was hoping Tractrix might defy some of that, but it looks in theory like the horn and driver throat size must be optimized for a successful two-way design with extended HF.

This is Deja-vu. We going back to the 4430??

Well, for me it certainly is. I've kinda grown to like 50° vertical beamwidth, but a 20° listening slit is, well, "untenable" thus far....

Yes I tend to agree. One of the reasons I like the 2344 and the PT1010


Rob

[Zilch]

Not so look at the conical lense. The serpentine and slat lense have minimal effect in that plane. You essentially go back to the horns directivity. Look at the directivity curve for the horn and horizontal pattern they mirror each other. They didn't plot the verticle but it would follow as the other plot does. That 22 degree and less wedge works in well with Jack quoted post.

http://www.lansingheritage.org/html/...nical/lens.htm

I noticed that the DI didn't support what I was saying, but chose to ignore it.

[O.K., I get that now.... ]

This is Deja-vu. We going back to the 4430??

Naw, it's de riguer - PT Waveguides at ZilchLab.

For a symmetrical waveguide, the little work I did with the Engebretson indicated it "promising." Maybe I'll continue some with that:

http://www.ddshorns.com/catalog.php?page=ENG190Pro

If it's good, someone should document the profile for DIY.

["Family".... ]

[dmtp]

OK, I finally had a chance to do some SPL plots. As follows:
1. No HF bypass (green)
2. 1.0 uF only (no L, no R) (magenta)
3. 0.68 uF (yellow)
4. 0.33 uF (orange)

Now with the smaller caps, we get less MF contamination, but we also get not enough VHF boost, so let's try a larger cap:
1. No HF bypass (green)
2. 1.0 uF only (no L, no R) (blue)
3. 1.5 uF (aqua)
4. 1.5 uF in series with 0.05 mH (magenta)
5. 1.5 uF in series with 0.1 mH (yellow)

To my eye, curve 4 looks the best as 5 gives up some VHF, so it makes more sense to me to go with a 1.5uF cap in series with a 0.05 mH coil and then try to tame the resulting MF/HF bump with an LCR across the LE85. Using a blow up of the above curve, I determined the F3l = 6300; F3h = 15000 (although very steep here). (F3h-F3l)=8700 width, "midpoint" = F3l+((F3h-F3l)/2) = 10650, but visually the midpoint measures out nearer 8750. I think I will try an LCR based on that freq. (with about 10dB total from 4k to 18k.)

[dmtp]

To answer Zilch's questions about polar response, I took measurements @ 0, 10, 20, 30, 45 degrees off axis. (The actual degrees may be a bit off, I was using a plastic protractor held on the horn's mouth with a stick to the mike.) I am not sure about the absolute dB as I am sure the distance to the mike varied as I moved it off center, but at least the shape of the curves should be correct. (I do not know how to do a polar plot from these curves.)
Green = on axis
Magenta = 10 degrees off axis
Yellow = 30
Aqua = 45

[Robh3606]

Looks to me like your best curves are without any HF boost. You may have to suck it up and either take what your getting or add a 2405. You can try what they did on the 4430 with a series LCR but it looks like you have a brick wall at 15K.

Rob

[Zilch]

Your L & C tests confirm my findings. As you raise the C, the boost starts at a lower frequency. As you lower the L, it cuts off at a higher one.

My approach to it was to start the boost where it's needed, above 10 kHz, and stop it just above 20 kHz. Try the combination I found worked best, 0.5 uF and 0.05 mH. That gives ~9 dB of boost between 10 and 20 kH, the max you're going to get out of 6 dB/octave topology, plus ~3 dB from resonance.

You're already too high at 10 kHz. It doesn't make a lot of sense to me to boost that even higher and then yank it back down with a deeper notch.

*****

Your beamwidth tests indicate that the VHF is concentrated in a 20° "window," as discussed above. For most accurate results, the mic has to be at the same distance for each reading.

I use the "Move the mic" approach, too, with string used to hold the distance to mic constant. Another approach is a lazy susan under the speaker to rotate it about the acoustic center. I have a motorized rotary table for that, but haven't built it up yet.

To plot in true polar coordinate format requires a level of precision in positioning I have not achieved here. That's also multiple plots at different frequencies, a different way of looking at it....

[dmtp]

OK, I have some interesting results. First the calculations:
Based upon a 10dB hump, I calculated R= 3.5
With F0=8750, F3h=15000, F3l=6300, I got L=0.05, C=5.37. I had a 0.06mH coil so used that with 5.5, 4.0, 3.0 uF caps.
First, here are the nulls (R=0) to show the center freq of the above combos:
green=no LCR (but WITH hipass = 1.5uF in series with 0.05mH, no R)
blue = 5.5uF
aqua = 4.0uF
yellow = 3.0uF

This pretty much confirms the F0 expected.

Then for each cap, I adjusted R for what looked like the best curve. Here are the results:
green=no LCR (but WITH hipass = 1.5uF in series with 0.05mH, no R)
aqua = 5.5uF, 2.1R
blue = 4uF, 2.5R
magenta = 3uF, 1.5R


To my eye, the magenta (3uF, 1.5R) looks the best, but it now has an 'M' - two humps and a notch which I think indicates I need a broader notch to pull down the humps on each side. That would require a smaller Q, but a smaller Q won't "pull down" the original hump enough. So now what?
Here are some 'families' of curves.
For 3.0uF, R varied 0, 1, 1.5, 2, 5



For 4.0uF, R varied 0,1,2,3



For 5.5uF, R varied 1,2,3 (I forgot to include the R=0, but you can see it above)


None of the curves seem to get broad enough to flatten things out. I'm not sure where to go next.

[dmtp]

Looks to me like your best curves are without any HF boost.

Looks like Robh might be right. Here is a recap of boost with just a cap
green=0
blue = 0.4uF
Aqua=0.5
Orange = 0.68
Yellow = 1.0
Magenta = 1.5


Per Zilch's suggestion, here are the results with 0.5uF cap
blue = no boost
green= just 0.5uF
magenta = 0.5uF with 0.05mH (Zilch's choice)
yellow = 0.5uF with 0.1mH

pumping in anything above 14k just raises 11-12k too much. I tried notching them out, but couldn't come up with anything worth posting as by the time I got the 10k notch tamed, I lost most of what I had gained above 15k.
I think at this point I amo going to work on getting the speakers finished and in the room and then maybe play with the XO more after listening to music.
(Now there's an idea!)

[Zilch]

You got within +/- 3 dB with a couple of those options.

That's damn good, I'd say....