"Unitized" Image Control Waveguide

[Patrick Bateman]

For the past couple years I've been tinkering with designing waveguides in 3D, and I decided to combine a couple of things I'm interested in:

1) Unity Horns

2) JBL's "Image Control Waveguide"

[Patrick Bateman]

For the sake of reference, here's the polar response of a JBL 2408H-1 on a JBL PT Waveguide clone. I'd argue that this performance is about as good as it gets; I think this combo is competitive with just about everything in the "great waveguide list."


Here's the polar response of my "unitized image control waveguide." This is using a BMS 4552. It's not quite as epic as the PT Waveguide combo, but it's pretty darn good I'd say. Since I'm a perfectionist, I'd argue that the slightly better performance of the PT waveguide is because it's better matched to the waveguide. Basically I designed my Image Control Waveguide to match the BMS 4552, but that match got slightly altered when I deadened the horn. Basically I apply about 2 millimeters to the waveguide to deaden it, and I should've accounted for that when designing the waveguide.

Again, this is totally splitting hairs, but when you're trying to make the perfect waveguide, a couple millimeters counts. It's still really good performance though




Here's a couple of polar measurements WITH constant directivity EQ. One thing that I really love about this design is how consistent it is, on axis and off. Because it's so darn consistent, it's REALLY friendly to equalization.

Here's what I mean by that:

With a lot of horns and waveguides, you'll see that there's an axis that measures particularly well. And the thing that sucks is that it's not always ON axis. IE, there are a lot of waveguides that measure better ten or fifteen degrees off-axis than on. This is problematic, because you don't want a set of speakers which sound better at one point in the room then another.

These PT waveguides and my image control waveguide don't have that problem. The variance between the on and off-axis response of my image control waveguide is about +/- 2dB, and the JBL PT waveguide is about ONE decibel! You could 'walk the beam' and the sound just isn't going to change.

The reason that I've posted a couple different measurements with EQ is because the design is so EQ friendly. You can basically 'dial in' whatever curve you want. No weird suckouts or peaks here, you can EQ without fear. (The BMS 4552 admittedly has a big peak at 20khz, but I'm not hearing it. The 2408H-1 is very similar in design, but it's phase plug is quite different. Last year I posted some speculation on why Voishvillo designed it the way he did.


Here's one of the EQ settings I used for CD EQ

[augerpro]

Looks cool. Can you swap drivers to remove that variable from the measurements?

[Kevmoso]

Looks really cool.
I have a few 4552nd sitting here so I will be watching this very closely.
Bigger version with midrange taps? I know you can't resist the midrange taps.

[norman bates]

I still believe there should be no corners, edges, beaks in the horn path, parallel sections, and short is better than deep.
Many monitors use horn loaded round short horns.
I believe holland and newel (sp ?) did this years ago.


My jbl 2384 can be improved by foam covering a very rounded edge to baffle of just the bottom side.
JBL 365359-001 2384 Horn/Waveguide for 3732 - Speaker Exchange

Short of tractrix, round, l'cleach, to me every horn is flawed causing reflections (standing waves seen on waterfall plots and Z ripples i think).

But........
Non round horns have less of a mouth standing wave.
And many (and me) like the 90 x 40 dispersion (less room interactive).
And cd horn get those highs everywhere far into a room.

Good work !!
I enjoy your journey and graphs.

Someday i need to hear the 2408 plus pt waveguide.

[Patrick Bateman]

Originally Posted by Kevmoso

Looks really cool.
I have a few 4552nd sitting here so I will be watching this very closely.
Bigger version with midrange taps? I know you can't resist the midrange taps.

You know it:




On the left is my "unitized" waveguide, on the right is the PT waveguide clone. Note how small these are. As usual, these are for my car, so I'm jamming them into a corner so that the corner extends the waveguide mouth. The reason that the waveguide on the left is incomplete is because I ran out of filament during the print.


For me, one of the most interesting things about my "image control waveguide" is this measurement. This measurement was done when the waveguide was only partially printed. Basically I was feeling impatient, so I ran a quick set of measurements on the incomplete waveguide. Look how smooth that curve is! This is really unusual performance for an incomplete and unterminated waveguide.

Charles Sprinkle, the inventor of the Image Control Waveguide, said this:

“The Bi-Radial horn that we have had for decades was a 90x60 horn, and not the best match for the low frequency device in the M2,” Sprinkle says. “This horn is 120 degrees horizontal and 110 degrees vertical. We knew that if we wanted a good directivity transition between the woofer and the high frequencies, we had to have that amount of pattern, so the waveguide was designed to have a pattern consistent with what the woofer was doing with no discontinuity at the crossover point, which is 800 Hz.

“The second thing we did was use a blending geometry—there are no straight lines, you’ll notice—that has a generally decreasing radius,” he continues, “forming an infinite number of reflections, and the net effect is that it smears the reflections coming back down the horn and negates them.

So it seems like there may be some merit to this. I wouldn't normally expect an incomplete unterminated waveguide to perform like this. What I think is going on is that a "conventional" waveguide or horn will have peaks and dips which are caused by it's symmetry. This is only logical; if the distance from the throat to the mouth is identical in all directions, then the peaks and dips that are caused by diffraction and reflections that go back down the horn/waveguide will be ameliorated by doing everything that you can to vary the geometry. There's lots of ways to vary the geometry:

1) Use a mouth that's not circular
2) Vary the pathlength by angle. (If you slice up the "image control waveguide", you'll see that the geometry of the horn varies with each slice. Some slices are 90 degrees, some slices are 95 degrees, some are 85 degrees. The coverage angle varies with each slice.


Here's what the waveguide looks like, once I deadened it with mortite, added the midranges and wrapped the whole thing in fiberglass to create a CLD composite.

[EarlK]

Nice!

[norman bates]

Any new news ?

[Patrick Bateman]

Originally Posted by norman bates

Any new news ?

I have two of the waveguides built now, and fiberglassed to a plywood baffle. I went crazy with the mortite and fiberglass, because I printed these waveguides out of PETG and I'm having a heck of a time getting a good print. PLA is way way easier. But I'll probably stick to PETG for the forseeable future, because it really sucks to have your waveguide melt due to the heat.

[Patrick Bateman]

When Charles Sprinkle designed the waveguide for the JBL M2, he wrote the following:

The second thing we did was use a blending geometry—there are no straight lines, you’ll notice—that has a generally decreasing radius,” he continues, “forming an infinite number of reflections, and the net effect is that it smears the reflections coming back down the horn and negates them.

Taking that to heart, I basically made a giant version of the waveguide from page one of this thread. Breaking up the symmetry was my primary goal with this waveguide. The compression driver is a bit off-axis, the mouth is not symmetrical, there's a very gentle diffraction slot on the vertical axis, just as the JBL PT waveguides and Image Control Waveguides have.







Some pics of the waveguide


If you look closely, there's a very subtle diffraction slot



Here's the measured polar response, with a BMS 4552, measured at a distance of 8ft.

Not sure what to make of this. The performance is good, but not as great as the JBL PT Waveguide. My DIY saw lenses seem to outperform both(1)

But it's still very good performance. Very wide bandwidth, and it's unusaly to see a compression driver than can do 1000Hz to 20khz with fairly consistent beamwidth and frequency response.

(1) Synergy Beolab