horn dispersion

[jdm56]

Until fairly recently, I was under the impression that a horn's dispersion was greatest in it's longest dimension. But then, I also (correctly) believed a direct radiator, such as a electrostat, or a line-source array of cones or domes, had it's dispersion limited in the plane of the driver(s) longest dimension. I don't know why I never saw the contradiction in my assumption about horn dispersion, and in fact, it still ~seems~ right to me, even though I know it's not.

But, my point is this. In light of this fact of horn dispersion, why was horizontal orientation chosen by PWK for almost all his designs? Is it because it is much more practical to stack the drivers and horns neatly on the baffle? (more compact) It does seem that a vertical mid and a tweeter horn sitting side by side would have some horizontal plane lobing effects in the x/o range, but the plus side would be much broader horizontal dispersion and limited vertical dispersion that would reduce the floor and ceiling bounce. IOW, I think you can make a good case that the "controlled dispersion" of horizontally oriented rectangular exponential horns is controlled in the wrong plane!

It sounds like I'm second-guessing PWK, but I'm not. I'm just trying to understand his design choice here, and thereby maybe understand horns a little better.

[boom3]

If you read some of Don Keele's articles in the JAES about his horn designs, you will have this explained far better than I can. Keele worked out some of the deeper science behind what Paul had discovered empiraclly.

My take on this question is that the ear's directionality in the vertical plane is poor and the lobing between the mid and tweet is less noticable if it is in the vertical plane. Paul's early mid horn, the K-5-J had flat, sides to control directivity. It was also cheaper to build that way. Since Paul believed the corner was the place of choice for any speakers, he also thought that 90 degrees dispersion-no more, no less-in the horizontal plane was the optimum.

IMO, the claim by folks like EV that their vertically mounted diffraction horns have good horizontal dispersion is hogwash. It just doesn't work and no one else in the industry followed suit. Every sucessful PA design uses horns oriented horizontally.

I do not hear a marked shift in timbre when I stand up after sitting in front of my Corns. If I did it would indicate that the lobing is marked in the vertical plane. I also hear a smooth transition between midrange and tweeter, so lobing in the horizontal plane must be very small. BTW, my Corns are about 2 feet out from the corners of a 16 foot wall, the room, is 25 feet deep. I moved them out from the corners to cut some of the tubbiness out of the bass.

[TBrennan]

JDM---Many horns have the widest dispersion along the wide axis. The T-35 tweeter PWK used supposedly had wider dispersion along the short axis and was used that way by EV. However some report that the dispersion is actually about the same either way.

Read this. http://aa.peavey.com/downloads/pdf/qwp1.pdf

[colterphoto1]

What TBrennan said. I believe I read in EV literature that the old standard 8HD should actually be mounted verticaly (umndown) for the widest dispersion along the short axis. Same for 350. I think it's like 100x 110 degrees so it doesn't make much difference. That is why Cornwall was built both ways IMHO, it didn't matter much. Just like PWK didn't think the edge diffraction caused by rear mounting the horns behind 3/4 motor board made much difference. He was a practical guy. No point doing something just for the theory of it, I guess.

This is also why the practice of 'toeing-in' Cornwalls is SO CRITICAL. You've got to keep the horn sounds from bouncing off the sidewalls first!

Modern horns with 40x60 dispersion are another thing altogether.

I've never in 2 years seen the actual dispersion characteristics of any of the K400, K600, K601, K700 horns printed here. Is it TOP SECRET?????

Michael

[D-MAN]

Whenever the subject of horn dispersion comes up, I like to interject the following on tight patterned horns:

It seems that the potential for throat overload (or something) is higher the tighter the dispersion pattern. For instance 60x40 is MORE LIKELY to be biting or harsh, where a 90x40 isn't, given same driver, same source signal, same volume, same gear, etc.

This could have to do with the "throw", i.e., distance from the mouth to the listening point, being that a tighter patterned horn is or could be intended to project the waveform farther than a wider one while retaining the acoustic energy as much as possible, but for the same distance for both of the above examples, the tighter patterned horn was certainly LESS pleasant to listen to. It could be that there is an optimal distance for the tighter pattern to be at its best, but I clearly was not sitting at the proper point, or something!

Tom Brennan pointed this out once, and it is certainly true by my empirical testing. So it is now a basic "rule" for me, and want to pass on.

DM

[jdm56]

So let me get this straight: I don't even know what I thought I knew? Horns don't ~necessarily~ have their widest dispersion in the plane of their smallest dimension?

...I think I'm getting a headache.

[boom3]

The 'rules' governing dispersion of direct radiators do not apply to horns. The theoretical models of direct radiators assume perfect planes (or, if you will, an array of points) moving perfectly in phase. The actual measurements are, of course, quite different. The initial flare of the throat of a horn sets the dispersion at the highest frequency of interest, regardless of the final shape or size of the mouth.

Paul once sent me an amplitude response curve of a Klipschorn at 0 and 30 degress off axis. The differences were rather small across the midrange and treble; the overall shape of the curve was essentialy the same as at 0 degrees. Of course, with a corner speaker, one cannot get more than 45 degrees off axis anyway.

[JohnA]

The short answer is there are some horns designed to have the long axis horizontal for widest dispersion and some with the long axis vertical.

The K-77/T-35A is a diffraction horn and has substantially wider dispersion with the long axis vertical from 3500 to 6000 Hz. Above that the difference is nil. Klipsch usually uses it above 6k. Klipsch' K-400 is the opposite.