ProcessingWhatsNew

Vertical Directivity, Grabbing the bull by the horns

The plot shown here is a VituixCAD simulation of my line arrays. To be more exact, it’s a plot of the vertical directivity of the arrays. Normalized on it’s listening axis. With that picture, the title of this post is easily explained. In the earlier post where I mentioned adding passive filters, I’ve explained my goal to bundle the directivity in the vertical  direction. It results in the array having even less floor and ceiling troubles/reflections than an unfiltered array has. While most of the vertical pattern is well behaved, two lobes stand out. Horizontal directivity in comparison, is way more gradual in it’s pattern control.

Directivity

It’s easy to see  what I called the “horns” in the  title within that  vertical directivity plot. Those horns are lobes of energy that develop due to the center to center spacing of the drivers. Compared to an unshaded array, the lobes are reduced in both energy and in numbers. But those two strong lobes are persistent as long as I use an array with this kind of spacing between the drivers. 

Directivity Index

To see what effect it has on our listening pleasure we can look at the Power and DI curves:

Both the Power and Directivity Index curve show a couple of dips/peaks at around 4 – 5 KHz. Right where  the energy lobes hit the floor and/or ceiling and reflect back to our listening spot. That’s giving us quite an accurate prediction of how a speaker will sound in the room. A gradual change  in the DI can be quite pleasing, as the room’s reflections/diffraction will still bare a striking resemblance to our direct sound. Any deviation of the DI could stand out, if we have a reduced level of reflections within the first 15-20 ms at our listening spot.

APL_TDA

What is the resulting effect we can perceive in our listening room? To find that answer I needed to return to the tool: APL_TDA. That tool shows the time arrival in high resolution of the wave front that hits our ears. So without further ado let’s see if we can find those lobes in our room:

Visible at about 5 KHz and a mere 5 milliseconds after the main pulse is a bump in the graph. That’s the remainder of the floor/ceiling reflection as measured inside the room. Those are caused by those horns or lobes. We see a lot of other bumps and peaks too, but those stem from other surfaces like walls and furniture etc.

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