| The distance to the seating position is 3 times the wavelength of the lowest frequency diffused. As you have found this can be quite large.
Ethan maintains that you can sit closer than this and still get worthwhile benefits. (I can't remember the exact post, but someone will)
When it comes to your solution, you have two main choices:
- What size panels
- How much work .. (how many fins)
The common size for commercial panels is 2 ft by 4 ft. This 1:2 ratio allows two panels placed side by side to form a square, which can be rotated 90 degrees if required for some modulation. I would probably stick with this ratio if it were me. Since 6 ft * 3ft is big, I would go for 3 ft * 1-1/2 ft. If you build 10 of these and stack 'em two high, you get 5 periods with coverage 6ft high by 7-1/2 ft wide. Make 8 normal panels and two invere panels.
How deep?
Fire up QRDude and reset to defaults. Switch to an inverse panel and adjust the depth of the deepest well until the period width is less than your desired panel width. Since the actual panel will be larger than the period width by 1 fin, build in a little slack - in your case, make the deepest well 8.5 inches. Now read off the design frequency - 797 hz. Round off to 800Hz
Whatever width you go with, this technique will give you the minimum design frequency that can be used for a given panel width.
If you want to use a true inverse panel in the mix, it will not have any zero-depth wells. This precludes using the half-width end wells for that nice build. A suggestion would be to use the fin material for the sides as well. Two panels side by side would then be out of sep by one fin thickness - not really an issue.
Now you have the design frequency, you need to look at how many wells.
Check the menu for "Advanced mode"
Check the menu for "Auto-optimise build depth in Advanced mode"
Check the menu for "Panel will be used in a sequence that includes its inverse"
Now step through the number of wells till your well width gets down one inch. You will see the following solutions
N7, N11, N13, N17
The N17 shows a period width greater than 1' 6"" so that needs to be left out.
As you go up in order, the bandwidth increases, but so does the amount of work.
The N11 has the same build depth for the standard and inverse panels , so that's nice
The N13 has different depths for the two panels. You are in the enviable position of having plenty of depth available, so turn off the auto-optimise. Rotate the phase wheel to the +2 position. This gives you a normal and inverse panel of the same depth - 7-13/16 inches.
This is your easiest to install, and best performing build in the 1:2 form factor.
So you see, there are compromises and decisions to be made along the way. I hope this little walk-thru shows how QRDude can be used to help make those choices. |