I'm building three line arrays with 6x GRS clones of the BG NEO 8 per speaker. I bought the Joseph Crowe Neo3 tweeter horn CAD file and elongated the design to fit the NEO 8. I then 3D printed the design in two different widths. There has been some discussion that blocking the 2 outermost slots in the NEO3/NEO8 speakers improves off-axis dispersion, so one of the designs only allows the center two of the four slots of the speaker to be exposed. I also tested two different sizes of rear chambers. The idea for my line array is to make very large (but shallow) speakers that will fit behind a 100" acoustically transparent projector screen. My modifications of Joseph's original design eliminates the nice round overs that curve to the back, so that the horns would fit flush in a large infinite baffle style speaker.
Here are all of the measurements together.
The complete Line Array would be 6x NEO8s stacked like below.
Here's the two designs, One Narrow/2-Slots Wide, one normal width/4-Slots.
These were rather rough prints with 1.0 x 0.3 mm layers. I printed in ABS because it sands and glues well. I spent minimal effort on sanding.
Here's the flat baffle I tested along with the large rear chamber (Old 6x9 Car audio box), rear chamber (green 3D print), and the two horns (2 and 4 slot).
The small chamber had a weird resonance around 2.4k The difference in level may not be real, as I forgot to test the small chamber, and had to re-set everything up to get the measurement. All of the other measurements below were done with the large chamber.
Small (blue) vs Large (red) chamber:
Large Chamber Distortion:
Small Chamber Distortion:
The flat baffle with flush-mounted GRS NEO8:
Straight-on measurement (0 degrees) of the flat baffle (red), narrow horn (green), wide/normal horn (purple).
15 Degrees. flat baffle (green), narrow horn (orange), wide/normal horn (red).
30 degrees:
Interesting that the narrow slot horn did help off-axis dispersion, but only above 16k.
45 degrees:
Flat baffle (no horn) 0, 15, 30, 45 degrees
Narrow Slot Horn at 0, 15, 30, 45 degrees
Normal Width Slot Horn at 0, 15, 30, 45 degrees
Final thoughts:
The normal-width horn did not have a very smooth output which was surprising, but it did have the same increase in output from 1k to 3k as the narrow horn.
I was also surprised that the off-axis levels diverged lower (1k vs 4k) with the horns.
Interesting that the narrow slot horn did help off-axis dispersion, but only above 16k; also interesting that the narrow slot was actually the loudest everywhere.
I don't think that I'm going to end up using the horns in my line array. The more gently upsloping response of the flat baffle should play well with low end lift that you get from a line array. And the lack of the sudden increase in response around 1k (that the horns have) should allow me to cross over the flat baffle mounted speakers lower (500-700 Hz).
Joseph already posted about a horn he actually made specifically for the NEO8. His wooden horn was much larger, and helps extend the usefull range. My 3D printed horn raised output down to ~1200 Hz, but Josephs's larger horn increased output down to 300 Hz! He posted about it here: https://www.diyaudio.com/community/threads/grs-pt6825-8-planar-test-results-300hz-horn.379684/
The fact that a horn-loaded NEO 8 can play down to 300 HZ is amazing. I'm convinced now that there is really no point to the NEO3. The NEO8 plays the upper range just as well, but allows a 2-way speaker with a lower crossover and probably more headroom as well.
Would anybody else choose one of the horns over the flat baffle in a line array? What do you guys think? Big thank you to Joseph Crowe for making his CAD files available, makes this silliness possible.
Here are all of the measurements together.
The complete Line Array would be 6x NEO8s stacked like below.
Here's the two designs, One Narrow/2-Slots Wide, one normal width/4-Slots.
These were rather rough prints with 1.0 x 0.3 mm layers. I printed in ABS because it sands and glues well. I spent minimal effort on sanding.
Here's the flat baffle I tested along with the large rear chamber (Old 6x9 Car audio box), rear chamber (green 3D print), and the two horns (2 and 4 slot).
The small chamber had a weird resonance around 2.4k The difference in level may not be real, as I forgot to test the small chamber, and had to re-set everything up to get the measurement. All of the other measurements below were done with the large chamber.
Small (blue) vs Large (red) chamber:
Large Chamber Distortion:
Small Chamber Distortion:
The flat baffle with flush-mounted GRS NEO8:
Straight-on measurement (0 degrees) of the flat baffle (red), narrow horn (green), wide/normal horn (purple).
15 Degrees. flat baffle (green), narrow horn (orange), wide/normal horn (red).
30 degrees:
Interesting that the narrow slot horn did help off-axis dispersion, but only above 16k.
45 degrees:
Flat baffle (no horn) 0, 15, 30, 45 degrees
Narrow Slot Horn at 0, 15, 30, 45 degrees
Normal Width Slot Horn at 0, 15, 30, 45 degrees
Final thoughts:
The normal-width horn did not have a very smooth output which was surprising, but it did have the same increase in output from 1k to 3k as the narrow horn.
I was also surprised that the off-axis levels diverged lower (1k vs 4k) with the horns.
Interesting that the narrow slot horn did help off-axis dispersion, but only above 16k; also interesting that the narrow slot was actually the loudest everywhere.
I don't think that I'm going to end up using the horns in my line array. The more gently upsloping response of the flat baffle should play well with low end lift that you get from a line array. And the lack of the sudden increase in response around 1k (that the horns have) should allow me to cross over the flat baffle mounted speakers lower (500-700 Hz).
Joseph already posted about a horn he actually made specifically for the NEO8. His wooden horn was much larger, and helps extend the usefull range. My 3D printed horn raised output down to ~1200 Hz, but Josephs's larger horn increased output down to 300 Hz! He posted about it here: https://www.diyaudio.com/community/threads/grs-pt6825-8-planar-test-results-300hz-horn.379684/
The fact that a horn-loaded NEO 8 can play down to 300 HZ is amazing. I'm convinced now that there is really no point to the NEO3. The NEO8 plays the upper range just as well, but allows a 2-way speaker with a lower crossover and probably more headroom as well.
Would anybody else choose one of the horns over the flat baffle in a line array? What do you guys think? Big thank you to Joseph Crowe for making his CAD files available, makes this silliness possible.
For someone that wants more typical vertical polar response, designs like the Neo3 provide it.
Don’t you normally want to limit ceiling and floor reflections? When would you opt for the neo3 over the neo8?
It depends on what you are trying to accomplish.
If you want a speaker that's not as position dependent, something closer to point source behavior can be preferable. The Neo3 would be beneficial then. The KEF LS50 for example, has nearly identical, wide-ish horizontal and vertical dispersion in a small package. You can sit down, stand up, walk around the room, and the overall frequency balance is quite consistent across all those positions. Some people feel this type of behavior also produces a deeper soundstage and overall more realistic imaging. While others find this type of presentation a little vague.
Other designs use more restricted dispersion to minimize room reflections, as you said. Sometimes that's vertical only, other times it's more restricted horizontally as well to limit side wall interaction. This can improve image focus, but when carried to extremes you almost have to have your head in a vise to maintain the image and frequency balance.
Middle length planars/ribbons can also be harder to balance across the frequency range, since they can be a point source vertically at low frequencies and a line source at high frequencies.
Full floor-to-ceiling line sources can eliminate the vertical directivity problem while also eliminating the floor/ceiling reflection.
Of course a lot of this just comes down to what each person likes.
If you want a speaker that's not as position dependent, something closer to point source behavior can be preferable. The Neo3 would be beneficial then. The KEF LS50 for example, has nearly identical, wide-ish horizontal and vertical dispersion in a small package. You can sit down, stand up, walk around the room, and the overall frequency balance is quite consistent across all those positions. Some people feel this type of behavior also produces a deeper soundstage and overall more realistic imaging. While others find this type of presentation a little vague.
Other designs use more restricted dispersion to minimize room reflections, as you said. Sometimes that's vertical only, other times it's more restricted horizontally as well to limit side wall interaction. This can improve image focus, but when carried to extremes you almost have to have your head in a vise to maintain the image and frequency balance.
Middle length planars/ribbons can also be harder to balance across the frequency range, since they can be a point source vertically at low frequencies and a line source at high frequencies.
Full floor-to-ceiling line sources can eliminate the vertical directivity problem while also eliminating the floor/ceiling reflection.
Of course a lot of this just comes down to what each person likes.
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