Unity horn with 2 x Eminence Alpha 6 drivers - Page 3

Well, I thought I'd quit at the "two hole" data set above, but I wanted to see if I could do better. I added another row of holes closer to throat, and ended up with this iteration. The "5/6/3/2" hole pattern seems to provide the best balance of low end and high end response (kind of looks like that sailboat I used to see on those old "light-brite" commercials from the 70's and 80's... or maybe just an origami paper hat).

I've shown comparison to the original "two rows" data (shown in my lat post) as well as another pattern in the hole plate. Notice the extended low end response of the BMS 4550 from 1-1.5k as well as the smother top end from 3-6k. And, compared to "two holes", I'm only taking <1db hit on the alphas from 350-500hz.




I'll now have to make a dedicated plate with only this pattern so that I can confirm its superiority and move forward with further testing. We'll see what happens next!

John

Edit: adding some construction data: hole plate 3/16" thick; distance to first row (the "5" of "5/6/3/2") is 7.3 cm compass radius from outside center point at CD mounting plate attachment




Edited by johnbomb - 9/25/12 at 7:07pm

Thanks, Derek.

I think your observations are correct. Many of the iterations that I tested (whose results I didn't post) had holes and other port shapes that were further out from the throat than what I am currently evaluating, and these all caused the alpha high end rolloff to occur at a lower frequency than I wanted. I suspect that I'm at the point of diminishing returns with respect to trying out new hole combinations, unless further testing of this "5/6/3/2" arrangement doesn't hold up to my requirements at 119db. I'll post those results when I have them, along with more specific design information if all goes well. That way, if someone wants to build one of these things, they will have the completed recipe.

John
Edited by johnbomb - 9/20/12 at 8:34am

That's a pretty cool idea, although I'm not sure how I'd get enough holes close enough to the horn with that pattern to get enough port area. Did you have a specific pattern in mind?

I've been reading the related threads at diyaudio: fascinating stuff. Here's the "daddy" thread:

http://www.diyaudio.com/forums/multi-way/100399-enabl-processes.html?perpage=25&pagenumber=1

From what I have gathered so far, this EnABL process is used to create a kind of diffraction grid to reduce (eliminate?) standing waves that originate from driver cones and speaker enclosures... potentially very useful in the horn domain, as the terms "honk" and "bite" come up quite often. I'll have to think about this some more and try to come up with a pattern to line the mouth of the horn.

Other methods for reducing horn harshness include surrounding the periphery of the horn mouth with absorptive material, stuffing the whole horn with 30ppi foam, and using exotic horn mouth terminus profiles such as that used by Le'Cleac'h

Hey guys,

Sorry I'm just now responding.

Bill- I'm not sure what to believe regarding enABL. The white paper posts some measurement differences toward the end, but I don't know what to make of them.

eXa- My hole arrangement is the best way I could find to balance the response of the sealed back alpha 6 drivers and that of the BMS 4550 compression driver. There are likely better arrangements to be had. I changed the original port layout because I was getting distortion and extreme port air velocities at very high volumes. I chose the sealed back drivers because they are the most efficient of the drivers I've tested.

Thanks,
John

Woops, reread your first post- I missed that suggestion the first time (time for me to go to bed!). See the last graph in post #47, which shows a FR comparison of the original ports to that of one of the multi hole iterations. The original port arrangement is less efficient than the newer multi hole layouts. Adding smaller holes next to the original ports might work, but that adds design complexity. I can drill a pattern of 1/4" holes quickly once marked out, and I don't need a router to cut the back flanges- only a recess bit, which is much safer to use.

Also, I think that multiple small holes produce less port noise than a single port of comparable area, presumably secondary to increased laminar flow of air.

John

Not yet, but hopefully before too long. I've been working on my theater. Thanks for asking!

John