Unity horn with 2 x Eminence Alpha 6 drivers - Page 3 - AVS Forum
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post #61 of 75 Old 09-18-2012, 08:13 PM - Thread Starter
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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





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post #62 of 75 Old 09-19-2012, 04:59 PM
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This thread is a great experiment and education tool. Hats off for all the effort to do this and share it with us. You sir deserve a DIY award of excellence.

Looking at your graphs it seems that covering more holes closer to the throat and CD benefits the low end extension of the CD. The mids seem to care more about the amount of breathing room. These observations and Ivan’s comments of position and wavelength leads me to wonder what would happen if you taped the rows closer to the throat? This would allow more un interrupted expansion for the HF driver. Any thoughts?

Derek
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post #63 of 75 Old 09-19-2012, 09:22 PM - Thread Starter
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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. smile.gif

John


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post #64 of 75 Old 09-27-2012, 02:31 PM
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Why not try to drill the holes like they do the EnABL process?

http://www.positive-feedback.com/Issue21/standingwaves.htm
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post #65 of 75 Old 09-27-2012, 07:35 PM - Thread Starter
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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?


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post #66 of 75 Old 09-28-2012, 04:59 AM
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No just thinking out loud.

There is probably somebody here that have more knowledge about exactly what pattern to use.
You could try to use tape and EnABL the area before and after your existing port.
Its suppose to do some kind of difference to diffraction horns. So why not try it?

The patent
http://www.google.com/patents/US5304746?dq=US5304746&hl=sv&sa=X&ei=8JJlUMiVHcSRhQeUgYHQDg&sqi=2&pjf=1&ved=0CDMQ6AEwAA

Maybe this can help you with ideas.
http://www.diyaudio.com/forums/full-range/146275-enabl-how-fostex-fe127e-other-speakers-2.html#post1865471
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post #67 of 75 Old 09-28-2012, 12:50 PM - Thread Starter
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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


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post #68 of 75 Old 09-28-2012, 01:13 PM
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Is there any objective evidence that enable does anything? Not being smart alecky, just wondering if there's some objective data out there somewhere.

DIY Synergy horn spreadsheet
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post #69 of 75 Old 10-03-2012, 06:34 PM
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Im fairly new to Unity/synergy so ive been reading several build threads lately (it passed seos as my #1 do want).
What seemes to be a rule of thumb is that they place the holes close to the corners in the horn because there is where it affects the CD the least, since the corners is where the horn loads/affects the CD the least.
And if your original holes didnt affect the CD very much, wouldnt it be a good idea to keep them and then use some small holes too, where ever you find that they affect the CD the least ofc.

Also, im curious as to why you choose closed back, instead of a small chamber behind the drivers ala Bwaslo? Or even a box ported into the horn ala Dag Johanson?

Oh and, awesome work cool.gif
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post #70 of 75 Old 10-03-2012, 08:49 PM - Thread Starter
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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


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post #71 of 75 Old 10-03-2012, 09:05 PM
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Ah, yes, ive red this thread too, so i got that much tongue.gif
You seemed to get good results with the original holes EXCEPT when driven hard due to port noise. So i was think why not keep them 4 big holes since they dont interfere with the CD anyways, and then just add some of thoose smaller holes(will need less of them with the bigger original holes in place) to get the air velocity down?
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post #72 of 75 Old 10-03-2012, 09:41 PM - Thread Starter
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Quote:
Originally Posted by eXa View Post

Ah, yes, ive red this thread too, so i got that much tongue.gif
You seemed to get good results with the original holes EXCEPT when driven hard due to port noise. So i was think why not keep them 4 big holes since they dont interfere with the CD anyways, and then just add some of thoose smaller holes(will need less of them with the bigger original holes in place) to get the air velocity down?

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


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post #73 of 75 Old 10-03-2012, 09:55 PM
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Yes, the swiss cheese aproach was clearly better for the mids, but screwed it up for the CD. Thats why i thought a combination would be good. Less smaller holes needed.
But yes, it would add to complexity, and create more work. And it may not even pay off, im just guessing here (purely based on the good results in the beginning).
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post #74 of 75 Old 02-13-2013, 05:07 PM
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Bump... just curious if there has been any progress?
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post #75 of 75 Old 02-14-2013, 11:23 AM - Thread Starter
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Not yet, but hopefully before too long. I've been working on my theater. Thanks for asking!

John


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