Diy 15" EOS waveguide in progress.... - AVS Forum
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Old 07-02-2014, 07:08 PM - Thread Starter
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Diy 15" EOS waveguide in progress....

I've been wanting to build some big elliptical Synergy horns for a while. In fact, they've been in the planning stages for almost two years now. It's time to get something done!

Before I start on the big boys I figured I should see if my construction method is going to work on something smaller. I got this idea from Tom Danley in an old thread on Audio Asylum. He said to cut out the desired mouth shape, stretch some type of stretchy material over it, and press down in the middle with a rod. You hit it with some 'glass resin and bam! Instant conical horn.

My method is a bit more complicated than that. I turned my drill press into a wood lathe to turn the OS throat profile to match my CD and the narrow (vertical) angle of the horn. My hope was that by turning my mold to the narrower vertical angle that the act of stretching the material would take care of the elliptical to round transition area. This will be my press to form the throat section.Then I made the form out of chipboard and a foam water noodle play thing.

The resin is still drying, but so far it looks pretty good! The horizontal round to elliptical transition isn't quite right but I don't think I had my material stretched quite enough before I pressed my throat mold in.

If I can get it off the mold in one piece I'll make up a mounting plate for my CD (BMS 4552nd) and get some measurements.
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Old 07-02-2014, 07:10 PM - Thread Starter
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I should add that what I have isn't a true OS profile but a close approximation. Horizontal angle will be 90° and vertical will be 80°.
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Old 07-02-2014, 07:32 PM
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I guess I am a big kid, cause the first pic looks like a condom (unrolled).

Have you looked up "the octagon" by PNW? He did some optimizing of directivity vs loading on the driver in an elliptical shape.

JoshK on most other audio forums
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Old 07-02-2014, 08:05 PM
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Very cool. DIY to the max eh. Can't wait to see how these turn out.
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Old 07-03-2014, 02:05 AM
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Ah someone beat me to it!! I have had that idea for ages, sure beats cutting complex angles.
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Old 07-03-2014, 06:47 AM - Thread Starter
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Josh - I'm also a big kid.......I can't believe I didn't see that myself!

Well waveguide V1 was a failure. It went better than expected, but I didn't think I was gonna nail it on the first shot. I designed my fixture to use a 3.375" mouth round over. I couldn't get it to curve nicely around the mouth, so I went to a 2.5" dia piece of foam. At the time I wasn't thinking that the mouth sets the geometry of the wg, so when I went with a smaller dia round over it threw everything off. As a result I have a sharp change of angle about 1.5" from the throat in the vertical.........diffraction horn!!!

That, and the Pam I used on the plug as a release agent didn't work worth a $#@t. However, the duct tape and Pam I used on the round over released quite well. Other than my throat plug being bonded to the waveguide, it looks really nice. The walls are super smooth. Once I get the bugs worked out I should be able to 'glass the back side of the wg to reinforce it, add my CD mounting plate and be ready to rock.

I'm gonna go after V2 today. I think now I can make the larger round over work, and I'm going to make a new throat plug that will allow the wall angle to be set entirely by the mouth geometry. Hopefully by the end of the day I'll have a good one.

IF this works out, I might try to build a cardioid enclosure for the TD15m I'll be using for a mid to get constant directivity down to 300hz or so, then I'll roll in my other sealed TD around 2-300 hz to bring up the falling response of my cardioid mid......but first I need good waveguides!
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Old 07-03-2014, 06:53 AM
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Awesome project! I love seeing someone tackle a tough, yet highly interesting idea that hasn't been done before!

How would this EOS-15 compare to the Seos-15? I am not very familiar with the EOS waveguides. Are they more round than retangular? I would guess that the EOS design has a slightly different directivity patern, right?
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Old 07-03-2014, 07:31 AM - Thread Starter
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Marty, it's all about the shape of the mouth. The "E" in EOS stands for elliptical, and the "SE" in SEOS stands for Super Elliptical. They're both constant directivity waveguides (at least hopefully mine will be!) the only difference being the shape of the mouth and the coverage angle. Mine are wider in the vertical and thus larger so they should hold directivity lower in the vertical plane. I won't say it's better or worse, it's just a bit different design with different considerations.
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Old 07-03-2014, 09:01 AM
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Potential. This thread has it.

-

"Too much is almost enough. Anything in life worth doing is worth overdoing. Moderation is for cowards."
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Old 07-03-2014, 09:14 AM
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Quote:
Originally Posted by Nate Hansen View Post
IF this works out, I might try to build a cardioid enclosure for the TD15m I'll be using for a mid to get constant directivity down to 300hz or so, then I'll roll in my other sealed TD around 2-300 hz to bring up the falling response of my cardioid mid......but first I need good waveguides!
I've tried a few Cardioid enclosures for the 15M and will be trying another one this weekend.

Here are two I've tried: http://i.imgur.com/RLOfNg7.jpg and http://i.imgur.com/RWaZYH0.jpg . The slot version is a little better behaved up top and IMO, more aesthetically pleasing. But, both only work to about 450hz or so before getting funky, fortunately, with the BMS coax, 450hz isn't an issue. A slightly narrower baffle(mine is 19") may help, but I'm going to try another idea version soon, hoping for even better aesthetics and smoother response up top. FYI, it will play down to 150hz without an issue: http://i.imgur.com/tfITrDk.jpg

Mike
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Old 07-03-2014, 11:06 AM - Thread Starter
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Thanks Face. If/when I get to that point I'll have to pick your brain.

V2 fixture is ready to roll with the 3.375" mouth round over. I tried a different throat plug I have, but it's still pinching the throat in the vertical so I didn't bother to glass it. I'm going to turn a new one now....
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Old 07-03-2014, 12:35 PM - Thread Starter
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Here we go. I still have some pinching in the vertical direction of the waveguide, I'll need to use filler to smooth it out here. I'm gonna hit it with one more coat of resin then I'll run and get some fiberglass mat to reinforce the back.
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Old 07-03-2014, 09:22 PM
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Is there any similarity between this and Paul Spencer's 24" Synergy horn?

http://redspade-audio.blogspot.com/
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Old 07-03-2014, 09:37 PM - Thread Starter
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Is there any similarity between this and Paul Spencer's 24" Synergy horn?
There will be. This one is about 18" across and is for a compression driver only. I believe Paul's Synergy is closer to 3' wide which is what I'm shooting for when I get my process nailed down on these "smaller" waveguides. He beat me to it!
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Old 07-03-2014, 09:54 PM - Thread Starter
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Well V2 has been reinforced, cd mounting plate attached, and I've got filler in the throat drying now. That said, I'm not so sure about the profile on this one....there's a bit more curve than I like. My throat plug keeps throwing things off; the material isn't stretching how I think it should. Hopefully tomorrow I can start testing or Saturday at the latest and I'll know for sure. AudioJosh, maybe I've accidentally stumbled on pnw's prolate spheroidal curve

As you can see this is my first time working with fiberglass mat



I decided to make another one since V2 is iffy. For this one I chucked my throat plug, and used a 1.125" dowel. I'll build up the throat and set the angle to match my cd with filler. Think the profile on this one came out better, and I don't have any pinching in the throat.

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Old 07-03-2014, 10:32 PM
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This is cool. Any chance you could shoot some video when you create shape ?
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Old 07-04-2014, 06:36 AM - Thread Starter
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You mean when I press the fabric then glass it? I could do that.
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Old 07-04-2014, 07:18 AM
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You mean when I press the fabric then glass it? I could do that.
Yup
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Old 07-04-2014, 04:23 PM - Thread Starter
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V2 has been measured. I did polars of the left and right side of the waveguide. I'm not surprised they differ but some of that could be the measurement conditions as well. I also did a set of verticals. My measurements were done about 4' from the mouth of the wg and the apex is at about 4' off the ground. Just over a 3ms gate. Cross Spectrum calibrated mic. 0-20° in 5° increments then out to 90° in 10° increments.

First will be the left side of the wg:



Now the right side:



Vertical:



Here's the impulse:



I just got all the data so I haven't really taken the time to study it. Some widening that I don't like from 3-5k but overall fairly consistant off axis. There are some abnormalities about 3-4" from the throat that still need work and I think that corresponds with the widening of the pattern at 4k. Also, I was hoping for a bit more low end extension. I'll be crossing around 1k so I should be ok though.

Going to work on V3 now, this is getting exciting. I was gonna head out tonight but I might keep working instead
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Old 07-05-2014, 08:25 AM
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Quote:
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V2 has been measured. I did polars of the left and right side of the waveguide. I'm not surprised they differ but some of that could be the measurement conditions as well. I also did a set of verticals. My measurements were done about 4' from the mouth of the wg and the apex is at about 4' off the ground. Just over a 3ms gate. Cross Spectrum calibrated mic. 0-20° in 5° increments then out to 90° in 10° increments.

First will be the left side of the wg:



Now the right side:



Vertical:



Here's the impulse:



I just got all the data so I haven't really taken the time to study it. Some widening that I don't like from 3-5k but overall fairly consistant off axis. There are some abnormalities about 3-4" from the throat that still need work and I think that corresponds with the widening of the pattern at 4k. Also, I was hoping for a bit more low end extension. I'll be crossing around 1k so I should be ok though.

Going to work on V3 now, this is getting exciting. I was gonna head out tonight but I might keep working instead
Perhaps I missed something, but, are these not going to be used with your BMS coax compression drivers and ran down to 450hz where you stated they hold pattern down to, and then running them up all the way as high as the BMS will go in something like a 2-way design?

The reason that I ask is because you stated that you were going to cross them at 1,000hz, and that seems like it would be a shame if both the waveguide and BMS compression driver are both capable of going down to 450hz.
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Old 07-05-2014, 09:55 AM - Thread Starter
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Quote:
Originally Posted by Martycool007 View Post
Perhaps I missed something, but, are these not going to be used with your BMS coax compression drivers and ran down to 450hz where you stated they hold pattern down to, and then running them up all the way as high as the BMS will go in something like a 2-way design?

The reason that I ask is because you stated that you were going to cross them at 1,000hz, and that seems like it would be a shame if both the waveguide and BMS compression driver are both capable of going down to 450hz.
Maybe I didn't say, but I'm using bms 4552nd drivers which are 1" exit. I don't have the coax drivers. This wg is not large enough to get pattern control to 450hz. I'll be building a larger wg in the future.
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Old 07-05-2014, 11:41 AM - Thread Starter
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It continues. I filled and sanded V2 again, focusing on the throat and 3-4" from the throat. I also got V3 sanded. I measured V3 first but I didn't like it as much as v2. There's a bigger dip at 0-5° and I wonder if that's the on axis dip we see with an axisymmetric wg (this one is a little more round). I also wonder if the widening of directivity in V2 at 3-4khz is the same dip, but it's spread out more due to the elliptical shape. Hmmm.

Anyways, I'll show V2 without eq and with eq. The eq is a 6dB BW hi pass at 6.5khz and a few notch filters. I also finally figured out how to make directivity sonograms in ARTA, which is pretty cool. The sonograms are raw data with no gating. I can't figure out how to get the sonograms to work with gating. I think I need the peak of the impulse at 0 and it's more like 600ms.

No eq:



My work in the throat seems to have improved the 3-4khz area a bit.

Eq/xo:



Eq directivity plot, 1/6 octave smoothing to make it easier to read:



You can really see the widening at 3-4khz here, changing from about 80° at 1.5khz to 90° at the "wide spot." Not too bad for 100% diy . I think I'm going to make another one. By rights I should use this one and make a mold so I can lay this up in 'glass and have 2 identical pieces...........but I'm not gonna do that.
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Old 07-05-2014, 12:06 PM
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What fabric are you using? I assume it's woven so that it stretches evenly in all directions. I bet the pre-tension on the fabric would change the curve a little - but maybe not.
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Old 07-05-2014, 04:29 PM - Thread Starter
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It's a woven polyester used for swimming gear. I asked for "stretchy fabric" at the fabric store and this is what they pointed me to.

Here's a video of the "waveguide press." This will be like the one from the measurements in my last post. I'm not sure, but I think the narrower directivity at hf is due to the curvature of the walls. I think if I would have went with a smaller mouth round over the curve wouldn't be as pronounced. I guess this is sort of between a conical horn and a traditional horn profile.

I've never posted a video anywhere so hopefully this works.........

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Old 07-05-2014, 08:17 PM
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This is pretty cool stuff.
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Old 07-07-2014, 04:37 PM - Thread Starter
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I'm still hard at it..........sanding and filling, sanding and filling, sanding and filling......but improvements are being made. In this set of measurements the entire guide has been smoothed and I paid particular attention to the throat. Nice and smooth. The only thing bugging me right now is the exit angle on my wg is about 2-3° or so steeper than on my cd and I'm at a point where I can't sand anymore without sanding into the fiberglass and making the entrance bigger. I might get a belt sander and take about .200" off my mounting plate/throat. This will allow me to build the throat into the correct angle with filler, but I'm not sure if it will be worth the effort.........it's fairly close as is. I measured both left and right sides of the wg and they match up quite well so my symmetry is better than I thought it would be.

I'm liking the improvements though. Over 5khz flattened out quite nicely, and the peaks that you see are mostly driver issues seen in the manufacturer's plots. I'm still not happy about the "hot spot" at 3-4khz but I'm not sure how to approach that at this time. I was thinking it might be the on axis dip due to mouth diffraction that's spread out due to the elliptical shape, but it seems to be happening too low in frequency. Any ideas?

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Old 07-07-2014, 06:02 PM
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Nice work Nate!

My guess is that you are correct. The on-axis "depression" is a lower Q version of the round OS "dip"...lower Q because the WG is somewhat asymmetric. Given "flat" OS walls, making it even more asymmetric may help. (That means a larger WG so it doesn't lose vertical pattern control at a lower frequency than desired.)

Keep up the good work!

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Old 07-07-2014, 06:26 PM - Thread Starter
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Thanks Paul. That was the idea with the elliptical.....to mitigate or eliminate the dip. Looks like I've mitigated it as it's nowhere near as extreme as it is in the Summa, but it's still there. If I were to do it over I'd make it a bit narrower in the vertical but I personally don't want to give up pattern control in the vertical.
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Old 07-08-2014, 07:37 AM
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Agree on the vertical pattern control. Important and too often overlooked.

Another thing that can help with the on-axis depression is to add a little curvature to the walls, biased toward the inside of the mouth. The trade-off is a slight narrowing of the HF pattern.

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Old 07-08-2014, 11:00 AM - Thread Starter
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That makes sense.....there was more curvature near the throat in my last set of data and the 3-4khz region looked better. Yesterday I focused on opening the throat faster and flattening out the walls.
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