The Great Waveguide Shootout!!! - Page 7 - AVS Forum
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post #181 of 190 Old 09-18-2013, 06:29 PM
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I would expect a waveguide to have less diffraction than a diffraction modeler suggests. Very odd.
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post #182 of 190 Old 09-18-2013, 10:30 PM
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Quote:
Originally Posted by mtg90 View Post

Yeah but switched early on from a baffle that rotates and mic stays put to a mic that rotates while the baffle stays put. That way I did not have to glue in the fiberglass waveguides which don't have mounting holes. If I hang the mic it will always point strait down while it rotates instead of always pointing at the center of the baffle.

I think that confirms it... it must be the wood strip on which the mic is mounted. That is why the dip is at the same frequency at all angles. If it was from the baffle, then the distance to the baffle would change with angle, producing different time delays at different angles.
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post #183 of 190 Old 09-19-2013, 11:25 AM
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Quote:
Originally Posted by tuxedocivic View Post

I would expect a waveguide to have less diffraction than a diffraction modeler suggests. Very odd.

The SEOS doesn't have a particularly large end radius.

I is curious ha something with high directivity is so sensiive o his, but Geddes makes a big deal over it.

Noah
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post #184 of 190 Old 09-19-2013, 11:58 AM
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Quote:
Originally Posted by mtg90 View Post

Yeah but switched early on from a baffle that rotates and mic stays put to a mic that rotates while the baffle stays put. That way I did not have to glue in the fiberglass waveguides which don't have mounting holes. If I hang the mic it will always point strait down while it rotates instead of always pointing at the center of the baffle.

I looked again at your setup in the first post. Maybe put a bunch of OC 703 rigid fiberglass or foam on the wood crossbar as well as the posts, which should knock out any reflections.

Also, measure a waveguide at 0 degrees first with the mic holding jig, then a measurement with the mic just hanging from its cable at 0 degrees with the wooden mic jig rotated completely out of the way. You could also do one with the jig set to 0 degrees with fiberglass/foam. Compare all three and see what you get.
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post #185 of 190 Old 10-17-2013, 08:34 PM - Thread Starter
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This thread is long overdue for an update...

Well it has been determined that the wooden mic support jig is at fault for the ragged response while mounted on the baffle.

It was almost three weeks ago Pitviper33 (another Matt smile.gif) came over for a few hours during the evening and we measured the response with the mic mounted in the jig vs. the jig moved away and the mic on a normal mic stand/boom. The mic stand measurement was free of the lumpiness exhibited with the wooded jig so the wooded jig must have been at fault. We then tried all sorts of different amounts and styles of damping material to knock out the reflection in almost every position or combination possible. Nothing worked to completely eliminate that reflection, not even coating the whole wooden jig with full 3-1/2" thick R-13 batts of recycled denim insulation!!!

Matt might have some pictures of our feeble attempts.

Here is a measurement comparing waveguide free air, waveguide in baffle with mic in stand, waveguide on baffle with mic in jig. Spaced 5db apart:



So at this time I am going back to the first idea which was to have the baffle rotate and the mic remain in a constant position which will allow me to use the mic stand which I know has no detrimental effects on the response. Matt did suggest an excellent way to setup the baffle so that I do not need to glue in the fiberglass waveguides to keep them from falling out and that is to measure my 0 with the baffle angled at 45 degrees on way then I can move the baffle in the opposite direction so that 45 degree measurement angle will have the baffle flat and at 90 degrees the baffle will be in the opposite 45 degree position.

The real problem now becomes how much time is left to take outdoor measurements. With my trip to Erich's next week I don't think I am going to get a chance to do much more work on it this season. frown.gif

Back when I started this I thought I could knock this out in a week or two, look how that turned out rolleyes.gif

So unless I get everything out sometime this next week or Chicago has some really nice weather this November/December I think this project might go into hibernation till spring rolls around.
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post #186 of 190 Old 10-17-2013, 08:46 PM
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could the whole thing be salvaged by mounting a triangle shape to the jig arm so that it doesn't reflect?

Listen. It's All Good.
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post #187 of 190 Old 10-17-2013, 08:52 PM
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something like this cut into strips and attached to the jig?



if the problem is something else, then just ignore me. :-)

Listen. It's All Good.
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post #188 of 190 Old 10-18-2013, 09:08 AM
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Quote:
Originally Posted by mtg90 View Post

Back when I started this I thought I could knock this out in a week or two, look how that turned out rolleyes.gif

So unless I get everything out sometime this next week or Chicago has some really nice weather this November/December I think this project might go into hibernation till spring rolls around.

biggrin.gif

Yep...I always think the same thing. That's just how it goes.
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post #189 of 190 Old 10-18-2013, 09:48 AM
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That's great! At least you what the problem is. We will be waiting come spring smile.gif
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post #190 of 190 Old 10-19-2013, 07:25 AM
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Quote:
Originally Posted by mtg90 View Post

This thread is long overdue for an update...

Well it has been determined that the wooden mic support jig is at fault for the ragged response while mounted on the baffle.

It was almost three weeks ago Pitviper33 (another Matt smile.gif) came over for a few hours during the evening and we measured the response with the mic mounted in the jig vs. the jig moved away and the mic on a normal mic stand/boom. The mic stand measurement was free of the lumpiness exhibited with the wooded jig so the wooded jig must have been at fault. We then tried all sorts of different amounts and styles of damping material to knock out the reflection in almost every position or combination possible. Nothing worked to completely eliminate that reflection, not even coating the whole wooden jig with full 3-1/2" thick R-13 batts of recycled denim insulation!!!

Matt might have some pictures of our feeble attempts.
I do have a picture!

I've been pretty swamped this summer/fall, so I haven't kept up with threads all that well. I should have posted this weeks ago.

We tried at least five different setups of absorbing material on that rig, and somehow we still never got a clean measurement. I don't have pictures of all of them. But the good news is that I think we settled on a method that should work when you next have time to test. The tilting table +45 to -45 should let you use the boom stand without worry of waveguides falling out.

Glad to hear you're heading down to Eric's. I'm sure with the two of you guys in one place, lots of interesting speaker things will happen! Let me know when you're back and find a reasonably warm day. I'd love to come over and help again for the real test!

I'm not into "thumbs upping" or "liking". Don't take it personally. Just assume that I found your post helpful. Unless it wasn't.
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