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Multi-Way Conventional loudspeakers with crossovers

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Old 8th July 2014, 09:57 AM   #691
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Yes, I have seen the video. It seems easy enough to make the curve you want, but I canīt make sense of the use of ellipses - it seems to me that what you need are sections of parabolas, mirrored on both axis. The focus of the parabola will be adjusted to get the curve you want. Iīm no math genious (thatīs an understatement :-)) but experimenting with ellipses they donīt seem to give equal path lengths - only approximations, whereas parabola sections will give exactly equal path lengths.

Sure, Iīd like to try it out with a 3D printer - but it would be nice to hear what others think first, if itīs an idea worth pursuing or not.
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Old 9th July 2014, 08:12 AM   #692
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Cookie Monster, I think your design looks promising. It might need to be a bit thicker, due to the reduction in the area, but YMMV
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Old 18th August 2014, 07:57 PM   #693
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Regarding your pile of junk dishes. Those are all offset types.
In other words, none of them contain "center" of the parabola.
There's a good chance you could clover 3 or four of them into
a much larger chunk of parabola without the leaves touching.

I had such a pile in my garage till recently...

Would be really hard to align for microwave purposes, which
was my original plan. But if you are just making a pair in the
back yard for acoustic toys....

Last edited by kenpeter; 18th August 2014 at 08:04 PM.
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Old 7th October 2014, 11:31 PM   #694
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Just thinking of a cross between paraline and Smith horn.
Straight internal reflectors at the top and bottom, rather
than the usual parabolic. Flat triangular expansion all the
way to the horizontal exit slot. Then two roundovers:
Halves of PVC pipe covering the entire frontal area.

Last edited by kenpeter; 7th October 2014 at 11:35 PM.
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Old 8th October 2014, 12:40 AM   #695
xrk971 is online now xrk971  United States
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Quote:
Yes, I have seen the video. It seems easy enough to make the curve you want, but I canīt make sense of the use of ellipses - it seems to me that what you need are sections of parabolas, mirrored on both axis. The focus of the parabola will be adjusted to get the curve you want. Iīm no math genious (thatīs an understatement :-)) but experimenting with ellipses they donīt seem to give equal path lengths - only approximations, whereas parabola sections will give exactly equal path lengths.
The definition of an ellipse is that a segment from one focus to any point on ellipse to the other focal point is a constant along any point in ellipse. So in theory, the ellipse is exactly the shape you want if you want to use two drivers and one each at a focus. A parabola is a flat slice along a 3d ellipse surface of revolution.

Last edited by xrk971; 8th October 2014 at 12:42 AM.
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Old 8th October 2014, 02:25 AM   #696
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Quote:
Originally Posted by kenpeter View Post
Regarding your pile of junk dishes. Those are all offset types.
In other words, none of them contain "center" of the parabola.
There's a good chance you could clover 3 or four of them into
a much larger chunk of parabola without the leaves touching.

I had such a pile in my garage till recently...

Would be really hard to align for microwave purposes, which
was my original plan. But if you are just making a pair in the
back yard for acoustic toys....
Have you tried making a microwave transmission line?
Specific India made aluminium D channel works very well for proper e/h wave propagation. You cut the slots, cnc etc. Gains of 30dBi. I like coplanars when omni is a must. Easy to make, basically velocity factor vs freq, cut each segment, no more than ten (pairs, +&-) is best. Alternate connections between shield and center conductor. Connector and done.
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Old 8th October 2014, 03:05 AM   #697
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Yeah, I shoved a sharpened 2x4 down a bunch of eggnog cans.
And using that as a form, hammered em' somewhat rectangular.
Getting them lined up well enough to solder, thats another story.
Trying to do one of those long slotted waveguide things, didn't
quite work as I had hoped, but probably my sloppy construction.

You mean coaxial co-linear? Those work great. I think a 2-hole
button between each segment works well to get things lined up.
I replaced the outer braid with brass tubing and run the center
wire down the outside of the brass for every other segment.
You still need to terminate the far end with a 1/4 wave stick
and the near end with 1/4 wave foldback balun. I put this all
in a loose fitting PEX pipe to protect it from collapse while also
minimize dielectric loading and losses.

Feed horns tried on the parabola were: a coffee can, and a patch,
and a quad patch, and a biquad with a reflector. And a very small
log periodic, and a 4 element Moxon cell Yagi.

Last edited by kenpeter; 8th October 2014 at 03:33 AM.
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Old 8th October 2014, 03:32 AM   #698
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LOL

You can't use ferrous metals to construct, must be non ferrous, eg copper, aluminium, tin, brass, silver, gold etc...
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Old 10th October 2014, 04:53 AM   #699
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Cassegrainalign???

I just figured how to maybe enhance my upcoming folded smithhorn.
Omit the optional parabola for now, not relevant to my immediate plan.
Bend the other way to match a narrow triangle to a wide triangle, thus
we are expanding faster all the way to the exit slot and roundovers.
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Old 10th October 2014, 07:27 AM   #700
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It will all make much less sense if I just post a picture.
Pardon lazy drawing of multiple layers as-if only one...

Just for purpose of thinking too hard:
The speaker hole maybe 3inch, the panel 48wide x 24tall.
Since narrowing vertical directivity would be a feature,
the exit slot could be twice as wide as I drew it, originally
thinking 1/4 wave at 20KHz... Sonotube for roundovers?
Attached Images
File Type: jpg Smithagrain.jpg (153.2 KB, 212 views)

Last edited by kenpeter; 10th October 2014 at 07:47 AM.
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