I'll measure it again with no time window. see if sanding made a difference and report back...
Thanks I'll try it, I'll look for harder shore D.
Which brand did you use?
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The problem here is that if you don't position the mic within a cm from whre it where in the first measurement, they are not comparable. Yes, its that sensitive.
I think your WG looks fine. Some measurements form different angles (every 10th deg?) are now more interesting
As mbat indicate... you should have a fix mic position and turn the horn around an imagined vertical axis positioned at the moth of the WG - that would be 12 and 6 o'clock on mouth staying in the same x,y,z position while you turn the WG.
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The mic and tripods haven't not moved in all these measurements.The problem here is that if you don't position the mic within a cm from whre it where in the first measurement, they are not comparable. Yes, its that sensitive.
I think your WG looks fine. Some measurements form different angles (every 10th deg?) are now more interesting
As mbat indicate... you should have a fix mic position and turn the horn around an imagined vertical axis positioned at the moth of the WG - that would be 12 and 6 o'clock on mouth staying in the same x,y,z position while you turn the WG.
//
I'm hoping to get polars in
10deg increment today...
Assumed the time window was the same.
The TD-2001 isn't the problem, it is about the match with a suitable horn.
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Rotation of the source can be problematic. A waveguide should rotate about the driver, as should the woofer. If measured individually that way they cannot be summed together to simulate the system. When the system is assembled, then the woofer and waveguide drivers will usually not be in the same plane (they shouldn't be.) So rotating creates some small issues. Its best to rotate about the front face of the system, or closer to the woofers driver. The aberrations will likely be greater for the woofer than the waveguide.
I would not recommend a lazy Susan bearing as these are not rigid enough and not necessary. Just two plates of melamine covered particle board, face to face, pinned at their rotation with some grease in between. This slides easily even with a lot of weight and is very solid and will not move when the system is excited. A very loose bearing is Not what you want.
Distance is important, but not critical. Too close is worse than too far, but you have to determine the ideal from the measurement room situation - path lengths to reflections should be maximized. Less than 1 meter should be avoided.
I would not recommend a lazy Susan bearing as these are not rigid enough and not necessary. Just two plates of melamine covered particle board, face to face, pinned at their rotation with some grease in between. This slides easily even with a lot of weight and is very solid and will not move when the system is excited. A very loose bearing is Not what you want.
Distance is important, but not critical. Too close is worse than too far, but you have to determine the ideal from the measurement room situation - path lengths to reflections should be maximized. Less than 1 meter should be avoided.
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In my studies, I have found that all separable coordinates systems have one thing in common, the "flare" goes as what you think of as the OS ( y(x) = sqrt(x^2 +Tan^(theta)) ) - any of them that would allow for a waveguide. From this, I think that it is easy to conclude that it is the curve that matters, no matter how the source is shaped (as long as the circumference of the source is a continuous curve in slope.) This, of course, excludes a square source because of the corners - how to handle those? Don't. Fit an ellipse as best as possible to the rectangle and use that.
For a rectangular source you need a different approach. With that you need to look at Prolate Spheroidal waveguides. But even there you have the same equation as above along the flaring surface.
Ellipsoidal coordinates have the same curve all the way around an ellipse.
Remember that these are exact only when there isn't a mouth, i.e. the way that they are terminated matters.
For a rectangular source you need a different approach. With that you need to look at Prolate Spheroidal waveguides. But even there you have the same equation as above along the flaring surface.
Ellipsoidal coordinates have the same curve all the way around an ellipse.
Remember that these are exact only when there isn't a mouth, i.e. the way that they are terminated matters.
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I know I am a bit off topic here - but I cannot visually connect oblate and prolate spheroid to a waveguide shape - or are we talking about the wavefront shape? I still wonder how one would make a meaningful waveguide for the rectangular Heil AMT-1. And even when I think of prolate as the waterfront shape, I cannot get my head over how to start a waveguide with a rectangle - if it should stay rectangular all the time, or?
In prolate coordinates the origin is a line, in OS it is a circle. The PS waveguide would not start at zero as the OS does, it would start some ways out on the spheroid - like a conical does. The wavefront would remain rectangular to the mouth. A flat wavefront is not a perfect match so this too will always have HOMs at some point, as do all waveguides I suppose.
Is the mouth elliptical and the throat round? If so and every arc from throat to mouth is OS then yes that is the idea.