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Contrac-T Conical/Tractrix Hybrid Tweeter


Guest David H

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Guest David H

I have been working with Conical/Tractrix hybrids, due to the interest in constant directivity horns.

What I have come up with is a 60/40 Conical mix. I was a bit surprised at how different it sounds compared to pure Tractrix, however that may just be due to the lower Fc of the Tractrix.

I am curently waiting for the polar mapping results, however the Contrac-T paired with the B&C DE-10 had smooth response to 18K.

post-24405-138196649415_thumb.jpg

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Guest David H

You have your standard conical to compare polars, right?

I do not. I am sure I can find some available though.

How did you decide on 60/40%?

T.L.A.R. engineering. That looks about right.

Built and listened to several, 50/50, 70/30, and the 60/40.

Dave

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Interesting project!

I am trying to understand your description. Does 60/40% mean the initial 60% of the horn length is a conical expansion and the last 40% is tractrix?.

Is there any special geometry at the horn's throat (for instance: oblate spheroid or Quadratic throat)?

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Guest David H

I am trying to understand your description. Does 60/40% mean the initial 60% of the horn length is a conical expansion and the last 40% is tractrix?.

Precisely

Is there any special geometry at the horn's throat (for instance: oblate spheroid or Quadratic throat)?

No, the throat is pure Conical, with a Tractrix mouth which should reduce edge diffraction.

I was under the impression the quadratic throat was to reduce distortion in a rectangular cross section Conical designs.

Dave

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I am trying to understand your description. Does 60/40% mean the initial 60% of the horn length is a conical expansion and the last 40% is tractrix?.

Precisely

Is there any special geometry at the horn's throat (for instance: oblate spheroid or Quadratic throat)?

No, the throat is pure Conical, with a Tractrix mouth which should reduce edge diffraction.

I was under the impression the quadratic throat was to reduce distortion in a rectangular cross section Conical designs.

Dave

The geometry at the throat is an interesting issue, and I certainly do not have a good understanding of it.

Oblate Spheroid (Geddes) and the Quadratic Throat (Hughes / Peavey) is an attempt to aid the transition of the wavefront from "flat" to "spherical". In fact Geddes argues strongly that it is this transition that can create additional reflections which are deleterious. The OS geometry will asymptote to a conical geometry. The advanatge to either of them (OS or QT - they are similar) is that the profile does not present any major discontinuities between the throat and the driver and the throat and the "middle portion".

If you are interested in trying them (don't we all love "volunteering" the guy with the CNC machine ....) the math is straight forward and there are spreadsheets available. You have already done the hard part, the mating of the conical to the tractrix mouth.

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Guest David H

If you are interested in trying them (don't we all love "volunteering" the guy with the CNC machine ....) the math is straight forward and there are preadsheets available. You have alsready done the hard part, the mating of the conical to the tractrix mouth.

I can do that. I will check into it.

Dave

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Guest David H

OS-Contrac-T

The OS throat efects the cutoff, and depth of the horn, makes Fc prediction difficult.

Here is a visual of the OS throat, you can see the flair at the throat expands similar to tractrix, them becomes very consistant mid way through the horn, them once again flairs at the mouth.

post-24405-13819665298352_thumb.jpg

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