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Horn adaptor for K-77 replacement


Dave A

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Finally got around to machining an adaptor to fit an APT50 super tweeter to a K-77 opening like on the La Scalas. Have not put one in yet but I have a pair of Pro La Scalas slated for this soon. Figure I can just bypass the zener's on the AA crossovers with these and not have to worry. May not be the final final but darned close. Will fit the stock screw holes with an extra one for safety and be flush with the outside of the motorboard for better sound..

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Well when I am certain they work well you would buy them from me since I am making them. I am sending a pair off to a guy for testing and then making a pair for myself to see what I think. One of the problems for sure is the paint on the horn. Using a standard tap which does not vary it is hard to screw the horn in until the paint is removed from the horn threads. I ran across this with an old horn and I could barely get the driver off. These big fine threads don't have much tolerance for problems before they seize and gall.

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A big part of the equation is the cutting of the conical shape. It takes a ton of little tiny cuts to make a smooth surface with the .06" radius bull nose cutter I used. I am going to try a 3/8" ball nose end mill and see what that does. In any case it needs to be no more than the same priceor very close  as other existing similar things. I have to see if I can get the cutting time down low enough to be worth it.

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5 hours ago, absolve2525 said:

Where can you buy those horns without drivers? I'd like to try those, but have plenty of drivers already. Looks sweet. 

 That reminds me. These are meant to be a direct drop in replacement for the K-77 in the La Scalas. If your driver is not small enough to fit the cabinet these will be of no use to you. If you have a custom cabinet with more space available that's a different story.

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1 hour ago, Marvel said:

Do those fit the old style APT50 or the standard 1 3/8 style threading?

 

Bruce

1 3/8 18 threads. Funny you should ask. I just came in from the shop where I installed a pair of these along with some soldered lug K-55-v's into my Pro La Scalas. Disconnected the Zeners because I don't have to worry about tweeters anymore. Fired these up and it was like new speakers had appeared. I did more than one thing so how much is due to each part of the equation I don't know. I am sending a pair of tweeter assemblies off to someone who can properly assess what I have done this coming week. Those KP-450's still are better but the improvement with the La Scalas was enough for me to think briefly about keeping them.

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I have seen pictures of the eliptrac and that did inspire me. Never had one to measure but I would imagine they are close. You create the geometry with a circle at the bottom and an ellipse as big as you can get to fit the opening and generate a surface between the two. The sides are actually a straight line from the circle to ellipse and generating a negative or positive bulge to change that is something that can be done but I figure simpler is better since I have no analytical way of designing a horn lens by math. That eliptrac looked to be a straight wall so I stayed with that.

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Listening to these yesterday and thinking how all the shrillness is gone. Between replacing the old round magnet K-77's and adding the dual phase plug K-55-V's and re-capping the crossovers made a huge difference. Have to admit they look nice to.

  I am going to get a price on Aluminum and have decided this latest version is the final one. Since I know how much time  it will take to cut I should have a price on these very soon for all who are interested.

 

 

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I was fiddling today thinking about offering customization on these with text or geometry. Have not made up my mind on this since each new one means a whole new machining program. I might limit it to just a handful. Need to figure out a way to fill the grooves with black paint and not be sloppy for it to look good if anyone has an idea on how to do that.

 

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