| tractrix horn/driver throat matching [message #48144] |
Fri, 11 November 2005 02:33  |
Thomas Agerbaek
Messages: 2
Registered: May 2009
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Esquire |
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Hello PISpeakers Forum,
I'm putting JBL 2445 and 2426 compression drivers on circular wooden tractrix horns integrated into the baffle of the cabinet.
The 2445 horn mouth is 240mm (ca 9.5in) dia, the 2426 horn is 110mm (ca 4.5in) dia. The problem is, the drivers' throats are conical, with exit angles of about 5 degs. However, the contours of the above tractrix horns will have throat entry angles of some 12 degs at the corresponding diameters (1in and 2in). This means that there is an abrupt change in the flare rate at the junction. Intuitively this is not good, because it would lead to jumps in the acoustic impedance, reflections, etc.
It would be much better to have the angles matched, but this would entail making compromises wrt the tractrix contour, by departing from the mathematically correct curve. Any input which could help me make an informed decision as to the best compromise wrt the horn countour would be greatly appreciated.
TIA Thomas
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| Re: tractrix horn/driver throat matching [message #48163 is a reply to message #48148] |
Sat, 12 November 2005 10:56  |
Thomas Agerbaek
Messages: 2
Registered: May 2009
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Esquire |
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Wayne, thanks for the info. 1. The quadratic horn paper was right on the money. Thanks. 2. I tried the hornresp program, but it appears to be directed to hornloaded cone divers, with TS parameters etc. How do you make a compression driver fit into that? TIA Thomas
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| Re: tractrix horn/driver throat matching [message #62043 is a reply to message #48144] |
Thu, 11 March 2010 11:43 |
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Wayne Parham
Messages: 18691
Registered: January 2001
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Illuminati (33rd Degree) |
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Well, that's exactly right. You really want the entry angle of your horn throat to match the exit angle of your compression driver.
You have a problem that doesn't have a good solution, I'm sorry to say. If your horn entrances are already exactly 1" and 2" diameter, as they should be, then you cannot easily make adapters that provide a flare match. That's what you want - to start at the driver exit angle and end at the horn entrance angle. Both entrance and exit are already the same size, so there is no way to make an adapter with a radiused expansion to match one with the other.
What I might suggest is to have the horns cut so you can make a proper adapter. Transition the conical section of the driver with the tractrix entrance using an adapter that is contoured to have a gradual transition and no abrupt change in area. The curve you choose is up to you - some would say stick with tractrix, some would want oblate spheroidal, some might prefer a quadratic.
Since you've already chosen tractrix, you may want to try and stick with that shape although the fact that you're matching an existing section with another that will ultimately be slightly longer will preclude that. My advice is that it is better to remove the abrupt change in shape with any gradually radiused shape than it is to leave the abrupt change there. Use an oblate spheroidal, tractrix or simple radius, anything smooth is better than a sharp change. If you want it perfect, you'll have to start from scratch, but I think an adapter with a nice radiused transion will get you 99% there.
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