Al Klappenberger:

I plan to run intermod distortion tests at 100 dB SPL on both the V-Track and my Trachorn to see how much the 2 inch throat reduces it.

Al, are you going to use white noise for this test?  Or do you pick your frequencies to do the test?

Greg

 Greg,

No noise for this one. I did it with the prototype Trachorn already. I use two pure sine wiave tones of 550 and 4150 Hz at 100 dB SPL (while wearing ear-plugs!). The intermod shows up as extra tones at 4150 +- 550 Hz. 

Here's what I did earlier.

Dr. Edgar showed a family of curves for "Throat resistance" in his article that I really don't understand

Al....This is what I gathered from that article and the curves you are referring too:

I was a little confused with the way he used the terms throat reactance and throat resistance....but...

His curves and comments concluded that the FR curves ..the peaks and valleys...are there as a result of the throat resistance.  This was noted when the flare rate of the horn was much lower than the mouth calculated size and when the mouth was too narrow.  The latter meaning the least amount of acoutic impedance swings ocurred when the mouth width was twice that of the mouth height.  (HAH...how is this an issue with constant impedance networks...I have to laugh a little...)

I believe the above principle is one of the main points that make an Edgar horn.  The 223Hz Fc Tractrix horn that Gothover makes is exactly twice the width times the height....I made it that way because of that articles point.   I wish he would have made reference to polars though with mouth shape and flare.

My take....

jc

 JC,

I haven't a clue about any of that!

Ask me about a filter! 

Al K.

There's a code snippet here that also computes the slope of the tangent line and the tangent angle of the circular Tractrix curve.

And for folks who are anal-retentive like me, the following will compute the area of the spherical Tractrix "bubble" wave front approximation, as well as of the circular wave front approximation, with "a" and "theta" defined as above:

/* Use spherical assumption to compute approximate area of wave front */
sphere_area = ((double)2.0 * pi * a * a * ((double)1.0 - cos(pi - theta)));
circle_area = pi * r * r;

Greg

Al, is this the calulations for the horn you presently sell?  I'm still trying to figure out the calultor, your offsets seem to be the same for the height but the over all width seems to be a few inches wider.  Or is it just a bunch of numbers used as a sample?

Thanks

CigarBum

 This is the program that was written to design the Trachorn and was used in its design. The difference in mouth width is becasue the Trachorn was cut down slightly at the extreme outer edges of the mouth. Doing that makes it far easier to build and sacrofices nothing as the extreme edges do virtually nothing.

Al K.