Jump to content
Sign in to follow this  
Guest David H

Round Tractrix

Recommended Posts

Guest David H

With all the talk of round tractrix horns lately, I though I would try my hand at a small horn.

Here is the drawing for the horn, notice the 7 concentric circles per cell, each circle represents a cuting depth.

post-24405-13819634158778_thumb.jpg

Share this post


Link to post
Share on other sites
Guest David H

After nearly 2 hours of cutting you can see the basic idea. Each piece is dowel keyed for alignment.

post-24405-13819634160708_thumb.jpg

Share this post


Link to post
Share on other sites
Guest David H

Here is the Basic buildup, I used square flange and motor mount for ease of mounting.

post-24405-13819634168662_thumb.jpg

Share this post


Link to post
Share on other sites
Guest David H

One more. I am not going to do any measurements on this one this was simply a test build. The next one I build will be a 300Hz version, and I run some tests on it.

Dave Harris

post-24405-1381963419031_thumb.jpg

Share this post


Link to post
Share on other sites

One more. I am not going to do any measurements on this one this was simply a test build. The next one I build will be a 300Hz version, and I run some tests on it.

Dave Harris

A round tractrix horn should measure very well because the driver is well loaded and there are few discontinuities. However, does the performance in a typical room benefit? While the sound from the round horn may have fewer reflections and refractions than similar cutoff rectangular horns, more energy would be reflected from the floor and ceiling of a typical room. I had thought about doing an elliptical tractrix to program the dispersion better than for a round tractrix, but with fewer discontinuities than found in a rectangular tractrix. The same possibilities would be present with other horn shapes such as exponential and LeCleach. With CNC, these should be doable...especailly with lots of hand sanding..

If you do A/B tests, you might need different equalization for round and retangular horns even when using the same drivers.

nat

Share this post


Link to post
Share on other sites

Dave,

VERY INTERESTING! That horn is a 2-inch but it's square mounting flange suggests a possible version that would fit into the Khorn frame along with the Fastrack K or K2 but would be a 1-inch and could be used with Selenium or B&C tweeter drivers as an option to the K77 or other popular tweeters.

AL K.

Share this post


Link to post
Share on other sites

After nearly 2 hours of cutting you can see the basic idea. Each piece is dowel keyed for alignment.

Very cool Dave. Did that take 2 hours for the CNC to cut out? Just curious as to production time with a CNC. How much tending did you do once the machine started? In other words, were you able to do other things while it worked, or did you have to tend to it the whole time? Did you have to change tools during the 2 hour process?

Greg

Share this post


Link to post
Share on other sites
Guest David H

Dave,

VERY INTERESTING! That horn is a 2-inch but it's square mounting flange suggests a possible version that would fit into the Khorn frame along with the Fastrack K or K2 but would be a 1-inch and could be used with Selenium or B&C tweeter drivers as an option to the K77 or other popular tweeters.

AL K.

That't the idea Al, I just did this with a 2 inch driver because it is much easier to build and sand. This is a 600hz lens.

The tweeters will come soon enough, but I need to build a sanding jig.

Dave

Share this post


Link to post
Share on other sites
Guest David H

Greg, the routers requires no babysitting, and I used a single bit for this project.

The cutting time is only one percent of the project, it takes hours to input the hundreds of line of information to cut the horn and weeks to leard to use the learn the graphic and machine software.

Here is a sample of the program output.

Dave Harris

post-24405-13819634201414_thumb.jpg

Share this post


Link to post
Share on other sites

Dave,

I have had some experience with interfacing engineering programs to external instruments like the CNC machine computer. I have done several using HPIB (IEEE 488) buss. I have that sort of setup doing computer testing of the networks I make, I envision a horn design program that will dump the cutting data directly into the CNC. I also think that the next iteration might be a Tractrix with an elliptical mouth that will fit in the Fastrac K Khorn frame for a mid-range. I know I can write the program to design the horn. How about that for a fun project?

Al K.

Share this post


Link to post
Share on other sites
Guest David H

Dave,

I have had some experience with interfacing engineering programs to external instruments like the CNC machine computer. I have done several using HPIB (IEEE 488) buss. I have that sort of setup doing computer testing of the networks I make, I envision a horn design program that will dump the cutting data directly into the CNC. I also think that the next iteration might be a Tractrix with an elliptical mouth that will fit in the Fastrac K Khorn frame for a mid-range. I know I can write the program to design the horn. How about that for a fun project?

Al K.

ALK, you have got my utmost attention. [:P]

Share this post


Link to post
Share on other sites

Dave,

I think I can write the design program very quickly. Doing the interface will be a bit more trouble considering your CNC machine and I are 2000 miles apart! For starters, just to verify the validity of the elliptical Tractrix, the data could be input to the machine manually for a while.

Al K.

Share this post


Link to post
Share on other sites

Tiger..,

The program I am thinking about would bypass the AutoCadd stage entirely. My initial thinking is the program would ask for mouth width and height plus the round throat diameter, just as the Trachorn.exe program I wrote does, but would also ask for how may segments. It would then output the data on how to cut each segment directly to the CNC computer. I don't know how Dave's machine handles the data though. A simple 3 inch computer disk to transfer a file might be the way to go, at least initially.

Al k.

Share this post


Link to post
Share on other sites
Guest David H

Al, my router uses HPGL files, but will also accept GCode. There are so many machines to consider it might be best to have the program output a graphics file like CAD because the layers have to layed out and optomised before cutting anyway.

Then again, I have very little experiance with NC machines.

Dave

Share this post


Link to post
Share on other sites

Dave,

I think a few sample files would get me started. Maybe an example of whatever data is required to do one segment or even just a single elliptical cut. Maybe you could send me one by email. AutoCadd script files is not a problem either. Trachorn.exe makes one for the curved side. There's no hurry though. I need to get my head into gear to do the Tractrix design part first. Another thought is the conical segment at the throat that djk suggested in another thread to improve the HF dispersion. I should be able to work that in too pretty easily.

Al k.

Share this post


Link to post
Share on other sites

Al: I have been interested to learn what kind of difference it makes to match the initial throat geometry of the horn to the exit angle of the compression driver in use. Seems that matching the angles would go a long way to eliminate horn throat related reflections back into the driver. Of course there can also be some reflections in the horn and from the mouth of the horm as well. Less reflections should be the desired goal. Have you read anything about this? Manufacturers don't seem to address this in their literature.

It would seem a little self serving of manufacturers to lead consumers to think that a given comp driver could be mated up with any available fitting horn but as we know some combinations work better together. If we assume that loading of the comp driver is fairly consistant from one good horn design to another then geometric related reflections might be the primary source of sonic differences and performance between different driver/horn combinations. This is likely a very simplistic appraisal of the situation but it would seem to be worth discussion. regards Moray James.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

×