DIY Round Tractrix Horn

[Fjd]

I don't think you would want the tractrix flare on the adapter, but you need something like Dave Harris' 1.4 to 2.0 adapter. You just need to extend enough on your horns with the present flare in the throat to get to the 1.5".

Actually Dave's adaptor is a conical tractrix flair used to match a smaller throat driver to the 2" Eliptic horn and keep a tractrix flair throughout the entire horn. I think we may have been trying to say the same thing, but with slightly different dialects? Given that, I was curious if the stock snout (1.5" to 2" expansion of an unknown flair rate) of Rudy's driver could be exchanged for a conical tractrix flair (similar to what Dave's adaptor accomplishes) to give the driver (from the 1.5" exit point) a full tractrix horn expansion.

Do you mean a "circular cross-section tractrix flair"? The term "conical horn" describes a very particular area expansion which always has the same shape for a given cross-sectional shape (so all circular horns have the same angle of the flare for a true conical horn).

Sometimes I think the colloqial language gets confusing because some of the simplified conclusions/rule of thumb stuff is only applicable for the strict definitions of the terms.

Btw, the tractrix flare is determined by the desired Fc of the horn, but also intertwined within that definition is the beaming of the HF energy. If you don't follow the expansion, but instead stick to a straight-walled adaptor that matches the 2" throat angle, then you wouldn't get the additional beaming...but then you have to address the new impedance mismatch. And this is where I think most of the modern horn designers start to diverge from the "magical expansion formulas" to start balancing some of the compromises that need to be made....like trading low frequency impedance matching for more consistent HF polars....or making the horn longer to make up for the low frequency impedance matching degredation...

I dunno, just thinking out loud...

Good point and I don’t know. In an effort to help the subsequent analysis/interpretation aspect of this thread we may need Dave to address this aspect since I pulled the terminology from his website. I think it has stimulated some thought that Rudy seems to enjoy, but I probably should have added the disclaimer that “This information was derived from Dave’s website, publicly available information. Although I believe that such information is reliable, I have not had this information verified by any independent sources.”[]

[Rudy81]

I beleive Dave's adaptor is round, at least by looking at the pictures. My only question right now is if there is any change to the Fc by extending the length of the 'horn'. I need to run the software and see what it says.

I sent Dave some questions on the subject since he has forgotten more about horn construction than the sum of my knowledge on the topic.

Edit: Just ran the software horn calculator and it does not seem to change the characteristics of the horn to add enough length in order to create a 1.5" throat vs. a 2" throat. I have no way of knowing how the change in throat from the stock driver to the tractrix model will change any HF beaming patters etc, but I suspect the changes will be subtle. It will take some time to build the adaptor and then test to see what changes. I will also have to find some M6 threaded rods for mounting the driver. I had no luck at the local hardware finding anything other than the ones that came with the driver. They worked fine, but I had to change my mounting system a bit.

[Marvel]

My point, not well stated, was that this part of the throat is not expanding much at all. Most of the software to design the tractrix flare just goes on and on getting smaller.You mostly just cut it off at the drivers throat size.

Bruce

[Guest David H]

Do you mean a "circular cross-section tractrix flair"? The term "conical horn" describes a very particular area expansion which always has the same shape for a given cross-sectional shape (so all circular horns have the same angle of the flare for a true conical horn).

You are correct, and I have been meaning to correct that for weeks.

Corrections have been made, the adapter is conical in shape, however it is Tractrix expansion.

Dave

[Guest David H]

I sent Dave some questions on the subject since he has forgotten more about horn construction than the sum of my knowledge on the topic.

Way too much credit. I am learing more about horns on a daily basis.

Just ran the software horn calculator and it does not seem to change the characteristics of the horn to add enough length in order to create a 1.5" throat vs. a 2" throat.

I also ran the calculations, and the extension has little to no effect on the horns Fc.

Dave

[DrWho]

Edit: Just ran the software horn calculator and it does not seem to change the characteristics of the horn to add enough length in order to create a 1.5" throat vs. a 2" throat. I have no way of knowing how the change in throat from the stock driver to the tractrix model will change any HF beaming patters etc, but I suspect the changes will be subtle. It will take some time to build the adaptor and then test to see what changes.

Keep in mind that the phase plug will have been designed for the flare angle of the original adaptor, so you might see similar behavior. It might get shifted higher in frequency, which may be enough to push it out of the audible band.

Btw, I wouldn't look at some of these dips as issues that would show up in the tonal balance, but moreso issues happening in the time domain causing some smear, which really affects the entire passband...not just the frequencies where you see the dip.

[Rudy81]

DrWho, I had been wondering about the effects of removing the snout. The HF200 engineers designed the driver for use in a 2" horn and so I imagine the snout is 'part' of the driver. In removing it and trying to force the issue I may make things worse. Not that they are bad now at all.

This really is a non issue since I won't be getting around to messing with that for a long time.

[Bacek]

Rudy81,

I may be wrong, but what you did to hf200 seems to be sold with name hf140 (few usd less)

http://www.faitalpro.com/products/schede/cd.php?id=502020150

[Rudy81]

Rudy81,

I may be wrong, but what you did to hf200 seems to be sold with name hf140 (few usd less)

http://www.faitalpro.com/products/schede/cd.php?id=502020150

They sure do have similar specs too!

[Rudy81]

After another 3 hours or so of casual listening, I decided that the DIY horns are for sure staying. I did more listening between horns and like the 'larger soundstage' that the round tractrix horns provide. I'm sure there is some trade off vs. the professionally manufactured CD horns, but I like the ambiance of the round horns. They have now moved center stage on my DBBs.

[Rudy81]

I mounted my third P. Audio BM-D750 on the center horn. As you can see I still need to pretty up the hole left by the old horn, but you get the idea.

My next plan is to zero out all the EQ in my Ashly crossover and see what Audyssey Pro thinks of the new horn and driver combination. One issue that may be a problem is the timbre matching between the center and main channels. I beleive that the two drivers are very close in performance except for the very high end, so am hoping I can get away with not buying another HF200.

If it wasn't for the Klipsch Pro cinema effects, the RSW-15s and the half La Scala, I would have to rename this the DIY Home Theater. I can't believe how many hours I've spent on the subs, the DBBs and now the horns...not to mention the screen, wiring etc....at least its been fun! [H]

[Bacek]

Rudy81,

It wont cost you nothing. Could you measure hf200 without that extension to 2'' on you horn? Will see if there is any noticeable difference.

[Rudy81]

Rudy81,

It wont cost you nothing. Could you measure hf200 without that extension to 2'' on you horn? Will see if there is any noticeable difference.

The problem with mounting the driver without the snout is that the threaded studs will now be very long for the mounting system. I will have to try and get some much shorted mounting hardware before attempting that measurement.

[aj01]

Rudy - what did you use to cut your circles? Jasper jig and a router? Any tips for cutting the holes by hand?

[Rudy81]

Rudy - what did you use to cut your circles? Jasper jig and a router? Any tips for cutting the holes by hand?

I used two jasper jigs, one for the small circles and another for those larger than 7". Yes, jasper jig, a router and a LOT of time and patience. The best tip I can give you is to order them from Dave and save yourself a whole bunch of time and aggrivation. That is, if he is making round ones for sale.

[Rudy81]

Quick update to anyone following this thread. It was not until this evening that I got to listen to the system with a 7.1 movie. It did not take long for my family to complain about the lack of intelligibility of the center channel. I also found it to have a certain resonance or ringing which made dialog less than what it used to be. The only change in the center channel had been the horn. Driver was the same P. Audio (K69).

We watched the movie and then I took everyone's opinion on the dialog channel. I then put the driver back on the P. Audio horn and ran several scenes of the movie again. Some movies have a poor dialog channel and I wanted to rule out that as a possibility. Well, it was not the movie. It most certainly was some characteristic of the horn that makes dialog an issue. There is not doubt in my mind the P. Audio horn is going back in on the center channel.

That experience has made me wonder about vocals in the main R and L channels. I have, up until now really liked the greater soundstage and what I perceive as increased depth with the new horns. But, I want the best sound, so I will spend some time tomorrow putting the P. Audio horns and listening again to see if my initial impressions hold. I have been living with the round horns for music for about a week now. It will be instructive to go back to the old setup and see how that stacks up.

In any event, the horn is NOT useful for a center dialog channel. This was very easy to discern and it wasn't just me, which helps when others reinforce my perception.

[DizRotus]

Thanks for the candor. It's refreshing.

[Rudy81]

Thanks for the candor. It's refreshing.

My goal is the best sound I can get....doesn't matter how I get it. I do what I can to be as objective as possible and find it difficult at times to differentiate between 'this sounds good' from 'this sounds different'. My acoustic memory sucks! A/B runs between horns and drivers is frustrating because I can't seem to accurately remember how something sounded a few minutes ago. That is one reason I have worked on learning how to take rudimentary measurements vs. just trusting my ears. I'm just not very good at this.

I actually love it when something is so different, good or bad, that it is easy to tell. In this case the horn clearly did not work for movie dialog.

I am anxious to go back to my P. Audio horns tomorrow and have a listen to 2 channel.

I know the round horns radiate sound in all directions vs. the horns I have used in the past. My room is well treated for first reflections, to include the ceiling, so I don't beleive the problem is due to sound reflections....but you never know. In any event, the P. Audio horns don't present that problem, so the center channel horn is back in.

[Rudy81]

I think I have audio nervosa! Somebody help!

[DrWho]

Interesting. It might be worthwhile to double check simple things like xovers settings, polarities, delays, and all that fun stuff. I'm wondering if maybe something got goofed somewhere?