Jump to content
The Klipsch Audio Community
Sign in to follow this  
Al Klappenberger

A time-aligned top end - Part II

Recommended Posts


I'm going to start by repeating the opening idea for all this from the first "Time aligned top end" thread:

-------------------------------------

I have always maintained that there is no good reason to go to a 2-inch horn to replace the K400 in the Khorn. A 1-inch horn is by far the best bang for the buck. 2-inch horns are for movie theaters but there is some advantages to upgrading the K55 driver. The problem with that is there is simply no 1-inch driver in current production that will operate cleanly down to 400 Hz where the Khorn must be crossed over. Evan the 1-inch JBL 2426h will start making distortion at 450 Hz let alone down at the 400 Hz required by the upper limit of the Khorn woofer. It was designed to be crossed over at 800 Hz but JBL says that it will operate down to 500 at reduced power. That's fine for the Belle or LaScala, but not the Khorn. Only a 2-inch driver will go down to 400 Hz. If you are ready to make the leap to a 2-inch horn and driver you might as well go a step further and make it really worth doing. B&C Speakers makes a coaxial version of their DCm50 driver, which is exactly what the doctor ordered for the Khorn squawker, a design specifically for a 400 Hz crossover. It's the DCx50. It uses the same midrange "guts" as the DCm50 but has a tweeter built right into the throat that extends the frequency range to 16 KHz. That's the same upper limit as the K77 tweeter that most of us have been listening to for years. A response that extends above that is nice but chances are only your dog is going to appreciate it! The big plus with a coaxial is that it's as close as you can get to having the midrange and tweeter occupy the same place at the same time. That means the propagation time from both drivers to you ears is virtually equal! That's TIME ALIGNMENT!

Time aligned drivers let you use a far less aggressive crossover than the extreme-slope networks needed to eliminate the driver interference caused by two sources of sound located in two different places. The interference between drivers is significantly reduced. Another advantage here is that the DCx50 requires a crossover at 9 KHz rather than the 6 KHz required by the K55. This adds up to a far less aggressive network with fewer parts of smaller size. It will cost less than an extreme-slope network. Another advantage of the time alignment is the opportunity to us a phase-coherent type of network called a 4Th order Linkwitz-Riley. This type of network is usually only appropriate for sub-woofers as active filters where the wavelength is extremely long.

-----------------------------

In the other thread, I had only Dave's (Gothover) Fastrac K2 horn to test with and no parts to build the Linkwitz-Riley network. Since then, Dave has sent me his prototype Eliptrac 400 elliptic tractrix horn. I also have received the parts and have bread-boarded the 9 KHz Likwitz-Riley crossover network.

I had a very difficult several days going through all this. I kept getting all sorts of conflicting and illogical acoustic measurement for the two horns I was testing. I first thought the network itself was the problem. I bread-boarded a version of the AP15 series network, which is a 9 KHz 6 Ohm version of the Universal network high section. I also pulled an old ES7500 extreme-slope network out of the attic.

After testing all three of these networks on both horns I continued to go bonkers getting all sorts of stupid plots. Finally I moved the horn off the workbench and set it on a chair facing out of the door. WOW, what a difference! It seems all of the hell I went through was due to the room! I don't think it was reflections either. The low frequency driver alone looked fine. I don't know what was going on, but it all went away when I moved the horn! Oh, for an anechoic chamber! The real tip-off to what was happening was the plot below. It's using the ES7500 network that has a "notch" in the lowpass section that rejects everything at 8800 Hz. DEAD! Notice that there is a big dip in the acoustic plot right at the notch. That says that only the tweeter is making a sound there. Obviously the dip could not be interaction when there is only one driver making the sound. It had to be the room! I also discovered earlier that both the two DCX50 drivers I have seems to have their two drivers mismarked. They are out of phase with each other. I am trying to resolve this with B&C Speakers now. That is why I tried both phases on the tweeter. The dip was identical both ways. That is further evidence that it was not an acoustic cancellation.

Al K.

post-2934-1381963453868_thumb.gif

Share this post


Link to post
Share on other sites


The network ...

The Linkwitz-Riley network is simply 4th order singly terminated Butterworth lowpass and highpass filters tied together. The main difference between these two and the usual crossover filters is that the two are 6 dB down their slope rather then the usual 3 dB at the crossover. To make a constant-impedance network both must be 3 dB down. The 6 dB crossover makes the impedance rise at the crossover. In this case, the 6 Ohm design impedance rises to about 12 Ohms at 9 KHz. To compensate, I added a simple R-L-C section. It could be simply left out since it just sucks a little energy out of the amp at the crossover, which makes it draw the same amount of current at all frequencies. This is what constant-impedance means. It does not contribute to the crossover itself at all. The reason for doing it is to provide a constant termination to the low frequency woofer to mid-range crossover network "upstream" that feeds it.

One of my dreaded paste-ups is below. It shows the measured complex impedance at the input without the impedance compensator (top left) and with it (bottom left). The upper right is the picture of the jury-rig bread-board. The lower right is the response plot of the two filters. Note how the phase of the two filters virtually sit one on top of the other and the crossover point itself is 6 dB down.

Unfortunately, I don't expect to make this design public as a DIY project for two reasons. The first is that a 6 Ohm attenuator is required. That's not an off-the-shelf item. Even worse is that a very small inductor of only 69 MicroHenries is required in the highpass half. It will require an accurate inductance meter to make it. The smallest inductor Solen makes is .10 MilliHenries. You must either pull turns off (a lot of them) or graft two together with a precise spacing between them and the leads connected in parallel properly to use the mutual inductance between them to set the value. That is what I did and it wasn't easy!

Al K.

post-2934-1381963453995_thumb.jpg

Share this post


Link to post
Share on other sites

The two horns ..

I tested the two horns for frequency response using the Linkwitz-Riley network. The plots are shown next to the two horns. The on-axis response of both horns is within +-5 dB. The 30 deg off axis was also good on both horns. The K2 horn, which is the Bruce Edgar type wood tractrix clearly has problems off axis when you get to the point where the curved sides start to obscure the throat. This doesn't seem to matter with a single midrange driver, like the B&C DCM50 but starts to cause trouble with the coaxial DCX50. I'll leave it to the horn experts to explain that! The elliptic horn had a smooth response even farther off axis.

post-2934-1381963454173_thumb.jpg

Share this post


Link to post
Share on other sites

Dave will be sending me a second prototype of the Eliptrac 400 horn. When I get it and finish building up the networks properly I will actually be listening to his combination!

Al K.

Share this post


Link to post
Share on other sites
Guest David H

Wow Al. the picture really sings a thousand songs in this case. I never really thought about it but the off axis response is restricted by the squeezing at the throat which is necessary to retain Tractrix expansion in an Edgar type horn. The Eliptrac on the other hand is not contrained in this manner and is evident from the picture alone. The conical throat I suspect is the key to retaining good off axis response.

I guess I should find a good driver to test the feasability of the Eliptrac 400 for 2-way operation.

The response plots look very promising, I am anxious to see the all encompasing results.

BTW, prototype horn #2 is on its way,

Dave

Share this post


Link to post
Share on other sites

In my listening room I'm looking right down the throats of my horns at my listening position. I would literally have to be out of the room before the driver was obscured by the side walls of the horns. I'm thinking off axis distortion wouldn't be a problem for my set up, unless it somehow interferes with the signal coming directly at me from the horn. Am I reading this right or am I missing something obvious here?

Keep us posted on your great work!

Share this post


Link to post
Share on other sites

Guys,

I don't think the sidewall obscuring the throat is a problem at all for a simple driver with a single diaphragm used as a mid-range. It just seems to mess things up when the two drivers of a coaxial need to work together. Notice the green plot on the K2 horn goes west right at the 9 KHz crossover. That's where the two drivers are both operating and must sum together cleanly. Earlier tests with the DCM50 driver showed good off axis response all the way to 10 KHz, Dr. Edgar expected his type of horn to be crossed over far lower than that anyhow! I'm not sure what would happen to the off axis response with a wide range driver. I don't have one here to try. For use in the Khorn, it would need to extend all the way down to 400 Hz without distortion too. That's a tall order! That's why PWK couldn't do a 2-way. This is really the reason for doing a coaxial. It's to get as close to a 2-way as possible.

Al K.

Share this post


Link to post
Share on other sites

Nice work GotHover..!

The elliptic horn looks to have the highest potential and best performance of any I've seen you have made so far IMO.[Y]

mike tn

Share this post


Link to post
Share on other sites

"I guess I should find a good driver to test the feasability of the
Eliptrac 400 for 2-way operation."

This driver looks interesting:

http://www.faitalpro.com/img/products/schede/CD/HF144/HF144_datasheet.pdf

The driver is on an elliptical tractrix horn designed to be crossed at 800hz for PA use.

This is the horn:

http://www.faitalpro.com/img/products/schede/HRN/LTH142/LTH142_datasheet.pdf

The driver graph shows loading down to almost 400hz (in 4Pi), with a small trap centered around 1.5Khz (3dB or so) this would be very flat.

Based on prices in Europe, the driver should be around $210~$220, the horn around $65~$70.

The minimum crossover frequency of 700hz is based on high-power PA use on their (smallish) horn. For home use on a bigger horn it could be used with a lower crossover point.

Share this post


Link to post
Share on other sites

Dennis,

That driver looks very pretty! It's another 1.4 Inch. These seem to be pooping into my view more and more. I was looking at a 1.4 Inch Altec (390) design made by Great Planes that might be a good candidate too. I think maybe we need to push Dave into making a 2 to 1.4 Inch round extension to put on the Eliptrac horn. I think it would be a neat accessory. That is if Dave can find the time to do it. I suspect he's got a lot of projects going already! I would love to do some testing on it.

Al K.

Share this post


Link to post
Share on other sites

The new 9 Khz Linkwitz-Riley network is all done and everything is set to listen to the B&C DCX50 coaxial driver mounted on the Elliptic tractrix horn. I hooked up everything late last night. I expect to do some listening later today.

AL K.

post-2934-13819634919204_thumb.jpg

Share this post


Link to post
Share on other sites


The initial listening tests shows the merits of the time-aligned high end. The most obvious advantage is the stereo image. There is simply no need for a center channel speaker. I had it turned completely off but you would never know it! The high end is somewhat subdued from what I am used to with the Beyma CP25 crossed over at 5800 Hz. The 9000 Hz crossover is so high that the mid-range driver is doing almost all the work. The tweeter is just adding "crispness" to the sound. You can actually remove the level adjustment plug from the tweeter attenuator disabling it completely without a major degradation of the sound. The midrange quality is very similar to the Bruce Edgar type tractrix horns popular now. The off axis dispersion is as good as with most separate tweeters as long as the throat is visible as it is with the elliptic tractrix horn. Unless you are really sitting close in, that will be the case. Instrument test showed that the curved sides of the Edgar type horn obscured the throat and interfered with the off-axis dispersion.

Al K.

Share this post


Link to post
Share on other sites
Guest David H

Dennis,

That driver looks very pretty! It's another 1.4 Inch. These seem to be pooping into my view more and more. I was looking at a 1.4 Inch Altec (390) design made by Great Planes that might be a good candidate too. I think maybe we need to push Dave into making a 2 to 1.4 Inch round extension to put on the Eliptrac horn. I think it would be a neat accessory. That is if Dave can find the time to do it. I suspect he's got a lot of projects going already! I would love to do some testing on it.

Al K.

I can do that.

Share this post


Link to post
Share on other sites

Dave,

I have no doubt you could do it. The problem would be finding time! The Eliptrac horn itself needs to have some manufacturing problems ironed out. It is obviously a nightmare to make. A round tractrix extender to reduce 2 inch diameter down to 1.4 inch should be a cake walk by comparison!

Hopefully a second generation Eliptrac could be auditioned by someone other them me. I do not trust my ears. I have very little opportunity to listen to live music. All I can attest to is that it sounded very good! With the addition of a 1.4 inch adapter and a full range driver it could be tested for its full potential.

BTW: One of the two Eliptrac horns is being shipped to Lee Clinton for more testing. We are hoping to do polar plots. He also has a DCX50 driver on an evaluation / purchase deal from B&C to use with it. The two drivers and LR24-9000 networks are being shipped out tomorrow too. That's all I can do for now. I wanted to have a guy here in town, who's opinion I trust, listen to them, but there just isn't time.

AL K.

Share this post


Link to post
Share on other sites
Guest David H

It's great that Lee is going to run some more tests, and I agree I need to get some more ears on these. I am currently working on the manufacturing issues and have put all additional new developement on hold til the Eliptrac is ready.

A round tractrix extender to reduce 2 inch diameter down to 1.4 inch should be a cake walk by comparison!

Yes it will.

That's all I can do for now. I wanted to have a guy here in town, who's opinion I trust, listen to them, but there just isn't time.

The work you have done so far shows me the Eliptrac has serious potential, hopefully Lee Clintons test will support these findings as well.

Dave

Share this post


Link to post
Share on other sites

Great Work!

How about going all the way to a 1" adaptor and the Great Plains 902? (500 to 20,000+ Hz for La Scala and Belle owners)

Share this post


Link to post
Share on other sites

Great Work!

How about going all the way to a 1" adaptor and the Great Plains 902? (500 to 20,000+ Hz for La Scala and Belle owners)

Could this also work for a Jubilee ??? or would a 2" work better.....

Share this post


Link to post
Share on other sites

"How about going all the way to a 1" adaptor and the Great Plains 902?"

I did a quick computer run on that possibility. The adapter would be roughly 4 1/2 inches long to take 2 Inch down to 1 inch. Reducing it to 1.4 inch would be shorter. Assuming I started with the right mouth size, both look practical.

Al K.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...