A K-402-Based Full-Range Multiple-Entry Horn

[mark1101]

Chris,

 

What EQ settings did you use on the 305 when you used it stock?  I am interested in those.

[Chris A]

Yikes!  I tried to anticipate requests for data for a lot of things, but that one didn't occur to me.  Well, I do have the settings used for the JuBelle (the first plot above uses those settings with the KPT-305 instead of the Belle bass bin)...reproduced again just below:

 

 

Look at the four "Out1" PEQs in those Dx38 settings (really just three PEQs - the last one is at 500 Hz - above the lo-pass crossover frequency).  I'm reasonably sure that I didn't change them for the plot above. 

 

I assume that you'll let me know if I'm wrong...

 

Chris

[Chris A]

One of the things that some of you might wonder about is my statement that it's not really the length of the horn that's important, but rather the mouth size--if you are willing to consider conical throat sections and tractrix mouth sections used in series. 

 

Here is a very interesting article written by Bruce Edgar on the subject of tractrix horns.  Note that the effective length of the K-402 "modified tractrix horn" is not 17", but rather more like ~50 inches due to its use of a conical profile at the throat area and a shift toward a tractrix about 2/3 the way toward its mouth.  That gives a "mouth cutoff frequency" of about 30 Hz when used along a wall in figure 5, or about 20 Hz (above the 30 Hz curve) in figure 6 when used in a corner of a room.  That's what I was referring to. 

 

The K-402 is actually providing horn loading down to those very low frequencies that you would not get with a simple sealed box or even bass reflex box.  That's part of the "magic" of using the current design to get a much smaller profile, thus apparently violating Hoffman's iron law without the same levels of harmonic and modulation distortion that you would see if you simply used the twin 15" woofers in reflex or sealed box enclosure. While you do lose efficiency, what you don't get is all the harmonic and modulation distortion that you'd otherwise get with a direct radiating bass box.

 

Chris

Edited January 21, 2016 by Chris A

[mark1101]

I only use the 305 from 300-600hz in my MCM..........and while everyone tosses around the term "mid-bass"  like it's some "cool sound"..............when I isolate that 305 box and listen to just it alone..............honestly, it's a lot of shimmering junk.  I don't here anything beautiful in what comes out in that FR.  

 

Obviously, you are using it quite differently.  But as the box it is designed to be it has a very narrow focus in the MCM system, and a huge spike in the 500 hz. range.

[Chris A]

I think that the KPT-305 is really limited by its 8" driver, which isn't terribly impressive when you hold it in your hands. 

 

Also, that driver is mounted on the apex of the K-402 horn, which doesn't load the driver at low frequencies very well due to the flare rate present in the apex (throat) of the horn...versus at a point about 4 inches in front of the throat, i.e., the off-axis ports in the current design.  That's the secret in the Danley multiple-entry horn design.

 

Chris

[mark1101]

Since you have posted most of your information if not all, and are mostly responding to questions and comments I'll go a little further here.  You are the only person I now know that has 305s besides me and has measured them.

 

I originally ordered XII modules from Klipsch.  I was borrowing JC's at the time and had them in my MCM system, liked them, wanted a pair.  The XIIs were the 305's predecessor and were 12" drivers (on a tractrix horn?).  What showed up at my doorstep with no explanation was the 305s with their 8" drivers.  I was like "what are these things"?  I didn't order these.

 

I took them in and installed one.  I measured against the XII and listened as well.  As I mentioned this FR sounds like junk and so the listening tests had to be "whole system" tests.  I never thought the 305 sounded as good as the XII.  However, in reality I think it really is a better horn for the MCM because it's a 402.  When Klipsch updated the top horns in the MCM to 402/510 the XII was left unlike the others.  I'm not sure what type of horn the XII was, but you could tell by looking at it that's not the same type of horn as the 402/510.  So I kept my 305s.  I EQ'd the 305s with a couple of PEQs so the curves lined up exactly on top of the XII and left it that.

 

But over time I reduced the crossover from 800 down to 600..........which over time proved to be an overall improvement.  I still consider today raising the MWMs from 300 to something more like 400 or even 500 which is a stretch.  It just seems like I find my ears telling me to squeeze the 305s out of there.  Now it has been a few years and this is what my ears still say.  Sounds great as is, but I have another system at the other end of the room that sounds sweeter in the lower registers honestly, and everything points to the 305s.  Spitting hairs here.  Just my 2 cents.

Edited January 21, 2016 by mark1101

[Khornukopia]

I have been reading through a lot of specs lately and noticed the following info. 

 

The newest Model KPT-MCM-II Cinema speaker brochure specifies the KPT-305-MB now employs a 12" driver operating at a bandwidth of 340 Hz - 1520 Hz.

 

[Chris A]

The newest Model KPT-MCM-II Cinema speaker brochure specifies the KPT-305-MB now employs a 12" driver operating at a bandwidth of 340 Hz - 1520 Hz.

 

I ordered my KPT-305 in early June and had it under test and listening evaluations within a couple of days in mid-June.  It has an 8" driver, which is now sitting in my "extras" room with it's baffle compression slot plate and mounting bolts.  The specs that you refer to may be in error, since I remember that conversation here on the forum.  The XII module had a 12" driver and a much larger throat.  A 12" driver on the 2" throat of the K-402 horn is a bigger compression ratio than I typically see from Klipsch--they typically use a 3 to 3.5 compression ratio on the designs that I've looked at.

 

 

 

What showed up at my doorstep with no explanation was the 305s with their 8" drivers. I was like "what are these things"? I didn't order these.

 

I remember that part of the story, Mark.  Perhaps Roy might chime in here with the design goals of the 305.  I assume that the XII module was somehow obsolete - i.e., unable to get either the horns or the drivers, and that the "big company" need to keep inventory to a minimum was a factor in the process (i.e., we're not talking about a JIT supplier concept whereby the supplier makes the part(s) after the customer's money is in the bank - sort of like Dell does things).  I further assume that there isn't a large demand for that particular item, so there needed to be a stopgap design that would do the job - nothing spectacular.  I see the KPT-305 as that stopgap product.

 

For my needs, it had the box and the horn exactly as I needed them, so I used my own drivers and cut four more ports in the horn for the current configuration, and fixed the woofer mounting pads to those ports on the back side of the K-402 horn, all of which transformed the KPT-305 design into something completely different. 

 

I didn't have to buy a KPT-305 - I could've just bought a K-402 and built my own box, but it was convenient at that time to buy the 305.  I don't plan on doing that again (buying more KPT-305s) and I don't really recommend it to others now that the performance of the current configuration and the design needs are known.  I'm working on a much better solution than that.

 

Chris

Edited January 21, 2016 by Chris A

[Khornukopia]

It will be interesting to read about your listening impressions of your New Center speaker after you get a chance to take them outdoors. In the past, I have noted that the La Scala sounds very good outdoors.

[mark1101]

 

I have been reading through a lot of specs lately and noticed the following info. 

 

The newest Model KPT-MCM-II Cinema speaker brochure specifies the KPT-305-MB now employs a 12" driver operating at a bandwidth of 340 Hz - 1520 Hz.

 

 

Chris's explanation above is correct about the 305.  Roy eventually did explain it to me when I asked.  The info on the website is wrong.  I told Amy but it never got fixed.  I mentioned it more than once, and it still got overlooked.  They carried over the description of the XII into the 305.  The 305 is an 8" driver with a can on it so it is sealed.  The box is open in the back.

 

Chris I understand why you purchased a 305.  Makes perfect sense.

 

Chris

Edited January 21, 2016 by mark1101

[ClaudeJ1]

Since I was using a K-1133 driver in my 402's, crossed at 320 Hz. I never needed a 305, which I thought was a very narrow band device for higher output in a commercial theater environment.

[DrWho]

I never thought the 305 sounded as good as the XII.

 

Interesting - how would you describe the difference? Or what is it about the 305 that you don't like?

 

Do you think it could be a xover/acoustical summing issue with the other units in your system? Or maybe that you just listen too close to the entire system? (not enough space for the wavefronts to become coherent). Off-axis polars in the xover range? Distortion?

[mark1101]

The system sounded fuller and deeper with the XIIs.  This is with the curves of the XII and 305 one on top of the other.  I felt the 305 just sounded slightly thinner.  It was noticeable but not nearly enough for me to reject them altogether.  If I came across another pair of XII today that were in nice shape, I'd pick them up for sure though.

[DrWho]

Also, that driver is mounted on the apex of the K-402 horn, which doesn't load the driver at low frequencies very well due to the flare rate present in the apex (throat) of the horn...versus at a point about 4 inches in front of the throat, i.e., the off-axis ports in the current design.  That's the secret in the Danley multiple-entry horn design.

 

 

Does mounting the driver further down the horn actually increase acoustic loading at low frequencies, or does it just have less loading at all frequencies which makes the rolloff seem less?

 

In other words, put 1Vrms at a low frequency into the driver mounted at the throat of the horn. Does it produce more SPL (in the far-field) than the same driver mounted further down the horn? I would expect the SPL to drop slightly.

 

Or maybe the issue is a reactive component in the horn? Kolbrek shows this in Figure 2 on Page 3:

https://www.grc.com/acoustics/an-introduction-to-horn-theory.pdf

Is offsetting the driver actually shifting the reactive portion of the horn in such a way as to actually improve the coupling?

 

The part I struggle with is that if I put the driver all the way at the mouth of the horn, then there is no acoustical loading provided by the horn. Perhaps there is an ideal offset for a given low frequency target? I wonder if this isn't what Roy is alluding to in his comments about tradeoffs: a slight decrease in efficiency. Although that should be balanced against the idea that we can have more drivers summing coherently with such an approach...and amplifier power is effectively free from a sound quality perspective. I'd even go so far as to argue that increasing the amplifier power requirements is a sonic benefit (in part reference to PWK's funny article on the LSH speaker: https://community.klipsch.com/dope/Dope_740400_v14n1.pdf)

Edited January 21, 2016 by DrWho

[Chris A]

The following figure is also found at post #49 (page 3) of this thread.  It comes from the Danley literature and is referenced in the patent(s), especially the Unity horn patent (US 6411718. now expired). 

 

[DrWho]

Ya, I'm familiar with that plot, but it's not the same as showing throat impedance. That plot correlates the slope of the instantaneous area expansion to the slope of an ideal expansion for a given Fc. It's a subtle difference, but I'm not convinced the expansion rate itself is what dominates the loading presented to the driver.

 

Let's take two horns both using the same driver:

• Horn A has an area expansion slope of X starting at the throat.
• Horn B has an area expansion slope of X starting at some distance away from the throat.
• They both have the same final mouth area (which means Horn A is longer than Horn .

At the point where the driver enters the horn, the actual cross-sectional area will be smaller on Horn A than on Horn B. Doesn't this mean Horn A has a larger compression ratio than Horn B? And by extension, wouldn't that mean Horn A will have a higher throat impedance, and overall be a more efficient horn?

 

Am I missing something?

 

The attached equation is for the throat impedance of an infinite conical horn. St is in the denominator, so a larger St has less impedance. St would be the location where the driver enters the horn, right? This is also assuming an infinite horn - I've not seen any calculations for a truncated horn, but I'm sure someone has determined those equations at some point.

[DrWho]

Different subject, but here's an interesting thesis on beamwidth calculation techniques:

https://digital.library.adelaide.edu.au/dspace/bitstream/2440/41350/8/02chapters1-4.pdf

 

I came across it looking for an equation for a truncated horn.

[Khornukopia]

DrWho,  Thanks for providing the above links. The papers were good reading, but I did skip much of chapter 4 with all the equations that I don't plan to use.

[Khornukopia]

It will be interesting to read about your listening impressions of your New Center speaker after you get a chance to take them outdoors. In the past, I have noted that the La Scala sounds very good outdoors.

 

 

Considering the fact that this thread is about the development of the K-402 based Full Range Multiple Entry Horn, which may become THE best sounding loudspeaker for accurate, dynamic music reproduction, I want to expound on the statement I made earlier.

 

The La Scala sounds very good outdoors... for casual listening such as a neighborhood block party or while working in the garden. It also sounds very good outdoors, compared to how it sounds when played at high SPLs in a small reverberant listening room. 

[ClaudeJ1]

not convinced the expansion rate itself is what dominates the loading presented to the driver.

 

I think the compression presented by the "smaller than average throat" multiple entry apertures loads the driver just fine and they feed into a pretty small "corner" when looking back at the apex. It's very far from "direct radiator bass" as some suggest. After owning 18 of these types (15 sealed, and 3 ported) designed by Danley in 3 different rooms, all I can simply say is IT WORKS and it sounds great and they are small relative to all other horns for the bandwidth they provide.

 

Chris, mine being the exception, almost all the comments provided here are by "armchair quarterback" types..............long on opinion with no ownership, meaning, no skin in the game. Theorists rather than doers. Not trying to insult anyone, but it is what it is. All I can say is "try it, you'll like it."

 

Chris, You put some MONEY and time into this new path, just as I have in 2014. Even though hearing is believing, living with this type of point source speaker for a long time tells a better story than a quick demo and makes it difficult to go back, so to speak.  However I am working on a 2-way factory K-402 driven by TAD 4002's with twin 15 OB bass, just for fun, but these Unity Summation Aperture TD-1's from Danley former company as well as the Synergy Horns from his new company are my new benchmarks of excellence, period.

 

And no, the SH-50 was also designed to be used at home, since it outperforms 99 percent of the overpriced "pretty" speakers at Axpona at a fraction of the cost and is quite competitively priced against Khorns and LaScalas, even in the used market. Tom Danley has his original prototypes in HIS living room, just like Paul Klipsch had factory Walnut Khorns in his. I'm fairly sure if he were still alive, he would approve of these designs, even though, as young as 81,  he was an irascible curmudgeon for sure. But when "home" speakers have an efficiency above 100 db/octave, they are powerful enough to be used in larger than living room applications, or outdoors.

Edited January 22, 2016 by ClaudeJ1