Klipschorn Driver-Horn Design Criteria of PWK

[mikebse2a3]

@JRH

@Chief bonehead

@dBspl

 

I'm focusing this question on the Klipschorn because it was arguably PWK's most important design and I've seen many assumptions expressed on the forum over the years that I believe are misguided about how and why certain drivers/horns were used by PWK.

 

Mr. Hunter as you mentioned in another thread "PWK experimented with EVERYBODY's drivers and horns" 

 

Can you or any others that worked with PWK give us some insight on PWK's criteria and their order of priorities (ie: performance, availability, price, ...etc.....) for using the components he did in his beloved Klipschorn?

 

 

I see many assumptions/speculations expressed on the forum about PWK and of course this speculation is easy to get started and spread through the forum as factual when there is a vacuum of actual first hand knowledge from those that actually worked with and spent significant time with PWK. I sincerely hope You, Roy and Kerry can and will help to clear up the assumptions and misinformation that has existed far to long on the forum so that we all can come closer to knowing the real PWK that so many of us admire and respect.

 

 

miketn

[Deang]

Just a fun read. 

 

http://www.aes.org/aeshc/docs/afternoon_klipsch.pdf

[dBspl]

 

I doubt I'm going to give you the king of answer that you're looking for, but here's my perspective with regard PWK and the Klipschorn.

 

Most of the (interesting) history happened before Roy or I (and even Hunter) were around. I do think his criteria and priorities were pretty well stated in everything he wrote on the subject, though.  And you didn't have to be around PWK very long to realize that's exactly what he believed. He was pretty much: This is the way it is, and if you want challenge that - you'd better have the facts AND data to back it up.  A good example of this is that he never really accepted the Tractrix horn until he read a PhD thesis comparing an exponential horn to the Tractrix.

 

Nevertheless, the Klipschorn had already matured in its design by the time I started with the company. Only the occasional refinement were being applied throughout the early years of my employment. However, PWK did want a 2-way solution for the Klipschorn. And he did continue to experiment with new horn & driver designs during the time I was there. I got the opportunity to run the data on several of his experimental horns.  

 

He had abandoned the original 2-way design (and eventually the K-5-J horn) during the late 50's because he couldn't get the extended high frequency response necessary. Using the tools that we have today, it really isn't that difficult. But in those days with the limitations they had in equipment, it was probably out of reach. With the switch to the 3-way design, and the introduction of the K-400 horn, the Klipschorn had achieved a level of performance that it would only require the occasional refinement after that. But apparently, the 2-way design never left him, because it was a fairly big deal to him during the time I knew him.

 

PWK didn't seem to care for the original K-5-J horn. The K-5-J is essentially a constant directivity horn design, which does require significant equalization for a flat response.  I know that was a factor, but he may have also had an issue with how the radial horn mouth set-back into the cavity of the HF section and the issues that brought with it. The K-400 horn solved all of this.  The horn had a flat mouth and easily mounted to a baffle. The horizontal coverage is fairly consistent at 90 degrees, but he did sacrifice vertical coverage to improve horn output at higher frequencies. This is the self-equalization characteristic that compensated for the driver's rolled off power response. This was the technique he seemed to prefer. I say this because the experimental horns he later designed still used this approach.  Now, I do seem to recall the one horn design he was leaning toward did have flat sidewalls angled at 90 degrees.  This was more similar to the K-5-J, but the vertical was all K-400 style.

 

We did continue to experiment with the LF section, too.  But PWK was fairly comfortable with the LF design and didn't get too involved in those experiments.

 

Kerry          

 

       

[mikebse2a3]

Thank you Kerry....!

 

What's important to me is the insight that individuals like you can bring to help us to grasp more fully PWK as a person and his thinking. From the time I first began reading his papers describing his work and discoveries I was drawn more into what I perceived was an Individual with high integrity and someone searching for the truth as the facts revealed themselves to him.

 

I't has been one of my highest pleasures to have obtained the Jubilee 2-way as envisioned by Roy using the Jubilee LF and also made possible by Roy who has been willing to put up with some of us nuts on the forum and a part of me hopes and believes PWK would be very proud of this design because of the excellent data/performance it is capable of.

 

By the way did you ever meet Richard Heyser? PWK and Richard Heyser were the 2 largest influences in how I think about sound reproduction.

 

Oh yea... Roy may have had some influence on me in the last 10 years I been knowing him..!!!  :-)

 

miketn 

[garyrc]

What was the motivation to replace the K400 with the K401?  Who designed the K401 (I heard it may have been Keele).  Did it actually measure better?

[Chris A]

11 hours ago, dBspl said:

But apparently, the 2-way design never left him, because it was a fairly big deal to him during the time I knew him.

I'm not sure that the casual reader understands the implications of this.  

 

Paul wrote the 3-part article on modulation distortion pretty early on (JAES, 1969) when it was much more difficult  and costly to measure the individual components of FM and AM distortion.  He was very aware of FM (i.e., Doppler distortion) and how much of an issue that is was in mid-high frequency full-range drivers. (AM distortion is the dominant type of modulation distortion at woofer/bass bin frequencies.)  But he was still quite enthusiastic about 2-way designs.  Since he was clearly very sensitive to performance of his loudspeaker designs, this tells a pretty big story. Having a second crossover and added tweeter driver/horn above the bass bin-midrange crossover is much more problematic. 

 

The tradeoff in many people's eyes that frequent this forum is usually focused on performance, so it seems to me the performance tradeoffs were:

• how much did you trade away in a little added FM distortion using compression drivers from ~400 Hz to ~20 kHz vs. the advantages of not having the added circuitry (two crossover filters, one each for a midrange and tweeter), and
• how much added performance do you get from not having two drivers interacting in the critical hearing bands (1.5-6 kHz), not having polar mismatches, not having interference bands (lobing and general relative phase issues)

Apparently, the tradeoff is strongly in favor of two way using 2-inch-exit compression drivers in this case so that you have much lower harmonic and thermodynamic (air-water vapor nonlinearity) distortion, while also covering the required pass band with ease.

 

Other factors that people typically forget about include cost, complexity, obsolescence, reliability, and ruggedness/survivability.  Most people do not know how little power it takes to blow a K-77 diaphragm and how much attenuation and other circuit design details are required to keep that from happening by the owners.  Additionally, the midrange low-pass performance variability from supplier to supplier (you mentioned this elsewhere) becomes a manufacturing surveillance issue, as well as the obsolescence issues of the midrange and tweeter drivers over a very great span of time.  Sourcing one driver is a lot simpler than two, especially since the technology is basically still advancing in 2" compression drivers relative to the type of midrange and tweeter drivers used on the Heritage series (1-inch-diameter-exit midrange, small and relatively inexpensive phenolic diaphragm tweeter/horn with small frontal-plane area).

 

11 hours ago, dBspl said:

PWK didn't seem to care for the original K-5-J horn. The K-5-J is essentially a constant directivity horn design, which does require significant equalization for a flat response.  I know that was a factor, but he may have also had an issue with how the radial horn mouth set-back into the cavity of the HF section and the issues that brought with it. The K-400 horn solved all of this.  The horn had a flat mouth and easily mounted to a baffle. The horizontal coverage is fairly consistent at 90 degrees

This is something that I didn't really realize until you said it.  It answers a few questions that I had on why Paul wrote the long article on the K-400 when it was introduced, and why he even revealed where the inspiration for that horn came from (i.e., someone else's trash bin).  I had assumed that there would be a large difference in performance, but as it turns out, he stated it wasn't that big of an audible difference over the older midrange horn with a tacked-on tweeter inside the horn's mouth.  That was a pretty big admission in that day (early 1960s).

 

What you said about the flat mouth K-400 indicates to me the amount of weight that might have been put on design appearance in addition to performance.  It would have been easy to hang the K-5-J horn out a little over the front of the bass bin, but IIRC, the midrange horn mouth was actually set back away from the frontal plane of the bass bin. That says to me that buyer acceptance of the design aesthetics might have been a big factor.

 

Thanks for the insights, Kerry.

 

Chris

[Chris A]

12 hours ago, dBspl said:

Now, I do seem to recall the one horn design he was leaning toward did have flat sidewalls angled at 90 degrees.  This was more similar to the K-5-J, but the vertical was all K-400 style.

This must have been the K-403 horn, two of which Seti has on his Jubilee clones.  They have wide and short horn mouths that clearly rely on collapsing polars, like the K-400 series, and flat sides, IIRC.  I'm also not sure if everyone reading this understands the difference in sound that the K-510 and especially the K-402 (as well as all the other modified tractrix horns that Klipsch produces) has over the earlier collapsing polar, full expansion profile exponential horns. 

 

I assume that Paul was semi-retired during the period when these new horns were being developed (early-to-mid-1990s).  Also the advent of new, affordable, and high-performance digital crossovers were just entering the scene about 2002, the year of Paul's passing. 

 

Chris

[dBspl]

17 hours ago, garyrc said:

What was the motivation to replace the K400 with the K401?  Who designed the K401 (I heard it may have been Keele).  Did it actually measure better?

 

The K-400 and K-401 are the same horn design.  The 400 was die-cast aluminum, whereas the 401 is injection molded. I believe the 400 horn tool had worn out, and the decision was made to move it to an injection molded (plastic) horn.  I know Jim Hunter was responsible for putting the K-401 into production.

 

Don Keele wouldn't have had anything to do with the development of either one of those horns.  The 400 was well before, and the 401 was well after, his time at Klipsch.   

 

Miketn,

 

I never met Richard Heyser, but I'm a fan of his, too. He passed away about 7 or 8 months after I started with the company. I still remember the day PWK's assistant got the message he had passed, and was on her way into Mr K's office to give him the bad news.   

 

Kerry