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BeFuddledinMn

The Klipschorn Woofer Polarity Challenge

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The measured behavior of the Klipschorn has always been of interest to me across woofers, motorboard slots and crossovers. Over time and a lot of measurements, I've noticed that the frequency response behavior of the Klipschorn seems to change quite a bit depending upon woofer polarity. No kidding, lol. But much like the 3x13 vs 6x13 slot riddle, is there a polarity riddle in the Klipschorn as well? 

 

I'll start it off this way:

 

Here's an illustration of a tested Klipschorn Woofer & Midrange combination using a simple first order "a" network with the two woofer polarity alternatives, matched or reversed, disguised and generically labeled as option A, or option B:

 

58dfe5d2a0f00_KlipschornWooferMidrangePolarityIllustration.jpg.54a1b86880c87ec42412268222ea9ae6.jpg

 

Then, let's look at the same measurements, but with the separate woofer trace added:

 

58dfe65c267a0_KlipschornWooferMidrangePolarityvsWoofer.thumb.jpg.f63898f484a5f0d572582882b3e62f5e.jpg

 

And finally, the two woofer/midrange polarity options against the separate midrange trace:

 

58dfe6bf0b3b0_KlipschornWooferMidrangePolarityvsMidrange.jpg.4551497131fe76332bfc5facc506f936.jpg

 

In my experience, this scenario is repeated regardless of woofer, slot size, or midrange horn/driver using any variety of the simple 1st order based "a" or "aa" or "universal" networks. Adding to the suspense, it's been well noted over the years that Klipsch did not "match" polarity until the late 1950's I believe. An apparent fact that is hard to reconcile given my own experience listening to Klipschorns with a variety of stock woofers, slots and midrange horn/drivers - under straight and reversed polarity - and there is a very noticeable difference to my ears. Did PWK ever speak on the topic in detail? 

 

Let's keep it simple: Looking at the actual measurements, which polarity option is correct, and why?

 

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Alright, maybe we need to make this more interesting. 

 

Here's another Klipschorn measurement comparison with the always familiar Crites/k401/k55 setup:

 

58e277a32eec8_CritesK401Rvs.S.thumb.jpg.92350f6540e401b535d8b6ed18bb4c89.jpg

 

Same question as above, which woofer polarity option is correct, A or B, and why?

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On 4/1/2017 at 0:51 PM, BeFuddledinMn said:

Did PWK ever speak on the topic in detail? 

I believe he did, you could post the basic question in the Ask the Historian section and Jim Hunter could tell you what he has seen on that subject.

 

Travis

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The only thing which makes sense to me is that we're seeing that the bass and the mid are pretty much in phase until the bass is reversed in polarity.  Then there is “destructive interference” when polarity of the bass unit is inverted. 

 

This is of course limited to the frequency range where they are both sounding.  Your graphs are in that range.

 

The extent of this is a bit surprising but not beyond the range of possibility.  The K-400 is strong down to 270 Hz and then there is some modest output below.  The K-Horn bass bin has some modest output above 400 Hz.   The crossover filters are not very steep and so do not cut off either unit very much in the critical region. 

 

WMcD

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On 4/3/2017 at 2:47 PM, WMcD said:

The only thing which makes sense to me is that we're seeing that the bass and the mid are pretty much in phase until the bass is reversed in polarity.  Then there is “destructive interference” when polarity of the bass unit is inverted. 

 

This is of course limited to the frequency range where they are both sounding.  Your graphs are in that range.

 

The extent of this is a bit surprising but not beyond the range of possibility.  The K-400 is strong down to 270 Hz and then there is some modest output below.  The K-Horn bass bin has some modest output above 400 Hz.   The crossover filters are not very steep and so do not cut off either unit very much in the critical region. 

 

WMcD

 

WMcD,

 

I've always appreciated your informed, clear and insightful contributions in the forum, and your comment here is no exception. I've always understood the internal speaker polarity issue as you've described the issue - polarity alignment creates a sum of parts in the crossover regions between drivers, while a polarity reversal, or mismatch creates a cancelling or, as you've put it so well, "destructive interference."

 

Having done a lot of testing/measurement of Klipschorn performance over the past year or so, what I'm finding is "destructive interference", as illustrated in the first set of graphs above, appears to occur on either side of the woofer/midrange crossover region, depending upon the polarity choice one chooses. Neither choice appears to deliver a clean, sum of parts result in measurements. Thus, apparently, one is left to choose between "destructive interference" occurring in the 275-350hz range, or the 375-500hz range, more or less. So it would appear that another way to pose the question I raised initially is to ask whether it is better with the Klipschorn to accept the "destructive interference" in the relatively lower, or relatively higher band of the woofer/midrange crossover region.

 

In any event, it seems that something is either wrong or there is a Klipschorn puzzle here. The issue here seems to hold true across the range of woofers, midrange horns and crossover points used by Klipsch, but I've observed that the relative magnitude is different, as illustrated earlier above. One suspicion is that the optimal polarity choice may be different for different Klipschorn woofer/midrange combinations and crossover points. I've left the polarity options disguised to produce a fair discussion on theory and practice, but unfortunately this thread hasn't generated much discussion. With your permission, I'll PM you.

 

-BeFuddledInMn

 

 

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Because the bass frequencies do not propagate straight out from the front center of a Klipschorn, microphone distance and room interations can be big variables in measured frequency response, more than when testing other speaker designs. In spite of that, the Klipschorns usually sound really good at the listening position, and the fact that the bass radiates out along the walls is probably why they sound so large.

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6 hours ago, BeFuddledinMn said:

 

 

Having done a lot of testing/measurement of Klipschorn performance over the past year or so, what I'm finding is "destructive interference", as illustrated in the first set of graphs above, appears to occur on either side of the woofer/midrange crossover region, depending upon the polarity choice one chooses. Neither choice appears to deliver a clean, sum of parts result in measurements. Thus, apparently, one is left to choose between "destructive interference" occurring in the 275-350hz range, or the 375-500hz range, more or less. So it would appear that another way to pose the question I raised initially is to ask whether it is better with the Klipschorn to accept the "destructive interference" in the relatively lower, or relatively higher band of the woofer/midrange crossover region.

 

In any event, it seems that something is either wrong or there is a Klipschorn puzzle here. The issue here seems to hold true across the range of woofers, midrange horns and crossover points used by Klipsch, but I've observed that the relative magnitude is different, as illustrated earlier above. One suspicion is that the optimal polarity choice may be different for different Klipschorn woofer/midrange combinations and crossover points.

 

 

You have hit upon a long recognised problem, not just for Klipsch speakers. The interference you have measured produces a "smearing" of sound and is detailed by Al Klappenberger in his paper A Case for Extreme Slope crossover networks - http://www.alkeng.com/dload/esxover.pdf

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Thank you very much gentlemen.

 

Khornukopia,

Complete agreement. I've always believed that room conditions are the single biggest factor in speaker sound performance in terms of frequency response. And it fits well with PWK's belief that frequency response was the fourth priority in terms of judging a speaker. I would have to agree as well, that the Klipschorn is a tough one to measure. To help clarify my work here, you'll note from the first set of graphs that I've measured not only the woofer/midrange combinations under both polarity scenarios, but also included separate overlays of the woofer and midrange traces as well - measured in the same room, same time, same distance, etc. My experience has been that setting a mic on axis about 8ft out from a Klipschorn in a proper, unobstructed corner, with a height equal to dead center of the midrange, captures the in room performance measurement that a listener would hear. Is the sound and measurement "room contorted"? yes, but all of the traces that I've done to display this polarity puzzle, are on the same room playing field. 

 

Wirrunna,

I either missed, or forgot the potential connection with the Al Klappenberger piece, thank you very much. It makes sense when considering that any slope greater than a first order, would by definition reduce the likely interaction opportunities which would create polarity discord to begin with. Of course, PWK used the first order approach for a long, long time, and more puzzling, didn't publicly observe driver polarity alignment for a significant period of time. In any event, it's always humbling to go down the path and stumble on a sign that's says "Al" or "Bob" etc, was already here, lol. Thanks much for bringing it to my attention! 

 

When testing the polarity alternatives, I noted the second order harmonic distortion created under each scenario, and again, there was a tradeoff with each. I've considered that perhaps one polarity option may measure and theoretically look more correct, but conceivably sound worse - per the singing in the shower analogy. But when you have a 5-7db frequency response difference in a crossover region, it's hard to imagine that PWK didn't notice that in the 1950's. In the absence of a factory polarity standard, did PWK believe then that it made no difference to the ear? 

 

 

-BeFuddledInMn

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On ‎4‎/‎5‎/‎2017 at 0:55 PM, BeFuddledinMn said:

Neither choice appears to deliver a clean, sum of parts result in measurements. Thus, apparently, one is left to choose between "destructive interference" occurring in the 275-350hz range, or the 375-500hz range, more or less. So it would appear that another way to pose the question I raised initially is to ask whether it is better with the Klipschorn to accept the "destructive interference" in the relatively lower, or relatively higher band of the woofer/midrange crossover region.

 

I don't think a clean, sum of the parts is possible with the Klipschorn (but that hasn't stopped folks from trying).  The 80Hz debit in the response is near the horn cutoff and, below that, the blue response is woofer mounted in a sealed enclosure.  At higher frequencies (pink) the air column defined by the folds define an air column to the woofer which results "horn action".  The horn action has maximum sensitivity in the neighborhood of 100-300Hz where the output is a combination of horn action plus resonances.  Horn action runs out of steam around 300Hz and the response drops but resonance peaks ride it on the way down. 

 

Say the response between 200-500Hz is the combined output of the midrange + bass resonance peaks + horn action.  Swapping the woofer polarity changes the polarity of the horn action output and resonance peaks output relative to the midrange output.  Peaks becomes suck-outs (and vice versa) and the horn action either contributes or debits. 

 

Klipschorn1.jpg

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This says that issues with driver polarity was observed and made consistent in 1958.

 

https://2d73e25b29782b6d6766-9c8af5cbfef16739445bc76457060528.ssl.cf2.rackcdn.com/KhornTimeline_635116436015580000.pdf

 

I'm not too surprised at the source.  One fellow on the forum installed a Max Potter P-trap.  His daughter recognized the change with no prompting. 

 

WMcD

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John, thanks for your insights on Klipschorn behavior and woofer polarity. I think that your knowledge of the fundamental workings of the Klipschorn - as a horn - with variable horn loading properties within the woofer range - is very helpful here and well communicated/illustrated.

 

Thus far in the discussion, we've considered the impact of horn loading/unloading and gentle slope networks in creating some level of "destructive interference", and thus the results illustrated earlier with the Klipschorn. If we accept that with the Klipschorn there will be an inevitable amount of "destructive interference" between the woofer and midrange horns, we are still left with the question as to which woofer polarity option - which appears to offer a choice on the "destructive interference" position along the 200-500hz range, is "correct" and why? If we consider the two disguised options - matched or reversed woofer polarity - as illustrated in measurements with a standard Crites/k400/k55/"a" network below, does theory or known Klipschorn behavior suggest which is the "correct" choice? 

 

58f3ba49cd2d0_CritesK401Rvs.S.thumb.jpg.0dd6495d58362d6c87fde263da5c4f84.jpg

 

- BeFuddleinMn

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5 minutes ago, WMcD said:

This says that issues with driver polarity was observed in 1958.

 

https://2d73e25b29782b6d6766-9c8af5cbfef16739445bc76457060528.ssl.cf2.rackcdn.com/KhornTimeline_635116436015580000.pdf

 

I'm not too surprised at the source.  One fellow on the forum installed a Max Potter P-trap.  His daughter recognized the change with no prompting. 

 

WMcD

 

WMcD,

 

When changing woofer polarities, I have measured differences of 5db on the modern K33/3x13 Klipschorn, and as much as an 8db variation in the crossover region with the older style 6x13 motorboard slot Klipschorn, so you'd think it would be clearly audible to just about anyone. 

 

The implications of your statement are both interesting and potentially profound! It's very unfortunate that once again, PWK, Max Potter and others, aren't here to help illuminate the subject further. 

 

- BeFuddledinMn

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On 4/5/2017 at 0:55 PM, BeFuddledinMn said:

 I've left the polarity options disguised to produce a fair discussion on theory and practice, but unfortunately this thread hasn't generated much discussion.

That's because for most of us, starting with me, I don't have enough theoretical/technical knowledge to discuss anything.

 

It would be far more interesting for you to explain your theory and let others examine it.  You might consider me the student in the third row listening to the professor's lecture, but every once in a while I might have a relevant question.

+++

 

Let me be practical for a moment.  Khorns are not the only speakers I own, or have owned; Khorns are not perfect.  It would be of more relevance for me to say for instance that there is a lack of articulation in the mid brass section as tuba, baritone and French horn all blur together.  If you would look at your charts and graphs and explain WHY that is, that would be relevant to me.

 

Then it would be HELPFUL to me in the real world if you said "to fix the fuzzy sound take the crossover and put a xxx filter here" or if you said "the woofer is playing above it's range, replace the woofer with XXX from Parts-Express."

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Wvu80,

 

I appreciate your point. To help clarify my approach here, I must first say that I too am a student here, and don't have any theory or theoretical depth on the subject to pose to the forum but instead, a lot of questions. In measuring Klipschorn performance which I've posted in the thread "comparing vintage Klipschorn woofer, motorboard, midrange performance, etc....." , I literally stumbled upon this puzzling woofer polarity question. I'm simply hoping that the way I've introduced the issue will bring out as much knowledge on the subject as is possible. My comment you quoted wasn't meant to be a complaint about not getting a free education, just an observation - more in line with "gee, maybe there is a real mystery here."

 

I think your input has been very helpful clarifying what could be misconstrued. I wish I did have the answers here, but simply put, I'm stumped and have raised the issue to learn. Apologies to any and all if if it has seemed otherwise. 

 

- BeFuddledinMn

 

 

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Given the horn was in production for about 10 years before consideration of the woofer polarity was an issue, that would suggest that the differences heard in listening tests were not considered significant.  Then, for whatever reason, Ms. Davis gives a Klipschorn a listen, hears a difference which was correlated to a given woofer polarity and history is made.  

 

 

 

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2 hours ago, BeFuddledinMn said:

Apologies to any and all if if it has seemed otherwise. - BeFuddledinMn

Apology?  Of course not, none needed.  It's pretty clear you are trying add to the body of information here, and you brought up a topic of interest which is a bit of a mystery.

 

My biggest quandary is that I am interested but not a big charts and graphs guy.  I own 1978 Khorns so due to the nature of their age, I will never know what they are supposed to sound like.  That leaves me with "how can I make them sound the best?"  And that starts with my own opinion on "how do they sound now?"

 

I have never understood how simply reading a graph can be translated to "how good is the sound?"  I believe the theoretical "perfect" graph would be a straight line, but if it's not, then what should it be?  If you took the best sounding speaker in the world (whatever that would be) then what does it's graph look like?

 

I know that is an elementary level, but that is my level, and I am willing to learn.

 

Go ahead with your discussions, I'll try to keep up.  B)

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Since the Khorn woofer is about 4 feet out of phase (greater than one wavelength) with the mid at crossover, along with the aforementioned crossover phase shifts which push the woofer even further out of phase with the mid horn, it's no wonder changing the woofer's electrical polarity yields little audible difference. Phase shifts greater than 1/4 wavelength do not allow for coherent summation of the woofer and mid horn outputs. The arrival times from each driver within the speaker need to be the same before polarity differences between the drivers can be consistently heard.

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On 4/16/2017 at 6:30 PM, wvu80 said:

That leaves me with "how can I make them sound the best?"  And that starts with my own opinion on "how do they sound now?"

A

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