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Droogne

How to dissect polar patterns and frequency responses for horns.

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Hey

 

I was recently looking into some big badass horns from Autotech, and was wondering what I should actually look for.. a lot of those horns only include size measurements and crossover point. Not a lot to go on.. The SEOS-30 horn were recommended to me once as a similar design as the K-402, but is this even? No way to know without some good comparisons. Sizewise it does look to match. But as it had so few info I was looking into some other horns, which had more info (I asked them, and if the info is not included on the site then they dont have them). Question is, what to deduce from the included specs? How much should I be looking at the frequency responses? I know "all compression drivers" and horns need EQ (which I will be applying, with lets say a Xilica), so are the ranges even relevant? And what about the polar maps (only horizontal), what is good? I'm guessing it should be a uniform as possible within the appropriate range (in my case that would be 500-700hz and up). Was hoping to maybe find a polar map of the K-402 as I know it to be excellent, but havent had any succes finding it. 

 

And, in your expert opinions, what look like the "ultimate horn" (design) for HiFi in a moderate room ((5x6m/15ftx18ft) with an adjoining room of 8square meter/40sqft).  Not super relevant in the question I want to be asking at this moment, but I will be going for the horn that best fits my size requirements (I actually only got one which is it shouldnt exceed 1,5-1,66 ft. in height). Design wise it will be matched with a LaScala bin (or maybe even a stack) and Faital HF200 (or 20AT) and I will also test it with the K55M (+ 2" adapter) and a K77 (or CT120) tweeter in a 3-way (I already have those, so it doesnt hurt trying it right) 

 

Hoping to get some good (general) info into horns and what to look for  when comparing them! Thanks!

E-JMCL300polar.PNG

E-JMCL300range.PNG

Iwata-300polar.PNG

Iwata300range.PNG

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This is what a perfect horn sonogram would look like:

 

directivity-ideal.gif.d5b60b1610646ad249e785d59f17c849.gif

 

The K-402 polar plot shows the -6 dB contour, both in the horizontal and vertical directions (corresponding to the junction between the red and orange colors on the above plot):

 

KPT-402-HF-Horz.jpg

 

 

KPT-402-HF-Vert.jpg

 

Note that the K-402 controls its polars to about 170 Hz (which is spectacular...and one of the major reasons why the horn sounds so good).  Most of the horns that you find control their polars down to perhaps 700 Hz--about two octaves higher.  EDIT: the vertical scales are in degrees coverage (twice the off-axis angle), NOT dB as is shown.

 

Chris

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I'm not sure how to interpret the plots you included, you say -6db but the plots show much higher values? And thanks for the perfect plot (the colored one), is it better if the plot stays narrow down to the lower frequencies, or is it more import how much of the used frequency range is within this -6db value? 

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The sonogram plots show the off-axis SPL vs. frequency of a horn with some compression driver attached for the test.  The horizontal axis is increasing frequency, the vertical axis is polar angle from the centerline of the horn/driver assembly.  The colors correspond to SPL scale to the right of the plot (relative to the on-axis sound pressure level).  Minus 6 dB indicates that at that frequency, it tells you at what off-axis angle that you have to be at with your microphone to read half amplitude SPL.

 

The color plots are nice, but as it turns out, the -6 dB contour plot actually tells you what you need to know. 

 

Now, what is not discussed above is why these off-axis plots are important.  All loudspeakers (including ones with horns) illuminate your room with acoustic energy.  Most of the reflected energy comes from off-axis.  Loudspeakers that win blind-blind listening tests have consistent off-axis energy (all other things being equal), as close as possible to the perfect case shown above. 

 

If the plot is uneven as you travel along in frequency on the horizontal scale, what you're doing is painting the walls, floor, and ceiling with acoustic energy that's like a badly designed loudspeaker: uneven in its frequency response.  That off-axis energy gets reflected back to your listening position and integrated with the direct-arriving (on axis) energy--corresponding to the following "early reflections" curve and "sound power" curve, shown below:

 

5a15897fe3a27_loudspeakerexampleon-offaxisFRcurves.PNG.6f90cbe899bb2408e048dbdb21e12cfa.PNG

 

The shape of the slight downward droop curve with frequency of the reflected energy curve is important--it partially determines how well the loudspeaker is reviewed by listeners.  The bottom curve--directivity index or DI--is the ratio of the direct energy (nominally the on-axis curve) divided by the sound power curve (the sum of all 360 degrees of measurement around the loudspeaker).  It tells you how well the loudspeaker is controlling its polars with frequency--and is probably the most important measure of performance after frequency response and harmonic distortion.  A flat line DI would be (notionally) a perfect loudspeaker--in terms of reflected energy.  However, there are issues with the DI measure that Roy has pointed out on this forum.  But in general, DI tells you what you need to know for a well-behaved horn/compression driver assembly, or horn-loaded bass bin like the Khorn, La Scala, Belle, or Jubilee.

 

Remember that the frequency response of a horn/compression driver can be equalized, but not its off-axis polars or its harmonic/modulation distortion.

 

Chris

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50 minutes ago, Chris A said:

The sonogram plots show the off-axis SPL vs. frequency of a horn with some compression driver attached for the test.  The horizontal axis is increasing frequency, the vertical axis is polar angle from the centerline of the horn/driver assembly.  The colors correspond to SPL scale to the right of the plot (relative to the on-axis sound pressure level).  Minus 6 dB indicates that at that frequency, it tells you at what off-axis angle that you have to be at with your microphone to read half amplitude SPL.

 

The color plots are nice, but as it turns out, the -6 dB contour plot actually tells you what you need to know. 

 

Now, what is not discussed above is why these off-axis plots are important.  It turns out that all loudspeakers (including ones with horns) illuminate your room with acoustic energy.  Most of the reflected energy comes from off-axis.  It turns out that the loudspeakers that win blind-blind listening tests have consistent off-axis energy (all other things being equal), as close as possible to the perfect case shown above. 

 

If the plot is uneven as you travel along in frequency on the horizontal scale, what you're doing is painting the walls, floor, and ceiling with acoustic energy that's like a badly designed loudspeaker: uneven in its frequency response.  That off-axis energy gets reflected back to your listening position and integrated with the direct-arriving (on axis) energy--corresponding to the following "early reflections" curve and "sound power" curve, shown below:

 

5a15897fe3a27_loudspeakerexampleon-offaxisFRcurves.PNG.6f90cbe899bb2408e048dbdb21e12cfa.PNG

 

It turns out that the shape of the slight downward droop curve with frequency of the reflected energy curve is important--it partially determines how well the loudspeaker is reviewed by listeners.  The bottom curve--directivity index or DI--is the ratio of the direct energy (nominally the on-axis curve) divided by the sound power curve (the sum of all 360 degrees of measurement around the loudspeaker).  It tells you how well the loudspeaker is controlling its polars with frequency--and is probably the most important measure of performance after frequency response and harmonic distortion.  A flat line DI would be (notionally) a perfect loudspeaker--in terms of reflected energy.  However, there are issues with the DI measure that Roy has pointed out on this forum.  But in general, DI tells you what you need to know for a well-behaved horn/compression driver assembly, or horn-loaded bass bin like the Khorn, La Scala, Belle, or Jubilee.

 

Remember that the frequency response of a horn/compression driver can be equalized, but not its off-axis polars or its harmonic/modulation distortion.

 

Chris

Thanks for the comprehensive explanation! Will have to read it again oncce or twice to understand it completely, but very well explained! 

 

And yeah I already knew about equalisation, which is why I was looking at other factors which doont benefit from EQ. Does any of the polars I included look promising (or even excellent?)

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11 minutes ago, Droogne said:

Does any of the polars I included look promising (or even excellent?)

 

Well, the Iwata-300/Beyma CP750Ti looks smooth but as you can see, its polar control gets progressively wider as the frequency decreases--something that's not nearly as desirable as the K-402 polar control. 

 

If you can get the polars to be controlled down to the so-called Schroeder frequency or otherwise called the "sparse mode frequency" of the room that they're in (usually this is below 200-300 Hz), then the horn-loaded loudspeaker will have almost "magic" performance in terms of speech intelligibility and clarity. 

 

If the horn/driver assembly loses polar control at some frequency above the Schroeder frequency for your room, or becomes progressively wider as the frequency decreases, like direct-radiating drivers (woofers, midranges, tweeters) and the Iwata/Beyma combination shown above, it will sound okay but not like the K-402 (a full range horn as in the MEH design, or the Jubilee with the KPT-KHJ-LF bass bins).  The same is true for the larger Danley Synergy designs with their larger pyramid-shaped horns (SH-50, SH-60, SH-96, etc.).

 

The key is to look at the lowest frequency of the horn/driver assembly that shows polar control, then look at the bass frequencies (in the case of the full-range MEHs mentioned above, that's below the typical consumer room Schroeder frequency).  If the bass bin polars match the horn/compression driver polars in each axis (horizontally, vertically), then the loudspeaker will sound very good.  If there is a mismatch in polars at the crossover frequency then it will sound not as good in-room.

 

Otherwise, a smooth and flat sonogram above the crossover frequency is most desired.  Anything that has uneven polars, like the Le Cléac'h horn with the same compression driver (above) are much less good in the ways that I've outlined above.

 

Chris

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3 hours ago, Chris A said:

EDIT: the vertical scales are in degrees, NOT dB as is shown.

 

Chris

Oh, that makes it a bit clearer already! Not sure what it means though, what do the degrees mean then? I'm seeing a 180° match at 170hz, does this mean it is controlled in the front field (as in 180 degree circle in front of the horn) for frequencies down to 170? And below that it's not able to direct/control them anymore and the soundwaves go everywhere and resonate? Or? 

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The 180 degree point on the sonograms above is measured from the rear of the horn-driver assembly.  The same point is 360 degrees on the K-402 plot - which is in "coverage angle", i.e., double the off-axis angle. 

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2 hours ago, Chris A said:

polar control gets progressively wider as the frequency decreases

Is this what is called "collapsing polars"? So a horn advertised as 90x60 degrees dispersion may become 180x90 degrees at lower ranges, affecting the frequency response in a room with hard walls? 

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Well, in a sense, yes.  A K-400 horn experiences a widening in its polar control in the vertical axis below about 1800 Hz, but not in the horizontal axis until about 400 Hz.  This is controlled by the size of the mouth of the horn--the bigger the mouth, the lower the frequency at which it loses polar control.  The K-400 horn (like all of the Heritage series midrange horns) is much wider than it is tall.  The loss of vertical polars was designed in so that the horn doesn't need equalization to achieve flat on-axis response, because it spills off acoustic energy on our ceiling and floor below the 1800 Hz point.  That was a design feature that PWK used to avoid larger crossover/balancing networks. 

 

Nowadays, if using a DSP crossover, EQing horns for flat on-axis response is trivial. So designing midrange horns to use a "collapsing polar" design is no longer required.  The K-402 and the K-510 horns both are designed so that they do not lose vertical polar control at a much higher frequency than the horizontal axis.

 

Chris

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Yes.  All loudspeakers that have irregular off-axis polars (either in the vertical or horizontal directions) will sound better outside--away from ceilings, walls and even floors.  Of course you lose boundary gain and low frequency extension due to that, but the overall sound will be very good.

 

Chris

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19 hours ago, Chris A said:

The sonogram plots show the off-axis SPL vs. frequency of a horn with some compression driver attached for the test.  The horizontal axis is increasing frequency, the vertical axis is polar angle from the centerline of the horn/driver assembly.  The colors correspond to SPL scale to the right of the plot (relative to the on-axis sound pressure level).  Minus 6 dB indicates that at that frequency, it tells you at what off-axis angle that you have to be at with your microphone to read half amplitude SPL.

Not super clear on this part. So the second (and third) graph are the "-6db" graphs? As in that the plot shows till what angle the pattern is controlled (aka -6db) for which frequency? Sorry I find it quite complex :s Cause why is it better that the -6db only falls at a low angle, and worse to be at like 360? Or is it vice versa, that the higher the angle shown on the plot, the lower db is at certain fixed angle? Again, not quite getting the plot..

 

19 hours ago, Chris A said:

 

The shape of the slight downward droop curve with frequency of the reflected energy curve is important--it partially determines how well the loudspeaker is reviewed by listeners.  The bottom curve--directivity index or DI--is the ratio of the direct energy (nominally the on-axis curve) divided by the sound power curve (the sum of all 360 degrees of measurement around the loudspeaker).  It tells you how well the loudspeaker is controlling its polars with frequency--and is probably the most important measure of performance after frequency response and harmonic distortion.  A flat line DI would be (notionally) a perfect loudspeaker--in terms of reflected energy.  However, there are issues with the DI measure that Roy has pointed out on this forum.  But in general, DI tells you what you need to know for a well-behaved horn/compression driver assembly, or horn-loaded bass bin like the Khorn, La Scala, Belle, or Jubilee.

Would you happen to know the polars for the LaScala and Jub? How important are those? The higher they can hold the pattern the better right? And does this have any affect on the crossover? As in to not cross this point.

 

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17 hours ago, Chris A said:

If you can get the polars to be controlled down to the so-called Schroeder frequency or otherwise called the "sparse mode frequency" of the room that they're in (usually this is below 200-300 Hz), then the horn-loaded loudspeaker will have almost "magic" performance in terms of speech intelligibility and clarity. 

"The key is to look at the lowest frequency of the horn/driver assembly that shows polar control, then look at the bass frequencies (in the case of the full-range MEHs mentioned above, that's below the typical consumer room Schroeder frequency).  If the bass bin polars match the horn/compression driver polars in each axis (horizontally, vertically), then the loudspeaker will sound very good.  If there is a mismatch in polars at the crossover frequency then it will sound not as good in-room."

 

I dont seem to be able to calculate my room Schroeder frequency (no idea what the reverberation time of the room is haha), but I'll do some sweeps and determine it that way it with my UMIK. Once I know that I could theoreticly match that with a horn design? And doesn't it matter that although the Schroeder would be 400 for a horn, but it's crossed at 500 this already is a perfect match, and only depends on the bassbin? Or did I misunderstand? Cause although I have LaScala bins now, I kept open the option open to build another pair (like the Jubs) in the future. 

17 hours ago, Chris A said:

 

If the horn/driver assembly loses polar control at some frequency above the Schroeder frequency for your room, or becomes progressively wider as the frequency decreases, like direct-radiating drivers (woofers, midranges, tweeters) and the Iwata/Beyma combination shown above, it will sound okay but not like the K-402 (a full range horn as in the MEH design, or the Jubilee with the KPT-KHJ-LF bass bins).  The same is true for the larger Danley Synergy designs with their larger pyramid-shaped horns (SH-50, SH-60, SH-96, etc.).

Aside from these horns, do you know some other HF horns that could achieve this? Something one would be likely to see on a second hand site? Like something from JBL (I know the 2360 isnt quite the K-402, but not sure where the weakenesses lay in the 2360) or some other brand (BMS, P-audio (lol), EV, .. and some I'm forgetting)

 

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17 hours ago, Khornukopia said:

 

17 hours ago, Chris A said:

Yes.  All loudspeakers that have irregular off-axis polars (either in the vertical or horizontal directions) will sound better outside--away from ceilings, walls and even floors.  Of course you lose boundary gain and low frequency extension due to that, but the overall sound will be very good.

 

Chris

 

Does this also explain why my humble ProMedia 2.1 Sound so good in nearfield use at my computer? Does sitting that close minimize the effect of reflections?

 

This summer I was casually listening to Hesesy 1s on my deck to confirm operation before taking them to a HS reunion.  I was captivated by how good they sounded outdoors.  I didn’t want to stop the music until failing light and mosquitoes drove me inside.

 

Thank you Droogne for your interesting and informative thread.  And thanks Chris for the information.

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31 minutes ago, DizRotus said:

Does sitting that close minimize the effect of reflections?

 

Yes, when you sit very close to your loudspeakers (generally less than 2 metres), the ratio of direct to reflected sound is made proportionately greater, just like the use of nearfield monitors in mixing/mastering control rooms.  The down side is much lessened sense of acoustic space and the loss very low frequency perception (below ~100 Hz). 

 

Chris

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In my opinion after doing a lot of searching there isn't anything commercially manufactured that is the equivalent or has similar performance to the K-402.

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8 minutes ago, jazzmessengers said:

In my opinion after doing a lot of searching there isn't anything commercially manufactured that is the equivalent or has similar performance to the K-402.

Well, I primarily started this topic to learn some more about horns and their specs/performance, but  also to convince me of the K-402. While I'm discussing here in this topic I'm trying my hardest to find a way to buy the K-402 (contacted over 200 klipsch dealers in Europe, and I have found someone who knows someone who has a K-402 in Europe. Waiting for their contactinfo.). 

 

What was the horn that came closest to the K-402? 

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7 minutes ago, Droogne said:

Well, I primarily started this topic to learn some more about horns and their specs/performance, but  also to convince me of the K-402. While I'm discussing here in this topic I'm trying my hardest to find a way to buy the K-402 (contacted over 200 klipsch dealers in Europe, and I have found someone who knows someone who has a K-402 in Europe. Waiting for their contactinfo.). 

 

What was the horn that came closest to the K-402? 

 

I believe the largest SEOS horns, but even they don't have excellent control down to what K-402 can do.

 

There is another graph of "globe view" (looks like the earth viewed from the north pole on a globe, not sure what this sort of plot is called) of K-402 polars but I don't have it saved to this computer. @Chris A do you have it?

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5 minutes ago, jazzmessengers said:

 

I believe the largest SEOS horns, but even they don't have excellent control down to what K-402 can do.

 

There is another graph of "globe view" (looks like the earth viewed from the north pole on a globe, not sure what this sort of plot is called) of K-402 polars but I don't have it saved to this computer. @Chris A do you have it?

I believe a lot of comparison were made between the Seos 24 and the K-402, but not with the (I think more recent) Seos 30. Not sure. Pair of black painted Seos30 with good drivers (HF200 from faital) would only cost me 1050eu. Still hoping to find a dealer to know the price for the K-402 (incl. all the shipping etc) so I know what I'm up against! To be clear: I'm 100% planning on buying the K-402, but depending on cost I might go for an intermediate. And before you say "that's gonna cost you more in the end", well that's true. But, I also have LaScalas for the rear and side (and center), and if the 2-way is something I like I could move the Seos to the rear/side when I decide to go for the K-402. Seos would be easier to have as a center too due to it's height (10cm). But who knows what I can come up with (rising the couches so the tv height isnt an issue anymore)(K-402 mounted above the tv? with bassbin beneath it, or to the sides?? )(synergy K-402? Not sure I have the skills to pull that off)(Seos as a center between K-402 rears, not sure about timbre matching, but who knows how good it turns out if I'd use the same driver as the K-402 + EQ)(insert random idea)

 

 

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