Design a better Khorn bass bin

[djk]

I call 16" 50hz.

PWK calls it 47 cycles. He mentions the area doubling in 16" several paragraphs of his 'new design' cornerhorn "so that the nominal cut-off is 47 cycles". A 15" diaphragm is mentioned. The drawings are those of the modern Klipschorn (not the strange thing in fig.10 of 'a low frequency horn of small dimensions', his experimental model).

"The cut-off of the horn is 47 cycles and the computations show poor performance below 55 cycles. But the measurements and critical listening tests show good performance down to 40 cycles".

The JAES 2000 article examines both the Klipschorn and Jubilee in great detail, I've quoted from it before. You will have to find your own copy as mine is still packed away from a recent move.

[WMcD]

There is not much chance that Klipsch and Delgato missed anything about bass horn design. One apparent constraint was that the Jubilee have the same footprint as the K-Horn. I'd have to check the height. Overall there is the same bulk.

So this must have been an exercise in maximizing the K-Horn performance. It would be "cheating" to just make a bigger horn.

The Jubilee has better performance.

For the most part, the Jubilee uses the same rapid initial expansion as the prototype K-Horn but uses two woofers and thus has twice the throat area.

In a horn, if you can increase the throat size, you can invest that in a shorter horn, or lower Fc (good for bass), or bigger mouth (good for bass); or a combination of them. That seems to be what is going on.

Also, if you have woofer(s) with less spring effect, you can get away with a smaller back chamber (that reduction can be invested too, per the above).

Note how the Jubilee has drivers with very low Fs. That is a sign of less spring. Please recall that PWK did some work on his orignal woofers with solvents to reduce the spring effect. So the same principle was applied again in a different way.

I had wondered why bass horns designed in the '50s and '60s, like the K-Horn and the respected JBL Hartsfield (two versions) were designed to be so dang complicated in construction. Designers must have contemplated the potential advantages of a Jubilee-like construction with two woofers.

The answer is, most likely, that high quality woofers were relatively expensive while cost of high quality woodworking labor was relatively cheap. E.g. the first Hartsfield has very complex woodwork (even by K-Horn standards) simply to allow the use of a smaller driver, much less two big drivers.

Gil

[ZAKO]

Pwk used a special solvent on outer surrounds to get free air resonence down below 30Hz. No woofer at that time was available to that spec. It would take about an hours work for each woofer. It was Stephens that finally gave him a woofer with his compliance requirements.

[D-MAN]

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On 3/3/2005 1:39:32 AM djk wrote:

I call 16" 50hz.

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Yep, ain't arguing the patent, so I would agree 100%.

However, I AM talking the production model Khorn, not the patent version.

Here's a pic that I hacked up to explain the measurments.

Please bear with me, I am doing this from memory, and I'm also at work, and I do not have the plans handy.

DM

[D-MAN]

The only two ways that a Khorn can be "improved" would be

1) lower fc

2) higher upper freq. band pass

Either choice would amount in a larger footprint or taller cabinet (or both). For an example, the EV Patrician, a solution that does both.

DM

[JBryan]

Hey guys,

Excuse me for breaking in but I would like some clarification. The cut-off for the Khorn's LF is 450Hz but what is the natural roll off? It was suggested that there is degradation of the mid to upper bass - beyond what frequency is the signal being compromised and would it be best addressed by adding a midhorn that can handle lower frequencies and cut-off the woofer at say, 200-350Hz?

Finally, if the cut-off is reduced, can a different driver be used to optimize the LF and increase output? Someone has said that a JBL D-130 seems to work well and is easier to drive thus simplifying the xover.

Thanks in advance for your help. Have fun -Bryan

[ZAKO]

Paul Klipsch didnt like the D130. Free air resonence was too high. He said some engins were too good for his horn. Lowering compliance using special chemicles worked for awhile. But he couldnt get JBL to supply cones with his requirements. It wasnt till JBL came out with the 2205 woofer that met some of those specs. The 2205 morfed into 2225 & resonense levels again moved up. Stephens & Emmenence filled pauls requiremence without modification. And were a damn site cheaper.

[D-MAN]

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On 3/8/2005 10:28:24 AM JBryan wrote:

Hey guys,

Excuse me for breaking in but I would like some clarification. The cut-off for the Khorn's LF is 450Hz but what is the natural roll off? It was suggested that there is degradation of the mid to upper bass - beyond what frequency is the signal being compromised and would it be best addressed by adding a midhorn that can handle lower frequencies and cut-off the woofer at say, 200-350Hz?

Finally, if the cut-off is reduced, can a different driver be used to optimize the LF and increase output? Someone has said that a JBL D-130 seems to work well and is easier to drive thus simplifying the xover.

Thanks in advance for your help. Have fun -Bryan

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The natural rolloff is a combination of the driver employed and its capabilities and the degree of distortion of the upper-and-mid bass frequencies that one can accept due to the folding and splay angles. Basically it is a coloration or a "muffling" effect. It also is a rather "peaky" response.

The traditional crossover point was approx. 400 Hz. Recently Klipsch has published 450Hz as the upper band-pass limit of the Khorn. That is about as far as I would want to push it too for the above stated reasons.

Mid horns (and drivers) capable of 250-300Hz are rare and therefore expensive, IME. They are also going to be larger than the bass horn cabinet in width and length, since they cannot be folded. The 400Hz is even quite limiting.

Once one gets into the 500Hz range, the available horns and drivers provides a wider selection.

DM

[JBryan]

Dman,

Thanks for the explanation. I have been looking at different possibilities and have come across a couple of horn/driver combos that will do the trick. The Oris 150 and 200 horns are capable of 150 and 200 Hz respectively when using the optimized drivers. There's also a 300Hz horn by Dr. Bruce Edgar which can be coupled with several drivers - from $ to $$$!

The Oris horns offer a bit more top-end and with the right drivers (AER, Lowther) the horns will exceed 20KHz - no tweeter necessary. The 150 goes lower but is rather large and projects less of a soundstage (width/depth).

I was thinking of using the 200 crossed over somewhere between 250 and 300Hz with a low-pass going through a second amp (100w) to the bass bin. I could start with a variable resistor to control the cut-off and a gain control on the amp to "dial" in the mix until it sounded right. It would also allow me to try lots of amps on the horn to find a good match.

I'm just throwing this out to see if there's any merit. Please don't hurt me ...

[D-MAN]

Yes, if you really want to head in that direction, you should look at a DIY mid-bass horn and consider a 10" or 8" cone driver for it. I know that some here have done that and report great results. I think TBrennan and John Warren, perhaps.

and now for your punishment regarding considering anything other than compression drivers for the midrange band-pass, bailiff, whack his ...!

DM

[mark1101]

This is a great thread.

Of particular interest to me is the discussion of the Jubilee and its seeming paradox. If PWK were a younger man at the time, it would be very interesting to see what or if he would have promoted as an improvement to the Khorn. Obviously, it looks like it would have been the jubilee. He just never got to finish.

[mark1101]

If the bass horn were not folded, how long would it be?

I keep looking at the picture in this thread as I have many times over the years and have a dozen questions. I don't completely understand the folding concept like some of you guys. It seems the woofer has to be actually mounted some distance inside the throat as opposed to being mounted at the supposed opening.

Is the folding supposed to be similar to an accordian style fold? Sorry.

[sunnysal]

Gil, do you have a copy of the JAES 2000 by Klipsch and Delgato? I lost my copy...perhaps a good candidate for a weekend reading publication? warm regards, tony

[D-MAN]

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On 3/8/2005 3:37:49 PM mark1101 wrote:

If the bass horn were not folded, how long would it be?

I keep looking at the picture in this thread as I have many times over the years and have a dozen questions. I don't completely understand the folding concept like some of you guys. It seems the woofer has to be actually mounted some distance inside the throat as opposed to being mounted at the supposed opening.

Is the folding supposed to be similar to an accordian style fold? Sorry.

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The Khorn is approx. 64 inches in length (measured center of channel), and has a mouth area of approx. 4 sq. ft.

When placed in a corner the mouth area "appears" to be 16 sq. ft.

The folding is not like an accordian (that would be bad) as turning 180 degrees is not a real good design approach.

The folding is basically applying a turn to the waveform in order to redirect it in a different direction within certain parameters.

The complication of the folds in a Khorn occur in after the first fold, and occurs again at the tail board. The Khorn secondary horn channel changes the proportions of the waveform from horizontal to vertical at the tail board. This "twisting" effect is not condusive to the propogation of upper-bass frequencies.

Also there is a tendancy to reflect directly back from the tail board being that it sits flat at 90 degrees, again not particularily optimised for the best response.

The throat is actually the smallest point (in cross-sectional area) in the horns expansion rate. The horn throat itself is where the throat splitting wedge sits. It's purpose is to bifurcate (or split into two equal sections) the horn channels turning the channel 90 degrees.

The throat cavity opening (the "slot") where the driver is mounted is actually 1/2 the size of the throat area cross-section. This was done to allow the K33E woofer to raise its response somewhere around 400Hz. The original size of the opening was 6x13 inches, and that can be used for other drivers than the K33E.

Bifurcating the horn channels at the throat keep the respective channel proportions somewhat managable, and allow for the folds to occure relatively close to the throat. That also allows the footprint to be the smallest for the given frequency cutoff of the horn. The further from the throat that a fold occurs is more liable to create standing waves due to reflections occuring in the folds. More or less, it is better to fold the waveform while its proportions are below a certain percentage of the wavelength being propogated to prevent standing waves.

DM

[D-MAN]

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On 3/8/2005 3:53:21 PM sunnysal wrote:

Gil, do you have a copy of the JAES 2000 by Klipsch and Delgato? I lost my copy...perhaps a good candidate for a weekend reading publication? warm regards, tony

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Tony, here you go!

DM

AES-Jubilee2.pdf

[greg928gts]

Boy that's an interesting read.

I see that designing bass horns is full of compromise. The objective is to reach your goals while minimizing the compromises.

I'm curious to know if this idea has merit; the bottom driver could have it's own horn, separated from the top driver, and each horn could be slightly different to perform certain tasks better. With fewer demands on each of the two horns, each would be limited by less compromises to consider and the resulting bass bin would be better as a whole, albeit a little more complicated to build.

D-Man, do you understand the design of the Jubilee bass bin? Can you follow the description of the angles and how the slight changes in those angles modifies the response? Because I don't follow it, although I understand the basic premise.

Greg

[D-MAN]

Greg, there are 6 basic changes in the Jubilee design that are not in the Khorn (ignoring the 2 throats and drivers, we'll consider that one driver and one throat for now).

1) particular attention has been paid to promote even rotational angles in the folds and turns.

2) 3 different exponential expansion rates are employed, the highest occuring in the throat, the lowest in the secondary channels and the final intermediate in the last portion to the mouth

3) the exponential path, expansion and folding is all in the horizontal plane. This prevents the twisting of waveforms and passes higher bass frequencies.

4) particular attention has been paid to the tail board in order to promote an even rotational angle which reduces turbulence and reduces reflections

5) the terminal mouths have a more direct splay angle from the corner, which promotes the propogation of higher bass frequencies at the listening position

6) the use of 12" drivers provides a higher frequency capability than the mass afforded by a single 15" driver

The change in expansion rates at the throat is called a "rubber throat". It allows for an extreme expansion to occur at the throat to be "squeezed" down later to a lower fc. This prevents high reactance at the throat than would otherwise occur with a less exagerated (and lower fc)expansion rate.

The secondary channels expansion rate is smaller (or lower fc) than the others. It will have a "balancing" effect between the throat and terminal channels and match the reactance between the two different fc expansion rates because it changes the overall available cross-sectional areas.

The La Scala does this in that the throat channels fc is 60Hz and the mouth channels are over 100Hz, resulting in an overall fc for the horn as somewhere around 70Hz.

The formulas employed are not available to me, but it can be easily estimated based on the above, I would think.

In essence, aside from having 2 drivers that feed into separate "rubber" throat channels which then merge into the two bifurcated channels at the first fold, the design is fairly comparable with most other bifurcated horns of PWK design.

The combination of these elements results in (I would estimate) at least as good and deep of bass response, but that depends more on the quality of the 12" woofers employed and the ability to propogate upwards of 800Hz with less coloration.

The more I look at it, the better I like it. Don't like 12" woofers, though, but that's just me...

DM

[Daddy Dee]

DMan,

Thanks. Good reading in these posts. Helps me understand why the Jubilee sounds like it does.

I think I've heard stories that Mr. Paul and Roy Delgado worked on ALOT of prototypes before they settled on the final bass bin design.

[D-MAN]

Dad, ironically, my new corner horns are smack-dab in the middle between a Khorn and a Jubilee, design and performance-wise.

So needless to say, my quandry is what do I do, move or stay where I'm at because all of the possibilites are right in front of me...

DM

[mark1101]

Thanks for the info. This is very interesting information.