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Question on K 402 horn dimension


Arizona Dan

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I have a question on dimensions of the K 402 horn.  The data sheet shows the width = 39.5 inch and the height = 25.5 inch.  Does this include the width of the flange?  If I were entering data into a tractrix calculator, would I use these dimensions or subtract the width of each flange?

 

I would like to thank everyone who posts on this site.  I read it and enjoy it quite often.  I do not post often, but I get a lot of joy from this site.

 

Dan

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Yes, it includes the flange. If space is tight, then the flange can be trimmed down some (table saws are useful).

 

I doubt the tractrix calculator will give the correct results. The shape (expansion rate)  is what Roy calls a "modified tractrix ". The controlled dispersion is one thing that makes a "modified tractrix" different than a "regular tractrix". This is potentially a big deal.

Good luck,

-Tom

 

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Isn't the flange part of the horn?  Roy warned me to avoid "steps" or other sources of reflection where the bottom of the 402 horn is resting since they could cause audible issues.  Accordingly, I used steel strapping to allow me to mount the 402 horns as closely as possible to the front edges of their mounting bases.  He also seemed to think that whether the sides had extended baffles or not would not make a significant difference.

 

I didn't ask him about "trimming" the horns.

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You'll need to be more specific about the application. Is the horn going to be free standing or in a box and surrounded by a baffle. If there is a baffle, then is the horn mounted flush (approximately). Are you trying to re-use and existing cabinet? In general, horns work better if mounted on a baffle. 

 

Tell us about the project.

Good luck,

-Tom

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10 hours ago, Arizona Dan said:

...If I were entering data into a tractrix calculator, would I use these dimensions or subtract the width of each flange?...

You'll get a horn that's 3x deeper than the K-402 if using a tractrix calculator.  The K-402 has a tractrix mouth flare only. 

 

The balance of the horn (about 2/3s of it, that is) is straight-sided.  That is to say, it's not "conical" but straight-sided.  For reference, the conical equation for area expansion, i.e., S = S1x2,  will not be correct (where S = area of cross-section, S1 is the area of the horn throat entrance, and x = distance along the central axis of the horn, starting at the horn throat entrance).  The K-402 straight-wall section has a more complex area expansion formula.

 

The flanges are 2" wide (4" total on the mouth width), so the horn mouth itself is about 35.5 inches wide and about 21 inches high...and about 17 inches deep.  After the mouth is constructed first (as the tractrix equation is usually portrayed--not from the throat), the horn itself is fairly easy to construct graphically:

 

517143346_TractrixhorncrosssectionconstructionfromBruceEdgar.thumb.GIF.72dc0bf0ccf41f327c1a4652fd4a32fb.GIF

 

Just cut off the throat at the right diameter.  For 2", the K-402 is 17 inches along the centerline.  If constructing a horn for 1.4 inches diameter throat, it's about 17 5/8 inches, and for a 1" throat, it's about 18 inches long. 

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I seem to recall Roy once saying that the flange could be removed and the horn would be fine, i.e., the horn doesn't rely on the flange for the sound.

 

My memory may be faulty but I'm at least 2% certain that's what I heard. :ph34r:

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36 minutes ago, Coytee said:

I seem to recall Roy once saying that the flange could be removed and the horn would be fine, i.e., the horn doesn't rely on the flange for the sound

Yes, in terms of the horn's acoustic length for crossing over well above ~170-180 Hz, since the axial length of the horn supports a 1/4 wavelength down to that frequency. 

 

Chris

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Thanks to everyone for helping me.  I suspected that the dimensions included the flange, but thought I should verify.

I am going to attempt to make a horn similar to a K 402.  I have no doubt it will not perform like the real thing.  It will probably be ugly and kinda rough, but what the heck, only cost a sheet of plywood.

 

Chris, thank you very much for the information.  I had the shape of the K 402 backwards.  I thought the shape from the entrance (small end) to about 2/3 of the length was Tractrix and the exit was straight.  Just to make sure I understand, I use the tractrix calculator using the mouth (large end) dimensions from the K 402.  Then draw a straight line like you show in red above to the mouth using the lengths that you provided.

 

I'll try to post some pictures tomorrow of what I am doing.  

 

I was wondering why the length of the K 402 is shorter than the Klipschorn midrange horn.

 

Does anyone know if the K 402 is available for purchase?  I thought it use to be available but no longer is.

 

Dan  

 

 

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On 8/8/2021 at 8:56 PM, Arizona Dan said:

 

I am going to attempt to make a horn similar to a K 402.

you can attempt , but  actually duplicate the k-402 horn , no   and yes , you can buy a pair of k-402 with the Drivers from klipsch

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On 8/8/2021 at 7:56 PM, Arizona Dan said:

Just to make sure I understand, I use the tractrix calculator using the mouth (large end) dimensions from the K 402.  Then draw a straight line like you show in red above to the mouth using the lengths that you provided.

Yes--to the throat, not the mouth.

 

On 8/8/2021 at 7:56 PM, Arizona Dan said:

I was wondering why the length of the K 402 is shorter than the Klipschorn midrange horn.

The K-402 employs a different design that was developed since the original K-400 horn was developed.  The curved sides near the throat of the exponential expansion K-400 horn create issues with polar coverage vs. frequency, whereas the straight-sided walls of the K-402 near the throat avoid that issue, which also reduce the axial length of the horn. 

 

On 8/8/2021 at 7:56 PM, Arizona Dan said:

Does anyone know if the K 402 is available for purchase?

If the Klipsch Professional line of loudspeakers is still being sold, my guess is that you can still buy a KPT-402-HF assembly with stand and K-691 compression driver.

 

Chris

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13 minutes ago, Chris A said:

If the Klipsch Professional line of loudspeakers is still being sold, my guess is that you can still buy a KPT-402-HF assembly with stand and K-691 compression driver.

Hmmmm.  Does that mean I should likely put that on top of the jbl dual 15" bass bins and go active...the mind wonders.  I have the space now. 

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10 hours ago, Arizona Dan said:

...is it wrong or in bad taste to discuss building a Klipsch product on a Klipsch site?...

 

Well, to be consistent, if you're going to ban discussion of K-402 horns, you'd have to ban any discussion of building your own Khorn, La Scala, Belle, Cornwall, Heresy, or any other Klipsch design on this site also, as well as DIY variants such as CornScalas and other home brew designs, like direct radiating bass bins...if it really is in "bad taste".  I think it's a compliment to the basic design that it's even attempted.  Besides, the K-402 horn profile is well over 20 years old now--mid-late 1990s--well beyond what any patents would protect...and there never was a patent on the K-402 horn profile, surprisingly.

 

A few people have done DIY on Klipsch products over 70+ years.  My father did a single Khorn in the 1950s while teaching EE as an assistant professor at SMU on a near-starvation salary using slave labor (also known as grad students) to test the resulting DIY Khorn in the EE labs.  That's a complicated plywood design that required tips and pointers from the original designer himself: PWK.  The two men met to discuss the DIY build in the mid-1950s on campus.  It certainly wasn't the first DIY instance nor the last that involved PWK's basic loudspeaker designs.

 

I don't think the marketplace is going to be filled with DIYers anytime soon building their own K-402 horns--because they aren't easy to build in DIY fashion.  They're large horns--larger than any other 2" throat horns that I'm aware of, save the old WE horns of the 1920s-30s that are curved axis horns.  So the visual image is not something that a typical female interior decorator would immediately approve of...although, that's really a conditioned response to "how things should look" which I actually don't share with those that complain. 

 

Additionally, some tolerance on symmetry of the finished area expansion and horn wall straightness/angle coverage is warranted acoustically. The K-402s also require EQ to function properly as hi-fi horns, due to their controlled directivity design which requires EQ.  Controlled directivity is something that you don't get with the older K-400 horn design which experiences vertical axis polar pattern flip below ~2.2 kHz

 

Chris

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12 hours ago, Westcoastdrums said:

Does that mean I should likely put that on top of the jbl dual 15" bass bins and go active...the mind wonders.

In terms of drivers and horns, that's what the K-402-MEH is within a single horn aperture in order to pick up the added horn gain and directivity below ~500-600 Hz (the crossover frequency) and pick up coaxial capability--which is a big deal in terms of polar coverage and absence of polar lobing, as well as having a much more compact package (~1/3 the height and visual presentation).

 

What you describe is also essentially what the KPT-942-B THX is. 

 

Chris

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Here are some photos of what I am working on.  It is open baffle bass with Klipschorn top end.  One may ask why is he doing this.  The simple answer is that I already had the 4 18" drivers and the subwoofer crossover and some plywood pieces.  All I had to buy was some 2X 4s and some screws.  I was able to try an open baffle design for less than $100.  

 

You may notice the tweeter location.  I wanted to see if physically centering it on the midrange horn made any difference.  I know I am making the time alignment worse, but only by a few more inches.

 

So, how does it sound.  Great.  For something that I just threw together, I am very pleased.  Next step is to try a differnt horn.  Why??  Good question.  The current Klipschorn horn sounds great.  I am very happy with it.  I even ask myself why go to the trouble of trying something else.  Basically, I am retired and need something to do.  Why not try to make the design as best as I can (without spending too much).

 

I need to buy a microphone and measure the response.  I am holding off because I have  no way to alter the response if it looks bad (which it probably will).  I plan on buying some sort of digital crossover (mini dsp or something), but I am still in the planning stage.

 

Enjoy the pictures.  Please don't laugh at the design.  OK - go ahead and laugh.  It looks like a Frankenstein.

 

Dan

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28 minutes ago, Arizona Dan said:

It looks like a Frankenstein

 

----why not   purchase a  used pair of klipsch Speakers ----Lascala  1 speakers bounce around anywhere from 1200 to 2k$  ,  Cornwalls start at 1k$ --   khorns  ,  3k$ ..... there are 2k$ of parts  in a Cornwall-lascala-khorn  prior to building DIY cabinets -

 

A new pair of AL5 cost 12k$ , khorns AK6 cost 15K$  before taxes -  used klipsch speakers ranging from 1k$ to 3k$  are a Bargain -

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This is the inspiration for my design - The PureAudioProject Trio 15.  The upper and lower drivers that I will be using were made by Adire Audio about 10-15 years ago.  They are 18 inch drivers called Avalanche 18.  The horn will be the best horn that I know about - Klipsch K 402.  My starting point is to attempt to make a similar horn out of wood, and then see how it goes.

 

Dan

PureAudioProject_Trio15_Horn1.jpg

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