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oohms

Klipsch K402 replica build

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I have always been intrigued by horns, especially in the way they control directivity and reduce the influence of a bad listening room - constant directivity horns in particular. The K402 seems to be the widely regarded pinnacle of CD horns, and going by images of them, fairly simple in design.

 

The only problem is that there are no drawings out there of them, so for me to replicate them to any degree, i would have to scour the net for every bit of information I can find and re-create the best estimation of them that I can. My philosophy is "close enough, where it matters" so I am not after a millimeter perfect copy, but one that is fairly close

 

Some fact finding and guessing based on images reveals that they are:

  • 1002x648x422 WxHxD in mm with flanges of roughly 64 L/R and 57mm T/B (measured by others on the net)
  • Modified tractrix, that I take to be a tractrix starting from the mouth and finishing when the tractrix line intersects with the throat, then that straight line continues to the 2 inch driver opening in the throat - without a change in angle to interface with the compression driver
  • The modified tractrix curve goes for roughly a third of the path length of the horn on the vertical sides, with the straight/tractrix boundary at the same point for both horizontal and vertical sections

 

This led me to come up with a solution using trial and error in CAD, first defining the horn dimensions, then using a tractrix curve spreadsheet to make curves at different frequencies until i found a solution that satisfied the conditions above (I decided not to include flanges in my version)

59ab7e0565162_k402combined.JPG.bfef161c5e1f2456e02676059e93f2ce.JPG

 

 

The curved section would be the hardest to build, and i decided to make them out of expanded polystyrene (XPS) foam, cut with a hot wire cutter, similar to what model aircraft builders do to test aerofoils

 

 

Templates were made, designed to glue onto 16mm MDF of the straight sections:

59ab8007a19b4_k402templates.JPG.c36970881fae886af4d968cbd3cc9cdb.JPG

 

 

 

Next, I used the synergy spreadsheet to lazily come up with a cutting list for the straight sided panels - using trial and error to come up with values that would produce a horn of the right size (we are not interested in the secondary expansion)

The green values are the put in, the rest are calculated by the spreadsheet

59ab810971d0b_synergycalcvalues.JPG.99157109fe49db460c4b6f37fcc58755.JPG

 

 

 

 

Next mitre angles and butt joint angles are calculated using http://jansson.us/jcompound.html

59ab815a68a1c_anglesetc.thumb.JPG.13fb3b6b28ab60cd04a0f2a2f8136e08.JPG

 

 

I decided to use butt joints with biscuits to line it all up as well as i could

IMG_20170525_221457924.jpg.d086e925eb58b9ba6839584ca17d832c.jpg

IMG_20170530_165526121.jpg.ea11a44f120ad079c3ab296ec2c6aac4.jpg

 

A quick test with the compression drivers

IMG_0612.JPG.c554967b77b54d221bf44680d3b27c27.JPG

 

 

The wooden blocks are for screwing the compression driver mounting plate onto. In hindsight, I should have glued on longer pieces and flush cut them for a better look

IMG_20170610_215008933.jpg.3a71768921bdcab1cf75ef9c12d96188.jpg

 

 

Then, it was off to building a foam cutting rig using spring loaded nichrome wire and a 12v power supply - cutting 50mm XPS from bunnings

IMG_20170617_131824003.jpg.a46d98b050248271d416005323df5727.jpg

 

The foam is cut using the blade tilt angle and mitre angle from the website above

IMG_20170617_162312954.jpg.d1d339c7e4d971a7ae01b89ff9b5c0c6.jpg

 

 

Glued on to the MDF with polyurethane glue. This cures with moisture, so I made sure to spray both faces with a water bottle and weighed it down as much as I could as the glue expands on drying (Almost like expanding foam)

IMG_20170617_182103465.jpg.02ff532f62875b155910a377ce6210ee.jpg

IMG_20170620_131356282.jpg.573b9d845364468740f0260c27ddb99d.jpg

 

 

 

After this, I decided to cover the flat faces of the XPS with 3mm MDF (again, glued with polyurethane and weighted down), to protect and provide better defined edges and corners and to have a smoother and easier to paint surface. Then it was filling time - trialling different fillers from bunnings and to my luck, they all stuck to the sanded XPS.

IMG_20170621_160809252.jpg.6e91c65ce429a90ce78509db7fb01cf9.jpgIMG_20170623_140716.thumb.jpg.5621ffdfedb2b87cddf48c6e00b65b70.jpg

 

 

Giving them a test run at a party

IMG_20170629_212826_HHT.thumb.jpg.664d5b1eabf1630e4238b699f30fb013.jpg

 

 

Then it was on to painting them with an undercoat/sealer, fine filling and sealer again

IMG_20170818_220247_HDR.thumb.jpg.a70b25165860d02dc4247ed1d2f3931b.jpg

IMG_20170821_090003_HDR.thumb.jpg.cb154dd69c0fac179c66540d78cbddef.jpg

 

 

2 layers of semi gloss black external paint nicely finishes the horns. You can use any kind of paint for these - the flat white finish of the undercoat looked very nice with the flat finish hiding imperfections

IMG_20170825_181409_HDR.thumb.jpg.931d7c68d644e199405ad4bfc83249b5.jpgIMG_20170826_120735_HDR.thumb.jpg.e06ee4d12fd121eab41b8c97676c678f.jpg

 

 

The back plate was made out of 3mm aluminium, a 2 inch (51mm) hole saw and extra holes for mounting

IMG_20170830_113342_HDR.thumb.jpg.8b2721604de27cd6816454012708d625.jpg

 

 

Compression drivers are P.Audio BM-D750 MKII - they seem to be the best value locally obtainable 2 inch drivers from what I could gather

IMG_20170830_113926_HDR.thumb.jpg.9bf2478dcbdd55c426c011e27fa7b5f7.jpg

IMG_20170830_114650_HDR.thumb.jpg.0c78fec2ae343d4b55da84100da513e8.jpg

 

Here is the final setup, perched on top of a pair of carpet covered Yamaha S250B 15 inch ported boxes I scored at a bargain - the inspiration for me to start this project

IMG_0613.JPG.58ffab3b4ec4320f41f1711b55da0926.JPG

 

 

How do they sound? Great!! - fantastic imaging, very dynamic. They really do cover the whole room in wonderful sound, and if you sit in the 'sweet spot' they image better than anything I have ever heard. The room has terrible acoustics and is probably too narrow to get the best out of these, but I am not dissapointed

 

Here is a quick youtube recording of the setup, recorded with a Zoom H1

 

 

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Driving this setup is a MiniDSP 2x4 integrated into an old sony 5.1 receiver. It is simply connected to the "5.1" inputs internally and fed with power from the unit to reduce external clutter. This is by far the easiest way to run a DSP powered setup while keeping a sensible gain structure and not exposing power amplifiers to potential full line level input.IMG_20170712_002504.thumb.jpg.3a8e7e15e1e1920e0c8954598fbb62a0.jpg

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Nice work! Great audio fun on a budget.

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yeah, amazing work and thanks for documenting!

 

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you can probably try the two way synergy concept with these. You have the part to hold the woofers in wood. Have you seen that project? It was documented in Klipsch forums and on diyaudio I guess. It was called a 2 way meh. Two 15" woofers and 2" cd on a k402. One of those project I wanted to try. 

 

If you can share the plans for your 402 replica, that would be great! 

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I'm glad you enjoyed it. I have had my eyes on the 'syntripp' project as something to do in the future, using JBL 2453h-sl tweeters - I think it's a good tradeoff between being easier to build and it sounding close enough to the K402 that i'd be satisfied. 

 

http://www.diyaudio.com/forums/multi-way/264485-syntripp-2-2-virtual-single-source-horn.html

 

Using foam is probably something i'd change, as it is too difficult to get the perfect finish and it is kind of fragile, even after I finished them

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Well done 

What cabinet design is on the bass bin also sensitivity & Htz rating / size of driver 

 

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5 hours ago, Full Range said:

Well done 

What cabinet design is on the bass bin also sensitivity & Htz rating / size of driver 

 

It's a Yamaha S250B cabinet that somebody carpeted, so 15 inch ported, i'm guessing 100L and 95db/w sensitive (maybe less) and from memory goes down to 35hz in room

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Should be a good match 

Definitely need fast and sensitive bass to match the horn 

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@Upfront

Check this bloke out, wow, what a great DIY horn.

 

To the Maker, well done Mate great work would be excellent

 

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[mention=111049]Upfront[/mention]

Check this bloke out, wow, what a great DIY horn.

 

To the Maker, well done Mate great work would be excellent

 

Always watching mate [emoji6]

@oohms what do you think of the drivers now you've lived with them for a bit?

 

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15 hours ago, Upfront said:

Always watching mate emoji6.png

@oohms what do you think of the drivers now you've lived with them for a bit?

 

Funnily enough i sold the whole setup to a mate.. he loves it (and i love to visit for listening sessions)

The drivers are great for the price.. there is a fair bit of breakup at 15khz but you can EQ it out. If i was to choose another driver, it would be the JBL 2453h-sl

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Funnily enough i sold the whole setup to a mate.. he loves it (and i love to visit for listening sessions)

The drivers are great for the price.. there is a fair bit of breakup at 15khz but you can EQ it out. If i was to choose another driver, it would be the JBL 2453h-sl
So what are you making now!?!

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On 03/11/2017 at 6:00 AM, Upfront said:
On 02/11/2017 at 9:39 PM, oohms said:
Funnily enough i sold the whole setup to a mate.. he loves it (and i love to visit for listening sessions)

The drivers are great for the price.. there is a fair bit of breakup at 15khz but you can EQ it out. If i was to choose another driver, it would be the JBL 2453h-sl

So what are you making now!?!

 

I'm taking a break for a little while, but looking at finishing the crossovers for the large 3 ways you can see in some of the photos above.. then maybe a pair of TC9 line arrays or a pair of syntripp unity horns

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Would it be possible to get a measured model of the 2

templates you made?

 

 

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2 hours ago, Pia said:

Would it be possible to get a measured model of the 2

templates you made?

 

 

I'm a bit hesitant to release any CAD files or accurate plans for these as Klipsch seem to have a very fine line between amateurs like us building one off copies for ourselves and people building them easily and/or for profit. This writeup is more about the methodology and some techniques and examples that people can use to make their own speakers/horns/etc.

 

If you are OK at image manipulation software, the notch in the templates should be 16mm deep and the thickness at the thickest point should be 50mm ;)

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Great work! I do not think that Klipsch would do anything as long as you were not making a profit off it. There are lots of plans floating around for the Khorns, La Scalas, and Belles, and they are even in their own forum.

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On 25/01/2019 at 4:03 PM, ellisr63 said:

Great work! I do not think that Klipsch would do anything as long as you were not making a profit off it. There are lots of plans floating around for the Khorns, La Scalas, and Belles, and they are even in their own forum.

Thanks! I have moved on to other projects, and if i was to do another K402, i would improve upon its design

 

You're more than welcome to use any information here to do with as you like :)

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On 05/11/2017 at 1:47 AM, oohms said:

TC9 line arrays or a pair of syntripp unity horns

Hah.   Also my next project(s), or inspired by.

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On 31/10/2017 at 8:09 AM, oohms said:

Using foam is probably something i'd change, as it is too difficult to get the perfect finish and it is kind of fragile, even after I finished them

Hi oohms

 

I am new to to this forum an wanted to say great build. I am interested to build one but adapted to 2.4 exit of Renkus Heinz SSD5600 drivers, AND with a cutoff frequency in the 150-200 Hz, the driver is announced as going down to 250.

 

How would you do differently than with foam ?

 

BR

Jean-Louis, from Luxembourg

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11 hours ago, JLOP said:

SSD5600

Wow.  Massive!

 

Set the horn load in relation to the Fs of the driver.... not based on what low frequency extension you desire.   :thumb:

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On 05/03/2019 at 10:48 PM, JLOP said:

Hi oohms

 

I am new to to this forum an wanted to say great build. I am interested to build one but adapted to 2.4 exit of Renkus Heinz SSD5600 drivers, AND with a cutoff frequency in the 150-200 Hz, the driver is announced as going down to 250.

 

How would you do differently than with foam ?

 

BR

Jean-Louis, from Luxembourg

I would make the same foam profiles but out of something like plywood laminated together to 50mm thickness - then use the templates to route/plane the curves, but otherwise saw them etc just like the foam

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