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Onken - Jensen UltraFlex with Altec and JBL Horns


MGO

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My build is an Onken-Jensen Ultraflex pair of speakers with Altec drivers.  JBL horns on top as alternative to 604.
 

Possible bass drivers include Altec 604-8K and 421-8H which could be converted to 416-8C.

 

The speaker cabs are being made by Alan Cook: www.alcojoinery.com 

Alan has done a great job on these speakers.  Highly recommended!

See progress on build below.

 

Using high grade 25mm Baltic Birch Ply.   Instead of T-Nuts and wood screws I’ll be using Nutserts.  These seem to be better than T-Nuts – more secure and no air leaks.  Wood screws will strip the timber with multiple ins and outs, NutSerts are metal and more durable - better.

 

I’ll try the HF part of the 604 as intended, using its built in duplex compression driver and horn.  But I think I may get better results with my separate JBL horns on top of the bass box.  The JBLs are 2451 with 1.5” throat and 2441 4” Al diaphragm, on a short throat 2381 horn.  With that combo and some passive eq I get a nice response from around 600Hz to 20kHz.  It may need a super tweeter for better ears than mine but it’s fine for me as is.

 

I recently heard MarcAL (SNA) Onken speakers and was very impressed with the sound and how they loaded the room.  Unlike anything I’d heard before.  I thought it was beyond Hi-Fi.  Hence this build.

 

My room is smallish and won’t accommodate the full 360 litre Onken speakers.  So rather than using the Altec 416-8 A or B, I’ll be trying the 604-8K, 421-8H and 416-8C so that I can make the cabinet smaller, 260 litres, and somewhat narrower: 650mm rather than 800mm.  All tuned to around 40Hz. 

 

If tuned lower, the port length becomes greater than the depth of the cabinet (from simulations using Onken calc and WInISD which predicts very similarly if I enter 8 ports of the 0.04 x 0.22cm in this cab). 

 

The height of the 604 driver was raised in the cab to 100mm from the top so that the horn is close to ear height when seated in front.  Making the cabs taller would have thrown out the dimensions for the Onken calcs.  I can always tilt the speaker up a few degrees if needed.

 

Basic Onken cabinet guidelines:

  1. In order to achieve an optimal quality (Qtc=0.707), the so-called Thiele Alignment (n) is used - usually n=5.7.  This number can be increased and most Altec 416 tuning is with n = 7 or above.
  2. The total area of the tunnels is about 90% of the total area of the active diaphragm surface in the best case.  With the 604 the surface area of the cone (Sd) is reduced by the horn and its surround in the middle. So the eight ports are 40mm by 220mm.
  3. Moved air masses behind the driver and in the tunnels should be identical.
  4. The resistance of the low-pass inductor is to be included absolutely also into the computation of the total quality factor (Qts)

 

I’ll be able to easily add an internal port extension to cater to the other drivers (421, 416-8C) to re-tune the box.

All the woofers I ran sims on for my speakers will go down to a little below 40Hz.  So, a sub or two is also needed. 

I have a pair of Rythmik 12” servo subs that should work well with these speakers to get well below 20Hz.  Measured them down to 16Hz in my room.

Here is a sample drawing not to scale and a bit different but very similar.

image.png.b335135e54ea6030629df5f96b51e7a0.png

Here is the Onken Calculator with some simulations.  Thiele and Small parameters for 604-8K.  Sd 720 with horn area taken out from total Sd of 850cm^2.

image.png.6817b1259b3287e0a3fb171ca1181c0c.png

 

Simulations give a port length of around 38cm.  Indicates F-3 of 39Hz.

Able to extend this another 5cm for fine tuning and alternative woofers.  See photo below.

 

image.png.0c0d5b4f36b5e82cf2e653275a913175.png

 

Initially will be using my electronic crossover a Pioneer D23, but will also build a Jeff Markwart time aligned passive described in the GPA site for the 604-8K.  https://greatplainsaudio.com/jeff-markwarts-corner/

 

image.png.9b2617caaa6a5272551e1ffccb9ed29b.png

 

Edited by MGO
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image.thumb.png.c91b11e5afc5b5950bd925c317cdd4ec.pngNot there yet.  No wiring or damping.  Will also add bracing to top, bottom, front and back.

Horns just placed on top.

I'll be running and sharing results of: frequency responses, distortion, waterfalls and spectrograms.  Stay tuned...

 

Some pics of build... 

image.png.c2ebd0b44a385116e5dd3b00429cc22b.png

image.png.b9a6a884ee30205f15eda92dd4826381.png

Preparing mitre joints.  Festool dominos.

 

    image.png.92120c24481138339e00492672f96813.png    image.png.60e1a7ec3b13f00de8d2476cc7ed1fda.png 

 

 

image.png.9ec8026f57ed3a8f075766733c14aa07.png  image.png.86094407bd1c5b814987c68ad22ae8cd.png

 

image.png.28e18fabe874580589b23f2b3a59947b.png image.thumb.png.603bf4f3e15a780aa59a9700887fc8a0.png

 

 

These are the internal port parts with 50mm extensions for further tuning. 

Rounded to reduce turbulence.

 image.png.ffe25ff72b234646c417ca67ede980c5.png       image.png.c28d1362fe7130a4c8f2ea82a22d61fb.png

                                                                                 Internal and externals taking shape. 

                                                                                 Shows structure of ports and cleats for front and back baffles.

image.png.d3baa2ef4f4e1c483da0a5c7041c0d0c.png    image.png.36634c9e759efa665615bfc42f44f9d5.png

 

image.png.729ae3b21dd56cf6e3c2777430f8b1c5.png   image.png.12aae39ed24c1a2464f7dde926257bce.png

Terminal Plate routing and postions.  This will be off-centre and symetrical “handed” to give easy access for connections - not much room to move once speakers installed.  

Terminal plate placement.  Jantzen from SpeakerBug in Brisbane.
image.thumb.png.39961a175785eccb869873f6f357158a.png

image.thumb.png.b483f7a71b3cd67ec6ae60dd44919fd3.png                                                                                                             

More to come as build progresses...

I'll be providing frequency response curves, distortion, subjective assessments etc 

 

Edited by MGO
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Nice concise write-up of your project, Mark, covering many bases.  Photos show the cabinets to be a high quality build and near complete so you may be pretty close to hooking up that D23. 

 

Following with interest, especially since the Ultraflex approach is rumoured to produce a distinct sound compared to conventional bass reflex ports.

 

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I noticed you said you were using a smaller box. My last Altec build was 220 liters...using 416 woofer and 564 Mantaray with 291 1.4 inch CD. That was a lovely combination, crossed at 750Hz.

 

I've always argued the two-way is gold if done correctly.

 

I also built the Model 19, which had a bigger cavity of 260 liters. That made quite a difference to the bass depth.

IMG_4561.JPG

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  • 4 months later...

Interested to hear an update on this project. Particularly WRT to rear or front mounting the driver..
 

I’ve ordered some 15” coaxial, however need some assistance interpreting the Onken calculator. How do we translate the port length etc. into the original French magazine plans for the cabinets? 
 

I’ve noticed there have been a few Onken projects by members - if anyone just has the plans / cutting list saved I’d be super appreciative (many of the links online from the early naughties no longer work!). 

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  • 1 month later...

Hi crtexcnndrm99,

The Onken project has been very good and continues to contribute musical and experimental pleasures.

 

With regard to front vs rear mounting, I have seen some quite vague reference to rear mounting being a little better.  However, I haven't read or heard anything concrete about it.  For me it's been an aesthetic thing to hide the speaker frame behind the baffle but needed to front mount the 18" speaker as it didn't fit inside the cab.  It all sounds good.

 

Yes the Onken calculators are cumbersome.  I believe that the same result can be attained using a standard T/S box design program like WinISD as long as you follow the Onken guidelines:

 

  1. In order to achieve an optimal quality (Qtc=0.707), the so-called Thiele Alignment (n) is used - usually n=5.7.  This number can be increased and most Altec 416 tuning is with n = 7 or above.
  2. The total area of the tunnels is about 90% of the total area of the active diaphragm surface in the best case.  With the 604 the surface area of the cone (Sd) is reduced by the horn and its surround in the middle. So the eight ports are 40mm by 220mm.
  3. Moved air masses behind the driver and in the tunnels should be identical.
  4. The resistance of the low-pass inductor is to be included absolutely also into the computation of the total quality factor (Qts)

Using WInISD I tried to get the port area in the range of 80% to 100% of Sd the speaker area.  So for the speakers I was trying, 8 ports with a width of 40mm and height 220mm, giving the port length of 380 to 430mm, depending on tuning.  With other drivers I sometimes needed to block some ports so that the tuning doesn't require a port longer than the cabinet, although this wouldn't strictly be an Onken as the port area is smaller than Sd.  Still worked well.

 

For a 416, my cabs were 260L.  1050 tall, 630 across and 530 deep.  25mm ply.  This is smaller than a Hiraga Onken but i have limited space in my room. Tuned to 40Hz, the port length is 380.

I tried tuning lower but preferred the extra slam the higher tuning gave.

 

MarkAL on SNA whose Onkens with huge Mantaray horns shown earlier in this thread made the full size Onkens and may be able to help you further.

 

Best of luck on the build.  Let me know how it goes.

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