Beyond the petite Onken

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Hi everyone,

About two years ago, we started to discuss here what would become a great project for me, the building of Eijiro Koïzumi's petite Onken design around a pair of Great Plains Audio 414-8B:

Since then, I had the chance to try it two ways with TAD TD-2001/Arai A-480FL with very good results. Last fall, I moved forward with Onken OS-500MT driver and Onken OS-5000T tweeters. So it is now a 3 ways design. This put the system to a new level of enjoyment.

In the last months, a thread captured my interest on a french forum. It was about Onken's WB300 speakers. This one is like a mini-VOTT with a smaller footprint and uses a 414 from Altec. Since my desire to get something more efficient, the perspective to add 3-4 dB with the Onken WB300 attracted me. But, gain to loss, the bass respond would not be the one of the petite Onken. It quickly appears that a design with the 416-8B would give more efficiency and more bass.

I started to talked about this around and some members suggested few things: Onken 360l, VOTT, Altec 19, etc... I even saw an interesting speakers in Ahikiko Kaneda's second system (first picture) close to what I'm looking for.

The fact is that I don't have a lot of space and WAF for something more larger and higher. Here's where André's (AJMARS) idea pops up with the suggestion to keep the same face dimension of the petite Onken but with a deeper enclosure. Bingo! He calculated me a 220l enclosure this way. This gives a 8.8 cubic feet, tuned at 29 Hz (second picture).

All in all, the specifications of this project are around these elements:

-use of GPA 416-8B;
-similar face dimension as the petite Onken;
-improve bass response;
-improve sensitivity;
-use of Baltic Birch plywood, 25mm;
-to use with Kanéda 228+ (29W/8 Ohms) amplifier or PSE 300B (15W/8 Ohms).

This thread is created to discuss this project.



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Petite Onken (the one Sebastian has) between Onken 360 and mini Onken (Focal)

I just take the size of the Petite Onken, and calculate a 250 l enclosure, to be used with a classical port to save volume.




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Exactly. The idea is a classical design as shown with André's plan above. To illustrated, he puts a cylindrical port but I'm interest in a rectangular one. As a joke with a lot of reality, André talked about a "Beyond Altec 19" project, which is quite true. With the advantage of a separated woofer enclosure to allow better alignement between all the emissive sources.

I'm not sure if I'll go to the Salon Son et Image (SSI). We'll see.



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No question the GPA drivers are great. I have sister company Iconic 165-8G, best I have been able to ascertain they are identical to the GPA part.

Let me know by PM if you decide to go to Son et Image, I will be going with two friends, and this will be my fourth year. Last year was quite good! Will meet up with some other Montreal audiophiles while there.

I've included a picture of my Onkens which are not very pretty.

GM and Pano were instrumental in helping me get mine together.

A certain someone ;) in Montreal sent me a box of felt which proved to be a much bigger improvement than I would have ever imagined.

You can play games with qts by adding some series resistance which with some other changes will allow you to extend the LF response of driver in a given box at the expense of some efficiency. (at least with solid state amp - the tube amp's high output impedance is a benefit and the losses are internal to the amp and not an external resistor) GM can explain the speaker end of it far better than I, suffice it to say I designed for a total Rg (value used in the spreadsheet) of 3 ohms which includes about 2.5 ohms for the amplifier which is a GM 70 SE without feedback and the dcr of the XO choke which is about 0.33 ohms.

I now use those square metal Russian PIO/PPIO caps sold cheap on eBay in the XO, have not heard anything better after multiple iterations with not so cheap plastic caps.


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Hi Kevin,

Glad that the felt was a good improvment. On my side, it seems to works perfectly with the petite Onken at a price so much less then wool felt. The good thing is that it has the same thickness, density and weight per inch that the wool felt Hiraga and la Maison de l'Audiophile use in their Onken project back in the days. I'm planning to use exactly the same one in my next project. Plus, I'm considering to also place the interior curtain like it was suggested in petite Onken's article (see below for a picture of the interior curtain).

Regarding the SSI, there is a friend in the Montreal audiophile/audio designer community which I appreciate who will demonstrate a new pair of speakers he designed in the last year. The demo will be in partnership with Coup de Foudre Audio (CDF) Montreal's audio store. The years I went to the SSI, CDF was almost always my best sound of show. They usually have 2-3 rooms.

In the recent years, I didn't went to SSI. It seems that DIY audio motivates me to go to DIY meeting in Montreal and around but not much about SSI.



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Here's few other question/discussion regarding the project.

For a drawing begginer like, which drawing program could be interesting and easy to use to make speaker's enclosure plan?

As keeping the same front panel as the petite Onken, I'm thinking to place the woofer at the same place as the 414. This said, I read that Koïzumi have done more than 80 different tries on its position!!! I'm wondering if there is serious thing to consider regarding this placement.

Concerning enclosure bracing, one advantage of the Onken design is that the port participate in the bracing of the cab. With a more classical bass-reflex design, we will be loosing that.

For sure, I'd like to keep the cleat of 25mm x 25mm situated just below the woofer (see picture above). But my question is more oriented on the lateral bracing of the enclosure. I'm wondering if a good idea would be to have a second 25mm x 25mm cleat in this axis. What do you guys think?

Have a good night,

Glad that the felt was a good improvment. On my side, it seems to works perfectly with the petite Onken at a price so much less then wool felt.

Looks like the old high quality jute [felt] used as under-layment with high end [commercial] carpet I've recommended when only the best will do. Got in good with a commercial carpet layer and it could be had in large enough scraps for 'pennies on the dollar' and was often free if off a used 'pull-up', which was still like new along wall edges, etc..

Swak, I do have space constraints and WAF limits. See the picture of my speakers and room last year. There is not much space left in width.

Regarding the felt, it's not exactly the same as the one I'm talking about, but it seems pretty similar.



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With high output impedance amps, the most efficient, flattest, extended bass is when the cab is tuned to the driver's actual Fs. Of course if this isn't what you want, then tune it a bit higher to get a more gradual roll-off.


GM, thanks for the article. I'll take time to read it. When I was on the beginning of my petite Onken project, I remember you talking about the influence of the damping factor on the right volume of enclosure to choose. This was a pretty interesting and not often said information.

I'm wondering if Ajmars can comment on this one. He had a similar project with GPA 515 where he also designed is own enclosure. I don't know which tuning he used nor its amplifier used for this speaker.

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