Onken Enclosures

[GM]

Greets!

The BMS is a poor choice also, though for a different reason. Today's prosound drivers have very stiff suspensions to keep Vas as low as practical to keep box size user/shipping/storing 'friendly', which yields a similar underdamped response as the high Qt drivers, though if you stuff the vents its response is somewhat better overall Vs the high Qt drivers. Still, it defeats the point of building an Onken, so why bother?

To keep the vent length <35 cm, a n = 18.4! was required, another consequence of the driver's relatively small Vas.

GM

[el`Ol]

I start to believe that an Onken is a good thing for a midwoofer, but not ideal for a sub. In the last Hobby Hifi they had a Linkwitz style dipole sub with 18" drivers, quite simple correction and very good frequency response. You have to move some air to make the acoustic short-circuit become irrelevant, and obviously this also works with large surface, not just with shwabbly 30mm excursion drivers.

[kevinkr]

Yeah I don't think the Onken would be my first choice for performance below 30Hz unless I had a lot of room..

According to my simulations the Eminence Delta Pro 15A will work well provided that you keep source impedance under an ohm or so. There are several other eminence drivers like the kappa pro which I think might also work ok. You may find several less expensive Eminence drivers that will work with the right rg in series with them.

I am currently building onken cabinets which will be stuffed with Iconic Speakers 165-8G. These are midbass drivers designed for horn loading and have an FS near 40Hz. These are basically the same as the last "real" pre Spark-O-Matic version of the Altec Lansing 515.

I designed my cabs to work with a number of drivers, with some compromises for some choices. Cabinet/port dimensions are fixed, only n and rg can be varied. Within those limits several drivers work well. The Iconic is the best match to the box, and despite its really high price tag is what I am getting.

I suspect it might be easier to design using an inexpensive 15" which is probably less expensive than even two inexpensive 12". Surface area of 2 x 12" is pretty close to that of a single 15" as well.

As GM states I will be using a fair amount of series resistance to get the low frequency performance I am looking for.

My cabs overall volume is about 11 cu ft. N=5.7 and -3dB right around 38Hz. Efficiency about 97dBspl estimated.

I just got a pair of JBL 4333 midrange horns with diffusers and am for the moment going to use a pair of either Fane st.5020 slot loaded horn tweeters or the st.5022 bullet. Later will go with JBL 2402 slots in all likelyhood.

Wrestling with the active/passive x-over routine, both are viable as I have plenty of amplifiers. A good active x-over that doesn't cost as much as the speaker system is a problem. (I'm using an all tube system.) A good passive x-over is non trivial design wise.

As I get all of this stuff together I will post my experiences.

[GM]

Greets!

Not quite, midbass/LF, though only for drivers with the right specs. For sure though, it's best suited for vintage drivers or more recent 'clones' such as Iconic's 165 series. For sub duty, EBS MLTL or TQWT works for me.

GM

[Pano]

Originally posted by GM
I've never seen the Nantex, but I've used both 1" no-void marine grade and Baltic Birch and both cuts like it's made of iron, so I wonder if it's basically like either of these.

Most likely. I think Nantex is gone, now. But it made a wonderful speaker cabinet. Any good, solid, no void marine plywood ought to do the same, yeah?

Below you will see a image taken from Jean Hiraga's 1977 article about the Onken. It shows the 25mm custom made "Shinban" plywood used by Onken. The plies were curved away from center before assembly, then hot glued in a ultrasonic 10 ton press.
The original Onken is said to be superior to even perfectly made copies, mostly because of the wood.



Hiraga also goes on to say that using inferior quality wood of double thickness really does not help anything. He suggests high quality marine plywood.

As for the bass reflex thing, Hiraga notes in the article that the Onken box is not a bass reflex, but rather an acoustic low pass filter.
Here is the equivalent circuit.

The caption says:
Equivalent Circuit of the Onken cabinet. This system was proposed by the Jensen firm before 1950. Very close to the "Acoustic Line" we see however, despite its exterior aspect, this cabinet is not of the "Bass Reflex" type. This equivalent circuit is, in fact, a damped low pass filter and not a resonant circuit.

Alas Hiraga does not give any formulas for calculating the Onken/Jensen enclosure. He simply says to use an Altec 416-8A as after many tests it is the only driver to give results close to the original Onken (in the 360 liter box).

It's interesting to note that the Onken version was introduced in 1973 and by 1977 more than 4500 Japanese DIYers had built one!

Time for me to cough up 50 Euro for the back issues of the Audiophile Revue on CD. Should be more info there.

[GM]

Greets!

Yes, any of the no-void plywoods at least 3/4" (19 mm) thick works well if braced. Here in the USA though, marine grade is not marketed as no-void anymore so I no longer recommend it, only 11-13 ply Baltic Birch and Apple ply. Bamboo ply should work well too if no-void.

He's absolutely right in that doubling inferior wood is just doubling your potential problems WRT cab 'creak' or 'squeak'.

A BR is a low pass filter and unless you design it as such, it's aspect ratio isn't high enough to be a ML-TL, though his plot's incorrect in that it's incomplete since it doesn't show the vent's pipe harmonics. To become a proper acoustic line, the vents must be considerably longer, like what is required for most current drivers, though its vents are obviously better damped than a typical BR's due to their sheer air mass.

GM

[Pano]

So can we come up with some Onken guidelines?

For example:
VAS greater than or equal to X
QTS = X or more (less)

That sort of thing.

If we had those it could mean a quick look at a driver's specs would tell us if it's suitable for Onken alignment, or not. Fine tuning could come next.

[el`Ol]

A different approach for vintage look and 250Hz crossover would be something like Klipsch La Scala.

[Pano]

I've never heard the La Scala, but it sure gets written about a lot. Maybe some day.

I loved the Onkens I heard much better than any other direct radiator of any style.
However, my favorite bass cabinet of all time is the good old VOTT A7. Reskinned with (above mentioned) Nantex, braced and reported, it was fantastic. Just a big BR with short horn. But did not sound like a box at all.
Just sounded like real music, played by real instruments. (a big Altec 1808 multi-cell mid horn sure helped).

So I guess the Onken alignment is going to be difficult with modern drivers?

[el`Ol]

The Supravox 285GMF is designed for Onken, but it doesn`t go that low and it would be a pitty to cross it at 250Hz.