choice of driver for Onken
I have gone through that exercise a while back.
I read the Thuras patent on which Onkens were based and read the French articles for all three sizes of Onken. acquired and double checked an excel based calculator for dialing in T-S parameters of the driver and calculating the enclosure sizes (still have it somewhere).
Well i have to tell you that this design is a VERY specific solution to obtaining a good sound. as i remember it calls for a driver with a large Vas and low Qts, and even then the original driver used was modified by the author. such drivers are not made nowdays at all. i ran the calculation for a number of available drivers (Beymas included) and could not find any to meet the requirement for maximum port length.
so now you know. Good luck.
I have gone through that exercise a while back.
I read the Thuras patent on which Onkens were based and read the French articles for all three sizes of Onken. acquired and double checked an excel based calculator for dialing in T-S parameters of the driver and calculating the enclosure sizes (still have it somewhere).
Well i have to tell you that this design is a VERY specific solution to obtaining a good sound. as i remember it calls for a driver with a large Vas and low Qts, and even then the original driver used was modified by the author. such drivers are not made nowdays at all. i ran the calculation for a number of available drivers (Beymas included) and could not find any to meet the requirement for maximum port length.
so now you know. Good luck.
By looking at it from a glance the Onken looks like a regular bass-reflex cabinet with slot ports on the sides.... so can you share with us the "secret" of the Onken ?
I do remember that the Onken-Focal's I heard had very tight bass, so probably they had some qualities.
I got one of the classic French articles translated back in the 90s and then reverse engineered the various designs. They are all a v specific alignment of a ported box which wholly rely upon the correct driver parameters which are almost never available in modern bass drivers. At the time I found one Focal unit, the 10C01 I think, which just about worked and built some cabs which I still have.
I built them to work with SE triode amps but realised they dont. They all need a v low series resistance from the amp output, and any choke in the crossover, and this needed to be included within the calcs fir the alignment. With an SS amp in a multiamp system they can be great.
Best of luck
I built them to work with SE triode amps but realised they dont. They all need a v low series resistance from the amp output, and any choke in the crossover, and this needed to be included within the calcs fir the alignment. With an SS amp in a multiamp system they can be great.
Best of luck
GPA is now making them to order for folks with 'deep pockets', so most folks just buy the 416-8C ferrite motor version.
Some of the GPA 515 series works well also when driven with a high output impedance. Ditto the 604 series duplex.
GM
FWIW, Al noted in an interview much later that he chose this particular alignment to keep his math super simple for the patent application to obviously protect his invention as much as practical.
Note that its 'good sound' is due to the vent's pipe harmonics comb filtering with the driver's output all the way into the mids; otherwise it's just a slightly under-damped reflex when N=6.34 and a T/S max flat alignment when N=5.7, so for those of us who prefer more accurate reproduction it's better to use modern drivers, which when tuned with just one or two vents will be long enough to get the same harmonic distortion, just not as 'strong' since the total vent area will be < Sd.
GM
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A guy I new once had a pair of Onken-Focal speakers that used Focal 10C02 woofers in an Onken enclosure. If I'm not mistaking they had high Vas and very low Qts. Such drivers are not easy to find anymore, that's true.
I seem to recall that this combination was a Focal kit design, looks very nicely done
Never got around to finishing mine off properly - photo is from about 20 years ago, but they still look the same.....
An externally hosted image should be here but it was not working when we last tested it.
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Considering the Onken's ~35 cm max vent length, it' not an option due to a ~81.4 cm calculated length for just a single vent.
GM
Please explain. What harmonics? Harmonics of the pipe mode resonance? I always assumed it was just a good implementation of bass reflex without any further magic. There are plenty of reasons for it to be a good layout anytime you can get away with a fairly large cross section:
- being a large port, to start with
- minimal midrange leakage compared to conventional large ports
- bonus cabinet wall bracing/thickening
- potentially sidestepping issues with unexpected port entrance location problems.
- possibly less likely for speaker placement to affect port function
...
Have people measured pipe mode resonance issues with traditional implementations of this? Obviously that could be avoided, if you set out to avoid it.
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SM115/N
The Beyma SM115/N is an almost perfect drop-in replacement for the Altec 416-8A (or B) for which the original Onken box was designed
Marco
The Beyma SM115/N is an almost perfect drop-in replacement for the Altec 416-8A (or B) for which the original Onken box was designed
Marco
If you cut back a bit on port size from 100% of cone area to 40-60%, that is still large compared to most ports, the port lenght will be resonable. The single 15" Onken does have that large port area and double rows of port slots. The dual 15" Onken on the other hand has a way smaller port and a totaly different port geometry. How that is tuned compared to the 1x 15" I do not know.
wow, a lot of good and correct info here. now this brings back some memories: I was also trying for target alignment of 6.34 and the total vent area of minimum 85% of the effective diaphragm area (sort of consented on the forum as a minimum for an “Onken”).
as for the calculation based on driver T/S parameters: acoustic mass inside the vents effectively determines the total vent volume & with total vent cross-section fixed to match that of the diaphragm, effectively determines the vent length.
Major design limitation: the max allowed vent length (~35cm): for the vent resonance f=c/sqrt(2L) (c=speed of sound; L= (corrected?) length) to stay out of the lower midrange (> 1kHz where the felt lining may be effective removing the sound emitted from the rear of the cone).
I was really interested in Onken at the time based on subjective impressions by others (Pano? et al.), “never sounds boxy” etc., but now I am leaning to trying an OB instead (my next project)
again: Good luck.
as for the calculation based on driver T/S parameters: acoustic mass inside the vents effectively determines the total vent volume & with total vent cross-section fixed to match that of the diaphragm, effectively determines the vent length.
Major design limitation: the max allowed vent length (~35cm): for the vent resonance f=c/sqrt(2L) (c=speed of sound; L= (corrected?) length) to stay out of the lower midrange (> 1kHz where the felt lining may be effective removing the sound emitted from the rear of the cone).
I was really interested in Onken at the time based on subjective impressions by others (Pano? et al.), “never sounds boxy” etc., but now I am leaning to trying an OB instead (my next project
)again: Good luck.
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