JBL 2235 in Onken

Help in fitting JBL 2235 spec into Onken Calculator NL. At first attempt with spec. sheet in hand and Onken Calculator waiting for input my first try was a success. The Bv. was 300-ltrs and F3 a respectable 40Hz. I may have made an error inputting data back when I first got these 2235 speakers/woofers cause now still with spec. sheet in hand from JBL Heritage download Box Volume is 3324-ltrs. What happened? I managed to get the calculator to remain steady at 300-ltrs but either the port is too long, or too short or port too small or too slots are not realistic size to the front dimension! Can this design be over-ridden to still have a good response?
its just a reflex with 2 slot ports?
Probably have to keep the port area small
So the ports are not too long. 2 slots sharing 3 walls
efficiency is low. So with higher correction factor it helps to keep the ports short
since they appear longer sharing walls.
Pretty standard slot port.
Far as I can remember the JBL B380 was around 130 liters
Should be a decent reference for what size reflex JBL put the 2235 in


Joined 2003
The spec sheet I had downloaded from JBL Heritage site. 2235H
OK, almost identical to mine, so no clue why you're getting such a large (Vb) compared to mine other than you'll have to 'juggle' box size Vs vent area Vs vent length to make it work properly with driver specs not suitable for Onken alignments just as its drop down prompts tells us with the easiest way being to change the 'n' value IME.
  • Like
Reactions: 1 user
Looking at Straight forward common Alignments

QB3 105.5 liters 30.6 Hz Fb
BB4 127.5 liters 20 Hz Fb
EBS -3db 294 liters 22.6 Hz Fb

I Would use the standard QB3


And yes if you look at what JBL did it is basically very close
to the good old standard QB3 or Quasi Butterworth.

Using 127 liters instead of 105 liters
Fb 30 Hz


Far as I know Japanese Onken cabinets appeared around 1965
and got more noted press in 1973 in Radio Experimenters Magazine.

Really depends on the actual driver being used and what the alignments
the Japanese actually choose.
Some were very large around 300 to 360 liters.
So they could have been large if the drivers was high Qts for
a normal Butterworth.
Or they actually used extended bass shelfs. Questionable.
360 liters sounds like a high Qts speaker or possible
Extended Bass Shelf.
This case a EBS for the JBL is ironically around 300 liters.

Onken has 2 slot ports on either side. Ports share 3 walls.
So correction factor would be K = 2.227
That is how you make them, cause its all they are.

and the real magic was likely a Extended Bass Shelf.
Which can be rather use ful and less " port" sounding
but most people dont understand them and huff and puff
about EBS

This case would just use 100 to 130 liters
and tune to 27 to 30 Hz.
With real world error factors about as close as you'll get.
to a normal QB3
Last edited:

Rg = 10 Ohms This is your problem!

This raises Qts to 0.575!! In EBS vented (extended bass shelf up to 0.63 Qts), sealed box specs 'territory'.

For n = 6.34: net Vb = 964.03 L, 13.57 Hz Fb, 300 cm^2 Av = (8) 37.5 cm^2 vents x 36.7 cm long

Is this the output impedance of a tube amp or just a typo? As a general rule 0.5 ohm covers some wiring, VC heating, losses, XO component resistance(s).
Or basically a petite onken
From Koizumi in 1976
is 150 liters.

Which works out fine for a 2235H
tuning needs to be slightly higher to get the
same basic transfer function. around 31 to 33 Hz

The petite ports are 38mm x 181mm
8 of them. 365mm length

Its tuned to 43 Hz

So to get it down to 31 Hz

Just make the ports 18mm x181mm
and same length 365mm

Easy as that.
Your basically changing total port area from
550 cm2 to 260 cm2
to get 31 Hz tuning

you can fine tune it to get 33 to 35 Hz

or use the same 43 Hz tuning
which gives a 3 dB bump.
Which somewhat makes up for full space losses.
Last edited:
  • Like
Reactions: 1 user
Thank you for all of the help in opening my eyes to a new (to me) type od speaker design. This is what I have come up with after taking a break and allowing what information provided, sink in!
Using 2235H spec. : Rg. = .254, port width = 3cm, port height =11.5cm, 6 count/ports, n = 6.34, Vb = 142 liters, f3 = 30.4Hz, SPL =91.2
I feel better about these numbers. Any questions remarks advise before I cut my wood?