Is anyone R-J-ing their hot FR?


Paid Member
2005-08-16 4:21 pm
seems like could at least be a fun experiment trying a temporary diffraction slot of cardboard placed in front of the driver. to get an idea of how it might sound and measure.

Typically the baffle was spaced on cleats about 3/4" to 1" from the slot.

JBL's slot would be one to try and at the bottom of the picture is one
to scale, print and cut for whatever size round speaker one wishes to use.
(the slot would have its long axis vertical)

There's very little front cavity so impact upon response isn't much.

The R-J when introduced was quite small compared to most other reflex boxes.

I have a 15" EV SP15 in an R-J and it sounded very good on Stanley Clarke's upright bass transients. (far better than an AN10 in reflex)

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Paid Member
2005-08-16 4:21 pm
I had 4 18" reflex boxes vented like the R-J but not with the constricted opening. One pair was about 235 liter, the other ~170 liter, using two different spec Eminence 18 inch

Sound quality subjectively was quite good with the smaller box and lower mass/qt=0.25 18 inch speaker.

One thing interesting was a microphone could be placed in the slot and measure the summed vent + driver system output without room interactions or having to drag a cabinet outdoors for measurement.

The heavier/23Hz fs 18" Eminence driver's midrange sounded better in a Karlson - type than as a direct radiator

"2x2" (~1.625" x 1.625") pine cleats spaced the inner baffle from the front.

That aperture came IIRC from an 18" R-J reflex featured in an early 1950's issue. That builder also used many de-Q-ing-holes drilled in the front and through the sub baffle. (both made of asbestos board !!)
of Audio Engineering


I have a rare "Slim-Line" R-J cabinet - but dropped a 12LTA, which knocked
the voice coil windings loose - when my health gets better, I'll try other 12s
in it.

The only real problem with the originals were use of 1/2" plywood and no bracing.
15mm Baltic birch plywood could be used if well braced.


Lafayette Radio offered their version with an oval slot which did not mask the driver called
the "Eliptoflex"

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Hi Freddy,
I need to try this one day. I have an old Wharfedale (just one) - would that be era-appropriate? One can strap it across +ve and -ve of a BTL Class AB Chip amp get summed mono out of it I think.

Need to measure TS, and make an Akabak simulation, then optimize, then build. This is all foam core stuff I am sure.

Alternatively, maybe a tiny RJ with some 3FE22 might be fun. That would make a cute little cube desktop speaker. Pretty decent sensitivity and bass down to 80Hz.