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plovati 14th March 2005 09:54 AM

RJ loudspeaker enclosure
I'm getting fascinated with this not so common loudspeaker load. The only documentation I found about this cabinet is the original patent by Frank Robbins and William Josep (the R-J of the name, I guess).
What about the design rule and formulas that applies to this cabinet? Is it a simple bass reflex in another form or is radically different? After radiotron there shoul be a fundamental paper in Audio Engineering 27.1 Jan 1953, by the same authors dealing with practical aspect of this load. Anybody has this paper and can shere it with us?

Somebody has experience with RJ loudspeaker?



GM 14th March 2005 01:35 PM


It's a type 2 bandpass so is quite common in car subs, etc., apps. LspCad (and I assume there are other programs) can accurately sim these with much more flexibility than the original simplistic formulas allow. Note that they are simplified Karlson designs and their patent is after his, so one has to wonder if they were just trying to capitalize on his work.

Like Karlsons, for wide BW use some experimentation is required to find the right amount of trade-off between gain and BW, with the K-slot being a better performer overall than those suggested in the patent, though of course they couldn't use it at the time.

Have fun!


plovati 14th March 2005 02:35 PM

Thanks a lot.
It seems that Karlson:

is quite different from RJ:

and not only because is more difficult to build. I'm going to download the Karlson patent and studying it.

In a previous reply :

You said that is aperiodic. This is a synonim for bandpass? To be a canonical bandpass, the RJ speaker seems having lost the front loading volume. I cannot see a straightforward analogy with BP enclosures like the ones used for subwoofer.


GM 14th March 2005 03:22 PM


You're welcome!

First off, AFAIK the Supravox cab is not an R-J concept, at least not any listed in their patent or any actual cab with their logo on it that I've seen, but an aperiodically loaded reflex suitable for damping high Q systems. Big difference.

That said, the R-J uses a small enough front chamber/exit slot to damp the impedance peak well enough to be considered aperiodic in nature, though not a 'pure' aperiodic unless additional resistive vent damping is used in the form of stuffing or as was done via dense grill cloth on at least one of their models.

Sounds like you're letting the Karlson's multi-stage reflex loading and other folk's erroneous assertion that it has any TL properties 'blind' you to the fact that it is basically a reflex loaded bandpass. A simpler solution is to substitute all those reflex chambers with a single reverse tapered TL.

No, it is not a synonym for 'bandpass'. 'Bandpass' means that it only allows the driver to reproduce a limited BW of 'x' octaves, like a horn's compression driver.

Maybe the typical USA car audio 'sub' boxes are not popular in your locale or you do not 'see' that the R-J is no different in concept than today's typical BP cab design consisting of a ducted port vented cab terminated into another ducted port chamber.


plovati 14th March 2005 06:20 PM

OK, there is some mess around the names of the these cabinets.
The Supravox-style enclosure is called at least in Europe as R-J and is being popular for full range because has a good extension in low end without big dimensions.

From GM's explaination seems a mix of aperiodic for the rear and quite aperiodic bass reflex port due to small dimension.

Nothing to do with RJ patents that resembles in different form a bandpass cabinet with front opening.

So if now the nomenclature is clear, how we can star to design a Supravox stile enclosure?



GM 17th March 2005 12:01 AM


Correct TTBOMK! Indeed, if you look in Cohen's 1956 book, the Supravox is a variant style of reflex defined as a Helmholtz Resonator to differentiate it from the typical cutout-in-baffle vent style reflex.
The original 'HR' layout has the driver mounted on the rear of the baffle board which in turn is mounted to the inside of the cab cutout. Done this way, it's simple to calc the effective vent area/length.

Accurately calcing the Supravox variant will be problematic since the driver is acting as a phase plug of sorts, but you can use a box program to find the cab's Vb and basic vent dims. Still, the layout allows relatively easy adjustability by altering the gap so I would make the baffle some high percentage in area to the cab face and try different air gaps, starting with a swept area = whatever the box program predicts for a short, low mach vent. Adjusting the gap can easily be done using 'T'-nuts and long bolts, then replacing them with something more rigid/cosmetic once you're satisfied with the performance.


plovati 17th March 2005 02:46 PM

Thanks GM.
I'd look at Cohen's 1956 book if I i'd got it, but unfortunately I haven't.
May You post a copy of the relevant page of this book that seems interesting?



consort_ee_um 29th August 2005 05:39 PM

Just came to the RJ enclosure via a different route. The 1952 Radiotron Handbook is on-line here: H4/
The loudspeaker section by langsford-smith shows that there was a pretty good understanding of loudspeaker theory back in 1952
As Langford-smith was Australian I wonder if he influenced Thiele?
The RJ was only design I had not come across in the section.

soongsc 29th August 2005 06:01 PM

If it's that box with damping material inside and opened on the baffle sides, it seems that you can just design the box size as a closed box and make the baffle height adjustable. The height can be such that the maximum opening area is not larger than Sd, then you can reduce the opening until you get the desired response. This kind of seem to be variable since there is more friction because air is moving in and out through the same port but in opposite directions. Look at how the impedance plot varies when you adjust the opening size, and you will get the hang of it.

consort_ee_um 30th August 2005 08:13 PM

2 Attachment(s)
Here's a fragment of the patent 2694462 filed in 1951
The radiotron link does not seem to work anymore. Apologies

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