I will share my CAD drawings and parts lists of the version shown here (rounded edges) or a simpler version with exposed plywood edges-- just email me: Jazzman1953@gmail.com
A RiPol is basically a compact, folded-baffle dipole, except the radiation pattern is not the classic figure-8 dipole but cardioid shaped, with a pronounced frontal lobe. It can play very low <20Hz), and because the cardioid pattern nulls the off-axis output, it's less prone than conventional monopole subs to excite the room resonance which can give bass the dreaded “one-note boom”.
Whereas a conventional sealed or ported box forces the woofer's resonance higher than it's resonance in free air, the resistance of the air masses within the Ripol's front chamber actually lowers the woofer's resonant frequency by as much as 10Hz (depending on chamber size, 7Hz is typical).
The result is lower distortion and improved tonal quality because most music contains little or no energy that low, so the woofers' resonance is not excited.
Ripoles pressurize the room differently than conventional subs. I would describe their sound as quality over quantity-- clean and unobtrusive, arising from nowhere and receding back to nowhere. Great for jazz-- not so much for HT sound effects.
The Peerless SLS 12” woofers are ideal for RiPol use, and fairly inexpensive, but are no longer sold in the US. I recently (2022) purchased several from a company named "THLP" in France, and they arrived in about a week.
I found no published modeling data for a Ripol so I based the dimensions on guidelines posted by a respected Ripol guru who goes by the user name "Rudolf" on the DIY Audio Forum, which I've paraphrased below:
Area of front chamber opening should be 1/3 to 1/4 of woofers’ combined piston area (SD).
For woofers having more than 10mm X-max, use 1/3 SD minimum.
For woofers with 10mm or less X-max, chamber area can be 1/4 SD.
Area of rear chamber opening should be 1/2 to 1 SD.
Chamber depth need not be greater than necessary to fit the woofer.
The front and rear chambers have rather chamber resonances which must be either avoided by setting the crossover frequency at least one octave lower below it, or by notching it out with a passive filter or parametric EQ.
For the Ripol shown here; the front chamber resonance peaks at 299Hz and the rear chambers at 294Hz. I simply avoid exciting these resonances using a 70Hz crossover with a steep filter slope (24db or 48db / octave).
The boxes are 3/4 red oak plywood, edge trimmed with quarter-round oak molding. The center C-section assembly glued up from solid white oak planks stained in a contrasting color for effect and indexed to the mating box halves with (4) 1/4 oak dowel pins on each side.
The assembly is held together with 1/4-20 all-thread rods and cap nuts as shown in the photos.
The woofer cutouts in the baffle boards are cut with a bit of extra clearance to allow the woofer magnets to center themselves in the holes in the outer panel. The holes in the outer panels allow .090" of clearance for the speaker magnets and I used foam speaker gasket tape to seal around the woofer magnets.
The two 8-Ohm woofers are wired in parallel and in phase (push/push, not push/pull), for 4-Ohm load.
Rabbit cut plywood cab pieces bank together to aid gluing:
Below: Cab clamped while the glue sets.
After glue-up, the cab edges were notched on the table saw to accept the oak edge members:
Red oak edge members were inserted and held in place with painter’s tape while the glue sets.
Cab with mitered edge members glued in and sanded.
Completed cabs, center section and hardware:
Subs were pre-assembled and edges were rounded-over to 3/8” radius on a router table:
Front view, ready for stain & satin clear coat.
The completed subs:
Rear view:
