I love my RiPol subs. They sound wonderful and just look cool. The configuration was patented by German speaker builder Axel Ridtahler, and the name "RiPol" is short for a "Ridtahler dipole".
A RiPol is basically a compact, folded-baffle dipole with two woofers in an opposing push/push configuration. Its radiation pattern isn't the classic dipolar figure-8, but cardioid shaped with a pronounced frontal lobe, and similar off-axis nulls.
Perhaps the most unique RiPol feature is its effect on the woofers' resonance. Every woofer has a natural resonance, which is typically loud and certainly undesirable because it's a distortion that isn't in the music. A conventional sub enclosure forces the woofer's resonance
higher than it's resonance in free air (FS). But a RiPol
lowers the woofer's resonant frequency by about 10Hz, and this has a profoundly positive effect on tonal quality.
Let's say we are using woofers that resonate at 30Hz in free air:
- A conventional enclosure forces the resonance
upward (more so in smaller box, less so in bigger or ported box, but always up/never down), which puts it squarely in the audible bass band. And if the music contains any energy at that frequency, the resonance will be excited and its distortion will be heard.
- A RiPol forces the woofers' resonance
downward about 10Hz (down to 20Hz in this case). Most music contains little or no energy down at 20Hz, in which case the resonance would not be excited so would not occur. And even if the music does contain energy that low, 20Hz is at the threshold of human hearing, so you might feel it but you wouldn't actually hear it as a tone.
Another advantage is the dipolar off-axis nulls, which tends not to excite room resonances that can render the bass sluggish and inarticulate, or even produce the dreaded "one note boom".
Dipolar bass isn't very efficient so I always recommend a pair of RiPol's rather than just one, and they don't pressurize the room in the same way as conventional subs. Not everyone likes them because they don't hit you in the chest like a sledge hammer... but I LOVE them. Their sound arises from nowhere and recedes back to nowhere-- wonderful for jazz, and simply the cleanest, most unobtrusive bass I've ever experienced.
Modak Akustik in Germany markets a similar sized RiPol sub which uses the same Peerless SLS woofers.
A Product Review of this sub by 6-Moons Audio includes the following statement:
"For music-first listeners who prioritize speed, articulation and enunciated clarity, it's the long awaited messiah."
Srajan Ebaen, 6moons.com
I share that sentiment, and I will share my drawing & parts list with anyone who asks-- just PM me an email address.