DIY Ripol Subs

[Jazzman53]

Hi All,

I'm pleased to share my latest Ripol sub project, which is a matching pair with Peerless SLS 12 woofers. Not everyone is familiar with the Ripol concept so I will first give my take on it, and why Ripol's are my favorite subs.

The configuration was patented by German speaker builder Axel Ridtahler, hence the name "RiPol" is short for a "Ridtahler dipole".
It's basically a compact, folded-baffle dipole with two woofers in opposing push/push arrangement. Its radiation pattern isn't the classic dipolar figure-8, but cardioid shaped with a pronounced frontal lobe, and off-axis nulls.

The most interesting characteristic of a Ripol is it's effect on the woofers' fundamental resonance. All woofers have a natural resonance which is typically loud and quite undesirable because it's a distortion that isn't in the music.

Conventional enclosures force the woofer's resonance higher than it's resonance in free air (more so in a smaller box, less so in a bigger or ported box, but always up/never down).

A Ripol enclosure lowers the woofer's resonant frequency as much 10Hz, which not only allows it to play lower but has a profoundly positive effect on tonal quality, as described below.

The Ripol patent includes measurements of a woofer having a free air resonance (Fs) of 25Hz, and the followings resonant frequencies in enclosures:

- The same woofer in a 150 liter sealed box resonated at 47Hz, which is within the audible bass band. So any music containing energy at that frequency would excite that resonance, and its distortion would be heard.

- The same woofer in a Ripol resonated at 17.5Hz! Most music contains little or no energy that low, in which case the resonance would not be excited, so would not even occur. And in the case where music would contain energy that low, it would fall in the infrasonic band where you might feel it but you wouldn't actually hear it as a tone.

Another Ripol advantage is its 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 Ripol's 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 Ripol sub which uses the same Peerless SLS woofers.
A Product Review of the Modal Akustik 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 about mine too, and I will share my drawings & parts list with anyone who asks-- just PM me an email address.

I have drawings available for the version shown, and also for simpler version with exposed plywood edges.

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Build info:

The woofers are Peerless SLS 12's and the cabs are 3/4 red oak plywood with oak edge members inserted and rounded over, which looks much better than exposed plywood edges but is a LOT MORE work. The center section is solid brown oak, indexed to the cabs with oak dowel pins. The cabs and center section are held together with all-thread rods and cap nuts.

The light-colored oak cabs were oil stained with a mixture of 1/3 golden oak, 2/3 natural, and a bit of powdered turmeric root added for a yellowish tint. The darker oak center section was oil stained with red oak, for contrast. The finish is sprayed-on coats of clear satin polyurethane with a sanding step between coats.


Enjoy!
Charlie in Savannah, GA

Below: Rabbited plywood cab pieces self-locate and bank together for gluing.


Below: Woofer cab glued and clamped.


Below: Cab edges were notched (rabbitted) on the table saw, to accept the red oak edge members.


Below: Mitered edge members installed and held in place with painter's tape while the glue sets.


Below: Cab with edge members installed and sanded flush.


Below: The 3-piece assembly details.


Below: Both subs temporarily assembled and edges rounded over to 3/8 radius on router table.


Below: Details stained and spray coated with clear satin polyurethane.


Below: Completed subs with woofers installed.


Below: Back view

[Jazzman53]

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