Yet another Ripole sub project

[Jazzman53]

Hi all,

I've built several pairs of Ripole subs in recent years, and I’ve just completed new pair which are smaller and more compact than any I’ve ever built with 12 inch woofers (Peerless SLS). I love the compact size!


I finished them today and this evening I've been enjoying some very demanding bass tracks...from Malia & Boris' album Convergence to Bela Fleck's Flight of the Cosmic Hippo. I was expecting some loss of efficiency with the smaller size but apparently not.

As with every Ripole I've heard, I can't localize them in space-- the bass just arises from nowhere-- and they sound RIDICULOUSLY GOOD!

It's astounding that subs this small, especially dipoles, can play this low (20Hz) and their tonal quality is tight and clean and beautiful !

Very happy !

BTW; I'm happy to share my CAD drawing and parts list if anyone wants them-- just PM an email address.

Description:
The woofer 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.

 Sections of 11/32" O.D. brass tubes hide the all-thread rods.

The light-colored oak cabs were oil stained with a mixture of 1/3 golden oak, 2/3 natural, and I added a bit of powdered turmeric root for a yellowish tint. The darker oak center section was oil stained with red oak, for contrast. The finish is sprayed coats of clear satin polyurethane with a #320 sanding step between coats.


Below: Rabbit cut plywood cab pieces bank together to aid gluing.

Below: Cab glued and clamped.

Below: Cab edges were notched on the table saw to accept the oak edge members.

Below: Red oak edge members held in place with painter’s tape while the glue sets.

Below: Cab with mitered edge members glued in.

Below: Completed three-piece assembly.

Below: Rear view, assembled with edges rounded to 3/8” radius on a router table.

Below: Front view / ready for stain & satin clear coat.

Below: The completed subs.

 

[Russr]

Wow! Awesome project, with great attention to detail!

What amp specs are needed to drive this "with authority"?

Could you provide a list of the core tooling that you used (/needed) to accomplish this?

 

[Jazzman53]

Wow! Awesome project, with great attention to detail!

What amp specs are needed to drive this "with authority"?

Could you provide a list of the core tooling that you used (/needed) to accomplish this?

The woofers are the 8-Ohm versions of the Peerless SLS 12, wire in parallel push/push, which makes it a 4-Ohm load (a bit less, as the woofers' impedance are a bit lower than advertised). I use a Carver TFM-25 (225 W/Ch) but they don't stress the amp at all so I'm thinking 50W/Ch would suffice or 100W/Ch would drive them with authority.

 

[Brandon Hartwick]

Another great looking subwoofer project. I'd love a copy of the plans if you're giving them away, I'll send you a PM later

Do you notice much difference between this and the previous ripole subwoofers you've built? I'm always jealous of other people's fantastic woodworking skills, these looks great

 

[Jazzman53]

Another great looking subwoofer project. I'd love a copy of the plans if you're giving them away, I'll send you a PM later

Do you notice much difference between this and the previous ripole subwoofers you've built? I'm always jealous of other people's fantastic woodworking skills, these looks great

My previous subs (built just last year) sound fantastic. I wanted to build a smaller version and I had expected a trade off in either quality or efficiency but I honestly cannot hear any difference, and these smaller ones are so much nicer aesthetically... it's just awesome!

Actually, I was building these for a friend who also has a pair of my ESLs, but now I don't want to part with them! Maybe I can give my friend a really good deal on my older ones....

 

[Robert D]

My previous subs (built just last year) sound fantastic. I wanted to build a smaller version and I had expected a trade off in either quality or efficiency but I honestly cannot hear any difference, and these smaller ones are so much nicer aesthetically... it's just awesome!

Actually, I was building these for a friend who also has a pair of my ESLs, but now I don't want to part with them! Maybe I can give my friend a really good deal on my older ones....

Are the woofers on both the old model and the new smaller ones the same, and its just a smaller cabinet?

 

[Jazzman53]

Are the woofers on both the old model and the new smaller ones the same, and its just a smaller cabinet?

Same Peerless SLS 12 woofers.

My understanding is:

A woofer is forced to behave differently in a Ripole than in a conventional sealed or ported box or even an open baffle, especially with respect its resonance frequency relative to it's resonance in free air (FS). And this resonance is the practical lower limit of the woofer's response.

The woofer's resonance is forced significantly higher in a sealed or ported box, and slightly higher on an open baffle (OB).

For boxed subs, increasing the box's volume only reduces the amount that the woofer's resonance is raised. Even if the box volume were increased to infinity, the woofer's resonance would not be reduced below its FS (it would be similar to an OB).

Hence; if we want a boxed woofer to play lower, we must use a bigger box (the response limit being FS at infinite volume).

In a Ripole however, the woofers' resonance is not only not increased but the acoustic impedance of the chamber(s) forces the resonance downward, as much as 10Hz below FS (!)...depending on chamber volume/opening area. And [down to some practical limit] the smaller you make the Ripole, the lower it plays! To me; that's absolutely astounding! And it's sound is so clean you have to hear it to believe it.

Ripole math is over my head but I'm rather certain there is a point of diminishing returns where it becomes impractical to go smaller.

After this build, I'm now pretty sure I could go even smaller without significantly affecting fidelity output.

 

[Brandon Hartwick]

Is there any reason you couldn't stack these?

 

[Jazzman53]

Is there any reason you couldn't stack these?

No reason at all, and the only limit is the height of your room!

 

[Robert D]

Same Peerless SLS 12 woofers.

My understanding is:

A woofer is forced to behave differently in a Ripole than in a conventional sealed or ported box or even an open baffle, especially with respect its resonance frequency relative to it's resonance in free air (FS). And this resonance is the practical lower limit of the woofer's response.

The woofer's resonance is forced significantly higher in a sealed or ported box, and slightly higher on an open baffle (OB).

For boxed subs, increasing the box's volume only reduces the amount that the woofer's resonance is raised. Even if the box volume were increased to infinity, the woofer's resonance would not be reduced below its FS (it would be similar to an OB).

Hence; if we want a boxed woofer to play lower, we must use a bigger box (the response limit being FS at infinite volume).

In a Ripole however, the woofers' resonance is not only not increased but the acoustic impedance of the chamber(s) forces the resonance downward, as much as 10Hz below FS (!)...depending on chamber volume/opening area. And [down to some practical limit] the smaller you make the Ripole, the lower it plays! To me; that's absolutely astounding! And it's sound is so clean you have to hear it to believe it.

Ripole math is over my head but I'm rather certain there is a point of diminishing returns where it becomes impractical to go smaller.

After this build, I'm now pretty sure I could go even smaller without significantly affecting fidelity output.

Wow, that's really cool and probably some really cool physics calculations you could do. Physics was always the one science subject I was weakest at. I taught biology and chemistry.
This makes me want to build a pair! I don't have the skills or tools though. I wonder, why don't hi-fi companies sell ripoles? The design seems to be superior to others, especially for people that don't have a lot of space.

 

[Jazzman53]

Wow, that's really cool and probably some really cool physics calculations you could do. Physics was always the one science subject I was weakest at. I taught biology and chemistry.
This makes me want to build a pair! I don't have the skills or tools though. I wonder, why don't hi-fi companies sell ripoles? The design seems to be superior to others, especially for people that don't have a lot of space.

Actually, you can buy commercial Ripole subs:
https://www.modalakustik.de/english-1/

 

[Robert D]

Have you tried using a ripole with another type of sub such as a sealed or ported? Wondering how the two teamed up would sound compared to two ripoles.

 

[Brandon Hartwick]

Those Peerless SLS woofers are a real pain to get in Canada, looks like I'd have to get them shipped from the UK. To buy 4 of them it works out to $150 each after shipping so that's not awful but I think I'll hold off on starting another project.

Thanks for making your plans public, I'll definitely have to make a set of these at some point!

 

[JonFo]

Congrats on an awesome-looking build; totally jealous of your woodworking skills. Love the idea of adding some turmeric powder to add yellow, genius.

The physics of a ripole are baffling, as I get how the FS of a driver can be lowered, but the in-room performance is the mystery, as one would think the dipole nature would lead to cancellations at certain frequencies.

In practice, is that not equivalent to a dual-woofer sub (drivers on opposite sides of a cube) with one of the drivers wired out of phase?

 

[Duke]

Yes. How do you wire them? Is this like an isobaric sub? Just asking you first!

 

[Jazzman53]

Yes. How do you wire them? Is this like an isobaric sub? Just asking you first!

The opposing woofers are wired in parallel (push/push).

The comparison to isobaric is a good question for which I don't feel qualified to answer, but my initial impression is that the two designs are similar in that both sides of the woofer(s) are within chambers. I'm wondering if isobaric likewise lowers the woofers resonance (?)

 

[Duke]

I wrote without remembering the isobaric needs an enclosed cabinet. It doubles the volume and fleshes out the lower register. Sorry for wasting your time with that. I appreciate that you have found something for me that might be way less expensive than a big cabinet.

 

[Robert D]

Long time ago I had a bandpass sub in my car stereo. Its been over 30 years now. It was very loud but not a lot of finesse. I'm wondering, what other subwoofer cabinet designs are there?

I wonder what a riploe sub that's sealed up and made into a bandpass would sound like? Probably just like a regular bandpass?

 

[Jazzman53]

FYI:

As mentioned earlier in this thread;
I recently learned of a German company, Modal Akustik, marketing a Ripol subwoofer in collaboration with the inventor, Axel Ridtahler. And it happens that the Modal Akustik sub and my sub use the same Peerless SLS 12 woofers.

Six Moons Audio reviewed the Modal Akustik sub and said this about it:

"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.

The Ripole design principal is not well known or understood-- I'm still struggling with it myself. Modal Akustik explains it as follows:

"The RiPol-principle explained:

The dispersion pattern of regular bass principles is, below a certain frequency, omni-directional. A dipol is physically clearly defined and shows a typical 8-shaped dispersion. The RiPol is a special kind of bass-dipol.

Its special enclosure gives a RiPol not that exact symmetrical dispersion. Because the intensity radiated from the front in relation to the back is different, a RiPol has an asymmetrical dispersion pattern, which leads to a beneficial in-room frequency response. Because the dispersion of a RiPol does not follow the classic 8-shape, a RiPol is not a typical dipol but one of its own kind. Dispersion diagrams show clearly the difference compared to a classical dipol, which justifies its own name, RiPol (as a combination of "dipol" and the last name of its inventor, Axel Ridtahler).

The RiPol-enclosure has a strong effect on its dispersion pattern. It prevents, that the air produced by the chassis movement gets out of the way too quickly, so that the radiation resistance increases. The natural resonance of the drivers is lowered when mounted in a RiPol-enclosure, which improves the reproduction quality of the lower bass region the smaller the enclosure gets (!!). There is however a limit, that is why the dimensions of a RiPol-enclosure have to be iteratively optimized, calculated and simulated. The arrangement of the two drivers opposite of each other in addition realizes a benefitial impulse compensation. At the same time the enclosure has a very small footprint.

A RiPol disperses low frequencies in certain directions, to the front and ,with different intensity and 180° revered phase, to the back. This attribute reduces harmful standing waves in the room. These are energy-retention effects within a room, also called room modes. In a listening room standing waves can cause the impression of inertial bass energy that does not fade away. Bass-heavy speakers float the room with bass energy and leave the impression of a slow or sluggish bass. A RiPol, through its rear chambers, produces "antimatter" at low frequencies, that prevents this effect to emerge. A bass impulse is created and, through its counter-wave that comes from the back, the continuance of the standing wave is prevented. As a result the signal is not blurred by its own overlay. These attributes make the RiPol one of the most musical bass-principles on the market.

And there is another effect of note: Because of the directed bass dispersion, to the left an the right side of a RiPol there is no deep bass. These areas are a good spot for placing sensitive components like turntables, amplifier, CD-players etc. Placed next to a RiPol these electronics are not disturbed by deep bass and can do their work without interference!"

A side note:
Now that I have the new Ripoles, I'm wondering what to do with the pair I built last year (shown below) and no longer need. They are in pristine condition, sound equally fabulous, and are same as the new ones except 1/2" taller and deeper.

Food for thought...

 

[Robert D]

The cabinets on those subs looks like plastic. I'm sure it's not? Strange.