Yet another Ripol sub build

[Jazzman53]

Hi all,

I've built several pairs of Ripol subs in recent years, and I’m currently building the pair shown below for a friend. These are the smallest, most compact ones I’ve ever built with 12 inch woofers (Peerless SLS). I think my friend will like the compact size!

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.

The light-colored oak cabs will be 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 will be oil stained with red oak, for contrast. The finish will be sprayed-on coats of clear satin polyurethane with a #320 sanding step between coats.

More to come but for now; enjoy the build pics.

Below: Rabbit cut plywood cab pieces self-locate for gluing.

Below: Woofer 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 cabs and center section disassembled.

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

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

Stay tuned... more to come!

 

[AdamG]

Fine job Sir. Remarkable craftsmanship. Look forward to following this build.

 

[Jazzman53]

Update Monday 12/12/22

All pieces were stained yesterday and this morning sprayed with the first coat of clear satin polyurethane.

 

[digitalfrost]

Very nice. I have some question about the design:

- How did you determine the size of the chambers? I guess for the rear chamber it's simply dictated by driver depth and otherwise as small as possible, but for the middle one, is there some rule of thumb how big it should be?

- Do you use a passive attenuator to get rid of the resonance peak at ~500-600hz that will result and if yes how did you calculate that.

 

[Jazzman53]

Ridtahler's patent is in German and I had no idea how to model a Ripol anyway so I just followed some basic guidelines gleaned from posts by a couple of the Ripol gurus (user names "Calvin" and "Rudolf") on the DIY Audio Forum:

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 openings should be 1/2 to 1 SD (of one woofer).

Chamber depth need not be greater than necessary to fit the woofer.

*******************
Calvin ran a sim for my previous Ripole build, which was only slightly larger than this one, wherein the chamber resonance peak was between 250Hz-300Hz, and also calculated *passive notch filter component values for same:

*Approximate values of notch filter with 4 ohm subs: L serial 3.3 mH, 0.4 Ohm Parallel LCR: 365uF, 1mH, 0.28 Ohm. Take these values with a grain of salt because you would likely need to do some measuring to determine the exact chamber resonance and then tweak the filter component values to exactly match up the notch to the resonance.
*********************

Rather than using a passive filter (hate them), I will instead avoid exciting the chamber resonance by crossing the sub in significantly below the resonance using steep filter slope. I will use my DBX Driverack Venu 360 DSP/Crossover with a LR filter at 80Hz & 24db/octave slope, and then use the parametric EQ's to fine tune the sound to my liking. This worked quite well with my previous Ripols so I foresee no problem doing the same with these.

 

[tinnitus]

The patent for the ripol expired in 2014

 

[Jazzman53]

Update Wednesday 12/14/22

Waiting for the woofers to arrive--- I think the new/smaller Ripoles will look very nice -

 

[Jazzman53]

Update Thursday 12/15/22:

My new Ripole subs are finally finished and I've been playing some very demanding bass tracks this evening...from Malia & Boris' album Convergence to Bela Fleck's Flight of the Cosmic Hippo-- and they sound ridiculously good.

As with every Ripole I've heard; I can't localize them in space-- their notes arise from nowhere and recede back to nowhere. And it's astounding that subs this small (especially dipoles) can play this low, and their tonal quality is tight and clean and beautiful !

Very happy !

BTW; I have a dimensioned CAD drawings and parts list if anyone wants it-- no charge.. just PM an email address.

A perfect match with my hybrid electrostats:

 

[Deleted member 15250]

Your friend is a lucky dude!

 

[Jazzman53]

FYI:

I recently learned of a German company, Modal Akustik, marketing a Ripol subwoofer (photo above) 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...

 

[Deleted member 15250]

You could do a rel style stack

 

[Jazzman53]

I've received requests for an easier-to-build version of my Ripole sub so I've drawn one up that omits the rounded edge members; living the plywood edges exposed. Below is a screenshot of the drawing. If anyone wants the CAD drawing just PM me an email address.

 

[Audius]

Hi Jazzman! I'm a beginner at making DIY speakers, but I love listening to music.
I am interested in learning to make stereo 2.2 speakers with 8 inch fullrange drivers and Ripole subwoofer.
My choice:
Drivers Fullrange 2 pieces 8” SB20FRPC30-8 / Paper. 8” SB20FRPC30-8 / Paper Drivers Ripole 4 pieces 5×8″ SB15SFCR39-4 / Paper (2 subwoofers) https://sbacoustics.com/product/5x8in-sb15sfcr39-4/

I have a few questions in building this speaker:
1. Are the fullrange driver speakers and Ripole drivers that I chose suitable and good to choose?

2. For the 5×8″ oval driver in the Ripole design, should I use 5" or 8" as a reference for the height of the box?

3. For the amplifier, I am thinking of using 2 class D amplifiers for each Ripoles and 1 class D or AB amplifier for the full range speakers. do you have any other suggestions?(Macbook - Topping DAC dx3 pro - Dsp JBL MS8 pro - 3 amplifiers - speakers)

Please provide enlightenment and suggestions in building my DIY speakers. Thank You!

 

[Jazzman53]

View attachment 323242

Hi Jazzman! I'm a beginner at making DIY speakers, but I love listening to music.
I am interested in learning to make stereo 2.2 speakers with 8 inch fullrange drivers and Ripole subwoofer.
My choice:
Drivers Fullrange 2 pieces 8” SB20FRPC30-8 / Paper. 8” SB20FRPC30-8 / Paper Drivers Ripole 4 pieces 5×8″ SB15SFCR39-4 / Paper (2 subwoofers) https://sbacoustics.com/product/5x8in-sb15sfcr39-4/

I have a few questions in building this speaker:
1. Are the fullrange driver speakers and Ripole drivers that I chose suitable and good to choose?

2. For the 5×8″ oval driver in the Ripole design, should I use 5" or 8" as a reference for the height of the box?

3. For the amplifier, I am thinking of using 2 class D amplifiers for each Ripoles and 1 class D or AB amplifier for the full range speakers. do you have any other suggestions?(Macbook - Topping DAC dx3 pro - Dsp JBL MS8 pro - 3 amplifiers - speakers)

Please provide enlightenment and suggestions in building my DIY speakers. Thank You!

Those 5x8 woofers should work OK. The Qts is a bit low (very low distortion but won't play as loud as a higher Q woofer would at same input power) so you would benefit from adding 6db/octave boost below the crossover frequency. Noting that your sketch shows the vertical beam is partially recessed into the Ripol enclosure (nice touch), I suggest orienting the those oval woofers vertically. Beyond that, minimize the volume of the rear chambers and size the box such that the area of the front chamber opening is about 1/3 the combined piston area of the two woofers.

 

[Audius]

Thank you Jazzman for the advice and enlightenment... I will try modeling in Vituixcad and/or WinISD first.

 

[goryu]

If these were made with a rounded rear surface in the chamber and non-parallel top and bottom surfaces in the chamber, the resonance could be basically avoided and these would be usable to higher frequencies.

 

[Jazzman53]

If these were made with a rounded rear surface in the chamber and non-parallel top and bottom surfaces in the chamber, the resonance could be basically avoided and these would be usable to higher frequencies.

Thanks for your input.

If I were to build another pair, I would evaluate your suggestion, using a front chamber arrangement like the one used in the Modal Akustik Ripol. Had I seen the Modal Akustik sub before building mine, I might have used that arrangement.

I will venture a speculation that the a curve chamber would also have a resonance, albeit at a higher frequency due to it's smaller size, and possibly of less amplitude since there would be no parallel surfaces creating standing waves.

Even a wine bottle has a cavity resonance so I doubt a resonance could be eliminated merely by changing the shape of the cavity. I will also speculate that the acoustic impedance of a smaller cavity volume would force the woofers' resonance lower (to good effect)--but at the expense of reducing efficiency.

I think your suggestion has merit, but I'm not ready to build another pair of subs.

I recently measured the resonance of my Ripol and found that the front chamber resonance is a sharp peak at 299Hz, and the rear chambers peak at 294Hz. I was pleasantly surprised that the resonance occurred this high.

In my setup, I don't need the subs to play up high anyway, and since I'm using a 48db/octave digital crossover way down at 70Hz, the woofers are not energized near the chamber resonance, and so that resonance is not excited/doesn't occur.

 

[goryu]

A wine bottle has a resonance because it is pipe shaped with parallel walls. With a curved back and sloped top and bottom, if the faces of the drivers are also at an angle, there would be no parallel walls and any resonance that occurs will be at a much higher frequency than the sub would ever be useful at. Yes, you are not using it near 300HZ so it is moot for you but for those who might wish to use such a configuration up higher and/or wish to use a larger set of drivers, it bears keeping in mind.

 

[Scgorg]

A wine bottle has a resonance because it is pipe shaped with parallel walls. With a curved back and sloped top and bottom, if the faces of the drivers are also at an angle, there would be no parallel walls and any resonance that occurs will be at a much higher frequency than the sub would ever be useful at. Yes, you are not using it near 300HZ so it is moot for you but for those who might wish to use such a configuration up higher and/or wish to use a larger set of drivers, it bears keeping in mind.

This is untrue. Even with no parallel surfaces the mass of air inside the cavity will still have a resonant frequency (owing to the fact that it has a mass and stiffness). Your suggestion might allow a smaller total cavity volume, which would push the resonance higher, but it's important to understand that the cavity resonance is inherent to the mass of air and its stiffness. Find a round bottle (or any other arbitrary shape) and it will still exhibit a cavity resonance. U-frame dipoles have the same issue.
This post by Ctrl may be interesting to you: https://www.audiosciencereview.com/...n-baffle-speaker-pitfalls.39216/#post-1384077
It shows clearly that a cavity resonance still exists for a V-frame dipole (U-frame with tapered walls).

Your suggestion might help defeat standing waves that form between the walls of the slot, but those are already at a relatively high frequency.

I had an interest in ripoles for a while, and so simulated them in AKABAK. The results were disappointing to me, so I decided not to move forward with making one.

 

[goryu]

A wine bottle is a type of Hemholtz resonator which is similar to a closed ended pipe wherein resonance forms from reflections in a cavity. Cavity is the key word. From https://www.britannica.com/science/sound-physics/Noise:

"An air cavity in the shape of a rectangular box has a sequence of nonharmonic resonances. In such a case the walls are nodal points, and there are standing waves between two parallel walls and mixed standing waves involving several walls. .... resonances are also readily observed in shower stalls and small rooms such as music practice rooms with parallel walls. Because of these resonances, practice rooms are often made with oblique walls."


There are two basic types of cavity modes - axial and non-axial. With non-parallel surfaces, we are faced with non-axial modes. Axial modes are stronger and of more concern as they have a larger affect creating peaks and nulls as well as modal ringing. Thus, non-parallel walls can be of benefit.

I am not saying that oblique surfaces will eliminate resonances, but my understanding us that they should shift the frequency higher and permit a wider application. The example above is for an enclosed cavity. With an open cavity, the effect should be even greater.

Here's a scholarly paper on the subject:

https://www.sciencedirect.com/science/article/abs/pii/S0022460X15009104

Acoustic resonances in a 3D open cavity with non-parallel walls​