Yet another Ripol sub build

[Scgorg]

What you're talking about seems to be something else than what I am talking about. It appears to me that you're talking about the standing waves that occur between boundaries (be they axial, tangential, or oblique). I am talking about the resonance that is inherent to a spring-mass(-damper) system. For a cavity this means that the air trapped in the cavity has a mass and a stiffness (and damping) which means it has a resonance frequency, just like a loudspeaker driver has a resonance frequency dependent upon its stiffness and mass. If the air is excited at this frequency, it will start oscillating/resonating heavily.

The more common term for a cavity resonance is "helmholtz resonance", which you may be familiar with. In the case of a ripole the helmholtz resonance of the slots is generally lower in frequency than the first standing waves in the slots, in other words increasing the frequency of the helmholtz resonance is a more efficient means of improving the ripole's bandwidth than making the walls non-parallel. Most helmholtz resonators are quite different in shape from the slots found in ripoles, but the basic principle is the same: a mass of air which oscillates strongly around a particular frequency.'

Let's say the largest dimension in a ripole slot is 34cm, in that case the first standing wave will occur at ~500Hz, which is already far beyond the frequency of the cavity/helmholtz resonance.

 

[goryu]

air trapped in the cavity

I don't believe there is any air "trapped" in any cavity- it is constantly moving in and out. The resonances come from the friction against the wings per the paper I cited above. If the back of the baffle is open on the top and rear, there is no closed cavity.

 

[Megumin]

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.
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Below: Woofer cab glued and clamped.
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Below: Cab edges were notched on the table saw to accept the oak edge members.
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Below: Red oak edge members held in place with painter’s tape while the glue sets.
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Below: Cab with mitered edge members glued in.
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Below: Completed cabs and center section disassembled.
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Below: Rear view assembled with edges rounded to 3/8” radius on a router table.
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Below: Front view / ready for stain & satin clear coat.
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Stay tuned... more to come!

Great looking build! Am thinking about building one myself, do you have any idea what the sensitivity is?

 

[Jazzman53]

Great looking build! Am thinking about building one myself, do you have any idea what the sensitivity is?

I'm not equipped to measure its sensitivity so I can't tell you what it is. Like all dipoles, Ripols are progressively less efficient with falling frequency due to the dipole phase-cancellation.

If you prioritize clean, articulate, non-boomy bass over efficiency, then I think a RiPol is a good choice. It's decently efficient at the upper end of the bass band but rolls off at 6db/octave with falling frequency, so less efficient down low.

Paradoxically; within its near-field lobe, a RiPol can play lower and cleaner than a typical box sub-- it's just less efficient.

A RiPol isn't going to thump you in the chest like a box sub, and it's easy to overdrive the woofers beyond X-max trying to compensate their lower efficiency by cranking the amp, so I always recommend a pair of 12" RiPol's rather than just one.

 

[Megumin]

I'm not equipped to measure its sensitivity so I can't tell you what it is. Like all dipoles, Ripols are progressively less efficient with falling frequency due to the dipole phase-cancellation.

If you prioritize clean, articulate, non-boomy bass over efficiency, then I think a RiPol is a good choice. It's decently efficient at the upper end of the bass band but rolls off at 6db/octave with falling frequency, so less efficient down low.

Paradoxically; within its near-field lobe, a RiPol can play lower and cleaner than a typical box sub-- it's just less efficient.

A RiPol isn't going to thump you in the chest like a box sub, and it's easy to overdrive the woofers beyond X-max trying to compensate their lower efficiency by cranking the amp, so I always recommend a pair of 12" RiPol's rather than just one.

Thanks for your insight, i am not really worried about the sensitivity in regard to the max volume as i don't really listen that loud. The sensitivity would have been useful to figure out if i could get away with using a receiver with +-10 dB volume control to directly run the RiPol with a power amp. Maybe it would work given the generally lower sensitivity.

The idea of clean but deep bass is what has brought me to the RiPol, and if the volume of one is not enough i could always add another one.

A RiPol isn't going to thump you in the chest like a box sub

Is there any inherent difference that would mean there is less "tactile" bass? Or are you simply referring to the lower overall output?

overdrive the woofers beyond X-max

Would i notice that before it does any damage?

Anyways if i go for the RiPol you'll probably hear from me again in the future. Greetings!

 

[Jazzman53]

Thanks for your insight, i am not really worried about the sensitivity in regard to the max volume as i don't really listen that loud. The sensitivity would have been useful to figure out if i could get away with using a receiver with +-10 dB volume control to directly run the RiPol with a power amp. Maybe it would work given the generally lower sensitivity.

The idea of clean but deep bass is what has brought me to the RiPol, and if the volume of one is not enough i could always add another one.


Is there any inherent difference that would mean there is less "tactile" bass? Or are you simply referring to the lower overall output?


Would i notice that before it does any damage?

Anyways if i go for the RiPol you'll probably hear from me again in the future. Greetings!

When I say that a RiPol (or any other dipole) doesn't thump you in the chest, I mean that it doesn't pressurize the room cavity to the extent that a monopole does. The same characteristic makes a Ripol less prone to exciting the room's resonance (i.e. it's not boomy sounding).

Any woofer not mounted in a box has no contained air mass to compress, so the cone is freer to move and does move significantly more. I would not recommend a single RiPol sub for that reason. With a pair of RiPols the excursion is halved for a given volume.

Fortunately; the Peerless SLS woofer has a progressive suspension approaching X-max so it can take quite a bit of abuse. It sounds pretty horrible when the woofers pushed so far the surrounds invert, but every time I've done that (twice with drunk fools cranking the volume, they righted themselves and keept on playing.

There is no problem with a pair playing at normal listening levels.

 

[Megumin]

When I say that a RiPol (or any other dipole) doesn't thump you in the chest, I mean that it doesn't pressurize the room cavity to the extent that a monopole does. The same characteristic makes a Ripol less prone to exciting the room's resonance (i.e. it's not boomy sounding).

Any woofer not mounted in a box has no contained air mass to compress, so the cone is freer to move and does move significantly more. I would not recommend a single RiPol sub for that reason. With a pair of RiPols the excursion is halved for a given volume.

Fortunately; the Peerless SLS woofer has a progressive suspension approaching X-max so it can take quite a bit of abuse. It sounds pretty horrible when the woofers pushed so far the surrounds invert, but every time I've done that (twice with drunk fools cranking the volume, they righted themselves and keept on playing.

There is no problem with a pair playing at normal listening levels.

Good to know about the X-max, in this case i could possibly get away with using a stereo class d amp like a fosi v3 or something (i think).

They are often used in near-field, how do they perform at around 3-4m distance? And somewhere i read that people use them below a coffee table in near field, have you tried something similar?

One thing i am also wondering about is if they could be rotated by 90 degrees without the dipol characteristic becoming a problem, i thought they are not supposed to have much output to their sides, which would then become their top side?

If that would not be a problem one could build something like the "RiPol 30" and just stack as many as one needs on top of each other? That would be very convenient in terms of upgradability and leave more possible ways to position the individual modules either vertically or horizontally.

 

[tinnitus]

here my "Stacks" with RIPOL Modules