SLS Ripole Subs

[jazzman53]

 

The speaker building psychosis got the best of me again after becoming intrigued by the unique dipolar subwoofers invented by German speaker builder Axel Ridtahler. The name "Ripole" is short for "Ridtahler dipole". I have two of these in my two-channel system and they fill in the bottom end very cleanly. I have dimensioned drawings of the version shown and an easier build MDF version available.

 

The 2-woofer Ripole has the woofers face-to-face in a push/push configuration. The resulting compression in the front chamber actually lowers the woofers' resonant frequency (fs) by as much as 10Hz,depending on the chamber volume and opening area. Thus; the Peerless 12" SLS woofers, which have a resonance of 27Hz in free air, can play all the way down to 17Hz in a Ripole configuration.

A Riplole is basically a very compact, folded-baffle dipole. It can play very low, and because it projects a “figure-eight†sound pattern that nulls the output off-axis, it excites fewer of the room resonances that can give bass the dreaded “one-note boomâ€. Ripoles are clean and musical but, being dipoles, they canâ€t pressurize a room with the kind of chest-thumping bass that many prefer for HT sound effects. I would say that Ripoles are great for music but not so much for theater earthquake effects.

I chose the Peerless SLS 12†woofers for their Ripole-compatible parameters and nice price. Rithadler's patent is in German and the math is over my head anyway so I just followed some basic guidelines gleaned from posts by some smart guys at the DIY Forum:

Area of front chamber opening should be 1/3 to 1/4 of woofers†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 opening should be 1/2 to 1 SD.

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

A rather loud chamber resonance will develop with a peak somewhere between 200hz-300hz, so must either test and build a compensating *notch filter or choose a crossover frequency and slope that keeps the output below the chamber resonance.

*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 as described above, I used a Behringer DCX 2496 digital crossover, with the crossover frequency set below the resonance using a steep slope, and then used the parametric EQ to fine tune the sound to my liking.

The boxes are 3/4 MDF, sheathed with 5mm red oak plywood, and edge-trimmed with quarter-round oak molding to match my other living room furnishings. The box center section pieces are solid white oak planks stained in a contrasting color for effect and indexed to the mating box halves with (4) 1/4 oak dowel pins on each side.

The box is assembled with 1/4-20 all-thread rods and cap nuts as shown in the photos.

Gluing on the plywood sheathing and edge-trimming the boxes is probably more work than most people would want to endure so Iâ€ve also attached a drawing and cut list for a simpler version, using only 3/4 MDF or plywood.

The woofer cutouts in the baffle boards are cut with a bit of extra clearance to allow the woofer magnets to center themselves in the holes in the outer panel. The holes in the side panels allow .090" of clearance for the speaker magnets and I used foam speaker gasket tape to seal around the woofer magnets.

The woofers are wired in parallel for 4-ohm load and Iâ€m using a Behringer DCX2496 crossover and Carver TFM-25 amp. For the initial setup Iâ€m using a 48db L-R slope and experimenting with various X-over frequencies.

Some people prefer to play their subs into the midbass region and others take the view that subs should never actually be heard, only felt. Certainly the latter view is best for subs that have heavy woofers but the SLSâ€s are lighter than most so would offer a wider clean-operating band. I prefer a lower crossover point so the subs aren't stepping on the TL woofers in my hybrid stats (which have a gorgeous tone).


Parts List for two Ripole subs (MDF version):
(4) Peerless SLS 12" woofers (Parts Express) $320
(2) Pair binding posts (Parts Express 091-1245) $18
(1) Sheet 3/4 MDF (Home Depot) $25
(4) 1/4-20 x 36 all-thread rod (Home Depot) $7
(16) 1/4-20 furniture cap nuts (Home Depot) $16
(8) 1/4-20 threaded wood-inserts (Home Depot) $8
(8) Speaker spike feet (Parts Express 249-727) $4
(1) 1/4 x 36 oak dowel $2
(32) #8 x 1†cap screws (Parts Express 081-425) $3
(1) bottle yellow wood glue $4
(8) Banana plugs (Parts Express 091-356) $11
(1) Roll speaker gasket tape (Parts Express 260-542) $6

Total $418

Tool List:

skill saw for first cut on MDF sheet
table saw
router with circle jig
3/4 Forstner bit for counterbores
1/8 & 1/4 drill bits
clamps for gluing

 

Version shown in photos:

 

Easy-build MDF version:

 

Box side shown slotted for quarter-round moldings:

 

 

 

 

 

Edited May 8, 2018 by jazzman53

[Orpheus]

Thanks, Jazzman, for sharing this project.

 

They have me thinking. Might be time for another attempt at integrating subs with my Quad 2905s, or my stacked Quad 57s. These might be worth a try.

[frankn]

I was thinking exactly the same for the 29's, and they wouldn't break the bank either

[jazzman53]

Thanks, Jazzman, for sharing this project.

 

They have me thinking. Might be time for another attempt at integrating subs with my Quad 2905s, or my stacked Quad 57s. These might be worth a try.

 

I had previously built a very nice self powered Dayton 12" sealed-box sub but I never could get it to blend seamlessly with my hybrid ESL main speakers and it tended to make the room boom.  MY hybrid electrostats have gorgeous low bass but a couple of 10's can only move so much air, and I really wanted to add some more bass in the lowest octave.  Like other dipole bass speakers, Ripoles are NOT very efficient and they won't take a lot of power before the woofers bottom out at X-max.  That said, they do blend very well with my system, they don't make the room boom, and they give sufficient volume for my favorite jazz at the listening levels I like.  

 

Even so, I'm always hesitant to recommend Ripoles (or other dipoles) to others who may not have experienced dipole bass.  Many people love the Ripole sound and others are disappointed in their low efficiency and the fact that dipoles can't pump pressure into a room to make chest thumping bass like mono-poles do.  Personally, I've grown to LOVE them. 

In my system I cross them in using a digital crossover at 50Hz with a 48db/octave slope.  Most music doesn't contain a lot of energy below 50 Hz but when I play something with profound bass, like "Flight of the Cosmic Hippo" by Bela Fleck, I really like what I feel and hear.  

[henry218]

jazzman,

 

thats a great project, have you measured how low can it go? im fascinated with the compact size, but not sure if they perform better than the BR.

 

cheers

henry

[jazzman53]

jazzman,

 

thats a great project, have you measured how low can it go? im fascinated with the compact size, but not sure if they perform better than the BR.

 

cheers

henry

 

 

Sorry I don't have any measurement equipment or software, Henry.  I'm an old dog who tunes by ear.  Not to mention, I'm rather technically challenged with computers and software anyway.  I guess I'm not familiar with the "BR" unless that's in reference to bass reflex.  

[henry218]

oops, yep BR = Bass Reflex.

 

i like the look and the execution of your ripole (where the back panel holds the magnet), with the chest pumping thing, my previous dual 15" OB using eminence Beta and Alpha gives me A LOT of chest thumping, but i EQ'ed it with miniDSP (something like Linkwitz Transform, but not as aggresive as the woofer dont have much xmax). Although i listened in nearfield, around 1.5m seating position.

 

cheers

henry

[henry218]

i remembered when i was watching Rise of Planet of the Apes, my mother in law was sitting near the woofer, she jumped from her seat on a scene where the gorillaz invade the bridge with lots of cars

[Orpheus]

I had previously built a very nice self powered Dayton 12" sealed-box sub but I never could get it to blend seamlessly with my hybrid ESL main speakers and it tended to make the room boom.  MY hybrid electrostats have gorgeous low bass but a couple of 10's can only move so much air, and I really wanted to add some more bass in the lowest octave.  Like other dipole bass speakers, Ripoles are NOT very efficient and they won't take a lot of power before the woofers bottom out at X-max.  That said, they do blend very well with my system, they don't make the room boom, and they give sufficient volume for my favorite jazz at the listening levels I like.  

 

Even so, I'm always hesitant to recommend Ripoles (or other dipoles) to others who may not have experienced dipole bass.  Many people love the Ripole sound and others are disappointed in their low efficiency and the fact that dipoles can't pump pressure into a room to make chest thumping bass like mono-poles do.  Personally, I've grown to LOVE them. 

In my system I cross them in using a digital crossover at 50Hz with a 48db/octave slope.  Most music doesn't contain a lot of energy below 50 Hz but when I play something with profound bass, like "Flight of the Cosmic Hippo" by Bela Fleck, I really like what I feel and hear. 

I have two minor problems with the 2905's which I need to solve.

 

First, they have a big hump at about 70hz.

 

Second, their lower bass is ill-defined.

 

I would like to take the duties from 80hz down away from the Quads.

 

I think these might be the answer. All I want is slightly clearer, more even bass from 70hz down.

[jazzman53]

Yes Henry, when listening near-field, you would be engulfed within the on-axis lobe of the figure-8 radiation pattern, and you would indeed get some thump I'll wager.  When I get my face within a couple of feet (2/3 meter) of the chamber opening of my Ripoles, they literally move the hair on my head.   

Edited September 15, 2013 by jazzman53

[gainphile]

Awesome project! 

 

I would prefer a push-pull though, to cancel out harmonic distortions. The loading effect to fs should be the same.

 

My own dipole subs, perfect CSD

 

 

As you said it will never punch like sealed subs but they play Daft Punk rather well, with 1000 watt amps

[jazzman53]

I have two minor problems with the 2905's which I need to solve.

 

First, they have a big hump at about 70hz.

 

Second, their lower bass is ill-defined.

 

I would like to take the duties from 80hz down away from the Quads.

 

I think these might be the answer. All I want is s-lightly clearer, more even bass from 70hz down.

 

The 70Hz peak you speak of is probably the resonance frequency of the diaphragm. 

 

The problem with ESL bass, and full range ESL's, has to do with the diaphragm's natural drum-head resonance.  ESL's are wonderfully low-Q and resonance free drivers throughout the entire audio frequency spectrum EXCEPT at the diaphragm's resonance frequency, and it's a savage resonance.  And as we know, any resonance is high-Q and uncontrolled behavior, so the bass output near this resonance frequency would be ill defined.  

 

Hybrid ESL's are challenged to achieve a seamless blend between the low-Q diaphragm and higher-Q woofer, but they do offer one huge advantage--- that is; it is not then necessary to play the electrostat near the diaphragm's resonant frequency.  For hybrid ESL's the rule of thumb is to cross the panel over to a woofer at least one octave above the diaphragm resonance with a steep 48db crossover slope or at least two octaves above resonance with a 24db slope.  

 

I'm not sure if you could notch out the diaphragm resonance without bi-amping the system with a steep crossover, and letting a conventional woofer handle everything below 200 Hz or so.   A woofer mounted in a transmission line or a dipole would blend better with a stat panel that a sealed or ported box woofer.     

Edited September 16, 2013 by jazzman53

[andyr]

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Thank you for alerting me to this design, jazzman.

 

They sound just what I need for my new house ... but I have a coupla Qs.

 

1. I presume the sound comes out of the slots which are shown in the above pic?  And there's one similarly-sized slot at the back?

 

2. So how close to the front wall can the back of the Ripole 'box' be?

 

3. Could the Ripole boxes be placed in the front corners of the room?

 

4. If they were sandwiched between the side wall and a record cabinet, how much gap would I need to allow either side of the Ripole box walls?

 

 

Thanks,

 

Andy

[jazzman53]

Thank you for alerting me to this design, jazzman.

 

They sound just what I need for my new house ... but I have a coupla Qs.

 

1. I presume the sound comes out of the slots which are shown in the above pic?  And there's one similarly-sized slot at the back?

 

2. So how close to the front wall can the back of the Ripole 'box' be?

 

3. Could the Ripole boxes be placed in the front corners of the room?

 

4. If they were sandwiched between the side wall and a record cabinet, how much gap would I need to allow either side of the Ripole box walls?

 

 

Thanks,

 

Andy

 

Hi Andy, 

The photo you showed is the back of the speaker, the front is shown below-- although I think you could turn them either way and it wouldn't make a huge difference.

 

Placement is always a compromise to our living space but the Ripoles should be at least a meter from the back wall and preferably nearer to the center of the room, so as to mitigate the dipole roll off, and so that the on-axis lobe would fully engulf the listening position at moderate power levels (without having to pump in more volume to project a larger lobe to engulf the listening position).  

 

Front: 

[tuyen]

Interesting concept!   Anyone with idea how they compare (both subjectively and objectively) to say running a pair of 12/15" woofers in open baffle?   This one looks like a smaller footprint.    Wouldn't mind trying to build one of these to place in centre between the bass horns.      

 

Best place to buy Peerless SLS woofers in AUS?  

 

Thanks for sharing jazzman53!

[henry218]

essentialaudio.com.au carries SLS

 

i think the H/W-frame will offer more output, but it wont play high, so it depends on your midbass/midrange config.

Edited September 16, 2013 by henry218

[gainphile]

Placement is always a compromise to our living space but the Ripoles should be at least a meter from the back wall and preferably nearer to the center of the room, so as to mitigate the dipole roll off, and so that the on-axis lobe would fully engulf the listening position at moderate power levels (without having to pump in more volume to project a larger lobe to engulf the listening position).  

 

Front: 

 

 

Below schroeder frequency the dipole would not form (as in outdoor/anaechoic). Due to the acoustically large  wavelength it couples with the room and might be better 'analysed' as multiple front-back firing subs with opposing phase. So it does need space but not necessarily 1m. I've lived with 40cm with no issues (which allows 80cm space from front panel).

[henry218]

andy,

 

thats good to know, 40cm is reasonably close! 

[tuyen]

nice cheers, henry.     bass horns go down to 50-60 cycles in room, so sub doesn't need run very high.  unit footprint size is important though.

 

 

Closer to 40cm from rear wall is bit more manageable. lol

[gainphile]

Yes, I could not get closer than that though, as it quickly 'degenerates'.

 

An old photo to show how close it is: http://1.bp.blogspot.com/-M-JaZxnOin0/TtIimerjZrI/AAAAAAAAGqQ/ei1MlV_UWjw/s1600/andi1.jpg

 

The midrange is most important with dipoles as the dipolar response would form. I guess it's the same with ESL and Planar speakers, they must need some space to breathe at midrange-higher frequencies.

[davewantsmoore]

perform better than the BR

 

Is that a trick question?   Everything performs better than BR.    ;-)

[henry218]

not really, im talking about extension, practicallity and conveniency

[henry218]

ive built TL, OB, U frame, BR, everyone of them have compromises

[davewantsmoore]

Really nice looking work here!   :-D :-D

 

I use them too in dipole and sealed+EQ woofers   

 

 

 

A Riplole is basically a very compact, folded-baffle dipole. It can play very low, and because it projects a “figure-eight†sound pattern that nulls the output off-axis, it excites fewer of the room resonances that can give bass the dreaded “one-note boomâ€. Ripoles are clean and musical but, being dipoles, they can’t pressurize a room with the kind of chest-thumping bass that many prefer for HT sound effects. I would say that Ripoles are great for music but not so much for theater earthquake effects.

 

(Not saying you do..... but)

 

Many people misunderstand the "pressurize a room" behaviour... and/or what it means for the sound.     It means naturally that a dipole will rolloff quicker than a monopole....   but it does not say anything about "chest thumping"-ness of the bass, when the dipole and monopole are equalised to the same output.

 

What it means is that you will need more woofers, or more EQ (hence more power), to get the same response down low from a dipole as a monopole... this is because the monopole receives a boost from the room.

 

....but, once you do have them outputting the same response, there's be no difference in "chest thumping"-ness.      So the idea of "not suited to home theatre" is not really right.   They just need more low boost for the same response.   Like all bass, setup (impossible without measurement) is the key.

 

 

 

.. and now the $64,000 question becomes, which is better?!  ....   sure, extra output for free (room gain) is always nice... and more excursion is bad (movement = distortion) ....   but do you really want 'room gain boost' ... or is the dipole (doesn't interact with the room) better ?!

 

 

Heh, I'd need to spend the 64k on a better house.   I need to be -6dB down at 20hz otherwise things move which are not supposed to  (the bathroom door makes noises which belong in a horror movie).

[davewantsmoore]

I should say, aside from the behaviour below the room fundamental.... but this is very very low... and would need a much bigger sub for this to make a difference ;-)

 

EDIT:  but I guess that depends on how small your room is... don't mind me, trahlahlaaa     

Edited September 16, 2013 by davewantsmoore