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As for me

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In Reply to: RE: Magnepan Review from TAS posted by MarcL on April 09, 2024 at 07:34:35

(and likely Wendell), I'd opt for half of the woofers on that third party product to be reversed to deliver the consistent directivity Tom mentioned that Siggy Linkwitz found important.

Follow Ups:

HAL's 8" H-Frame stack + Nexus DSP - emailtim 15:38:31 04/09/24 (0)
HAL's individual H-Frame modules are reversible so you could stack and wire them that way.
Something like this:

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- HAL's 8 (Open in New Window)
Edits: 04/09/24 04/09/24 04/09/24
RE: As for me - MarcL 15:27:26 04/09/24 (26)
So ... if you have four 12" drivers, what does it actually do to flip two of them around but also reverse their polarity? Does the back end of the cone push air differently than the front end? I could see that ... but why?

Agilist, Musician, Photographer, Audiophile
Magneplanar: 3.7, CCR, MC1,LRS, MMGW, DWM; Outlaw: UltraX12, LFM-1C; Emotiva: XMC-2; Nord: Nord One NC500DM, Nord Three 1ET7040SA; Outlaw: Model 7500; OPPO 205
- Dipole radiation - E-Stat 15:39:24 04/09/24 (18)
  like Magnepan's Condo prototype. And how the referenced Linkwitz design is applied...
  - Reversing half the woofers cancels odd order distortion (not related to directivity) - 13th Duke of Wymbourne 18:02:15 04/09/24 (12)
    You now get the same asymmetry of cone movement in both directions.
    - Correction - cancels even-order distortion (asymmetry) - 13th Duke of Wymbourne 22:43:32 04/09/24 (0)
      I can't correct the thread title without deleting - and I probably can't do that once there is a reply.
    - Making it full range dipolar - E-Stat 19:57:29 04/09/24 (10)
      does effect how it radiates into a room.
      
      Which is why I'm not a fan of hybrid stats.
      - It is already fully dipolar - 13th Duke of Wymbourne 21:03:45 04/09/24 (9)
        
        In Reply to: RE: Making it full range dipolar posted by E-Stat on April 09, 2024 at 19:57:29
        
        Hybrid stats usually come with a sealed or ported woofer - are we comparing apples and oranges? The bass augmentation units shown in the Absolute sounds video are open front and back - they are dipoles.
        
        For them, the only possible effect on radiation regarding which way the driver is mounted is that there is a basket behind the cone and none in front. But those dimensions are very small compared to bass wavelengths so if there is any asymmetry in radiation it must surely be tiny?
        
        RE: It is already fully dipolar - josh358 09:39:28 04/10/24 (1)
        
        In Reply to: RE: It is already fully dipolar posted by 13th Duke of Wymbourne on April 09, 2024 at 21:03:45
        
        Yes, it's tiny.
        
        WAF: That's what she said. (nt) - emailtim 10:36:24 04/10/24 (0)
        
        In Reply to: RE: It is already fully dipolar posted by josh358 on April 10, 2024 at 09:39:28
        
        nt
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        Apparently - E-Stat 05:23:44 04/10/24 (6)
        
        In Reply to: RE: It is already fully dipolar posted by 13th Duke of Wymbourne on April 09, 2024 at 21:03:45
        
        But those dimensions are very small compared to bass wavelengths so if there is any asymmetry in radiation it must surely be tiny?
        
        not enough for designers like Siggy Linkwitz . Speculate however you please.
        
        RE: Apparently - 13th Duke of Wymbourne 14:55:02 04/10/24 (5)
        
        In Reply to: RE: Apparently posted by E-Stat on April 10, 2024 at 05:23:44
        
        Linkwitz's DIY dipole sub designs always had one woofer pointing forward and one pointing back. In the linked article he shows an alternative with both woofers facing in the same direction to allow a slightly smaller cabinet/frame size but at the expanse of not cancelling even-order distortion.
        https://www.linkwitzlab.com/woofer3.htm (Open in New Window)
        
        RE: Apparently - emailtim 00:14:29 04/11/24 (2)
        
        In Reply to: RE: Apparently posted by 13th Duke of Wymbourne on April 10, 2024 at 14:55:02
        
        I built both of these test cabinets in addition to H-Frames.
        
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        Any conclusions? - 13th Duke of Wymbourne 16:05:21 04/14/24 (1)
        
        In Reply to: RE: Apparently posted by emailtim on April 11, 2024 at 00:14:29
        
        ?
        
        RE: Any conclusions? - emailtim 19:14:01 04/14/24 (0)
        
        In Reply to: RE: Any conclusions? posted by 13th Duke of Wymbourne on April 14, 2024 at 16:05:21
        
        The 1st 2 force cancelling builds are tombstone quiet as far as cabinet vibrations are concerned. They would make great pedestals for smaller studio monitors or an LRS stand.
        
        They also benefit from some "port" tuning. Shortening the back of the wells improved response. My next version will have U ports.
        
        You can feel the vibration on the H-Frame cabs even using 1.5" thick MDF on cab all members. The side walls don't flex, but the forward/backward movement is felt. My H-Frames use 3/4" deep rabbets and dados so they are interlocked tight.
        
        The H-Frame loads the room better. I attribute that to the symmetric front and back full length slots (e.g. OB line arrays) crossing more room nodal points.
        
        Combining those 2 observations is my current quest. Hopefully I get the best of both, ...., vs the worst of both. =)
        
        If you want something with higher frequency reach (or to experiment with more XO points), the H-Frame is probably better.
        
        I have been reading more about the Ripole/Linkwitz W-Frames to figure out how they tick vs just using %SD recipes floating around the web.
        
        Characteristics:
        
        - Limits HF extension by quarter wavelength of the well depth (act like a low pass XO).
        - Have a high frequency peak that needs to dealt with (well placed XO).
        - Lower FS (by up to 10Hz from what I have found)
        - Force cancellation.
        - W-Frame has for/aft linear averaging.
        - Lower output (nothing is for free).
        - Requires power.
        
        If you add mass to a driver, it lowers the FS. This can be done with physical weights or "air weight".
        
        There are FS and Compliance formulas using Mms and Cms values. These 2 formulas should help model/predict resulting FS based on cab dimensions and driver selections vs just using the %SD based formulas on the web.
        
        I used the 1st formula to calculate FS from multiple driver specs and the results appear to match the manufacturer's specs. The FS on my GR Research drivers are 28Hz. Hopefully I can drop that to 20Hz with just the cabinet (e.g. before DSP).
        
        Fs = 1 / (2 x pi x sqrt(Mms * Cms) )
        Cms = 1 / ( (2 x pi x Fs)^2 x Mms )
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        Yes - E-Stat 15:47:12 04/10/24 (1)
        
        In Reply to: RE: Apparently posted by 13th Duke of Wymbourne on April 10, 2024 at 14:55:02
        
        prototype vs production.
        
        I've seen this film before ... - 13th Duke of Wymbourne 16:53:11 04/10/24 (0)
        
        In Reply to: RE: Yes posted by E-Stat on April 10, 2024 at 15:47:12
        
        .. and sometimes the horse doesn't drink.
        
        For the record, Linkwitz used opposing woofers (W-frame) in the subs of the Audio Artistry Beethoven grand production speaker with four drivers per side and, I am sure, half faced in opposing directions for the linearity reason that he noted. I read through his Phoenix website avidly years ago and I do not recall anything about a change in radiation pattern whether the drive unit was mounted forward facing or reverse facing. In fact, he has used woofers facing the listener or perpendicular to the listener or at 45degrees to the listener and they all act as dipoles in the appropriate frame/cabinets.
  - RE: Dipole radiation - emailtim 16:03:25 04/09/24 (4)
    The prototype pictures suggests something else.
    
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    Edits: 04/09/24 04/09/24
    - Can't really see the drivers from those pics - E-Stat 19:56:08 04/09/24 (3)
      Wendell calls it a dipole - maybe it isn't.
      Thinking more like something you observed here .
      
      Edits: 04/09/24
      - RE: Can't really see the drivers from those pics - josh358 09:42:28 04/10/24 (1)
        
        In Reply to: RE: Can't really see the drivers from those pics posted by E-Stat on April 09, 2024 at 19:56:08
        
        It's just two columns of four drivers each on a V-shaped baffle. They're all facing forward and they're staggered vertically so the magnets on the left and right interleave. The main consideration was getting a lot of sound out of a compact dipole woofer that's unobtrusive or can be hidden behind furniture.
        
        Shaped more like a home theater bipole -nt - E-Stat 10:33:15 04/10/24 (0)
        
        In Reply to: RE: Can't really see the drivers from those pics posted by josh358 on April 10, 2024 at 09:42:28
      - RE: Can't really see the drivers from those pics - emailtim 20:21:22 04/09/24 (0)
        
        In Reply to: RE: Can't really see the drivers from those pics posted by E-Stat on April 09, 2024 at 19:56:08
        
        Magnepan Ultia-Wideband Bass System appears to be the current naming convention.
        
        There are some better images of the bass array in the video.
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        Magnepan Ultia-Wideband Bass System (Open in New Window)
- RE: As for me - emailtim 15:34:16 04/09/24 (6)
  It averages out the non-linearity between forward and reverse cone movements.
  Here is a woofer stack that does that plus throws in force cancellation.
  X is using 8 x $12 GRS 6.5" drivers per side. XO' points are @ 470Hz and 4,700Hz.
  The SLOB (Slot Loaded Open Baffle) baffle has a quarter-wavelength HF cutoff of @ 470Hz for 6.5" drivers.
  "... Note the extremely low 2nd harmonic distortion below 60Hz. About -55dB at 50Hz (that's very low for open baffle 90dB). ..."
  
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  - XSD Speaker (Open in New Window)
  Edits: 04/09/24 04/09/24
  - RE: As for me - MarcL 06:36:36 04/10/24 (5)
    Do I recall correctly that you did a bunch of tests with 12" drivers from GR and tested with and without servo from the Rhythmik plate amp?
    
    What were the results? How low can you go with stacked 12" OB dipoles? Does it matter if you have two or three stacked? In the video they have four ... what is the benefit of four vs three.
    
    This array of 6 1/2" drivers is like what Wendell is using in the V shaped woofer thing, and it seems they would need a sub below 60-70Hz? But perform really well down to there.
    
    Agilist, Musician, Photographer, Audiophile
    Magneplanar: 3.7, CCR, MC1,LRS, MMGW, DWM; Outlaw: UltraX12, LFM-1C; Emotiva: XMC-2; Nord: Nord One NC500DM, Nord Three 1ET7040SA; Outlaw: Model 7500; OPPO 205
    - One other observation - emailtim 12:39:01 04/10/24 (0)
      Room modes are in 3D.
      Having a small box focuses where the room modes are excited or not.
      Having a longer boxes, crosses/averages room modes possibly evening out room loading. I attribute this to the delta between the Linkwitz W-Frame force cancellation and the H-Frame experiments.
      Then there is boundary gain. According to the videos, Wendell tends to put the woofers on the side walls.
      When I had a single triplet, it benefited from boundary gain from being against a side wall (but wasn't stereo because I only had 1).
      I tried laying it on its side in the middle of the room instead of the sidewall. I got similar boundary gains from the floor, but the single triplet was centered.
      Depending on your floor space, a long centered mono-sub may serve double duty with boundary gain and as an amp stand in addition to cluttering up the room. =)
      I should have tried on the floor against the wall to get both floor and wall boundary gains.
      
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      Edits: 04/10/24
    - RE: As for me - emailtim 10:26:58 04/10/24 (2)
      I tested with 1, 2 and 3 GR Research 12" drivers before going to 4 in 3 different baffles.
      The subs are air pumps. The more air displacement you have, the better. I noticed better performance as displacement increased. More air volume also extends to low volume listening.
      The GR Research subs have 18mm XMAS and VD of 882.5 cm^3 (FS 28). The Dayton Audio Reference subs have 14.3mm XMAS and VD of 742.6 cm^3 (FS 31.6). Davey likes the DA drivers for OB subs.
      I am in the process of trying a 4th baffle design which is a spin off of the XSD project in a narrower footprint. It is a hybrid of what I learned in the preceding OB/Dipole tests.
      The H-Frame provided the most even room loading, but doesn't have the force cancellation benefits. The new hybrid baffle "should" merge those two issues (knock on MDF).
      I tried the front/back and all front facing drivers in the H-Frame and didn't notice much difference. To do it right, you need to do it in pairs.
      From my REW measurements, I found a stronger amp was able to set the drivers faster than the servo plate amp. This also depends on the strength of the sub's motor. I would guess if the servo used the same amp, it would have the edge.
      The electronics in the plate amp also got into the way of what I was doing upstream with XO and DSP ( dueling banjos ). It was much easier to control everything in 1 place than trying to stack controls so I sold the plate amp. It is a great one size fits all Swiss Army Knife amp, but to do so, makes general purpose engineering decisions. It is great if you lack alternate control means.
      One of the design goals of servos was to control the impact the back wave cabinet reflections have on the driver in boxed subs. With OB, there is no cabinet back wave, so the primary problem that servo was designed to control does not exist in this application.
      With my DSP, I was able to get below 20Hz, (FS 28) F3 of 15Hz-17Hz in my room with 4 x 12". Pushing them to 500Hz in an H-Frame cabinet showed some minor distortions coming in that were resolved by changing the 13" square chase to a 13" cylindrical chase.
      I have not heard the MG woofer stack, nor seen any frequency response plots on it from the various online posts/reviews so can't tell how low it goes.
      X publishes his XSD plots so you can see how low it goes.
      
      Drivers with a lower FS should play lower in X's SLOB baffle.
      X selected budget drivers (FS 69, VD 42). There are more expensive drivers with both lower FS and larger VD (e.g. FS 28.3, VD 149).
      The slot loading design supposedly lowers the driver's FS at the cost of HF extension.
      X also uses passive XO's so it might go lower with DSP. There appears to be at least 2 ways to get his SLOB design to go lower.
      
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      Edits: 04/10/24 04/10/24 04/10/24 04/10/24 04/10/24 04/10/24
      - RE: As for me - MarcL 05:45:19 04/11/24 (1)
        
        In Reply to: RE: As for me posted by emailtim on April 10, 2024 at 10:26:58
        
        Thanks Tim!!
        
        In this and your other responses you touched on all the things I was thinking about ... number of drivers, servo vs higher power amps, and laying the box on the floor to extend that baffle size.
        
        I've been planning on two boxes, 3-high. I might run them stereo for the L/R fronts, and also separately mix in LFE in mono to both. I have the room to lay them down several feet from the front wall between my 3.7's.
        
        With amplifier power being relatively cheap - and since I already have a couple miniDSP's and can do filtering in there - I was thinking about going that route.
        
        I'm just waiting on my niece's husband getting some time to build cabinets for me :-)
        
        Agilist, Musician, Photographer, Audiophile
        Magneplanar: 3.7, CCR, MC1,LRS, MMGW, DWM; Outlaw: UltraX12, LFM-1C; Emotiva: XMC-2; Nord: Nord One NC500DM, Nord Three 1ET7040SA; Outlaw: Model 7500; OPPO 205
        
        RE: As for me - emailtim 10:52:43 04/11/24 (0)
        
        In Reply to: RE: As for me posted by MarcL on April 11, 2024 at 05:45:19
        
        Here is the hybrid I am working on. Enclosed twin Ripole SLOB. Protruding magnets will be capped vs trying to gasket fill around the magnets.
        It has force cancellation in 1 plane.
        It has a centered full length slot in front. The 2 back slots are slightly longer than half height in the hopes they have better room loading than horizontal short slots of the Linkwitz W-Frame.
        It will have opposing U shaped slots fore and aft. My Linkwitz W-Frame benefited from shaping the back of the slots so hopefully the U shaped slots the ID of the speaker will carry over here.
        It is narrower and shorter than the H-Frames coming in just under 12" wide.
        My hopes are that it will have the room loading of the H-Frames (long slots fore and aft) with force cancellation in a smaller footprint that serves double duty as a matching pedestal.
        
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        Edits: 04/11/24 04/11/24
    - RE: As for me - josh358 09:46:11 04/10/24 (0)
      The CSS system isn't as simple as people think! I don't understand why they don't file for the patent so it can be discussed. In any case, it's basically flat to 40 Hz and has some response below that, though it isn't a sub. Comparable to the woofers on a big planar.

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