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Reversing half the woofers cancels odd order distortion (not related to directivity)

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13th Duke of Wymbourne

In Reply to: RE: Dipole radiation posted by E-Stat on April 09, 2024 at 15:39:24

You now get the same asymmetry of cone movement in both directions.

Follow Ups:

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)
  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)
    Yes, it's tiny.
    - WAF: That's what she said. (nt) - emailtim 10:36:24 04/10/24 (0)
      nt
      .
      
      2022/03/30 Historical Records CENSORED
  - Apparently - E-Stat 05:23:44 04/10/24 (6)
    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)
      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.
        
        .
        
        2022/03/30 Historical Records CENSORED
        
        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 )
        .
        
        2022/03/30 Historical Records CENSORED
      - 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.

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