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RE: MY Open Baffle Dipole Sub Results

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In Reply to: RE: MY Open Baffle Dipole Sub Results posted by MarcL on October 14, 2024 at 06:28:06

Congrats on extending the dipolar range!

As one who is OCD about some things, however, I find the choice of three drivers odd. You've got more blowing than sucking. ;)

Why not two or four?

Follow Ups:

RE: MY Open Baffle Dipole Sub Results - MarcL 14:22:05 11/03/24 (10)
Well there are a couple reasons for doing three. But ... there is no blowing and sucking. The three drivers are playing in phase. The middle one is physically reversed and the wiring is reversed, so it plays in phase with the other two. All three push and pull together.

Having three drivers results in more surface area so more amplitude for the same excursion. This helps with using the extension filter to play down into the teens.

The reasons for having the center driver reversed ... well that's how the plans were and I didn't feel like altering the plan. But it has been measured that reversing the center driver lowers overall distortion (per Linkwitz and others). It also physically balances the cabinet since the whole thing weighs about 180lbs.

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: MY Open Baffle Dipole Sub Results - josh358 12:08:01 11/10/24 (2)
  Not only does it lower distortion, it partially balances the forces on the baffles. Of course, two or four would be ideal in that regard, but I gather from what people have said that three is the sweet point (and Tim pointed out that four is impossible). This would be not just because of the increased driver area, but because the baffle is larger. (Wonder if anyone has tried putting them side-by-side on the floor for more floor reinforcement.)
  - RE: MY Open Baffle Dipole Sub Results - emailtim 19:35:59 11/11/24 (0)
    4 and 6 per side are possible with a different amp or 2 servo amps per side.
    
    I think there "was" a Hypex-based servo amp that could do 4.
    
    .
    
    2022/03/30 Historical Records CENSORED
  - RE: MY Open Baffle Dipole Sub Results - MarcL 12:19:59 11/10/24 (0)
    I actually did a ground plane measurement out in my back yard with the mic 6ft away. Laying the sub down on the ground resulted in about 2db gain, vs standing up at the same distance. This is with 14Hz extension filter, high damping and 10Hz rumble filter.
    
    I didn't repeat the test with two of them in my room, because I found I can definitely locate the source down to 30Hz and decided to keep them standing next to the 3.7 playing stereo for the 3.7 left/right speakers and of course bass management and LFE is mono to both subs. I also found that mixing a little of each sub to the other (I'm running them through a little mixer to combine LFE) reduced the time component of room resonance at 40Hz.
    
    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
- ??? - E-Stat 15:19:00 11/03/24 (6)
  But ... there is no blowing and sucking. The three drivers are playing in phase.
  
  Two one way, the other different.
  - RE: ??? - MarcL 16:14:18 11/03/24 (5)
    The middle speaker is wired with polarity reversed, so they all play in phase.
    
    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
    - Just - E-Stat 16:17:32 11/03/24 (4)
      The middle speaker is wired with polarity reversed, so they all play in phase.
      
      twice as much frontal radiation than rear.
      - RE: Just - MarcL 06:52:20 11/04/24 (3)
        
        In Reply to: RE: Just posted by E-Stat on November 03, 2024 at 16:17:32
        
        Speakers all radiate from both sides. With an open baffle dipole design the front and rear waves radiate into the room equally but with opposite polarity. The speakers are wired so they play in phase, even though the center one is physically reversed. All three speakers push a positive wave forward and a negative wave to the rear. It's like a figure 8 radiating pattern due to the dipole cancelation at the sides, top and bottom which reduces the response in those directions by around 25db.
        Quote from a forum post "Linkwitz and others proposed that due to the non-symmetrical construction of the woofer, cone, surround etc. they radiate distortion (non-linear properties) at different amplitudes front and rear. If both drivers are in the same orientation these sounds are reinforced. When one of the drivers is reversed, these artifacts are effectively cancelled."
        
        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
        
        Edits: 11/04/24
        
        Exactly! - E-Stat 07:18:49 11/04/24 (2)
        
        In Reply to: RE: Just posted by MarcL on November 04, 2024 at 06:52:20
        
        If both drivers are in the same orientation these sounds are reinforced. When one of the drivers is reversed, these artifacts are effectively cancelled."
        
        Siggy's speakers with dipolar woofers (LXstudio, Orion, LX521) use a pair of identical drivers.
        
        RE: Exactly! - Beardy 21:24:20 11/04/24 (1)
        
        In Reply to: RE: Exactly! posted by E-Stat on November 04, 2024 at 07:18:49
        
        With two drivers you turn one forwards and the other backwards and the one facing backwards is wired out of phase (-+ instead of +-). So both drivers move in the same direction at the same time (in phase). The reason is because if the driver motion is non symmetric (it moves differently forwards than backwards), then having one driver face forwards and the other backwards cancels out this source of distortion.
        
        Three is an odd choice. Driven by the needs of more surface area versus the inconvenience of four?
        
        RE: Exactly! - emailtim 23:01:58 11/04/24 (0)
        
        In Reply to: RE: Exactly! posted by Beardy on November 04, 2024 at 21:24:20
        
        The choice of 3 - 14 Ohm drivers is because of the combined load (4.6 Ohms) on the servo plate amp.
        The servo plate amp could not drive 4 - 14 Ohm drivers. Aggregate impedance (3.5 Ohms) would be too low.
        SW-12-16 parameters:
        FS 28.3Hz
        BL 14.07
        Mms 108g
        VAS 100L
        Qms 2.8
        Qts 0.85
        Sd 490cm^2
        Re 14 Ohm
        X-Max 16 mm
        Ideally, you would want even numbers of drivers to cancel out non-lineararities of the forwards and backwards cone movements.
        .
        
        2022/03/30 Historical Records CENSORED
        https://gr-research.com/product/sw-12-16fr-servo-sub-woofer/ (Open in New Window)
        
        Edits: 11/04/24

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