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RE: Magnepan LRS with two 1x12 OB subs and dspNexus 2/8 DSP control center

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In Reply to: RE: Magnepan LRS with two 1x12 OB subs and dspNexus 2/8 DSP control center posted by HAL2010 on November 17, 2024 at 18:00:35

A couple questions ... how are the GR drivers used without the servo? Are there better choices for a non-servo 12" in an H-frame? I built a 3X recently and tested response with the servo amp and three settings, vs a non-servo amp and I could see a definite difference in the impulse response (I used a miniDSP to get close to the shelf filter). But I didn't do listening tests.

Also ... folks tend to put Norez on the inner surfaces of the H-frame. I couldn't convince myself that the mass of Norez would make a difference relative to a 100lb MDF cabinet. I didn't see any anomalies in an outdoor ground plane measurement ... dead flat ... so can there be audible resonances in an MDF H-frame cabinet?

Thanks!
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

Follow Ups:

RE: Magnepan LRS with two 1x12 OB subs and dspNexus 2/8 DSP control center - HAL2010 11:25:25 11/18/24 (6)
I use the GR-Research drivers with custom EQ on the dspNexus and do not use the sense coils for the demo using original Orchard Audio Starkrimson monoblocks to drive the 1x12's. Since I only use the modular subs they are about 40lb each with the driver. Easier to move than the full 2x12 and higher driver arrays.

The servo amp does two basic things, first is use as a current output amp and second as a servo loop control with the sense coil. There is also a DC servo loop for the current amp. The sense coil needs correction to run the servo loop. I am using EQ to correct the driver in cabinet frequency response with a standard amp, no motional feedback.

There are other drivers for OB that would work in the OB H-Frame. One I have been told about is the Acoustic Elegance OB-12. They are about $600/driver so 2x the SW-12-16FR sub drivers. There are others that would fit the existing cabinet without modifications. They all require EQ to flatten the response for use.

I do not use NoRez in the OB H-Frame modular cabinets I have built from flat packs, so no way to compare before and after.

Any cabinet has resonances under acoustic drive. Instead of a frequency response, a waterfall stored energy plot would be better to see if there is any change in resonances. Should be able to do that with a groundplane measurement and possibly REW. MDF is usually chosen as well damped cabinet material. Subs are high SPL output, so more excitation to show if there is a problem area.
Better Living Through Audio Nirvana
- RE: Magnepan LRS with two 1x12 OB subs and dspNexus 2/8 DSP control center - MarcL 13:59:48 11/18/24 (5)
  Thanks!
  
  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
  - Thanks too. - 13th Duke of Wymbourne 10:57:30 11/19/24 (4)
    I have been thinking about making OB 'subs' and equalizing using a miniDSP but what drivers to use? Perhaps the GR drivers are a good choice as they are proven in the application but I already have suitable amps and I can apply the equalization in DSP so I am less interested in the complete GR system. Linkwitz applied equalization to make the total Q of the drivers in the frame to be 0.5, which implies you could use drivers with a range of Qs.
    I suspect the Rythmik amps use the high GR driver Q to push down extension at the cost of transient performance.
    
    Edits: 11/19/24
    - RE: Thanks too. - MarcL 04:39:05 11/20/24 (0)
      Ask ChatGPT:
      
      What factors influence woofer speaker driver design with respect to compliance of the surround material and the choice of cone material, and what is the optimal choice for open baffle dipole woofers?
      
      :-)
      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: Thanks too. - MarcL 04:32:49 11/20/24 (2)
      Fair to say the filtering required for dipole compensation can be done several ways. And it's good to be able to select amplifiers based on their design, power, etc.
      
      But one factor in answering the question of drivers is whether the GR drivers are designed in such a way that they perform best with the servo amp, and can't achieve optimal performance without it. Would a non-servo driver be designed quite differently with regard to material, compliance, damping, excursion? If so, could it perform better overall than the GR servo drivers? Or ... what are the tradeoffs?
      
      Maybe HAL2010 can comment on that.
      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: Thanks too. - 13th Duke of Wymbourne 17:43:33 11/23/24 (1)
        
        In Reply to: RE: Thanks too. posted by MarcL on November 20, 2024 at 04:32:49
        
        I am not really a speaker guy but that won't stop me from musing...
        Assuming you can get the same frequency response from the closed-loop system as applying equalization to the open-loop system the next thing has to be excursion and distortion. For the same acoustic output and the same cone area the excursions must be the same/very similar. A closed-loop system should have an advantage in overcoming deficiencies in the driver but I don't know how well this one works to reduce distortion. It is monitoring velocity, not displacement and the point of maximum excursion where the cone changes direction produces little/no velocity feedback. So I don't know if it is effective. Someone wiser than me pointed out on this forum years ago that the Rythmik feedback system was developed for sealed subs to overcome the air loading inside the box, which is not a problem for open baffles.
        
        Maybe, then, if you can get the frequency response you want and the excursion you want the rest doesn't matter?
        
        RE: Thanks too. - MarcL 09:16:38 11/24/24 (0)
        
        In Reply to: RE: Thanks too. posted by 13th Duke of Wymbourne on November 23, 2024 at 17:43:33
        
        Good points! I think the most benefit is gained by the open baffle dipole design, and the number of drivers which requires less excursion to move a given amount of air.
        
        Hard to do apples:apples with and without servo because you can't use the same amp and shelf filters. Frequency response is the same. In my tests I saw less distortion with the servo ... albeit under 2% down to 20Hz.
        
        But wow do they sound good!
        
        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

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