Vifa PL and MG series (what's the difference)

Discussion in 'Home Theater Projects' started by David Giesbrecht, Oct 19, 2003.

  1. David Giesbrecht

    David Giesbrecht Second Unit

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    I've been wondering what the diffences are between the PL and MG series drivers? Is it simply a question of quality or are the two better suited for different applications.
    Has any body used the MG series drivers in any projects?
     
  2. David Giesbrecht

    David Giesbrecht Second Unit

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    I've been fooling around with Lsp Cad and was wondering if you thought I was on the right track for a 2 way XO using the 7" MG Midbass and a Focal TC120TD5

    _(0.9mh)______________________

    >>>>>>>>>>>(1.0 ohm) Woofer Woofer
    >>>>>>>>>>>(30uf)
    ______________________________

    _(7.5uf)________________

    >>>>>>>>>>>(0.9mh) tweeter

    ________________________

    I tried my best
     
  3. ThomasW

    ThomasW Cinematographer

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    Might consider giving the tweeter a little more protection and using a zobel.

    Here's a TC120 schematic in a 2-way with the Hi-Vi M8a.

    XO schematic
     
  4. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    I don't quite understand the electrical XO you posted, could you post more info on it instead of just the components. I know the woofers are low sensitivity compared to that 93.5db tweeter, do you plan on like an MTM design?

    My guess is MG is a step above PL. I have a 7" PL driver, but never tried an MG so I can't really say if they sound different.

    I've found that's it's pretty hard to get advice on custom crossovers over the net. Even if it looks good on paper, it could end up sounding bad which is why people resort to measuring and testing.

    What XO point you trying to achieve? And what type of slope? etc..
     
  5. David Giesbrecht

    David Giesbrecht Second Unit

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    I was hoping to keep the component count to a minimum if possible. I was modeling the crossover after Wayne J's Eros design it seemed to provide good performance with few components. The XO diagram I posted of course is pretty hard to read I'm not quite sure how to post the graphs and circut diagram from LSP CAD to here. But it's really quite simple. It's a second order filer @ about 1750 hz (same as the Eros) The solid lines represent the wires, and the values in brackets that are in between the wires are supposed to be parallel I understand that it's difficult to read.

     
  6. ThomasW

    ThomasW Cinematographer

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    Wayne J's Eros uses at SS textile dome tweeter and that's a completely different animal from a Focal titanium dome.

    As a result you'll more than likely blow up the Focal TC120's using a second order XO at 1750Hz.

    XO design must be tailored to how the speakers themselves perform in the real world, not someone's fantasy about how they wish they could perform.

    If you're using the mfgr's specs to create the XO design then you're asking for trouble. The proper method for XO design is to use data YOU measured from testing the speakers in the baffle you're planning on using. Anything else is just a crap shoot and a recipe for disaster.

     
  7. David Giesbrecht

    David Giesbrecht Second Unit

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  8. Brian Bunge

    Brian Bunge Producer

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    I'll answer your question with another question. What makes a Volvo different from a BMW?
     
  9. ThomasW

    ThomasW Cinematographer

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  10. David Giesbrecht

    David Giesbrecht Second Unit

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  11. ThomasW

    ThomasW Cinematographer

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    There is a fundamental problem with your approach. That is you think up a design then ask for feedback. When the feedback is "don't do that because........", you reply with "I don't care, it's just for experimental purposes".

    Well if you aren't going to listen to the feedback, why bother wasting the bandwidth in the first place?

    Build whatever fantasy project you can dream up and live with the consequences.

    FWIW, you will end up spending a ton of extra and unnecessary money (something you say you don't have) with your approach to speaker building.

    BTW most 'experimenters' use $.99 tweeters from the closeout bins, not high-end titanium oxide domes costing $60+ a pop

    Good luck,
    Thomas
     
  12. David Giesbrecht

    David Giesbrecht Second Unit

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  13. ThomasW

    ThomasW Cinematographer

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  14. David Giesbrecht

    David Giesbrecht Second Unit

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    These are the specs from PE

    Scan speak 9500

    FS 550 hz
    Xmax +/- 0.4mm

    Focal TC120TD5

    FS 812 hz
    Xmax +/- 0.5mm

    The Fs on the focal is a little higher than the Scan Speak but still over 1 octave lower than an XO @ 1750 hz. I'm not sure if those xmax's are correct because the specs were a little confusing.

     
  15. Brian Bunge

    Brian Bunge Producer

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    David,

    As Thomas said, my answer was not meant to be rude, sarcastic or ignorant (or did you mean arrogant?). As Thomas said, it's a valid comparison. Two different drivers from two different manufacturers can sound very different and exhibit very different frequency response curves. Therefore, they will likely need much different crossover components, slopes, etc.

    It's like comparing the 0-60 times of two sports cars. That tells you nothing about how either of them handles, how the ride is, etc.
     
  16. David Giesbrecht

    David Giesbrecht Second Unit

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    I did notice that the Scan Speak starts to roll off under 2khz where as the Focal continues to be flat to 1khz. Is that why the Focal requires more attenuation? If I used a fourth order network @ 1750 hz would that provide enough attenuation?
     
  17. ThomasW

    ThomasW Cinematographer

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    David

    You do need to understand something. The name of the game here is DIY (Do It Yourself). And the essence of that game is we don't spoon feed you the answer to every question you can think up.

    I've already designed, built, and posted to this thread a fully optimized XO for a TC120. If you understand XO design you'll see that it is in essence a 4th order L/R topology with an additional Cauer/elliptical circuit that allows the TC120 to safely run down to 1500Hz.

    But you say you want to learn via experimentation, and not use anyone elses design. So I guess it's time for you to bring a halt to the questions, and begin the experimentation.

    Have fun....
     
  18. Dean-P

    Dean-P Stunt Coordinator

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    ThomasW:
    I'm confused,you say that your tweeter x-over contains 12 parts and the woofer x-over contains 9 parts, I count 15 & 13. Can you explain why I count thes higher numbers?

    BTW I want to build those sealed M8as, I've been following your other threads in HT Guide and in the AudioExpress and it looks like the sealed are better for me. Also I missed Sept issue, did I miss much as it looks pretty complete in Oct issue?
    One more thing, does each speaker (tweeter/woofer)connect to a single binding post together and then go from there?
     
  19. ThomasW

    ThomasW Cinematographer

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    Dean

    The text on the schematic page states that all resistor values less than 1.0 ohms are to be ignored, because those values are inherent in other components in the XO.

    Are you building the MKIII or MKIV version? The difference is the tweeter. And that my version of the MKIII (Focal TC120) detailed on the website has the XO baffle step compensation optimized for on-wall speaker mounting.

    If you're building the MKIV (Vifa XT25 tweeter) then having all three issues (Sept, Oct, and especially Nov) would be helpful.

    The woofer and tweeter share the same input
     

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