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Thread: quest for sub equalization...

  1. #1
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    Default quest for sub equalization...

    OK....so this evening I got TrueRTA working...purchased the level 4 version to take measurements at 1/24th octave slices. After watching a movie, I decide to to set it up and take a measurement.....so here is the graph.


    If you can't read it, it starts at 60dB and 10Hz. It has been a very windy night, so I am not sure how that effected the measurement.

    As you can see, it looks like I have a nasty dip at about 38Hz, and another at just about double that frequency.....how am I going to deal with those??

    I will mess around with it some more tomorrow afternoon.
    -curtis

  2. #2
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    Default

    ".how am I going to deal with those?? "


    Call Dr. Hsu. He'll have the correct answer as I'll have just AN answer.

    David

  3. #3
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    Curtis,

    I'm guessing those are room modes. Have you put your room dimensions into a mode calculator to see if it comes up with those frequencies?

    Do you have a graph that shows the response higher up (maybe to 160Hz)?

    Have you done the sweep with the phase reversed?

    Talking to Dr. Hsu is a good idea. With room modes, your options are generally changing seating position (often not an option), room treatments or EQ. Since this is a severe dip, EQ might not be a good idea.

  4. #4
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    Default

    Yeah, it looks like you're about 15dB down at 38Hz. If you have a proper WAF battleplan, I would try 2 or 3 different room positions with measurements after each. You're battling the room's black hole it appears.

    You might want to try messing with phase to see if you can better integrate the sub with your mains seeing that 75Hz kerplunker. It looks like you have another one at 90Hz too (which I have too). Does the VTF3 have a 0/180 toggle or infinitely variable dial?

    Show us a graph out to 120Hz if you can. That will show how smooth the sub blends with your mains, very important for smooth transitions.

    Working around that 15dB canyon at 38Hz is gonna be tough though.

  5. #5
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    Thanks guys!

    I have no WAF issues, but unfortunately, I only have two places where I can put the sub.

    The sub only has a phase switch.

    I will do more graphs and try the other sub position when I have more time this weekend.

    edit: I just looked around the room. With some small changes, I can possibly come up with two more locations.
    -curtis

  6. #6
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    OK.....did some more graphs:

    These were done with the test CD that came with my VTF-3, a 200Hz to 10Hz sweep. Sub in 0 degree phase is in green, 180 degree in yellow. This is in the front left corner of my room. The sub is in maximum extension tune.

    I still have that canyon at about 38hz....pretty happy with the response below 20hz, but I would trade that to get rid of the canyon.

    The next graphs will be in a different location.
    -curtis

  7. #7
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    Second location:

    orange - 0 degree phase
    turquoise - 180 degree phase
    -curtis

  8. #8
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    Third location:

    green - 0 degree phase
    purple - 180 degree phase

    Locations 2 and 3 are just about 7" apart....one being closer to the wall than the other.
    -curtis

  9. #9
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    Curtis,
    Are these reading all near a corner? I had to move mine away from the corner to get a linear reading.

    David

  10. #10
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    Well, at least you know which phase is best for integrating with your mains at the first position (0).

    David, getting out of a corner does not mean you will get flatter response. Moving my sub one or two feet into the room along the wall got me a worse response curve. I could try a completely different position in the room, but I haven't taken the time yet.

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