Subwoofer measurement question

Discussion in 'Home Theater Projects' started by Darren_T, Jun 29, 2004.

  1. Darren_T

    Darren_T Second Unit

    Joined:
    Oct 1, 2001
    Messages:
    494
    Likes Received:
    0
    Hi Guys,

    I've never been real particular about my sub and never measured it's response before, just calibrated it and called it good. Well I just completed a new AV15 Power Cube and took some measurements using the radio shack db meter C weighted and my Bass Mechanik CD test tones.

    The results were less than satisfying. Here they are... rounded to the nearest db. I didn't expect it to be flat but I didn't expect the HUGE variance. Any ideas? Just my room? I have a parametric EQ on my amp (PE 500w) but that will only take care of a part of this.

    Hz-db
    20, 85
    21, 87
    22, 91
    23, 94
    24, 96
    25, 97
    26, 99
    27, 99
    28, 99
    29, 99
    30, 101
    31, 103
    32, 105
    33, 107
    34, 108
    35, 108
    36, 108
    37, 108
    38, 108
    39, 107
    40-48, 106
    49, 105
    50, 104
    51, 100
    52, 102
    53, 101
    54, 99
    55-57, 98
    58, 99
    59, 100
    60-63, 101
     
  2. RodN

    RodN Stunt Coordinator

    Joined:
    May 9, 2004
    Messages:
    58
    Likes Received:
    0
    Did you make the relevant callibration adjustments to these figures? It can have huge effect on how the figures look.

    Other than that it looks like your sub has a 35Hz bass boost, or you have a room hump (usual) and a 55Hz dip (also fairly usual). Compared to some the variance is not that huge.

    Dunno what your amp can equalise but a Behringer BFD will remove them.
     
  3. Wayne Ernst

    Wayne Ernst Cinematographer

    Joined:
    Feb 24, 2002
    Messages:
    2,588
    Likes Received:
    0
    Darren,

    I've found the Bass Mekanik CDs to be less than desireable when testing out a new sub. I actually have a couple of those CDs sitting on my shelves collecting dust.

    However, here's a link to some sine waves that lots of us have used. You might consider grabbing these tones and re-running some of the tests.

    Sine Waves

    Also, as Rob suggested, some of the issues being detected could be room related.
     
  4. Darren_T

    Darren_T Second Unit

    Joined:
    Oct 1, 2001
    Messages:
    494
    Likes Received:
    0
    Thanks for the info guys. I was wondering if the Bass Mekanik CD was part of the problem. I do realize the room would create some of this. I was mostly concerned with the huge dip below 25hz.



    I adjusted the EQ (only has one filter that can be set)and added full boost at 20hz and tapered it off a bit and did improve the 20hz - 30hz numbers bringing them up a bit. I have thought about using a BFD but have never used one... while I've built several subs I have never tried to flatten the response.

    I'll download the Sine Waves and give it another run and see if I can improve the numbers. They aren't nearly as bad now that I've set the EQ but I'd still like to flatten the response a bit more if possible.

    Thanks.
     
  5. Lee Carbray

    Lee Carbray Second Unit

    Joined:
    Oct 23, 2002
    Messages:
    308
    Likes Received:
    0
    I wish I had a response like that.

    Like Rod said add in the corrections and the low end will not be as low as you think. Use the exel tool from the Snapbug site here. It will add the corrections for you. What do you have it coressed over at? Unless you are at 40Hz you should measure the responce up to at least 100Hz or more.
     
  6. Darren_T

    Darren_T Second Unit

    Joined:
    Oct 1, 2001
    Messages:
    494
    Likes Received:
    0


    Well, I tend to over-do stuff [​IMG] Now that I adjusted the EQ the 20 - 25hz range is up in the 95 - 98 db range. Much better than before. I'll re-measure tonight with the new tones and probably call it good.

    I'm hoping with the better test tones it will measure even better but I suppose it could measure worse depending on how accurate or inaccurate my first test was.

    I'll post my results tonight when I get home from work.
     
  7. ThomasW

    ThomasW Cinematographer

    Joined:
    Nov 6, 1999
    Messages:
    2,282
    Likes Received:
    0
    With the sub's tuning you should have even more output in the low 20's, this is a function of room gain. Check room placement, move the sub if possible
     
  8. Darren_T

    Darren_T Second Unit

    Joined:
    Oct 1, 2001
    Messages:
    494
    Likes Received:
    0


    Unfortunately it is our family room and the sub is in it's final resting place.... can't move it anywhere so I have to live with the current placement. [​IMG]
     
  9. Darren_T

    Darren_T Second Unit

    Joined:
    Oct 1, 2001
    Messages:
    494
    Likes Received:
    0
    Ok, I messed around with the single filter EQ on my plate amp and after trying several filters in different places I ended up boosting the 20hz with a rather narrow span. Here are the results corrected. Can't be compared to the previous numbers as I used less gain for this test:

    16 - 62
    18 - 82
    20 - 82
    22 - 86
    25 - 91
    28 - 92
    31.5 - 94
    36 - 98
    40 - 96
    45 - 97
    50 - 93
    56 - 90
    63 - 90
    71 - 86
    80 - 90.5
    89 - 88.5
    100 - 88.5
    111 - 84
    125 - 77
    142.5 - 69.5
    160 - 74

    Not too bad for minimal EQ. I'm pretty happy with the results. I tried flattening the hump that starts around 36Hz instead of boosting 20Hz but I wasn't happy with the results, seemed lifeless and was still lacking below 25Hz. Boosting 20Hz seemed to be the most pleasing to me.
     
  10. John E Janowitz

    John E Janowitz Second Unit

    Joined:
    Oct 30, 2000
    Messages:
    445
    Likes Received:
    0
    Darren,

    what are your room dimensions? You can find your 3 primary room modes easily by taking 565 divided by the dimensions. So say your room is 20ft x 15ft x 8ft ceiling.

    565/20 = 28.25hz
    565/15 = 37.67Hz
    565/8 = 70.625hz

    Those would be your primary axial room modes. You also have tangential(-3dB) and oblique(-6dB) room modes. If you want to find all the room modes in your system, this is a good javascript room mode calculator:

    http://www.mcsquared.com/modecalc.htm

    It gets to be a pain to take into account all room modes. Ideally when you design the size of a room it's best to try to dimension so that you have an even modal distribution.

    John
     
  11. Darren_T

    Darren_T Second Unit

    Joined:
    Oct 1, 2001
    Messages:
    494
    Likes Received:
    0
    Tough to say the dimensions as the room opens up to the rest of the house... basically 2/3 of one wall is wide open. How should I account for that?

    The room itself is 16' X 20' with a vaulted ceiling from 8' to 12' in the center. This is the first time I've tried to really get my subwoofer setup "right". I've had several different setups but thought it was time to have a little "fun" and see about calibraiting further.
     

Share This Page