Here's my room response BFD?

Discussion in 'Speakers' started by John Garcia, Nov 19, 2005.

  1. John Garcia

    John Garcia Executive Producer

    Joined:
    Jun 24, 1999
    Messages:
    11,571
    Likes Received:
    24
    Location:
    NorCal
    Real Name:
    John
    For my PB-10 ISD.

    Hz - dB @ frequency
    160 - 74.5
    142.5Hz - 77.5
    125 - 78.5
    111 - 79
    100 - 64
    89 - 82.5
    80 - 88.5
    71 - 76.5
    63 - 80.5
    56 - 72.5
    50 - 76.5
    45 - 82
    40 - 85.5
    36 - 83.5
    31.5 - 84.5
    28 - 82
    25 - 82
    22 - 81
    20 - 83
    18 - 82
    16 - 75

    (correction factors included) As you can see, the response is all over the place at the top. BIG dip at 100Hz followed by a big peak at 80Hz. Relatively flat at the bottom though.

    So, with that big dip, will a BFD help me at all?
     
  2. Ryan Schnacke

    Ryan Schnacke Supporting Actor

    Joined:
    Feb 5, 2001
    Messages:
    876
    Likes Received:
    0
    EQ often cannot help the really big dips as they tend to be caused by room nulls. Pumping more power in doesn't fix the problem, just wastes headroom.

    If we assume that your XO is at 80Hz and all speakers set to small then you're not really doing too bad. Your speakers can pick up a lot of the response at 100Hz. And even at 80Hz, your speakers and the sub split the signal evenly. So the peak at 80Hz may not be as bad as you think.

    I'd try measuring again, but this time run the tones through your speakers and sub so you can see what the final result looks like. If that's still not good enough then play with room placement. You really should find the best placement for your sub before resorting to EQ to fix it. Finally, use EQ to flatten out any peaks and to add a house curve if you so desire.
     
  3. Wayne A. Pflughaupt

    Joined:
    Aug 5, 1999
    Messages:
    6,061
    Likes Received:
    25
    Location:
    Katy, TX
    Real Name:
    Wayne
    Everyone says dips are a lost cause, but I’ve seen people make them disappear, time after time. Here’s one example, from Sonnie Parker’s installation:


    [​IMG]


    The thing to avoid is boosting nulls. However not all low spots are nulls. In fact, most of them are not. It’s easy tell a null – it won’t respond to boosting at all, so you don’t boost them ‘cause it does waste headroom.

    Other low points are caused by phase issues between the subs and mains and other factors, like the driver’s natural response. These typically respond to equalization and such should be equalized.

    However... ...you won’t know for sure if it’s a true null until you try to equalize it.

    Regards,
    Wayne A. Pflughaupt
     
  4. John Garcia

    John Garcia Executive Producer

    Joined:
    Jun 24, 1999
    Messages:
    11,571
    Likes Received:
    24
    Location:
    NorCal
    Real Name:
    John
    Yes, the x-over is at 80Hz. I will recheck with the mains on and see if 100Hz improves. The first time I ran the tones, I had the mains on and I noticed that higher up, there was more output up top, so you may be right Ryan. The bad part is I really don't have any options for locating my sub, the front corner is pretty much it; about all I can do is turn the sub 180 or 90 degrees. I may try playing with the sub's phase to see what happens too. Thanks guys.

    I'm fairly certain the 100Hz dip is a null because I could hear the same thing with my previous sub, a VTF-2.
     
  5. Brian L

    Brian L Cinematographer

    Joined:
    Jul 8, 1998
    Messages:
    2,902
    Likes Received:
    8
    John,

    Have you tried the RoomEQ Wizard software??? I can't say enough about it. It makes small work of dialing in a BFD, and already has the RS factors built in.

    Here's a link:

    http://homepage.ntlworld.com/john.mu...meq/index.html

    You may also consider taking finer readings. I last ran measurements at 1 hertz increments, which revealed issues that even 1/6 octave can hide.

    Brian
     
  6. Ryan Schnacke

    Ryan Schnacke Supporting Actor

    Joined:
    Feb 5, 2001
    Messages:
    876
    Likes Received:
    0
    I certainly understand that placement is not always an issue that is very flexible. Just wanted to make sure you had evaluated your options.

    Phase is a good thing to check, too - good call. You can calibrate phase by playing an 80Hz tone through your mains, measuring SPL. Then play it through your sub and adjust the level until it is the same as for the mains. Then play the 80Hz tone through mains AND sub and adjust phase until you get the highest SPL reading - should be 6dB higher than either sub or mains by themselves.
     
  7. John Garcia

    John Garcia Executive Producer

    Joined:
    Jun 24, 1999
    Messages:
    11,571
    Likes Received:
    24
    Location:
    NorCal
    Real Name:
    John
    Thanks Ryan! I'll try that out.
     
  8. al lout

    al lout Stunt Coordinator

    Joined:
    May 6, 2004
    Messages:
    164
    Likes Received:
    0
    John,

    I was eqing my sub earlier. Since I have the software open, might as well help you plotted the graph.

    Here is your sub measurements (before eq)
    [​IMG]

    I was playing around with a few filters.
    [​IMG]

    There is a big valley at 100hz, maybe playing around with the crossover and phase might help since different placement is not an option. I would also double check on the RS meter. Mine did went wack (sound seemed to be louder than what the meter said) today doing lots of measurements. I turned it off and switch it back on and it works perfectly again. Anyway, hope this helps.

    Al,
     
  9. al lout

    al lout Stunt Coordinator

    Joined:
    May 6, 2004
    Messages:
    164
    Likes Received:
    0
    In addition, a boost of +14db @100hz is probably not a good idea. I'm just playing around with the numbers to try to flatten out ur sub's curve. I do recommend download the software and try it out. Real cool software and it's pretty acurate, the best part is it's FREE.

    Al,
     
  10. John Garcia

    John Garcia Executive Producer

    Joined:
    Jun 24, 1999
    Messages:
    11,571
    Likes Received:
    24
    Location:
    NorCal
    Real Name:
    John
    Thanks Brian and Al, I'll check it out. No BFD yet, because I may be buying a new sub...[​IMG] (will probably still need the BFD though....).
     
  11. Brian L

    Brian L Cinematographer

    Joined:
    Jul 8, 1998
    Messages:
    2,902
    Likes Received:
    8
    One thing I would mention which RoomEQ Wizard software made clear, is that using test tones at the exact frequency of the crossover may not always produce the best results.

    Not sure if you recall, John, but I posted a couple screen captures over at Audioholics that illustrate that you really need to look at the region adjacent to the crossover, rather than just a fixed frequency.

    A series of tests I did in my 2CH rig showed that, while I had greater output at the crossover with my sub phase inverted, there were two very pronouced valleys that occurred. Swapping the phase to zero resulted in slightly less output at the crossover frequency, but the valleys went away resulting in smoother output throughout the region.

    Without RoomEQ software, or an equivalent, I would not have been able to see that.

    I can't seem to figure out how to post pics here, but here is a link to the Audioholics thread where I posted them.

    http://forums.audioholics.com/forums...ad.php?t=14683

    Brian
     
  12. mackie

    mackie Supporting Actor

    Joined:
    Feb 7, 2004
    Messages:
    568
    Likes Received:
    0
    John - I'd be curious to hear your thoughts and impressions of the differences between the SVS and HSU subs.
     
  13. John Garcia

    John Garcia Executive Producer

    Joined:
    Jun 24, 1999
    Messages:
    11,571
    Likes Received:
    24
    Location:
    NorCal
    Real Name:
    John
  14. mackie

    mackie Supporting Actor

    Joined:
    Feb 7, 2004
    Messages:
    568
    Likes Received:
    0
    Thanks John - that was a good read. Miss those types of discussions around here...
     

Share This Page