Tumult EQ....

Discussion in 'Home Theater Projects' started by Jeffrey Stanton, Nov 13, 2003.

  1. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Howdy folks:

    Could someone suggest a few BFD filters to apply to these measurements I took (uncorrected) for my sub (see below)? I notice there's a couple of nasty peaks centered around 48 and 80 Hz. Looks to me like they're about 15 dB above the rest of the curve...

    During testing my KSW-15 sub was running also (off of the center channel) along with the above LFE sub, so I'm sure it is probably contributing somewhat to those peaks. Which begs the question: Shouldn't I be EQing both subs individually to "FLAT" rather than EQing my LFE sub with my other center channel sub on and running also?

    I have a BFD and a Behringer DSP-8024 Ultra Curve Pro I can use.

    Here's the measurements I took, I started at 10 Hz (set at 75 dB):

    10 Hz--75 db
    12.5 Hz--77 db
    15 Hz--77 db
    17 Hz--78 db
    20 Hz--79 db
    22 Hz--79 db
    25 Hz--78 db
    28 Hz--78 db
    32 Hz--79 db
    36 Hz--80 db
    40 Hz--95 db
    45 Hz--95 db
    50 Hz--95 db
    56 Hz--87 db
    63 Hz--77 db
    71 Hz--91 db
    80 Hz--95 db
    89 Hz--95 db
    100 Hz--87 db
    112 Hz--80 db
    126 Hz--84 db
    142 Hz--85 db
    160 Hz--68 db
    201 Hz--68



    Thanks,

    Jeffrey Stanton[​IMG]
     
  2. Wayne A. Pflughaupt

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    Jeffry,

    It’s not going to be possible to get optimal performance with two non-matching subs, especially if they are in two different locations. You should know this going in. If they are in different locations they will need to be equalized separately. And even after getting an optimal curve for each, expect overall response to change when they are both run together.

    You will need to take new readings with only the sub we’re going to equalize running. The readings posted earlier reflect the contributions of both subs, including their respective phase issues. Obviously you can’t equalize away a peak if it’s being caused by the other sub - know what I mean? [​IMG]

    Regards,
    Wayne A. Pflughaupt
     
  3. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    I know exactly what you mean. It occurred to me as I was posting that if I tried to EQ the Tumult (LFE) sub while the center sub is simultaneously running, several situations could occur: e.g., IF the Tumult sub was already completely flat going in, I could very well be compensating for peaks caused solely by the KSW-15 but with the EQ being applied to the Tumult (instead of on the KSW-15, where it belongs). I guess theoretically you could do this but why bother?? It makes more sense to do them separately.

    It makes more sense to me to get them as flat as possible individually, and then turn them both on and see how flat I am after that. If they are both flat (as possible) individually, then if I'm getting some peaks with them on together, those would probably be phasing issues, right?

    I suppose at that point I could "de-tune" the KSW-15 to decrease any sub interaction peaks between the LFE and center sub.

    One thing: The phasing switch on my KSW-15 is broken, it's stuck on one side but appears to be stuck on the proper phase (did a phase test on it awhile back with some sort of test disk). The Tumult sub has no phase adjustment, so I guess phase adjustment for this sub will be left to switching the polarity on the speaker leads (if need be).

    I'll get some measurements done over the weekend and get back to you Monday.

    Thanks!

    Jeff S.
     
  4. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    PS I also ran the Axial Standing Wave Calculator on my room and it comes up with peaks at 47 and 71 Hz (as well as 28 Hz).

    48 Hz is exactly where one of the peaks is centered in my measurements, and 71 Hz is where the second peak starts. I guess that thing works...
     
  5. Anthony_I

    Anthony_I Stunt Coordinator

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    if it is phasing issues you cant correct it by reversing the polarity (i dont think)
     
  6. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Unless the sub in question was 180 degrees out-of-phase. Notice that a lot of subs (including mine) have only a 180 degree phase control flip switch? All that thing does is switch the polarity. Seems to me that there would be no point to having one of those phase switches on your sub if it did nothing to the phase. My guess is it inverts the line polarity, same thing as reversing your + and - speaker leads. Am I right?
     
  7. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Hey There Wayne:

    Here's the new measurements I took last night, with the other sub turned off. This time it does not look so flat. The first time I measured it and got a relatively flat response must have been some kind of anomaly as I and others had suspected. It WAS too good to be true. I used the Stryke Bass Zone test disc. The rest of my system's speakers were also on, so it is not the sub by itself alone. Here they are:

    10 Hz---86 dB
    12.5 Hz-93 dB
    15 Hz---97 dB
    17.5 Hz-96 dB
    20 Hz---96 dB
    22 Hz---97 dB
    25 Hz---99 dB
    28 Hz---99 dB
    32 Hz---99 dB
    36 Hz---94 dB
    40 Hz---93 dB
    45 Hz---94 dB
    50 Hz---93 dB
    56 Hz---89 dB
    63 Hz---82 dB
    71 Hz---86 dB
    80 Hz---84 dB
    89 Hz---74 dB
    100 Hz--79 dB
    112 Hz--85 dB
    126 Hz--91 dB
    142 Hz--90 dB
    160 Hz--83 dB

    I've tried using the BFD PEQ Excel spreadsheet to model some filters but can't get it to work for me. All the results appear to be off-scale once I enter the values, so I was hoping maybe you could suggest some filters to apply.

    Thanks,

    Jeff Stanton [​IMG]
     
  8. Wayne A. Pflughaupt

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    What's your crossover frequency?
     
  9. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    The standard Yamaha x-over, 100 Hz...[​IMG]
     
  10. DanWiggins

    DanWiggins Second Unit

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    Jeff,

    Use a rumble filter (2nd order, Butterworth, 20 Hz Fc), and I assume the crossover is active. I'd use the following filters:

    -10 dB @ 30 Hz, Q=3
    -6 dB @ 30 Hz, Q=1
    +6 dB @ 90 Hz, Q=3

    That should get you within a 5 dB window from 12 Hz and up. You do lose ~12 dB of peak output (you're cutting that much, so you'll need to bump gain up elsewhere), but other than that it looks relatively flat.

    Dan Wiggins
    Adire Audio
     
  11. Wayne A. Pflughaupt

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    Hmm... I calculate an 8-9dB window with those filters. Can’t hurt to give it a try and see how it works, Jeffery – things don’t always turn out they way they look on paper... If you don’t like what you get I have a few filters in mind.

    Oh yeah, probably no need to use the 20Hz filter – I hear the BFD brick-walls at 20Hz anyway. I guess we’ll see from your new readings whether or not that’s true.

    Regards,
    Wayne A. Pflughaupt
     
  12. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Thanks Dan and Wayne:

    Could you tell me how to convert "Q" values into the X/60 bandwidth values used by the BFD?

    My GUESS would be that one "Q" = one octave or 60/60ths bandwidth. Am I way far off in this assumption?

    The Mackie amp that I'm using to power the Tumult has a continuosly adjustable low-pass/rumble filter. I assume I can use that in place of the 2nd order, Butterworth, 20 Hz Fc filter. Set it at 20 Hz


    Thanks Very Much,

    Jeff S.


    PS By the way Dan, that's one helluva subwoofer driver you all have produced there. Watched Terminator 3 last night, which is basically just one big 90 minute explosion. The Tumult performed very impressively I must say. Yikes!!
     
  13. Wayne A. Pflughaupt

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    I’m sure there’s a conversion formula somewhere; all I have is a conversion table I snagged off the Live Audio Board:

    Q3 = 1/2-octave.
    Q1 = 1-1/3-octave.

    Regards,
    Wayne A. Pflughaupt
     
  14. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Thanks Wayne:

    I was WAY off then. I will plug Dan's #'s into the BFD tonight and re-take measurements afterwards. I'll post them back here Monday and maybe we can tweak further if warranted.

    Later,

    Jeff S. [​IMG] [​IMG]
     

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