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Is this an acceptable subwoofer frequency curve for a square room?

Discussion in 'Archived Threads 2001-2004' started by John H, Feb 12, 2002.

  1. John H

    John H Second Unit

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    I am using a pair of Paradigm Servo 15's in conjunction with a pair of Velodyne HGS-18's in a 16L'x16W'x8H' room.
    I use the 18's up front in each corner. The 15's are positioned along the rear wall on each side of my bed firing at each rear corner. The 15's are out of phase with the 18's up front.
    An Audio Control PCA III bass synthesizer is used on their signal. It is adding 35-17½Hz subharmonics from a 70-35Hz sampling range. An ART 351 is used for final equalization.
    I am using the Auto Sound CD and the RS SPL meter for measuring at the listening position.
    Below are corrected numbers.
    80Hz-87.0dB
    71Hz-94.0dB
    63Hz-88.5dB
    56Hz-84.5dB
    50Hz-86.5dB
    45Hz-90.0dB
    40Hz-86.5dB
    36Hz-90.0dB
    32Hz-86.0dB
    28Hz-83.0dB
    25Hz-84.0dB
    22Hz-87.5dB
    20Hz-88.0dB
    16Hz-87.0db
    The 80Hz reading is with both the Mains and subwoofers playing.
    There is no more room to reduce the 71Hz peak. The 351's 80Hz,63Hz and 40Hz sliders are at the bottom 12dB cut. No frequencies have been boosted.
    John
     
  2. Rick_Brown

    Rick_Brown Second Unit

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    I think yours is one of the flatter curves I've seen.
     
  3. Geoff L

    Geoff L Screenwriter

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    Wowzer:::
    I think many would hope for a responce that flat and that DEEP in a square room!
    In your stated room size, I ~{can only imagen}~ *the max spl* (down low 25hz and below) your capable of...
    Have you run the MAX numbers.... Sounds very scary with the woofage your running, even with the 4 monsters not coupled...????
    Regards
     
  4. John H

    John H Second Unit

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    Should I install a parametric EQ and attempt to achieve even flatter responce?
    Also, how would I measure maximum output at various frequencies? I assume subwoofer distortion is not an issue with the servo units.
    I have heard high amplitude sine waves can melt voice coils.
    Thanks,
    John
     
  5. Wayne A. Pflughaupt

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    Wayne
    John,

    Not sure why you want to find out, but all you need to do is turn up the volume until your courage gives out or the sub shows audible signs of distress.

    And yes, sine waves at this level can turn your voice coil to smoke, so you'd better not leave it on for more than a few seconds at a time. Best to leave some cool-down time between tests if you plan to do this for each frequency.

    Your readings are very good, but as you’ve seen, 1/3-octave EQs have their limitations.

    But I wouldn’t worry about tuning further with a parametric EQ. I have 1/3-octave correction in my room and I thought I had done a good job of EQing. However, when I recently took 1/6-octave readings, I discovered what my RTA could not tell me: I had a significant 1/6-octave peak at 45dB, and a 1/6-octave null at 71Hz.

    The thing is, though, those problems have never shown up with program. On music CDs with bass lines running from very low to very high, every note is the same volume as the next.

    So, bottom line, it sounds fine even if it doesn’t measure perfect.

    The only thing that looks questionable to me is that your response is virtually the same at 20Hz as it is at 80Hz. Response like results in rather “limp” and unsubstantial bass, in my opinion. Noted equalizer manufacturers like Ashly and AudioControl recommend a “house curve,” or gradual rise in response at lower frequencies.

    I found that bass sounded warmer with music and had more impact with movies after a house curve was applied into my subs. Things worked best for me with a gradual 9dB boost spread between 100 and 32Hz, with response flat below 32Hz. (I didn’t like the way things sounded when I continued the rise below 32Hz; I got a lot of unnatural and extraneous near-subsonic energy with most program signals.)

    The amount of house curve needed for natural-sounding bass is room-dependant. Smaller rooms need more than larger rooms. However, smaller rooms tend to get it naturally due their increased cabin gain. My total listening space (including all rooms open to the home theater area) is 6200 square ft., if that helps.

    Regards,

    Wayne A. Pflughaupt
     
  6. John H

    John H Second Unit

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    I changed the value of the subharmonic filter module in the PCA from 15Hz to 8Hz 18dB slope. I also decreased the ratio of subharmonics added to the signal.
    Below are the new corrected numbers.
    I also added 14 and 12hz measurements to the list.
    80Hz-88.5dB
    71Hz-93.0dB
    63Hz-88.5dB
    56Hz-84.5dB
    50Hz-86.5dB
    45Hz-89.0dB
    40Hz-89.5dB
    36Hz-91.5dB
    32Hz-88.0dB
    28Hz-85.0dB
    25Hz-87.5dB
    22Hz-90.0dB
    20Hz-91.5dB
    18Hz-91.5dB
    16Hz-92.5db
    14Hz-91.0dB
    12Hz-86.5dB
    John

    Edit: All the above measurements were taken with an 80Hz highpass with subwoofrers and mains playing.
     
  7. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    John, do you have the PCA active during this? I think you'll want to have it bypassed.(if you dont already)
    The 71hz peak could be tamed more with a parametric...you can cut a freq 30dBs with a PE17 if you needed.
    Have you tried running the curves with the rear woofs in phase, and then with the opposing *like* models out of phase with one another?(one HGS and one 15" servo out of phase with it's brother?)
    I doubt you'l find a better combination...but you seem to like measuring so I thought it would be interesting to see the results[​IMG]
    If you want to run high level response checks...I would DL spectraplus and run high level sweeps instead of sines. Spectra will also allow you to take rt60s and 3-D decays of the room.
    TV
     
  8. John H

    John H Second Unit

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  9. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    Hi John,
    There's definitely no *right* way in this...as the simple addition of a box like the PCA pretty much ends that type of debate[​IMG]
    I liked flattening my response...and THEN adding the PCA on top of that. But it's clearly a preference thing here.
    Let me know how the out of phase trials go if you decide to do them.
    TV
     
  10. John H

    John H Second Unit

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    I installed a Rane PE 17 parametric EQ in series with my ART 351 and smoothed the the final curve even further.
    This is still with the PCA processing engaged.
    80Hz-83.5dB
    71Hz-84.5dB
    63Hz-83.5dB
    56Hz-84.5dB
    50Hz-84.5dB
    45Hz-85.5dB
    40Hz-84.5dB
    36Hz-83.5dB
    32Hz-84.5dB
    28Hz-83.0dB
    25Hz-84.0dB
    22Hz-85.5dB
    20Hz-85.0dB
    16Hz-83.5dB
    John
     
  11. Geoff L

    Geoff L Screenwriter

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    John,
    1)- Now that you have expanded your eq-ing even further to obtain your current posted readings, have you listened to this sub-eq-ing (*NO House Curve*) with a variety of your music & Movie collection???
    2)- What do you draw from the newest in room responce?
    Do you like it with your music, that is if you have had time to try things out, considerig all the time spent eq-ing. Fun, fun, fun, well sometimes.
    (Your newest posted paper readings, they do look even better, flat wise.)
    And lastly, as (Wayne my EQ hereo) has stated, adding a house curve for him, (and I agree) will add much with little, to what I term a very dry and lack luster bottom end! Once eq-ed out as flat as your last post shows with it's numbers, to dry for me, even when running it a little hotter on the sub volume.
    The curve and to what extent it's used and (where) is as suggestive as anything else in sound reproduction. Nothing is set in stone, and ones apple pie is anothers rotten egg.
    3)- Are you finding your hard work for the flat responce to be pleaseing, and have you experiment with the house curve?
    Wayane, and others here, are *Extremly Sharp* in these areas. Room problems and speaker/sub eq-ing and how to apply it. I know I speak for many, when I say thanks! [​IMG]
    Many read and never post, only to go experiment with what they have just read. And with that, I say thank you for all of us.
    Regards
    Geoff
     
  12. gomez_a

    gomez_a Stunt Coordinator

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    What is a PCA box, what does it do?

    Thanks!
     
  13. John H

    John H Second Unit

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    Geoff,
    The measurements are "final" readings. An Audio Control PCA III bass synthesizer is used on the signal. It is adding 35-17½Hz subharmonics from a 70-35Hz sampling range.
    The equalization is applied to the PCA's input signal through it's processing loop.
    With the subharmonics added the posted measurements do have a "unseen" rising slope from 71 to 35Hz. This is due to that the RS meters "correction" values have not been applied to the 35-17½Hz subharmonics added to these frequencies.
    I'm I correct on this assumption?
    When running Waynes A/C Weighting test on my subwoofer pink noise test there is a 22dB discrepancy between the two.
    I have read the RS meter measures a subwoofer test tone 2-3dB low compared to a RTA. Since my test tone has subharmonics added in I set it even 2dB lower. 5dB below the other channels.
    I guess my thread title is misleading as my curve is far from accurately flat.
    It might not be a "house" curve but it does work for me! [​IMG]
    John
     
  14. Geoff L

    Geoff L Screenwriter

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    John
    Yes Im following you on this now...:b
    In a different round about way, yes you do have the curve ball going on.
    If you like your progressed out-come, than thats what counts. Sounds as though you got a good grip on things in your room.
    =======
    Just out of curiosity, how much time you got tied up in playing to get your results?
    =======
    Also John, excellent posts by the way.
    Geoff
     

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