EQ frequencies posted...please offer suggestions

Discussion in 'Archived Threads 2001-2004' started by Gary Thomas, Jan 24, 2002.

  1. Gary Thomas

    Gary Thomas Second Unit

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    Freq.Seat1 Seat2 Seat3

    17hz77.576.578.5

    20hz86.584.586.5

    22hz85.583.585

    25hz84.58282.5

    28hz84.58380.5

    32hz858581.5

    36hz8384.580.5

    40hz8767.585.5

    45hz827684.5

    50hz8274.574.5

    56hz8267.575.5

    63hz74.568.580

    72hz6967.575.5

    80hz68.576.581.5

    89hz55.572.580.5

    Everything looks great below 40hz... It's amazing how different the response can be from the 3 locations. Seat 1 is my recliner, seat 2 is a loveseat in the center of the room and seat 3 is a couch along a side wall.

    What adjustments should I start with on my BFD?
     
  2. ColinM

    ColinM Cinematographer

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    Watch the movie from seat 3!
    [​IMG]
    Sorry....
     
  3. Wayne A. Pflughaupt

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    Gary,

    Which is the primary viewing position? That’s the one you want to EQ for.

    In my experience, if the main position is in the room (i.e., out some feet from the wall) you can EQ from that position, and it will deliver acceptable sound at all other positions except those situated against a wall.

    Regards,

    Wayne A. Pflughaupt
     
  4. Gary Thomas

    Gary Thomas Second Unit

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    The main position would be seat 2, which is a loveseat directly facing the tv. So, should I cut the frequencies to match what's happening at 40hz?
     
  5. Ray R

    Ray R Stunt Coordinator

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    Before starting with the BFD, I would suggest moving furniture. It doesn't have to be a complete shuffle. A few inches might make the difference. Play the 40 Hz test tone while sitting in position 2 and then move the soundlevel meter front and back a few inches. If your lucky it will only take that much and you will have the room to move the seat. You could also try moving your main speakers a little as well, but this could effect all listening positions. Moving your sub might also have an effect.

    Something else that effects the cancellation frequencies is the subwoofer phase control. My sub has a continually variable phase control as opposed to a 0/180 switch. I know that minor adjustments to the phase control will effect dips, but I was unsuccessful at making this work to my advantage.

    Once you done what you can with moving things, then I would take Wayne's suggestion and just EQ for on position. You will drive yourself crazy otherwise.

    One last thing, when you start EQing with the BFD notice if the cancellation frequencies change slightly. I was able to get good results, but I did notice a slight shift in the frequencies where I had cancellation. Just wondering if others have seen this happen.
     
  6. Wayne A. Pflughaupt

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    Gary,

    Unfortunately, your response is very ragged. The two major problems are the huge 17dB “cliff” above 36Hz and below 40H, and the deep notch centered at 40Hz.

    Separately, EQing below 36Hz and above 40Hz is no problem, but blending the two “plateaus” will be problematic – seriously so. Bottom line, Gary, it will be virtually impossible to achieve smooth response with the sub in this location.

    The notch suggests some cancellation. If the seat is halfway between the sub and a wall, you will need to move it. A couple of feet will do.

    Do you have the sub in a corner? The ragged response suggests that it is not. Corner placement will give the smoothest unequalized performance, with any response peaks easy to EQ.

    If the sub is already is in a corner, try a different one. Typically you want the corner with the longest uninterrupted wall length (i.e., no open doorways, etc.) in both directions.

    If you end up moving the seat and/or the sub, post some new readings for us.

    Regards,

    Wayne A. Pflughaupt
     
  7. Gary Thomas

    Gary Thomas Second Unit

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    Thanks Wayne:

    I tried the sub along a side wall, the only other acceptable position, and the response was worse! I'd love to stick it in the corner where it belongs, but it's not aesthetically possible w/ our tv & furniture. (speak to my wife!)

    Anyway, the only real problem area, even uncalibrated, is at 40hz from the loveseat seating position. I was able to get an excellent curve from my recliner, but I had a pretty good curve to start with.

    Given my placement restriction, I'm not sure if the eq really helps all that much...a few db's here & there.

    I had all of the other speakers turned off. Unfortunately, I upped the volume a few db's for my final reading, but you can see the relationship between the frequencies on the before & after readings:

    Recliner Before After

    16hz 69.5 82.5

    20hz 80 86.5

    22hz 78.5 89

    25hz 78 88.5

    28hz 77.5 90.5

    32hz 80.5 91

    36hz77.5 87

    40hz81.5 85.5

    45hz76 83.5

    50hz74.5 83

    56hz74.5 81.5

    63hz68.5 74

    72hz60 63.5

    80hz56.558.5

    89hz6257.5

    100hz58.556

    Loveseat BeforeAfter

    16hz68.581

    20hz78.582

    22hz76.586

    25hz7584.5

    28hz76.587

    32hz8188

    36hz78.585.5

    40hz60.562

    45hz6974

    50hz67.572.5

    56hz55.561

    63hz60.561.5

    72hz58.557.5

    80hz61.558.5

    89hz62.558.5

    100hz5956

    Couch BeforeAfter

    16hz71.583.5

    20hz8084.5

    22hz78.588

    25hz7685

    28hz74.585

    32hz7684

    36hz72.579.5

    40hz79.582

    45hz7983.5

    50hz69.574.5

    56hz69.572.5

    63hz7071.5

    72hz65.564.5

    80hz66.563

    89hz55.553.5

    100hz6057
     
  8. Wayne A. Pflughaupt

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    Gary,
     
  9. Gary Thomas

    Gary Thomas Second Unit

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    Wayne: I sincerely appreciate all the effort you put in to helping me! I can't wait to try out the suggestions.

    I've thought of another possible spot for the sub. If you check out my HT Pics, I'm thinking of a spot next to the recliner, below a side speaker. What do you think?

    As far as amp capacity, I should be ok w/ a Samson 1000. It has 500w. The sub I'm using is a SVS CS-Ultra.

    I'll be home Friday & plan to try out the new sub location. If I don't get a better response, I'm planning to try out your eq suggestions.

    Thanks again!
     
  10. Wayne A. Pflughaupt

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  11. Gary Thomas

    Gary Thomas Second Unit

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    So...using a side wall will give me an additional boundry as compared to corner placement.

    Given this, with the current location of the sub, the opposite wall is probably 30 feet away, whereas a side wall placement would have the opposite wall only 14 or 15 feet away. This would produce cancellation at 22hz. So...it's probably not a good idea to move the sub to a side wall!

    If I leave the sub in it's current spot on the front wall, how close to the wall should I place the sub? I can go from 0 - 2 feet.
     
  12. Wayne A. Pflughaupt

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  13. Gary Thomas

    Gary Thomas Second Unit

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    OK Wayne...one last time!
    Here are the un-equalized measurements from the center (main) listening position:
    17.5hz: 89.5
    20hz: 97.5
    22hz: 95.5
    25hz: 96
    28hz: 96.5
    32hz: 98
    36hz: 97.5
    40hz: 82.5
    45hz: 87
    50hz: 86.5
    56hz: 79.5
    63hz: 75.5
    72hz: 71.5
    80hz: 78.5
    89hz: 80.5
    100hz: 76
    I took the measurements with only the sub active, all other speakers have been disconnected. Normally, I set my mains & all speakers to "small" and use a 80hz crossover.
    What's your eq prescription?
    Thanks!!![​IMG]
     
  14. Wayne A. Pflughaupt

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    Gary,

    Thanks for the readings. I’ll study them and post recommendations tomorrow.

    Regards,

    Wayne A. Pflughaupt
     
  15. Wayne A. Pflughaupt

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    Gary,

    Sorry, but these readings are the worst yet.

    Comparing all four plots (including the first one from the love seat location, and the second “before” and “after” readings), I think the first readings you give us are the best (despite what I said before). They only had a 17dB response deviation, compared to 26-32(!) dB for the others.

    Common to all readings is the null at 40Hz. As I’ve mentioned, it may or may not be possible to address this with equalization. More hopeful is the valley above that point, shown in varying degrees between 45 to 100Hz. It’s too wide to be a null, so it probably can be equalized.

    Therefore, Gary, I’m basing the following recommendations on the first readings you posted. Hopefully that is a location you can put your sub permanently.

    First I suggest taking new baseline readings, and don’t change the volume setting until equalization is completed. It is not necessary to duplicate the previous readings that were posted. I’ll use the old readings, but indicate the amount of change you should see (i.e., “+4dB”) at each frequency. Thus you will be able to know what changes to expect with your current readings.

    Also, I don’t know how it escaped me before, but some of your previous readings were way too low. When you get SPL readings down in the 50s, you are competing with ambient room noise, which can obscure and prevent accurate readings. For best results, I suggest making sure the lowest readings are above 70dB. 75dB would be even better, if that’s possible.

    First set a filter for 2/3-octave, centered on 32Hz and cut 6dB. Technically, the outer fringes of the filter should be 25Hz and 40Hz. If the BFD’s filters behave like most, the filter will actually extend a little past the technical fringes with a cut this deep. If so, then you should see a 1dB reduction at 25 and 40Hz, which is what we want. If you see no changes at 25 and 40Hz, increase the bandwidth incrementally until you see a 1dB change at 25 and 40Hz.

    After applying this filter you should realize changes in this region similar to this:

    22Hz 83.5 (no change)

    25Hz 81 (-1dB)

    28Hz 79 (-4dB)

    32Hz 79 (-6dB)

    36Hz 84.5 (-4dB)

    40Hz 67.5 (-1dB)

    45Hz 76 (no change)

    This leaves us with a slight peak at 20Hz. You may or may not want to reduce this. I suggest setting a filter for it, and then decide with listening tests if you want to use it or not (often some boost at the lowest frequencies is desirable).

    Set a 1/3-octave filter for 20Hz and cut 2dB. The outer limits of the filter are 17 and 22Hz. Since this is a small cut, you should see a 2dB reduction at 20Hz, and no change at 17 or 22Hz. If so, incrementally narrow the filter until there is no change at 17 or 22Hz.

    After EQ, the readings in this region should look like this:

    17Hz 76.5 (no change)

    20Hz 82.5 (-2dB)

    22Hz 83.5 (no change)

    Our next problem is bringing up response above 40Hz.

    Set a 1-octave filter at 56Hz and boost 8dB The outer limits filter should technically be 40Hz and 80Hz. Again, a filter this deep should “spill over” beyond the limits, which is okay. However, we don’t want more than 2dB increase at 40 and 80Hz. Again, incrementally tighten the bandwidth if necessary. Not knowing exactly the filter “shape” some of the readings might vary a dB or two, as indicated.

    After applying this filter, you should see the following changes in this region:

    36Hz 84.5 (no change)

    40Hz 68.5 –69.5 (+1 or 2dB )

    45Hz 78-79(+2 or 3dB)

    50Hz 78.5-79dB (+4 or 5dB)

    56Hz 75.5 (+8dB)

    63Hz72.5-73.5 (+4 or 5dB)

    72Hz69.5-70.5 (+2 or 3dB)

    80Hz77.5-78.5 (+1 or 2dB )

    89Hz72.5 (no change)

    I experimented with boosts of 6, 8, and 10dB; on paper it looks like an 8dB boost will give the best results. You might try experimenting with a 10dB boost and see what you think of the results.

    There is still a narrow spike at 80Hz we can deal with. Set a 1/3-octave filter at 80hz and cut 4dB.

    The outer limits of the filter should be 71 and 89Hz. However, this is not a deep filter, so the outer limits should not change much. In fact we don’t want them to change at all. If they do, tighten the bandwidth a little.

    Readings in this range should now read:

    72hz69.5-70.5 (no change)

    80hz72.5 (-4dB)

    89hz72.5 (no change)

    This leaves the 40Hz null. You might try addressing it the way I recommended in the post above. Remember, if an 8dB boost gets only gets a 2-3 improvement, it would be best to leave this problem alone.

    The new full-range readings (including the 20Hz filter, but not addressing the 40Hz null) should be:

    17Hz 76.5dB

    20Hz 82.5dB

    22Hz 83.5dB

    22Hz 83.5dB

    25Hz 81dB

    28Hz 79dB

    32Hz 79dB

    36Hz 84.5dB

    40Hz 68.5 –69.5dB

    45Hz 78-79dB

    50Hz 78.5-79dBdB

    56Hz 75.5dB

    63Hz72.5-73.5dB

    72Hz69.5-70.5dB

    80hz72.5dB

    89hz72.5dB

    The response deviation has been reduced from 17 to 14dB. Ignoring the 40dB null, the response deviation has been reduced from 17dB to 11dB.

    Hope this helps. Keep us posted on the progress.

    Regards,

    Wayne A. Pflughaupt
     

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