Wayne A., BruceK or any BFD vets... please help with frequency response and filters!

Discussion in 'Home Theater Projects' started by Glenn Baumann, Oct 21, 2003.

  1. Glenn Baumann

    Glenn Baumann Stunt Coordinator

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    I have acquired a Behringer Feedback Destroyer and have plotted my rooms frequency response. Can someone please help me assess my initial dB readings and share with me how I might best utilize my particular responses attributes if any. What are my responses basic strengths and weaknesses and what overall efficient strategy might I employ to optimize! I would like to try some sort of house curve with my response.

    My setup consists of dual SVS 25-31cs subs with a 22Hz tune powered by a Samson S700 (350 x 2) amp. The subs are both located together side by side on the left side of an 8 foot wide entertainment center right behind the left front main speaker. The subs are a little bit boxed in between the entertainment center and the left side wall of my 7.1 setup which occupies the left half of my rectangular 3500 cubic foot room. In the front middle of the room is a 3ft. wide by 7ft. high opening to another room that also has about 3500 cubic feet of volume. In other words, the frontal soundstage is located on the long wall in the left half of the room.

    My Denon receiver is crossed over at 80 Hz and I have the sub level at 0dB and the sub amp at 75%. The receiver volume level was at -20 when playing sine wave test tones from the Stryke's Basszone Test CD. The receiver was in direct mode with the main left/right speakers and (2) subs in the equation.

    Here is the room's frequency response measured with the Radio Shack SPL meter set for slow response / C weighted from the sweet spot:

    Corrected (compensated) SPL readings

    Hz Corrected SPL

    15 ......... 91.75
    17.5 ....... 91.00
    20 ......... 93.50
    22 ......... 95.50
    25 ......... 97.00
    28 ......... 96.00
    32 ......... 97.00
    36 ......... 100.50
    40 ......... 103.50
    45 ......... 95.00
    50 ......... 89.50
    56 ......... 83.50
    63 ......... 80.50
    71 ......... 81.50
    80 ......... 79.50
    89 ......... 73.50
    100 ........ 81.00
    112 ........ 83.00
    126 ........ 87.50
    142 ........ 79.50
    160 ........ 73.50
    201 ........ 76.50
     
  2. Thomas J. Coyle III

    Thomas J. Coyle III Stunt Coordinator

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    Hi Glenn

    Go to the following website and all of your questions will be answered: www.snapbug.ws/bfd.htm
    Regards,
    TCIII
     
  3. Wayne A. Pflughaupt

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    Try these two filters. Bandwidth is given in octaves - you’ll have to translate that to “BFD speak” fractions.

    1. Center Fr. 40Hz, bandwidth 1/3-octave, cut 12dB.
    2. Center Fr. 25Hz, bandwidth 1/3-octave, cut 4dB.

    Afterwards take new readings and post them here. We’ll probably want to do a few more filters before we’re finished.

    Regards,
    Wayne A. Pflughaupt
     
  4. Glenn Baumann

    Glenn Baumann Stunt Coordinator

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    Thomas:

    Thanks for the great link... very informative indeed!


    Wayne:

    Thanks for the response! I applied the two filters as you suggested and below are the results.


    Hz Corrected SPL

    15 ........ 85.75
    17.5 ...... 91.00
    20 ........ 89.50
    22 ........ 91.50
    25 ........ 91.00
    28 ........ 90.00
    32 ........ 87.00
    36 ........ 88.50
    40 ........ 90.50
    45 ........ 85.00
    50 ........ 81.50
    56 ........ 78.50
    63 ........ 77.50
    71 ........ 81.50
    80 ........ 78.50
    89 ........ 73.50
    100 ....... 80.00
    112 ....... 82.00
    126 ....... 86.50
    142 ....... 79.50
    160 ....... 74.50
    201 ....... 75.50
     
  5. Allen Ross

    Allen Ross Supporting Actor

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    that dip around 50 isn't going to sound nice for music, try another filter say at 50 hz, a plus 5 db with a narrow bandwidth, say 30,

    I am just going off the top of my head on this, i never really liked my system when it was "Flat" i always liked a bit off a boost, mostly because i am listening to music.
     
  6. Glenn Baumann

    Glenn Baumann Stunt Coordinator

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    Wayne:

    After applying the two filters you suggested and listening to some music I immediately noticed an overall improvement in the quality of the sound, everything sounded smoother and much more integrated/ blended. I imagine getting rid of that peak centered at 40Hz very much helped in ridding my response of that bloated sound. Also, being that the lower end at 30Hz and below was tamed I dont hear as much of those strange rumblings that I was previously plagued with.

    Remember, I have only done some casual music listening since applying the initial suggested filters and things are obviously much improved but I realize I have to experiment and fine tune the response. The real test will be some critical DVD soundtrack listening as I heard a lot of unatural reverberations/ rumbling during some DVD movie passages and I really want to rid myself of these abberations. What causes these rumblings? Is this subharmonic stuff or something? Can this be eradicated via EQ'ing?

    I am finally really starting to figure out how to use this BFD and I can see that this is an invaluable tool!




    Allen:

    Thanks for your response! After applying your filter suggestion late last night and performing some quick music listening I immediately realized that there really was indeed a lot of sound information at 50Hz that I was missing. After initiating the filter I could really feel the music. I noticed more weight and presence to the sound and when I cranked up the sound for a short period I could really feel more slam and fullness to the sound. I am guessing that when I listen to some DVD soundtracks cranked up tonight that I am going to really feel some chest pressure... I really like that clean blow your hair back feel when it is called for!

    When I get home tonight I will rechart the additional filter change and post the current readings. So far so good and I am looking forward to tweaking further and fine tuning!

    I am realizing that the biggest part of EQ'ing my subs is going to be understanding how the adjustment of the various frequencies affects the overall soundscape with regards to how I like it to sound and defining what my tastes really are.

    Does anyone think that I should concerned about that dip in response at 89Hz! Is this telling me something about my crossover and main speaker/sub interaction? Sould I maybe cut back 71 and 40 Hz a bit? What else should or could I be doing to my response to improve things? In the meantime, I am going to recreate the current filter setup within another BFD preset and experiment to see what I really might like tastewise and how to achieve it. What else might I be looking to do?

    Glenn
     
  7. Wayne A. Pflughaupt

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  8. Glenn Baumann

    Glenn Baumann Stunt Coordinator

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    Wayne,

    Sorry if I did not make my self clear... what I meant was there was unatural excessive energy BEFORE I applied the suggested filters. After your suggested filters the strange reverberations were completely gone! I also added the third filter at 50Hz as suggested by Allen although I ended up using a narrower bandwidth of only 7. The sound is quite pleasing now, I am very content... I can really enjoy movies now that all the boom is gone!


    I must say, this BFD is worth it's weight in gold, at least in my situation it has helped a lot and I could not imagine not using the BFD with this new setup... things are tamed! Great stuff! Now that it seems I have a much improved in room response I can really enjoy movies while I still experiment further.


    A few questions. Should I be concerned about the 7dB rise from 56Hz down to 50Hz? Should I really be looking to cut everything back by about 10dB, so at 20Hz I would be at 80dB flat up to 32Hz then slope down another 10dB from 32Hz up to 100Hz ending there at 70dB ( a 10dB downward slope). Can the stuff above 100Hz be cut back into the 70dB level? That would be a lot of cutting back to match the lower levels and I tried a little boosting on some of the lowest valleys to no avail. Maybe I should just cut back 40Hz 2.0dB and call it a day as I am driving everyone nuts with the test tones including my self!


    I thank everyone for getting me started with this BFD. I am no longer intimidated, you just have to play with this thing! My latest SPL readings are posted below, any comments would be most welcome.




    Hz Corrected SPL

    15 ....... 85.75
    17.5 ..... 90.00
    20 ....... 90.50
    22 ....... 90.50
    25 ....... 91.00
    28 ....... 89.00
    32 ....... 88.00
    36 ....... 89.50
    40 ....... 91.50
    45 ....... 88.00
    50 ....... 87.50
    56 ....... 80.50
    63 ....... 78.50
    71 ....... 81.50
    80 ....... 79.50
    89 ....... 75.50
    100 ...... 80.00
    112 ...... 83.00
    126 ...... 87.50
    142 ...... 79.50
    160 ...... 72.50
    201 ...... 76.50


    Glenn
     

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