Speaker placement and FR

Discussion in 'Archived Threads 2001-2004' started by Brian Fellmeth, Jan 1, 2002.

  1. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    I posted this awhile ago, but didn't link the graph, so I'll try it again because this was surprising.
    In a quest for a flat bass FR, I decided to see what effect a small movement in main speakers made. This is a 2 channel stereo setup. These plots are sine waves, rat shack meter corrected. No sub, just stereo moniters with 75Hz line filters. The ONLY difference was moving the speakers from a foot from the wall to 4 feet out-NOTHING else was changed.
    [​IMG]
    I was amazed at the huge impact of a small speaker position change. There is a room mode at about 55Hz that is in both plots (much worse without the 75 Hz filters). But a deep, wide trough centered at 80 hz shifted to 65 Hz and became much shallower just by moving away from the wall a few feet. The plots are about 16 dB different between 75 and 95 Hz. A lot of people harp about the importance of room effects and placement importance, but I had no idea how right they are.
     
  2. Mac F

    Mac F Agent

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    glad you reposted with the graph. Quite impressive. What are your room dimensions, that might explain the 55 Hz peak if it a room node. Was the microphone in one position or several?
     
  3. Philip Hamm

    Philip Hamm Lead Actor

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    Very cool! Thanks for sharing. I always knew that speaker placement made a big difference to my ears but it's nice to see a scientific measurement that confirms that.
     
  4. BruceD

    BruceD Screenwriter

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    Brian,

    Do you have a coffee table in front of your listening position?

    If so, moving that out of the way will also provide some interesting changes in your FR.

    BruceD
     
  5. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    Mac,

    Room is a rectangle 13 by 23 feet. Speakers are 9 feet apart along a short wall. Ceiling 8 feet. Maybe the dimensions are close enough to 2 to 1 to combine to make the node. Mic was placed near the center of the room about 4 feet from the floor (and ceiling), never moved.

    Bruce- As a matter of fact, there is a coffee table right between the speakers- 5 feet square, surface about 6 inches below the woofer. Another thing to worry about ? If I get ambitious enough to run the curves before and after moving the coffee table, I'll report. My wife thinks I'm nuts enough without moving furniture to make the stereo sound better !

    When I get around to setting up my BFD programs, looks like I'm going to have to have 2 sets depending on whether the speakers are in the "stored" position (near wall) or "critical listening" position (out from wall). In either case, it looks like I'm going to just about kill sub output around 55 Hz because the mains are so loud there. Then the sub curve will have a double hump. Its probably going to end up a mess......
     
  6. Mac F

    Mac F Agent

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    I ran your room dimensions through the SGHT spreadsheet, and it doesn't predict a peak at 55 Hz.

    As an experiment, set your signal generator to the problem peak and make measurements about a foot either side of the center line in the room, about seated ear height from the floor. move the sound level meter around to see if it changes with location. Also, listen as you move your head in this general area, you are looking for loud and soft spots.

    Surely some time your wife has asked you move a sofa, bed or heavy cabinet just to "see if it looks better against that wall".
     

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