Test tones are bad...

Discussion in 'Archived Threads 2001-2004' started by Chuck Bogie, Mar 24, 2003.

  1. Chuck Bogie

    Chuck Bogie Second Unit

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    Argh. I picked up an Avia disk this weekend, and started playing with the 200-20 sweeps...

    Wish I hadn't... Now I've _gotta_ get new speakers - I played with just about every crossover/speaker size combo available on my receiver (Denon 1803), and my front speaks (Infinity Entra Twos and an Entra Center) have a serious spike (at least 10-12db - pegging the meter, and I had it "centered" on the left side) at about 150hz, then things drop off (to "normal")again, and come back up at around 60-50hz (regardless of if I was using the front speaks set as large with no sub, or if I was at small with a sub)... This was tested with sub both on and off, and on and off at the receiver. Maybe this is a feature, not a bug...

    Changing speaker sizes didn't make a difference either, except that it'd cut out below the crossover points when set to small. Current setting (judged to be the "least worse") is all small, xo at 100.

    So, I'm definitely gonna build something now...
     
  2. Seth_L

    Seth_L Screenwriter

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    Chuck,

    It's probably not the speaker. It's most likely your room. Speakers are generally rated +/-3dB in an anechoic chamber. Meaning in order to get the spikes you're talking about you need to have signigicant room interaction. Try relocating them before you go all out building new speakers only to find the same room problems still exist.

    Alternatively if you're using seperates you can EQ all your speakers flat with multiple 31 band EQs.

    Seth
     
  3. TimForman

    TimForman Supporting Actor

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    Ditto the above. That sounds like room acoustics. Changing speakers won't help much. Check out the great info on this site. Galen Carol Audio
     
  4. Chuck Bogie

    Chuck Bogie Second Unit

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    So it did it with all three speaks (using the different sweeps).

    I guess it's couch/coffee table/doors/windows.
     
  5. ThomasW

    ThomasW Cinematographer

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    The bandwidth of 1/3rd octave (aka 31 band) EQ is too wide to properly shape the in-room FR of a speaker. Use parametric EQ for this function.

    Chuck

    Changing the 'size' of the speakers with the prepro will do nothing, since what you're dealing with is the interaction of the soundwaves with the geometry (size/shape) of the room

    Move the speakers around in the room if you can do that. If not then use parametric EQ to 'cut' the spikes and flatten the FR.
     
  6. Ronnie Ferrell

    Ronnie Ferrell Second Unit

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    If you want to really be dis-heartened, play a continuous tone at a given frequency. You can pick what ever frequency you want. Then take the RS SPL meter and walk around the room, raising and lowering the meter in height. Notice how only a few inches can raise or drop the Db. My room sucks so bad that moving the Db meter less than a foot can lower or raise the sound level by +/- 10 to 15 Db on certain frequencies. In one of my chairs off to the left side of center, you cannot here the sub at all.


    Ronnie
     
  7. the saddest one for me was with the BPD1503. It has the inductance hump around 60 hz. I also had a HUGE room mode there and nulls on either side of it. ...and I had some ground loop humm leaking in.

    ==> new room arrangement and drivers [​IMG]
     

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