Explain these SPL readings, please (Avia sub balance)

Discussion in 'Archived Threads 2001-2004' started by Brett Miles, Dec 17, 2002.

  1. Brett Miles

    Brett Miles Stunt Coordinator

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    I have been doing some tweaking lately and I discovered something interesting/sucky. I have my front 3 channels balanced pretty well (surrounds are a different story because they are set differently to maximize balance at multiple seats), and I think I had previously only used the left-SW tone in avia to balance the sub. What I have discovered after trying the other tones is that despite the balance of the 3 speakers, the sub readings are different. The right-SW tone shows the sub being about 2+ dB higher in comparison to the left. The center is also different (lower than the left), but not by as much. What's the deal?
     
  2. Doug BW

    Doug BW Stunt Coordinator

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    I've noticed the same thing. Here's why I think it's happening.

    The Avia tone you are referring to is not produced on the LFE channel but rather on the left, center or right channel (as appropriate) and relies on your bass management to redirect the bass to your sub. I believe the Avia tones contain pink noise between 40 and 80 hz, so if your crossover is 80 hz, then you are getting a considerable amount of the sound being played by your main speaker in addition to the sub.

    The overall SPL level that you measure is a combination of the direct and reflected sound coming from the sub and either your left, center or right speaker. Since the reflected sounds from each of your main speakers will differ in terms of strength and phase from one another, the amount of reinforcement/cancellation will also differ, thus you end up with different SPL levels.

    Or I could be wrong...
     
  3. JohnDG

    JohnDG Stunt Coordinator

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    I've identified the same thing.

    Interesting was that, by using the phase control on the sub, I was able to "tame" a bass hump on my right front at around 80Hz caused by an odd room formation and speaker placement.

    My suggestion is to average your l/r fronts -- or check whether or not adjusting the phase flattens-out your frequency response curve for the individual speakers. Also experiment with crossover settings. By moving up to 100Hz (from 80Hz) on the receiver, I was further able to tame the base humps caused by speaker placement.

    jdg
     
  4. Brett Miles

    Brett Miles Stunt Coordinator

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    You guys are absolutely correct. I didn't realize I had sound coming from my mains during the SW part of the test. I think the problem is my room. I live in an apartament, and you walk in the front door through a short hallway to the living room. This is the side of the room that is the front of the HT. This means that while the left speaker is "in the room" it still has that hallway opening directly to the left. The right speaker is then probably getting a bass reinforcement from being in the corner. I turned off the sub amp and ran the test again to see just how much sound was coming from the main speakers. Varying the crossover from 80 to 40 in 10hz steps didn't seem to anything, but I hadn't tried anything higher. My sub is DIY and the amp doesn't have a variable phase. The only phase option is "normal/reverse" on the receiver. I think I'll just have to live with the problem, since I don't want to reverse the positioning of everything in the room to give each main speaker a corner. I purposely set it this way originally in attempt to avoid glare on the TV from a sliding-glass door on the right side of the room. Plus, now that I think about it if I did reverse things I wouldn't be able to use the door because the speaker would be in the way. So basically, I'm screwed either way [​IMG] ! Thanks for the help though.
     

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