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  1. #1
    DIYaudiophilehack
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    New Avia ?????'s

    Been fiddling around with Avia disc again and encountered a strange problem. When checking sub vs sat SPL levels I find that sub output varies with each sat. For example, when playing the alternating tone tracks for each speaker vs sub, I get left front at 70db, sub at 67 db. Center channel at 70 db, sub at 67db, right front at 70db, sub at 75db. Right rear at 70db, sub at 70db. Left rear at 70db, sub at 67db. Sub level has been previously set with tone generator on receiver and Avia disc using Rat Shack meter and should remain consisitent instead of varying. Each comparison tone (sat then sub) is separate and should eliminate improper phase as cause since only the sat or sub is playing at any given time. To be sure, I also have triple checked phase with Avia as well. Any thoughts?

  2. #2
    Loving This kexodusc's Avatar
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    I haven't got a clue as to what's going on here...At what frequency does this tone run? Would your SPL responses change with frequency?

    The only thing I can think of is the fact that it could be impossible to set the sub to match all satellites at once. Room acoustics will change the apparent bass SPL from each satellite in the room. If you level match the speakers to match a reference SPL that's not affected as much by room acoustics, you could be encountering some variance at lower frequencies giving you the results...For exampe, if your speaker's position is such that the bass waves are being cancelled somehow then the absolute gain sent to the system to get the right fromt speaker at 70 dB could be higher, thus bringing the gain to the sub up even more.


    Just a shot, but it kinda makes sense.

    I wonder if the problem is the signal from Avia itself?

    Note: My Toshiba SD-4960 stopped reading DVD-A's this week...not sure what happened,
    SACD's and DVD's play fine, just not the DVD-A files...won't even show these options in the menu.
    Good news is Toshiba's support is excellent...they sent a courier to my house to pick it up the next day and told me I can expect a replacement within a week. (the store I bought it from went out of business).

  3. #3
    Forum Regular edtyct's Avatar
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    Toenail and Kexo,

    I recalled that SVS addressed this issue with AVIA on their website in the FAQ section and went to check. I quote:

    "During calibration of your subwoofer level, you usually don't have an ability to independently adjust the strength of bass coming from each main channel. This can mean that you find the SPL reading of subwoofer tests vary depending on which channel is being tested. The most common reason for this is a difference in how the bass is being processed (one channel is large while the other is small). Since you can't independently adjust each, it is reasonable to either average for the front three channels or simply concentrate on getting the front channel right since that one carries the most work in a movie soundtrack."

    This paragraph doesn't seem to cover all of the bases, but more details follow. Also, I think that "front channel right" in the last sentence should be "center channel right." Another cause of level discrepancies might be the phase setting on the sub.

    Ed

  4. #4
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    Quote Originally Posted by edtyct
    Toenail and Kexo,

    I recalled that SVS addressed this issue with AVIA on their website in the FAQ section and went to check. I quote:

    "During calibration of your subwoofer level, you usually don't have an ability to independently adjust the strength of bass coming from each main channel. This can mean that you find the SPL reading of subwoofer tests vary depending on which channel is being tested. The most common reason for this is a difference in how the bass is being processed (one channel is large while the other is small). Since you can't independently adjust each, it is reasonable to either average for the front three channels or simply concentrate on getting the front channel right since that one carries the most work in a movie soundtrack."

    This paragraph doesn't seem to cover all of the bases, but more details follow. Also, I think that "front channel right" in the last sentence should be "center channel right." Another cause of level discrepancies might be the phase setting on the sub.

    Ed

    This makes sense to an extent. All speakers are set to "small" and I would think that left and right mains would be mirrored in that they would show equal output to the sub channel though. My results showed left main sub output at 67db and right main sub output at 75db.

  5. #5
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    Quote Originally Posted by kexodusc
    I haven't got a clue as to what's going on here...At what frequency does this tone run? Would your SPL responses change with frequency?

    The only thing I can think of is the fact that it could be impossible to set the sub to match all satellites at once. Room acoustics will change the apparent bass SPL from each satellite in the room. If you level match the speakers to match a reference SPL that's not affected as much by room acoustics, you could be encountering some variance at lower frequencies giving you the results...For exampe, if your speaker's position is such that the bass waves are being cancelled somehow then the absolute gain sent to the system to get the right fromt speaker at 70 dB could be higher, thus bringing the gain to the sub up even more.


    Just a shot, but it kinda makes sense.

    I wonder if the problem is the signal from Avia itself?

    Note: My Toshiba SD-4960 stopped reading DVD-A's this week...not sure what happened,
    SACD's and DVD's play fine, just not the DVD-A files...won't even show these options in the menu.
    Good news is Toshiba's support is excellent...they sent a courier to my house to pick it up the next day and told me I can expect a replacement within a week. (the store I bought it from went out of business).

    Sorry to hear about the 4960. The output of the disc may actually be in question. There should be no cancellations because the subs position never changes and the tone is sent only to the sub, not sub+sat.

  6. #6
    Loving This kexodusc's Avatar
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    Toenail: I wasn't really referring to cancellations between the speakers and sub, but rather the subs output with it's own sound reflections (room acoustics)...it's very possible, and likely, though I wouldn't have the foggiest notion of how to verify it...hope you figure this out...keep us informed.

  7. #7
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    I guess I'm not overly concerned about it at this point. Sound quality when listening in 5.1 is great and the problem only seems apparent when testing with the Avia disc. Just curious how it was happening.

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