Avia Sub Calibration Channel Dependent?

Discussion in 'Speakers & Subwoofers' started by Brian Henchey, Jul 16, 2003.

  1. Brian Henchey

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    Normally, I select Avia's left front/subwoofer level to calibrate my subs, then run the left front/LFE frequency sweep to gauge the effectiveness of positions/settings. Last night (while experimenting with new subwoofer locations), I noticed that the sub level in the left front/subwoofer test tone (as calibrated with an SPL meter to match the alternating left front pink noise level) is lower than in the other two channels. In other words, switching to the center/subwoofer or right front/subwoofer test tones gives (i) the same db level of the speaker pink noise but (ii) a much higher subwoofer reading than with the left front. All speakers are small with an 80hz crossover. Which channel should I be calibrating the sub to?
     
  2. Edward J M

    Edward J M Cinematographer

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    Brian:

    I have all sorts of trouble calibrating the subwoofer with Avia.

    Avia is true Dolby Digital and therefore allows the surround speaker in question to contribute significant amounts of bass to the subwoofer tone.

    I have found the amount of bass each surround speaker contributes is highly dependent on the speaker design itself, and its room location. My left main is several dB higher than any other channel on the subwoofer tone. The best way to check all of the differences in the surround channels is to power down the subwoofer and run the Avia sub test tone for each channel.

    With an 80 Hz crossover, it is pretty remarkable how much sound pressure the surround channel speaker can contribute to the subwoofer tone when using Avia. My left main contributes about 82 dB to the sub tone when it is calibrated to 85 dB with surround tone. This "surround speaker contribution" phenomenon can result in undercalibrating the subwoofer. For this reason most HT enthusiasts end up setting the subwoofer about 8 dB higher (93 dB) and wonder why they need to run it so hot when in reality they are not.

    After calibrating the surround channels with Avia, I leave the Master Volume untouched and I actually resort to using the discrete test tones from the AVR as my initial sub calibration guide.

    Here's my advice:

    1) Calibrate all the surround channels to 85 dB with Avia.

    2) Leave the Master Volume untouched.

    3) Run all the discrete surround speaker test tones in the AVR and note the average volume. It likely won't be 85 dB, but they should all be about the same. Let's say for example, they are at 82 dB.

    4) Run the discrete subwoofer test from the AVR and calibrate the sub level 3-4 dB hotter than the SPL noted in 3) above. In this example, you would calibrate the sub to 85-86 dB.

    5) Now run the subwoofer test tone in Avia. I'm betting money it will show the sub running about 8 dB hot.

    Regards,

    Ed
     
  3. Brian Henchey

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    Thanks, Ed. Interestingly, difference in calibrated levels of the speaker channels (L/C/R/RS/LS) between Avia and my pre-pro's internal test tones is negligible. When I calibrate the sub to the discrete, internal test tone of my pre-pro however, the Avia reading is far below that of applicable speaker channel (and conversely, the Avia-calibrated subwoofer level is way above the speaker levels in the discrete test tones).

    According to the manufacturer, the internal pre-pro test tone is flat across all frequencies and suggested that I have a serious null in the 30hz to 40hz range, probably due to multiple (non-colocated) subs and room response. Lo and behold, running the LFE freq sweep with Avia revealed a serious null in that freq range. After some limited trial and error with location and phase, I now have the subs colocated in one corner and the freq sweep is no longer showing a strong null at 30-40hz (I have not yet looked at what the internal test tone is doing at this location yet). Next step is to make a CD with test tones and start quantifying the room responses at different locations (including, I think, separated subs at the 1/3 and 2/3 location along the front wall).
     
  4. Edward J M

    Edward J M Cinematographer

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  5. Brian Henchey

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    I will give the internal tones in the pre-pro another shot. Just for the record, however, the problem I was having was the opposite of that which you are describing in that calibrating with the discrete pre-pro tones resulted in *too low* of an Avia reading v. *too high*. Hopefully, the new placement will sort this out...
     
  6. Edward J M

    Edward J M Cinematographer

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    I misread your last. I would say your experience could be related to that room null, then. Fix the null and re-try both discrete and Avia and see what happens. Good luck.
     
  7. Jeremy Anderson

    Jeremy Anderson Screenwriter

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