You have been doing some runs of the calibration process with AVR and the AVR is now reducing the subwoofer level by 10 dB (or X dB). But... you bought a subwoofer to have more bass, not less! Why is the AVR doing this? And is this an issue?
Most modern AVRs aim to calibrate each speaker in your system to the same relative sound level, usually targeted at 75 dB. These 75 dB will take into account the input gain settings on your subwoofer, the master volume if you're not in Ref. Mode on, the room gain, the AVR gain. As the only thing it can change by itself during the calibration run is the AVR gain, it will reduce it to get 75 dB if the subwoofer is too loud.
There is nothing wrong about it. The only issue could be if the AVR can't get the subwoofer quiet (or loud) enough by itself. A message would pop up saying the AVR is too loud/weak. You would then need to change the input gain and/or the master volume. For normal modern AVR’s we recommend the input gain to be +6dB (if you have 1V output), or 0dB (if you have 2V output).
Some AVR's have 4V output, then set input gain to -6dB, if you have 8V output set to -12dB.
If you experience any issues during the calibration process, feel free to reach out: email@example.com