Originally Posted by senzaparole
During calibration did you turn the gain of the subwoofer to get a level of -3db at the end of the calibration?
XTZ wrote to me that a level too low does not activate the subwoofer:
If it has set it to negative value, ie. -6 dB or similar, the signal to the subwoofer is probably too weak to trigger it. Then you can lower the gain on the bit subwoofer, run the calibration again. Repeat lowering the gain until the value for the subwoofer output level is 0 dB or even up to +3 dB. This way, the receiver will be able to react.
Several others, including both Feri and Alan, have already addressed this issue. But, let me add that I believe you are overthinking this. You do not
need to follow XTZ's specific recommendation for the trim level unless you actually are
having a problem with the subwoofer coming on from Auto mode, with a lower trim level. You will surely be able to tell whether the sub comes on or not, and you can adjust the trim up and down to test it as much as you like.
The best practice recommendations in the Guide are somewhat generic, without the advantage of knowing what specific subwoofer/AVR combination you have. And XTZ's recommendation is also generic. For instance, it would be much more applicable to older generations of Yamaha AVR's, which sent a lower-voltage signal to the subwoofer unless the trim level were high, rather than to Denon/Marantz AVR's.
As explained in the Guide section that Alan linked for you, there are actually two reasons why individuals may be better off using higher subwoofer gain settings, and correspondingly lower AVR trim settings. The first reason involves the possibility of the subwoofer clipping at higher trim levels when they are combined with louder overall master volume levels.
The second reason involves the fact that not all subwoofers can achieve max volume levels unless the gain is set relatively high. That sometimes varies with subwoofer models, even within specific subwoofer brands. The best practice guidelines are merely intended to provide general guidance to avoid those two potential issues. But, individuals are always perfectly free to experiment for themselves, and to decide for themselves what specific advice is directly applicable to their situations.
I'm writing this for others who may be reading along, as much as I am for your specific situation. Rather than overthinking it, I recommend that you just discover for yourself at what AVR trim setting your subwoofer will reliably turn-on from Auto mode.
Edit: Noticing your other question, I should add that the port plugs change the tuning point of your ported subwoofer. I assume from your statement about having two foam plugs that you have a 17 Series subwoofer.
If you are plugging a port, the one you choose to plug will affect the frequency response of your subwoofer, as will plugging both ports. As Feri said, you will have to decide for yourself which mode you prefer. The one port plugged mode will give you the deepest extension, and the most SPL below 20Hz. XTZ explains what the different port tunes do on their website, and they include frequency response graphs for the different options which are available to you.
It may be important that you change the setting on the subwoofer's plate amp to correspond to the new tuning point you are trying. You have the option of EQ1 and EQ2. The digital signal processing (DSP) in the subwoofer is intended to correspond to the various plug configurations, and you have quite a bit of user adjustability. You should rerun Audyssey if you change the tuning point on your sub.
In my opinion, this issue of port configuration is actually much more significant, with respect to your overall bass, than the issue of gain/trim setting. This is where I would spend some of my time reading the XTZ website, and then experimenting to discover what combination of port plug and DSP sounds best to you.