Originally Posted by Kilian.ca
Whether it's 2CH (in the OP's case) or MCH both PLIIx and PLIIz modes apply bass management so I don't see how the centre channel is set explains the bass discrepancy the OP hears between them.
Allow me to explain further. In playing 2-ch sources in PLII (or PLIIx) Music mode, the CW control spreads the center signal to include the L/R (and C) speakers. The sum of all three are power compensated to be the same as the C channel alone if coming from the center speaker (as would be the case with Movie mode).
For example, when two satellite speakers play the same signal, the SPL increases 3 dB. So when PLII steers a phantom vocal signal to the center speaker, it is 3 dB louder than either of the 2 original speakers so it maintains the same loudness in the overall mix.
However, as wavelengths increase, the power compensation would need to change. Two subwoofers playing the same signal can increase the SPL as much as 6 dB (if near each other), and even when spaced it is more than 3 dB. Dolby and THX found it was typically 4.5 dB in real rooms.
On top of that, bass management uses electrical summation which adds the L/C/R bass following the "6 dB" intensity law (not the 3 dB power law). So just taking the stereo signal and summing the bass to feed the subwoofer by itself adds a degree of bass elevation relative to each channel played alone, and adding a third component from center adds a little more.
However, when we designed PLII, we chose not to mess with applying gain shifts or filters to attempt to compensate any of this added bass from the use of three channels vs two.
You can prove it for yourself. Play 2-ch music in PLII Music and Movie modes. Music will have a little more bass.
Originally Posted by mannetti21
Just double checked and PLIIz is definitely under the MUSIC Listening Mode subcategory on the receiver, as well as the MOVIE modes.
That may be true, but it does not mean that the Center Width control is supported individually as it is in PLII Movie/Music. Can you adjust CW in PLIIz? If so, where is it set? If not, you can easily find out:
Play some mono program (AM radio or whatever). Select PLII Music. Notice the sound comes from L/C/R.
Switch to PLII Movie. Notice the sound comes only from C.
Switch to PLIIz. Where does it come from?
Furthermore, with my additional 2 channels set as height channels in the receiver, PLIIx isn't even an option.
That's because there are only 2 surround speakers. PLIIx needs 4. But PLII Movie/Music still works in your setup.
Looking at Dolby's website, PLIIz and PLIIx are indeed both marketed as being suitable for music and movies.
Well, how would it do to tell people that their shiny new PLIIz mode did not work for music?
Based on my understanding, PLIIx is available when you have front wide surrounds, or additional rear surrounds
Only for additional rear surrounds. PLIIx/z do not understand about wide speakers.
whereas PLIIz is implemented when the additional surround channels are front height channels.....neither of which should affect the bass response IMO.
Neither should, I would agree. But as I explained above, they might.