Originally Posted by neutro
Pure Direct mode won't use your subwoofer as it completely bypasses the crossover.
Also depending on your bookshelf speakers it could be adequate to use a higher crossover frequency
Originally Posted by Gurba
The Pure Direct in Yamaha might use the subwoofer if you have extra bass active.
As always, Neutro is spot on.
Regarding Gurba's proposal... it's definitely an interesting thought, but I just now checked it out, and it doesn't.
My AVR is a Yamaha RX-A2010.
Configuring the fronts to "Large" on the A2010 allows the use of "Extra Bass", which sends the front speakers' full-range signal to my SVS SB12. On the SB12, I have the Low Pass filter set to "Disable" (on its 400W Sledge amp, about 180Hz or so), so all low-frequency signals are sent to it, but the output frequencies start to loose amplitude at about 130Hz, and are completely gone at 180Hz.
Configured as above, switching the A2010 to "Pure Direct" mode completely bypasses those configurations... and when the source is only 2-channel, no signal is sent to the sub at all. Of course, if the source is multi-channel, and has actual content in the .1 channel, it will
receive that signal... but my assumption is that we are only discussing the processing of a 2-channel source here.
If the fronts are configured to "Small", the A2010 has myriad processing modes (I tend to prefer "Straight", although I occasionally use "Nine Channel" if I want to engage my surrounds). Needless to say, in all of those modes, it sends the low-frequency crossed-over portion of the 2-channel signal to the sub.
But again, switching it from any of those modes to "Pure Direct" results in a "pure" 2-channel signal being sent solely to the front speakers, and no signal is sent to the sub at all.
Hope this helps!