Thank you for writing this article. I agree with the recommendation that setting the crossover of the main speakers (front, center, surround) to 80Hz or above for better acoustics. All sound below 80Hz will go to the subwoofer when the AV receiver has the main speakers set to SMALL and the subwoofer set to LFE. However, what I don't quite agree on is setting the subwoofer crossover automatically to 120Hz. The reason why people experience muddy sound is likely due to BOTH main speakers and subwoofer having OVERLAPPING SOUND between 80Hz and 120Hz! From a technical perspective and from my experience, I find the bass to be more seamless when setting the AVR to have BOTH main speaker crossover set to 100Hz AND the subwoofer crossover set to 100Hz! This is also with the speakers set to LARGE and the subwoofer set to LFE+Main on the AVR (more on this later).
Even though my main speakers can go down to 60Hz (as determined by Audyssey, and the frequency range of my speakers) doesn't mean I should automatically set the crossover to 60Hz or even 80Hz. Looking at the frequency graphs of my speakers show that the DB sound level starts to taper down starting at 100Hz! If I were set the crossover below 100Hz, the main speakers would struggle to produce volume between 60Hz to 100Hz. Since my subwoofer volume is flat across the 150Hz down to 20Hz frequency range, it makes more sense to have the subwoofer produce sound from 100Hz and below since it can produce more consistent volume levels at that range.
So why set the speakers to LARGE (vs. SMALL) and the subwoofer to LFE+Main (vs. just LFE)? The reason for this is so that ALL frequencies are sent to the main speakers ABOVE the crossover point. Also, any LFE signal PLUS bass frequencies intended for the main speakers would go to the subwoofer. The sound produced with this setup gives the impression of much larger main speakers compared to when the speakers are just set to SMALL and the subwoofer set to LFE on the AVR. When set to SMALL + LFE only, the AVR sends ONLY the LFE signal to the subwoofer WITHOUT sending the bass intended for the main speakers due to DSP circuits removing frequencies it doesn't believe small speakers can handle.