Thanks for clarifying it and I agree with you. When he stated he set the M80s to "large" ( as opposed to small) I intrepreted that to mean he was running them full range and not crossed which would have duplicated the LFE channel.
But this brings up a question I‘ve been wondering about for some time. If duplicating low frequencies between the “large” speakers and the subwoofer can cause so many problems why do so many people recommend using multiple subwoofers to even out the bass? Won’t the same issues apply or does evening out the bass outweigh the other issues most of the time?
One of the biggest challenges with integrating subwoofers is getting the speakers and sub(s) to blend properly with as flat FR as possible and minimal phase interference. Getting the speaker/sub frequency interface as smooth as possible is best achieved when you have the low pass filter (frequency and slope) at the crossover point producing a smooth summed response from the sub and speaker. If you have the speaker producing LFE and essentially no low pass filter operating it becomes next to impossible to blend the sub and speaker so the net outcome is more room reinforcemnt and cancellation and phase problems throughout the low bass range.
Now if you have the speakers low frequency output filtered out and you have it crossed to the subs it effectively removes one set of problems to worry about ie. resulting from uneven FR between the sub and speaker. There are other concerns such as getting the multiple subs behaving in a linear fashion but that can be achieved if the speaker interaction is set up right.
In other words getting flat FR in room is easier with the speakers crossed to the subs.
As you go from one to multiple subs studies (such as the famous Harman study on multiple subs) have shown that the greatest benefit to achieving flat response by reducing nodes throughout the room happen when you add a second subwoofer. Adding additional subs helps further but not as much with four subs being about the limit for further improvement in flattening FR. Getting them placed properly and operating in phase is another involved topic but the benefits are clear with less need for room treatments or equalization. A couple of years ago out of curiousity I bought 3 EP 600s and 2 EP500s to see for myself and 4 subs does provide the optimal benefit.
