Originally Posted by Audioguy78
I have been on this forum for some time now but don't visit or post often.
I will admit I do not have "a lot" of pro experience in HT design and set up other than designing my own (now fairly dated) budget system (and it still needs much improvement), but I do have >13 years in live sound work on stages building and operating sound systems for anything from small events (<100 audience) to large festivals (close to 10,000 concert goers per day) and I have done arena tours and a world tour as well so I am not exactly a "new-be" to sound equipment and acoustics (but not totally up on the home theater front).
What I can add to this talk about subwoofer settings is:
1) the power supply in your multi-channel receiver is only capable of a certain amount of current which then feeds each of the amplifiers. IF ALL OUTPUTS ARE PLAYED AT THE SAME HIGH LEVEL AT THE SAME TIME then the power supply will be the limiting factor to output power for each channel. Even if you are using 7 amplifiers watching a movie and a loud sound flies around the room (from one speaker to another) then each amplifier should be able to produce the full output power as specced, since the current is only used as the amps play louder sounds and not full time.
2) The less sources of a single sound, the more natural they will sound (in most situations). The biggest cause of unnatural sound is multiple sources of the same sound. Since each source is slightly out of time with the next (for instance if you are 1/2 a foot closer to one speaker than another then there will be a very slight- barely measurable volume level change, but the difference in time between the 2 speakers will cause phase problems that are more apparent- the more distance the lower the effected frequencies. Most frequencies will couple together making it sound louder, but a few frequencies will cancel causing those frequencies to seem to disappear!). This is why receivers have distance controls (or automatic setup that controls this for you now). The only problem with this is if you are not in "the sweet spot" then you wil not assume the benefit of the time correcting controls! IF you don't believe me then listen to your pink noise play... In a perfect world the tonal quality of the pink noise will be the same from all speakers. Now make a disc or file of pink noise and make it play in all speakers at once... move around and you will easily hear the coupling and cancelling of different frequencies as you move around the room!
3) Low frequencies are also more prone to the cancellations (above) being noticeable. Due to room modes alone, you will hear each speaker's natural sound coupling with reflections of walls. These 2 "sources" will cause coupling and cancelling (most cancelling will be in the higher frequencies of the sub unless your in a very large room). Now if you play your main speakers at full range and your sub plays the lows along with the mains then remember each of the main speakers have main sounds and reflections as well and they are all adding up and cancelling at your ears. Most rooms wont have "cancellations" below 100-150 hz (estimated) due to the rooms being too small; all sounds below will couple and be louder at those frequencies; large rooms will have lower frequency cancellations.
4) Low frequencies are less efficient to reproduce in most speaker systems, and require more power to produce the desired levels. even if your main speakers are capable of producing "sub" frequencies in order for them to do so requires more power amplification. Speakers should be capable of producing all frequencies within their range clearly but some people have found slight improvements when the speakers don't need to produce as many sounds at one time. Some concert tours have gone as far as flying 2 separate pa systems side by side and routing the sounds of main vocals and certain key instruments thru one system while the rest of the program plays thru the other because the clarity is slightly greater (this is for major tours with open-ended budgets, and very few major tours actually went this route).
With all this in mind, IF you have the proper power available to power your "large" speakers then the benefits of producing all your sound thru your mains will be noticed (and louder, more dynamic passages wont be limited by system resources). With most receivers (rated ~100w/ch and probably not accurately rated and really doing less for long term use) you may be better off sending all your low frequency energy to your subwoofer which has a separate amplifier, hopefully more powerful to handle the low frequencies; and the speaker and enclosure is tuned better for these low frequencies; at the same time the amps in the receiver don't need to work as hard since they are relieved of the hardest job of the system and the main speakers don't need to produce nearly as much program and can concentrate on the rest of the sounds in the room.
Remember, however, that in h.t. use, most of your sound is being produced by the center channel and that is what really needs to be the clearest so setting a higher high-pass filter on this and leaving the l/r to play lower frequencies may benefit the system.
Whatever you do, remember a couple of things: the "LFE" (.1) channel is programmed with sounds as high as 120hz so its not a good idea to set it lower with the subwoofer's lp filter; use the reciever's lp filter if you can to control the sub because (I believe but could be wrong) that the receiver will route the lfe sound appropriately (if you set it to <80 then I believe it will send the 80-120 material to your mains? someone correct me if I am wrong.) or it will send the full LFE sounds to the sub and only use the crossover filters to control sounds originally routed to main speakers. You want all frequencies to go to a speaker capable of reproducing the sounds, so don't let the fronts play full range (no filter) unless they really can play full range, or else any sub-bass sound in the program may not make it to the room!
I found that in my system (without any special eq or room deadening material other than couches) it is hard to make the subwoofer transparent and I can hear where it is, and the only real way to make it really mate well with the system is to use low crossover / lp filters on it, so the main speakers need to be able to produce low enough frequencies to make the crossover transparent (crossover being the frequency/ies from the l/c/r to the sub, not a particular piece of equipment)
These are all ideas to consider, not direct directions of how to set up your system. There is no "perfect" solution and all systems will have a compromise somewhere so understanding all the details will help you choose the best compromise.
I found that the reading material on the Hsu Research website for sub placement and sub setting is not the same as most people recommend, but from an acoustical analysis point of view I found it very helpful in making some decisions in how to set up my system, and I recommend reading it for further ideas (not anything I pointed out here, so it is all new!)