Quote:
Originally Posted by
jimshowalter 
Why would you do it that way instead of running the dedicated LFE from the Oppo to both subs, and Y'ing the L and R full-range from the Oppo to both subs?
Sorry for the dupe post!!! I forgot to include the quoted post that I'm replying to.
Well, mainly because of a post i read awhile back in Audioholics by a poster with the user name Soundhound:
I have used my subwoofers in "stereo" for years. Read the following and see if you think you might get some benefit from this setup. To do it, all you need is two powered subwoofers with internal line level crossovers, and two extra interconnects.
While it is true that low bass is in theory non directional, the way that bass mixes in the room is not. An example - suppose that you have a group of performers on a stage and they are being recorded by two or three omni directional microphones in front about 15 feet away, which is a common technique. Now say you have someone playing a bass drum or string bass on the extreme left of the stage. The sound of that instrument will reach the left microphone earlier than the right microphone. Considering the frequency of the instruments will be be around 30 Hz in the case of the bass drum and 40 Hz in the case of the bass, the delay in the sound reaching the left and right microphones will be as much as half a wavelength. If you were to play this with a single subwoofer, or two subs with the bass between the channels summed by the crossover as it is when you use the "sub/LFE" output on your pre/pro, this acoustic delay would simply cause peaks and dips in the response of the bass from that instrument. However, if you use stereo subs and are hearing ture stereo bass, this delay between the sound reaching the left and right microphones is heard as natural acoustic mixing of the bass frequencies from those instruments in the listening room, just as it did in the original recording venue. The way the bass mixes in the room is natural, acoustic, and dynamic over time.
As an example of another real-world benefit of stereo subs located next to the main left and right speakers, consider the following example. You have your single subwoofer connected to the "subwoofer/LFE output of your pre/pro, and the sub is located next to your couch, and you have it crossed over at 80Hz (in other words, a pretty conventional arrangement). The distance from your listening position to the mains is 10 feet (the sub is 10 feet from your mains). You play a studio recording that has a bass player coming from the right speaker. He plays an open "E" string. Guess what? The fundamental frequency of that string (about 40Hz) will come from the subwoofer next to you. The second harmonic at around 80Hz will come from both your sub and your main speakers. The 3rd harmonic (and above) of the bass will come exclusively from your mains. As you can imagine, this plays absolute havoc with the harmonic presentation and structure and of the instrument! The effect is of the same type, if not to the same degree, of taking the tweeter out of your speaker cabinets and relocating them a couple feet away. Fundamental frequencies coming from one place, and the harmonics coming from another. The closer the notes being played are to the bass crossover frequency, the worse this disembodiment of the fundamental from it's harmonics will be, as the phase difference between the two will be greater due to the higher frequency. Adjusting the "phase" control of your subwoofer will not correct this: it only corrects for one specific frequency, that of the crossover, and musicians hate being restricted to playing only one note (at least good ones!).
Electronics designers take great pains to ensure that all the frequencies in an amplifer (especially at the low end) are amplified with a minimum of phase shift (this is the reason for DC coupling) - Why mess this up if you don't have to?
I notice an increase in sense of "air" and "realism" on almost all recordings that have live performers, even studio recordings. While low bass cannot be heard as "directional" in the traditional sense, the way the bass interacts as it mixes acoustically in the listening room certainly can be sensed and felt as added realism, and the filling in of that dimension that you are in the space where the recording was made. In addition, sound effects that were recorded in stereo for movies will have their bass reproduced in stereo. This is especially apparent in city street scenes when a bus or train passes. It just sounds more "real" as a result of the way the bass mixes in the room, just like it would if you were there. This benefit wil also be apparent when playing multi-channel discs like SACD and DVD-A, as the main left and right channels will give this added realism from the natural acoustic mixing of the low bass.
This setup is completely transparent to HT, multi-channel, and stereo playback, as anything you throw at it will have the bass reproduced correctly, regardless of format. No more fooling around with the logisitics of what to do with the subwoofer when playing SACD/DVD-A - the bass just reproduces seamlessly.
And best of all, if you have the two subs and extra interconnects, doing this costs nothing.
The ".1" channel is a convention that came from the movie industry, and had no precedent in the music recording industry. It works for movies since in a large theater, very few people are in the "sweet spot", so a mono LFE track is a reasonable compromise.
The ".1" track is a bad fit for music however. Forcing the "movie" model for speaker configuration on a system playing music where a significant number of people are in the "sweet spot" does not work well - it's a kludge in my opinion.
You're basically thinking of your main speakers/subs as _very_ extended full range speakers that can take the demands of film/HT, while at the same time being optimal for music. The LFE track in movies is simply being routed as a mono signal to both of your mains, where it ends up in both of your subs, just the same way it would be if your subs were connected conventionally to your pre/pro with a "Y" adapter. When playing music (either stereo or multi-channel SACD/DVD-A), the entire music spectrum, including the bass, is in stereo, and coming from where it should be: next to (or part of) your mains. One of the results is a cleaner, more coherent and focused soundstage. I've also noticed a heightened sense of realism, and of feeling I'm in the recording venue. Even hearing the low frequency content of the air conditioning rumble and "room tone" that exists in all large spaces in stereo rather than mono enhances the sense of realism. A side benefit is that in movies, you will hear the extremely low frequency content of stereo sound effects (like street scenes with busses and trains etc) that reside in the main left and right speakers in stereo - something that you won't hear in a movie theater, or even on a movie dubbing stage since the mains in these venues only respond down to around 40Hz.
If you have to use a single subwoofer for whatever reason, at least take into consideration the above and place the sub as close to the mains as possible, preferrably equal-distant from both. This is still a compromise however, since a single sub is still a significant distance from one of the mains.
While it is true that as the frequency of sound goes down, the ability to locate the source diminishes, but there are a lot of other things to take into consideration. It's just not as simple as "bass is omni-directional so it doesn't matter where you put the sub"!
To configure your system to take advantage of stereo bass, do the following:
First of all, move one subwoofer as close as possible to your main front left speaker. Move the other subwoofer as close as possible to your main front right speaker.
In the preamp's speaker setup menu, set your main left and right front speakers to "Large". Set the subwoofer to "Off". Set your center and surrounds to "small" or "large" depending on their size. Most setups use the "small" speaker setting.
Disconnect the subwoofers from the LFE/Subwoofer output of the preamp. Run an interconnect from the main left and right outputs of the preamp to the "line input" of each subwoofer - the left output to the left subwoofer, and the right output to the right subwoofer. Run an interconnect from the "line output" of your left subwoofer to the input of your left channel power amplifier. Run the right subwoofer's "line output" to the input of your right channel power amplifier.
Set the crossover frequency of both of your subwoofers to the crossover frequency you used previously in your preamp. You will probably need to re-adjust the level controls of your subwoofers.
