LFE vs High-level subwoofer connection, for FIDELITY

@larryincmh 

isn't bass mono and omnidirectional by nature, so bass should not be evident from a left channel or right channel anyway. It should just be sound pressure in a room.

Omnidirectional is not the entire picture, especially in a real room. SPL is exactly how microphones and your ears can localize it. Further, you can localize it by feeling it. You can also localize it from feeling and hearing room distortion. That's from 40Hz that you have to rely on additional senses and clues. 50Hz and above, it's pretty easy to directly localize with just the ear. Now if it's an anechoic chamber, I would say it's hard to localize bass below 80Hz. But in a real room, I say below 40Hz.

You can also confirm the metadata in your music using a visualizer. It will show you a lot of localizable bass from one channel but not the other, or modulating between both channels to create the stereo effect. A good example I quickly use is the intro to the band Soundgarden, Fell on Black Days. There's a guitar solo extending to around 50-60Hz on only the right channel. You can easily pick it up with just the ears in that frequency range. I can upload a screenshot of a visualizer later.

@bartsw so I had to listen to that Soundgarden song on my system. As the song starts I hear the music only on the right channel which is the guitar solo. Then a few seconds in just left of center another guitar comes in followed by drums somewhat in the center and then the entire soundstage fills from left to right. As for the bass what I feel is the pressure in my chest and in the room I don’t specifically hear the low notes from any particular location.   Hopefully the OP doesn’t mind that we slightly hijacked the thread for this conversation.

@larryincmh yes a guitar solo. I was incorrect when I said it was around 50-60Hz. It's actually below 50Hz. And as you stated, you could simply hear it on the right channel. I'll attach a picture of the visualizer on my streamer to show it when I get to a computer. Therefore, if you have an 80Hz crossover using LFE, it will come from both channels instead of just the right. It will be less stimulating and dynamic.

@larryincmh here's a visualizer screenshot from my streamer. You see there's signal in the right channel but there are no vertical bars above 50Hz. That means the signal is below 50Hz.

https://mega.nz/file/yAwmySqR#aYn8_6T69zXXvNwx3Ld3mGVuzhXlRoIrA9w6mQx39s8

This is what a more full signal looks like

https://mega.nz/file/OcpiBRRZ#KCpKJ74dFsX-ZwSlyTb7bxrltwYbFxvCfE1IVPR9V_I

I also have a desktop software that shows more detail when I get to the PC.

There has been some very good technical explanations thus far. Just adding a couple of extra points of clarification.

LFE = Low Frequency Effects and is strictly an AV/Surround Sound term. It’s the .1 or .2 part of a 5.1 or 7.2 system reserved for sound effects like explosions. The subs are sent 100% of the LFE content + whatever content is sent from the main and surround speakers as per their crossover settings, unless they are set to large. The sub is simply configured to bypass it’s internal crossover if the AVR is managing the signal sent to the subs.

In a HiFi stereo set up, there are many examples of music where lower frequencies are coming mostly, or exclusively from one channel or the other, or separate sources of low frequencies coming from left and right (E.G., Friday Night in San Francisco.).

So with stereo subs, while it is ideal that you can’t "hear" the localized subs , each sub should seamlessly augment the L or R main. Yes there will be some mono-blending.

The other advantage of treating subs as stereo pairs, is adjusting for the room (assuming you have good EQ capabilities built in or use external DSP). As an example, many of us have rooms that are not acoustically symmetrical, even with treatment. So using REW measurements, the EQ settings of my subs are each set differently.

Subs also pressurize the room. In my case they are behind the MLP, closer than the mains, to pressurize the open space behind the MLP and to tame bass build up in the corners of the front wall. (Pics in my virtual system). I cannot tell that I have subs behind me. My baby MBLs just sound really big.

Point is, properly located and configured stereo subs do more than just augment omnidirectional bass.

If you have incremental phase adjustment, rather than just 0 or 180 like REL, you can potentially bypass the sub crawl mentioned earlier by reversing the polarity on your speaker taps and playing a tone at the crossover frequency to L/R speakers separately. Adjust phase for each sub until the tone is the quietest. They are now in phase. Don’t forget to put the speaker cables back to the correct polarity.

@larryincmh I have a Yamaha AVR powering the living room AV system. Are you using stereo mode in the app or Patterns to switch from Stereo to Surround? Depending on your subs, Patterns might give you more options to set up the subs in "full stereo" vs. "mostly-stereo" mode. Just a thought.          

Lastly, if you choose a straight-up high-level / speaker-level connection, you can connect from the speaker tap(s), which may be more convenient that connecting to the amp, or use less wire.

FWIW, hope it helps.