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LFE & Bass Mgmt settings

Orbison

Well-Known Member
Just read a couple of interesting articles on this stuff - don't remember seeing some of it discussed here before.

One article recommended setting crossovers for all speakers in 5.1 & 7.1 systems to the same freq to avoid phase cancellation problems.

The other article suggested that LFE program content goes up to 120 Hz, so the LFE low-pass filter should be set to 120Hz.

So the question is, how many of you have your system set up this way? I've been using an LFE low pass freq of 80Hz but I'm going to try 120Hz.

Comments?
 

Zing

Retired Admin
Famous
Setting the LFE low pass for 120Hz is not a bad thing at all, electronically speaking. There's nothing wrong with keeping all that low frequency content out of your speakers. It only becomes a problem if your sub isn't ideally placed because those sounds may be localizable.

As for the phase issues, I'll defer to the more knowledgeable.
 

Towen7

Well-Known Member
Staff member
Moderator
I have matching speakers in all five positions so of course I use the came crossover frequency for all (70 Hz IIRC). The LFE crossover frequency is set to 80 Hz though because I don't want to send frequencies higher than test to the sub because I dont want to be able to "locate" the sub by having it play frequencies that high. That said my sub is located near the front left speaker so that may not be a factor worth worrying about. I'll try it but I don't expect a significant difference.
 

Orbison

Well-Known Member
Yeah I know about "locating the sub" with freqs higher than 80Hz, but at the same time I wonder what LFE content I might be missing if I set the LFE freq to 80Hz.

"if your sub isn't ideally placed" is the key. The article also recommended 4 subs - one on each side of the room, so I guess the author wasn't concerned about location higher LFE freqs in a setup like that.
 

Zing

Retired Admin
Famous
Orbison said:
...but at the same time I wonder what LFE content I might be missing if I set the LFE freq to 80Hz.
You won't be missing anything. It'll just be produced by another speaker instead of the subwoofer.
 

Towen7

Well-Known Member
Staff member
Moderator
Wait... Isn't the LFE channel discreet and sent to the sub only? Which speaker(s) would get the frequencies above the cutoff?
 

Zing

Retired Admin
Famous
You know, I hadn't considered that. I always assumed everything above my 80Hz point would go to my mains but you're right, it is discreet. If it's put solely in the LFE channel, it's not going anywhere else.
 

Flint

Dog Faced Pony Soldier
Superstar
LFE is the .1 of the 5.1 or 7.1 soundtrack and can have content as high as 120Hz in it. Because of this, the subwoofer's built in crossover should be disabled or adjusted to the highest frequency do it will reproduce the higher frequencies when the receiver sends the LFE signal to the subwoofer output. We have talked about this in great length at our former home.

The subwoofer crossover frequency in the receiver is to adjust the crossovers for the main, center and surround speakers so that bass which is in their recorded channels in the soundtrack can be send to the subwoofer (which is also getting the LFE signal) in order to ensure the smaller HT speakers are not attempting to produce deep bass and that the bass gets reproduced by something when those speakers cannot. This is the "bass management" part of bass management. Setting all the speakers to the same crossover frequency makes sense for a non-ideal setup where you are not 100% in control of the acoustics and the room. It is an easy way to get past some of the gotchas associated with bass management. However, if you can adjust your room, speakers, acoustics, and measure their performance with a decent measurement setup, it isn't necessary to set the crossover to the same frequencies.

If you set the crossover for each speaker type to be most appropriate, then you get the highest fidelity, but it can be tricky to make it perfect. If you set the crossover to the same frequency for every channel, it the bass will be at least consistent even if it isn't the best possible sound for each speaker.

So, setting the channel crossovers is separate from setting the LFE crossover - they are two different things.

When you set the channel crossovers, the bass below the crossover point for each channel is sent to a Subwoofer mixer which combines those signals together into one signal which is sent to the subwoofer output. It also combines the LFE channel into that output, so you are in essence sending up to 8 channels of bass to one output. You have the bass for each of the main speakers (LF, LR, C, RSS, LSS, RRS, LRS) plus the signal in the LFE channel all going to the same speaker - which can be very difficult to reproduce and which is why an excellent subwoofer is clearly audibly superior to one of those cheap small noise makers.

In my rig I have these signals being combined and sent to my subwoofer(s):

Left & Right Stereo = 40Hz and lower
Center = 50Hz and lower
All surround channels - 60Hz and lower
LFE = entire channel at 120Hz and down

My preamp has the ability to set a crossover on the LFE channel and redirect the higher frequencies to my main speakers, but I choose to not use that feature.
 

soundhound

Well-Known Member
I use a crossover point for my VOTTs of 100Hz which cures a room issue, but my subs are right next to them and run in stereo. The surrounds are run full range ( I don't use a center speaker ). The LFE is passively mixed into the subwoofer channel and has no upper bandwidth limit.
 
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