LFE LPF vs Crossover Frequency

Eppie

Eppie

Senior Audioholic
In another thread they were discussing various sub-woofer settings. The comments on LFE LPF and crossover settings had me a bit confused. Why are there separate settings and how are they related? A little on-line research cleared the air. (I'll refer to the Denon manual as that is what I own.)
(Feel free to quote any errors below and I'll amend the post accordingly. This is my basic understanding of the topic and hopefully kept the explanation simple enough for beginners to understand.)

LFE, or low frequency effects, is part of the digital surround sound spec, or the 0.1 in the 5.1. There is a good explanation of its development in this article:
https://hometheaterhifi.com/editorial/the-misunderstood-01-lfe-channel-in-51-digital-surround-sound/
I highly recommend this article if you want a deeper understanding of bass management in movie sound tracks.

This is a separate low frequency effects channel and while it's not considered part of the lower frequencies in, say, music, it can contain low frequency content from other channels so it is not an entirely separate channel in the strict sense. If that sounds confusing, read the above noted article. It's primarily the digital channel for your movie rumbles and explosions. When you set the LFE LPF (low pass filter), you are setting the highest bass frequencies that will be sent to your sub for effects. It's labeled as a low pass filter because there is a hard cutoff at 120Hz in the spec, but since most sound engineers roll off the effects at 80Hz, many AVRs default to a LPF setting of 80Hz. Since the LFE channel incorporates sounds from other channels, you can set the LPF to values higher than 120Hz but it is uncommon to use a higher setting.

Going over the Denon manual, setting the subwoofer mode to LFE passes the low frequency signals from all speakers set to "small" to the sub. Setting the mode to LFE+Main sends the low frequency signal from all channels to the sub, regardless of the size setting. The distinction is that if speakers are set to large, they still get the full range signal with the low pass filter also sending low frequencies to the sub (deep bass from both the sub and mains/speakers set to large). Using combinations of large / small and LFE / LFE+Main you can control where the bass effects are sent, although it is most common to set all speakers to small and let the sub handle bass effects (LFE setting). Technically, with all speakers set to small, LFE+Main should yield the same result.

With most AVRs, if the subwoofer channel is enabled, you can set the crossover point for all speakers or individually set the crossover point for each pair of speakers (channel: front, center, surround, back, etc.). The Denon manual states that the low frequencies will be output to the subwoofer if enabled. The LFE LPF and crossover frequencies both default to 80Hz, but potentially they can be different. The crossover setting covers content not delivered to the LFE channel as part of bass effects. The above article implies that there is some overlap here, so there is some magic in the surround spec with multi-channel bass management, but this primarily covers 2 channel content and the rest of the bass in multi-channel content. Offloading the deep bass to the subwoofer has certain benefits but I won't go into details here.

Why the two settings? Many people will likely opt to have the LPF and crossover set to the same frequency in the 80Hz to 100Hz range. While deep base has the property of not sounding directional, those with speakers capable of going very deep might opt to have the LPF higher for movies but prefer a lower crossover point for music to keep most of the sound emanating from the front stage. Others may prefer a high crossover point to clean up the main speakers. Others may use different frequencies to fine tune a system to match a room's acoustics. It's about flexibility and personal preference. The two settings are there because modern AVRs have the subwoofer doing double duty, playing both surround effects and deep bass content.
 
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lovinthehd

lovinthehd

Audioholic Jedi
I don't know why they put the LPF of LFE in avrs generally, it causes more confusion than benefit IMO but it only limits the LFE channel content (the .1 channel if present/used in a recording like a movie or multi-ch music discs). While there can be more content than the usual limit of 120hz in the LFE channel, nothing to really anticipate/worry about in any case. Bass management is a bit different than managing LFE, too, and depends on mix of speakers/subs. Some mix up LFE and subwoofer in terms of using the terminology, too. My .02....
 
Pogre

Pogre

Audioholic Overlord
Setting the mode to LFE+Main sends the low frequency signal from all channels to the sub, regardless of the size setting.
This is AKA "Double Bass" on some models, and generally not the preferred setting.

I know which thread you're talking about!

*Edit: Wait, LFE + Main sends low frequency signals to both your subs and your main speakers, AKA "Double Bass".
 
TLS Guy

TLS Guy

Audioholic Slumlord
This is AKA "Double Bass" on some models, and generally not the preferred setting.

I know which thread you're talking about!

*Edit: Wait, LFE + Main sends low frequency signals to both your subs and your main speakers, AKA "Double Bass".
Actually that is the preferred setting for capable speakers. If you have speakers with a good accurate bass, and good power handling in the bass that is what you should use.
 
lovinthehd

lovinthehd

Audioholic Jedi
Actually that is the preferred setting for capable speakers. If you have speakers with a good accurate bass, and good power handling in the bass that is what you should use.
Why? And define "capable" speakers.
 
Eppie

Eppie

Senior Audioholic
Actually that is the preferred setting for capable speakers. If you have speakers with a good accurate bass, and good power handling in the bass that is what you should use.
There is some logic to that if your speakers go low enough. It would be similar to having multiple subs, except you don't have the ability to move them around the room as you do with dedicated subs. I think that gets into a deeper discussion of what low frequency bass can do in a full range cabinet and what happens when you try to send frequencies below what a speaker is rated at but that's getting beyond my current level of knowledge. Should be some speaker design articles on the web that explain that.
 
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M

Mr._Clark

Audioholic Chief
In another thread they were discussing various sub-woofer settings. The comments on LFE LPF and crossover settings had me a bit confused. Why are there separate settings and how are they related? A little on-line research cleared the air. (I'll refer to the Denon manual as that is what I own.)
(Feel free to quote any errors below and I'll amend the post accordingly. This is my basic understanding of the topic and hopefully kept the explanation simple enough for beginners to understand.)

LFE, or low frequency effects, is part of the digital surround sound spec, or the 0.1 in the 5.1. There is a good explanation of its development in this article. I highly recommend this article if you want a deeper understanding of bass management in movie sound tracks.

This is a separate low frequency effects channel and while it's not considered part of the lower frequencies in, say, music, it can contain low frequency content from other channels so it is not an entirely separate channel in the strict sense. If that sounds confusing, read the above noted article. It's primarily the digital channel for your movie rumbles and explosions. When you set the LFE LPF (low pass filter), you are setting the highest bass frequencies that will be sent to your sub for effects. It's labeled as a low pass filter because there is a hard cutoff at 120Hz in the spec, but since most sound engineers roll off the effects at 80Hz, many AVRs default to a LPF setting of 80Hz. Since the LFE channel incorporates sounds from other channels, you can set the LPF to values higher than 120Hz but it is uncommon to use a higher setting.

Going over the Denon manual, setting the subwoofer mode to LFE passes the low frequency signals from all speakers set to "small" to the sub. Setting the mode to LFE+Main sends the low frequency signal from all channels to the sub, regardless of the size setting. The distinction is that if speakers are set to large, they still get the full range signal with the low pass filter also sending low frequencies to the sub (deep bass from both the sub and mains/speakers set to large). Using combinations of large / small and LFE / LFE+Main you can control where the bass effects are sent, although it is most common to set all speakers to small and let the sub handle bass effects (LFE setting). Technically, with all speakers set to small, LFE+Main should yield the same result.

With most AVRs, if the subwoofer channel is enabled, you can set the crossover point for all speakers or individually set the crossover point for each pair of speakers (channel: front, center, surround, back, etc.). The Denon manual states that the low frequencies will be output to the subwoofer if enabled. The LFE LPF and crossover frequencies both default to 80Hz, but potentially they can be different. The crossover setting covers content not delivered to the LFE channel as part of bass effects. The above article implies that there is some overlap here, so there is some magic in the surround spec with multi-channel bass management, but this primarily covers 2 channel content and the rest of the bass in multi-channel content. Offloading the deep bass to the subwoofer has certain benefits but I won't go into details here.

Why the two settings? Many people will likely opt to have the LPF and crossover set to the same frequency in the 80Hz to 100Hz range. While deep base has the property of not sounding directional, those with speakers capable of going very deep might opt to have the LPF higher for movies but prefer a lower crossover point for music to keep most of the sound emanating from the front stage. Others may prefer a high crossover point to clean up the main speakers. Others may use different frequencies to fine tune a system to match a room's acoustics. It's about flexibility and personal preference. The two settings are there because modern AVRs have the subwoofer doing double duty, playing both surround effects and deep bass content.
Ed Mullen has a pretty good explanation of this at the following link. It seems to me that the asymetry in the high and low pass filters at the crossover frequency is guaranteed to result in a bump if the speaker and the sub both have a relatively flat SPL in the crossover region.

>>>“Here is the best way to understand Small/Large , LFE/LFE+Main and the LPF for LFE.

  • Small applies a 12 dB/octave high pass to the speaker at the selected crossover frequency.
  • Small sends a duplicate signal to the subwoofer and applies a 24 dB/octave low pass to the subwoofer at the selected crossover frequency.
  • LFE means the subwoofer gets the LFE channel and redirected bass from any channels set to Small.
  • Large sends that channel a full-range signal. This is also known as ‘Full Band’.
  • LFE+Main sends a duplicate signal to the subwoofer for any channel set to Large and applies a 24 dB/octave low pass to the subwoofer at the selected ‘crossover’ frequency1.
  • When set to LFE+Main, the subwoofer still gets the LFE channel and redirected bass from any other channels still set to Small.

1 Note if the mains are set to Large and the subwoofer mode is set to LFE, there is no crossover selection available for the mains. If the mains are set to Large and LFE+Main is selected, then the ‘crossover’ selection becomes available for the mains. This really isn’t a true ‘crossover’ at all, because the mains are still being sent a full-range signal. What the ‘crossover’ becomes when LFE+Main is selected is the low pass filter setting for the duplicate signal being sent to the subwoofer. In this sense, the user can select the amount of ‘overlap’ between the mains and the subwoofer.

This distinction is not well understood by most enthusiasts, nor is it well communicated by the AVR GUI menu. It suggests or implies a crossover is still being applied to the mains when they are set to Large, when in reality that is not the case.

The LPF for LFE is the low pass filter setting for the LFE channel. Normally this is set to 120 Hz, since that is typically the upper limit used by DVD mixing engineers.”<<<

 
TLS Guy

TLS Guy

Audioholic Slumlord
Ed Mullen has a pretty good explanation of this at the following link. It seems to me that the asymetry in the high and low pass filters at the crossover frequency is guaranteed to result in a bump if the speaker and the sub both have a relatively flat SPL in the crossover region.

>>>“Here is the best way to understand Small/Large , LFE/LFE+Main and the LPF for LFE.

  • Small applies a 12 dB/octave high pass to the speaker at the selected crossover frequency.
  • Small sends a duplicate signal to the subwoofer and applies a 24 dB/octave low pass to the subwoofer at the selected crossover frequency.
  • LFE means the subwoofer gets the LFE channel and redirected bass from any channels set to Small.
  • Large sends that channel a full-range signal. This is also known as ‘Full Band’.
  • LFE+Main sends a duplicate signal to the subwoofer for any channel set to Large and applies a 24 dB/octave low pass to the subwoofer at the selected ‘crossover’ frequency1.
  • When set to LFE+Main, the subwoofer still gets the LFE channel and redirected bass from any other channels still set to Small.

1 Note if the mains are set to Large and the subwoofer mode is set to LFE, there is no crossover selection available for the mains. If the mains are set to Large and LFE+Main is selected, then the ‘crossover’ selection becomes available for the mains. This really isn’t a true ‘crossover’ at all, because the mains are still being sent a full-range signal. What the ‘crossover’ becomes when LFE+Main is selected is the low pass filter setting for the duplicate signal being sent to the subwoofer. In this sense, the user can select the amount of ‘overlap’ between the mains and the subwoofer.

This distinction is not well understood by most enthusiasts, nor is it well communicated by the AVR GUI menu. It suggests or implies a crossover is still being applied to the mains when they are set to Large, when in reality that is not the case.

The LPF for LFE is the low pass filter setting for the LFE channel. Normally this is set to 120 Hz, since that is typically the upper limit used by DVD mixing engineers.”<<<

What Ed says, has some merit. However you actually get a dip as when you add speaker roll off and the receiver high pass roll off you get a sixth order roll off. So actually a fourth order roll off actually splices with the sub fourth order low pass roll off if you use LFE plus main.
 
flyboylr45

flyboylr45

Full Audioholic
I know this is well explained but for some reason, I still don't quite understand it. Which setting would you use to send LFE to both subs and mains? In my case, I want the mains to get full range and LFE. Also, I want the subs to get the same low-frequency signal and LFE from the other channels that are set to small. Is it possible to send the bass signal from all channels set to small to both the mains and subs?
 
T

Trebdp83

Audioholic Field Marshall
I know this is well explained but for some reason, I still don't quite understand it. Which setting would you use to send LFE to both subs and mains? In my case, I want the mains to get full range and LFE. Also, I want the subs to get the same low-frequency signal and LFE from the other channels that are set to small. Is it possible to send the bass signal from all channels set to small to both the mains and subs?
If using a Denon, set it to LFE+MAIN.
 
T

Trebdp83

Audioholic Field Marshall
While Denon has been criticized for their manuals in the past, o_O, I do like their explanation of the use of LFE+MAIN. I think SIGNAL/CHANNEL is too often left off of LFE. The LFE SIGNAL/CHANNEL carries low frequencies meant for a subwoofer. Low range signals can be played from mains but should not be confused with the LFE SIGNAL/CHANNEL. Many speakers aren’t up to the task.

I sort it out in my own head by thinking of the channels as lanes. The truck/LFE lane does the heavy lifting. Sure, some guy in the fast lane has a pretty big truck/speakers loaded up with lots of weight/sound but he’s gonna’ come upon a big hill/bass and need to unload some of it on a semi/sub meant to do the job. The .1 channel/lane will have loads exclusively assigned to them that simply cannot be hauled in another lane by a lesser truck. Hell, some movies require a separate track, train track that is, that runs alongside the road.:D

Though they are few, there are some 5.0 signals. If one was running speakers at FULL RANGE on that track, low range signals would not be sent to the sub without setting LFE+MAIN to ON because there is no .1 channel load to carry and the the crossover is disabled with the FULL RANGE setting. The LPF? Well, it justs limits the speed/range of the semi. You don’t want it audible/in your lane.:oops:
FD6105BD-5290-40EC-A75B-887D85A0E18F.jpeg
 
flyboylr45

flyboylr45

Full Audioholic
So with LFE+Main, both the subs and front channels will be getting the .1, correct?

Sent from my SM-N975U using Tapatalk
 
Pogre

Pogre

Audioholic Overlord
Actually that is the preferred setting for capable speakers. If you have speakers with a good accurate bass, and good power handling in the bass that is what you should use.
I did say "generally" and I'm a little foggy on what you mean by capable speakers...
 
Eppie

Eppie

Senior Audioholic
So with LFE+Main, both the subs and front channels will be getting the .1, correct?

Sent from my SM-N975U using Tapatalk
From the article I linked to above:
"So, on some soundtracks, sending only the LFE to your subwoofer could leave it with nothing to do while your mains struggle. While some people like to feed a full range signal to their main speakers, they should in addition send those channels’ bass to the sub so it can fill in the extreme bottom octave information that might be in those tracks. Mains which can reach as low as a dedicated subwoofer are few. Unfortunately this flexibility is not always available on consumer equipment; setting a main speaker to ‘large’ often excludes the subwoofer from getting a share of that signal.
On the flip side, you don’t need a subwoofer to hear the content of the LFE track. If your mains are of substantial mettle, and you don’t have a sub, bass management can usually re-route the LFE to your fronts.
Therefore, the subwoofer jack can contain only LFE (not recommended), a mixture of LFE and bass from the main 5 channels, or nothing at all."

The .1 is a dedicated effects channel. With no sub enabled, I would expect the effects channel to be mixed with the mains (as mentioned above), otherwise you would be missing content without a dedicated sub. With LFE+Main, the description is that the mains (fronts) get a full range signal and some of the bass is mixed into the LFE channel. What it does not mention is any LFE signal getting mixed into the mains. My interpretation of that would be that no, the front channels do not get .1 in LFE+Main. If you have a dedicated sub enabled, then the LFE channel is directed just to the sub.
 
Eppie

Eppie

Senior Audioholic
I know this is well explained but for some reason, I still don't quite understand it. Which setting would you use to send LFE to both subs and mains? In my case, I want the mains to get full range and LFE. Also, I want the subs to get the same low-frequency signal and LFE from the other channels that are set to small. Is it possible to send the bass signal from all channels set to small to both the mains and subs?
My interpretation of that article is no to your last question. Bass signals from speakers set to small get mixed into the LFE channel and routed to the sub. What you are suggesting is that bass from the surrounds set to small get mixed into both the LFE and the mains (set to large). There is no mixing between main and surround channels in an AVRs DSP. Only mixing into the LFE channel, which is important for 5.0 content (and music).
 
William Lemmerhirt

William Lemmerhirt

Audioholic Warlord
So with LFE+Main, both the subs and front channels will be getting the .1, correct?

Sent from my SM-N975U using Tapatalk
What are your mains? Sending full range signals down into the 20’s is a task for most loudspeakers out there. But sending the .1 seems like a good way to destroy them.
 
flyboylr45

flyboylr45

Full Audioholic
So in LFE+Mains, Mains will get LFE (.1) and so will the subs. All other speakers set to small will send their low level info to the subs only, not the mains. Correct?

Sent from my SM-N975U using Tapatalk
 
flyboylr45

flyboylr45

Full Audioholic
What are your mains? Sending full range signals down into the 20’s is a task for most loudspeakers out there. But sending the .1 seems like a good way to destroy them.
RBH SVTRS and 2 RBH SV1212NR in the rear when I get them.

Sent from my SM-N975U using Tapatalk
 
Eppie

Eppie

Senior Audioholic
So in LFE+Mains, Mains will get LFE (.1) and so will the subs. All other speakers set to small will send their low level info to the subs only, not the mains. Correct?

Sent from my SM-N975U using Tapatalk
My understanding is that the Mains do not get any LFE with the LFE (subwoofer channel) enabled. Only when the LFE channel is disabled does it get mixed into the Mains. The whole point of the LFE channel is to offload deep bass from the mains to improve headroom / dynamic range in both the original mix and the mains themselves. To feed LFE to the mains would defeat that purpose.

To recap, LFE mixes bass from small speakers to the sub. LFE+Mains mixes bass from all speakers to the sub. If all speakers are set to small, then the effect should be the same with both settings.
 
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Teetertotter?

Teetertotter?

Audioholic
I have the crossovers for all my speakers manually adjusted to 80HZ, via the Denon AVR. Speakers are all on SMALL. It works well in my application with accurate sound from my system. I listen to mostly movies, and some internet Mp3 on occasion. My Denon auto senses DD Movie + Surround and MP3 Multichannel. The sub reacts accordingly. I guess there are some technicalities. ;)
 
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