Why is LFE so hard to pull off well? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 20 Old 04-21-2020, 09:52 AM - Thread Starter
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Why is LFE so hard to pull off well?

Let’s start off with an example: take two UM18 and a nu6000, what is the most asked question after this? “How do I get more midbass?” And the direct opposite: the VBSS, “I want more low end rumble”. Which brings me to my point.

In order to do LFE right you will need two or more subs with a xo playing at different frequencies with different alignments and or different drivers. Also, just because you modeled your driver and it SAID it CAN play a frequency doesn’t entirely mean it should.

I know of different style of drivers - pa, home theater and car?

Box alignments- IB, ported, sealed, horn and the list goes on...

By definition LFE is everything below 120hz and I know a lot of people only focus on under the xo point (around 80hz).

Soooo..... what do you do to get the best LFE? What setup, box and or driver mix? Do you only care about lower than xo? Is there a one sub does it all? I thought IB but I’ve heard some still look for midbass. And horns do 20-100hz but lack the rest. Maybe four 21” sealed?

This is not a question for my setup, This is just a random - how did/do you do it?
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post #2 of 20 Old 04-21-2020, 10:09 AM
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Quote:
Originally Posted by Audiophile75 View Post
Let’s start off with an example: take two UM18 and a nu6000, what is the most asked question after this? “How do I get more midbass?” And the direct opposite: the VBSS, “I want more low end rumble”. Which brings me to my point.

In order to do LFE right you will need two or more subs with a xo playing at different frequencies with different alignments and or different drivers. Also, just because you modeled your driver and it SAID it CAN play a frequency doesn’t entirely mean it should.

I know of different style of drivers - pa, home theater and car?

Box alignments- IB, ported, sealed, horn and the list goes on...

By definition LFE is everything below 120hz and I know a lot of people only focus on under the xo point (around 80hz).

Soooo..... what do you do to get the best LFE? What setup, box and or driver mix? Do you only care about lower than xo? Is there a one sub does it all? I thought IB but I’ve heard some still look for midbass. And horns do 20-100hz but lack the rest. Maybe four 21” sealed?

This is not a question for my setup, This is just a random - how did/do you do it?

I have kind of done it the "wrong" way imo, by running a mini marty and now 4 vbss subs, which illustrates your point about having a Marty and then coming to the realization that I now want "mid-bass" = add some vbss subs.

I don't think it's hard to get it all, its more about doing it right from the start.

If I were to do it over, I would probably build 2-4 21" Devastators and call it done. They pretty well check all my boxes
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post #3 of 20 Old 04-21-2020, 10:15 AM
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Yeah I would be keen to know if there is an effective mix of styles or sizes to cover all the basses (see what I did there ? )

I currently have 1 x 15" 20hz ported, 1 x Boss Platform with 3 x 15" drivers and 5 x dual 4.75" little 30hz ported subs (these 5 are driven from speaker level set to large).

However I am planning on replacing the 15" ported with 4 x 15" LLT tuned to 15hz so would be interested to see if that is the way to go or if there would be a better combination.

And don't forget that the 80hz Xover is only for the speaker channel output - the subs are still receiving 120hz (or higher depending on your LPF setting) signal from the .1 LFE channel.
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post #4 of 20 Old 04-21-2020, 03:09 PM
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Why is LFE hard to get right?
  • Requires the ability to measure the response
  • Room modes
  • Boundary interactions
  • Listening position variablities
  • Variable subwoofer capabilities
  • Difficult speaker/subwoofer splice
  • Phase issues between subwoofers
  • Phase issues between subwoofers and speakers

How to do it right?
Implement a system that provides smooth frequency response with the extension, output and target curve one desires by addressing all of the above.

Have fun!

Craig

Lombardi said it:
"Perfection is not attainable, but if we chase perfection we can catch excellence.
My System (Edited Feb. 2020 to add 4K and Atmos updates)

Last edited by craig john; 04-25-2020 at 04:56 AM.
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post #5 of 20 Old 04-21-2020, 07:25 PM
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Quote:
Originally Posted by Audiophile75 View Post
This is not a question for my setup, This is just a random - how did/do you do it?
Last time (now packed away to be shipped to my new/old home) was 4 FTW21s, sealed with power and EQ to do below 45Hz or so, and the mains had 2 AE TD15S to do from there up to 300Hz to xover to the Unitys. Plus a Crowson.



Most people want too much from too little, that's why they have problems. You can't expect a heavy coned high excursion driver to play well up into the lower midbass like a PA driver can. Plus most people use someone else's design which may not have the actual characteristics they want. Designing my own stuff from scratch makes it easier on my part.



Next time, because I'm back to the huge cathedral ceilinged room, I can afford to go full horn again; Unitys, one of two midbass FL horn designs and some THs to get me to approx 20Hz, and the FTW21s behind the couch for LFE, plus the Crowson. Now I have 4 extra 15's for the surrounds, they be like a Seaton Catalyst 12 in layout, but with 15s.
I had a 5 way fully FL horn system in this room before I moved to a smaller apartment to get work.

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post #6 of 20 Old 04-21-2020, 08:13 PM
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Red face

I looked at lack of coloration lack of distortion and went concrete box ib to 60 hertz , then i wanted a clear dialog center channel and went with 16 midwoofers per l , c, r, ls, cs, rs and for below 20 hertz i went three 15s boss platform that i am changing to use twelve drivers of ten inch diameter to ensure i get some tactile response at my couch.

Back to sanding as i have a looong way to go before the new boss platform is ready.
Hopefully twelve drivers will do it?

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post #7 of 20 Old 04-21-2020, 09:01 PM
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Quote:
Originally Posted by Audiophile75 View Post
By definition LFE is everything below 120hz and I know a lot of people only focus on under the xo point (around 80hz).
Yes, the LFE channel material can be encoded as high as 120Hz. And most AVRs and processors allow one to set the LFE low-pass ('LPF of LFE') to 120Hz which allows the entire LFE channel to be sent to the subwoofer(s) no matter how low the individual speaker channel xovers are set.

However, how much material is actually encoded in the LFE channel between 80Hz and 120Hz is arguable and varies from soundtrack to soundtrack. Some people actually prefer setting the LFE low-pass to 80Hz, instead, and there is some theoretical thought to support that. The difference between using an 80Hz LFE low-pass versus using a 120Hz LFE low-pass is actually quite subtle.
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post #8 of 20 Old 04-21-2020, 09:56 PM
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Quote:
Originally Posted by Audiophile75 View Post
Let’s start off with an example: take two UM18 and a nu6000, what is the most asked question after this? “How do I get more midbass?” And the direct opposite: the VBSS, “I want more low end rumble”. Which brings me to my point.

In order to do LFE right you will need two or more subs with a xo playing at different frequencies with different alignments and or different drivers. Also, just because you modeled your driver and it SAID it CAN play a frequency doesn’t entirely mean it should.

I know of different style of drivers - pa, home theater and car?

Box alignments- IB, ported, sealed, horn and the list goes on...

By definition LFE is everything below 120hz and I know a lot of people only focus on under the xo point (around 80hz).

Soooo..... what do you do to get the best LFE? What setup, box and or driver mix? Do you only care about lower than xo? Is there a one sub does it all? I thought IB but I’ve heard some still look for midbass. And horns do 20-100hz but lack the rest. Maybe four 21” sealed?

This is not a question for my setup, This is just a random - how did/do you do it?
I have 4 capable subs with no need to monkey with crossovers on them to get good chest slam and tactile feel/shake. But, my room is only 2350 cu ft. Were I in a larger room, I might need 4 considerably more potent subs than I have now...

IMHO, it's mostly a case of people's reach exceeding their grasp and not using enough (quality and quantity of) subs for the job at hand.

MiniDSP 2x4HD, UMIK-1, REW... The holy trinity for running multiple subs.

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post #9 of 20 Old 04-21-2020, 09:56 PM
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Originally Posted by A9X-308 View Post
You can't expect a heavy coned high excursion driver to play well up into the lower midbass like a PA driver can.

I have a pair of Behringer B215XLs as my Front L&R - are you saying if I set them to a 60hz crossover (they are only rated to 55hz) I will get good/better mid-bass ?
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post #10 of 20 Old 04-22-2020, 11:58 AM
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I have a pair of Behringer B215XLs as my Front L&R - are you saying if I set them to a 60hz crossover (they are only rated to 55hz) I will get good/better mid-bass ?
If you are sending material below rated tune of a ported box, then yes. This applies to any ported box.

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post #11 of 20 Old 04-22-2020, 02:28 PM
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It's hard to get coz we don't want to move our subs(to a better location)!

I am guilty of that for a very long time, just decided two days ago to move them around a bit and take some measurements. didn't image 2-3ft only for each sub would make an ENORMOUS difference in output and everything else!

confirmed it with measurements in REW too.

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post #12 of 20 Old 04-22-2020, 09:32 PM
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Originally Posted by Balbolito View Post
It's hard to get coz we don't want to move our subs(to a better location)!

I am guilty of that for a very long time, just decided two days ago to move them around a bit and take some measurements. didn't image 2-3ft only for each sub would make an ENORMOUS difference in output and everything else!

confirmed it with measurements in REW too.
Yeah, bass is all about the room.

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Espon 5050UB, 120" screen, AppleTV4k, Harmony Elite, Sony UBP-X700, Pioneer Elite VSX-LX504, Outlaw 7000x, MiniDSP 2x4HD, 2x HSU TN1220HO subs, 2x HSU VTF-15H Mk2 subs, Defintive Technology speakers: CLR2002 x3 for FR, C, FL; BP2x SR & SL; BP1.2x SBL & SBR; ProMonitor 800 x4 height speakers.
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post #13 of 20 Old 04-23-2020, 03:42 PM
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It's hard to get coz we don't want to move our subs(to a better location)!
You may not want to, but many here do it as a matter of course.

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post #14 of 20 Old 04-23-2020, 03:49 PM
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Originally Posted by Audiophile75 View Post
Let’s start off with an example: take two UM18 and a nu6000, what is the most asked question after this? “How do I get more midbass?” And the direct opposite: the VBSS, “I want more low end rumble”.
Of course, those can be the responses of 2 individuals to the same reality.

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Originally Posted by craig john View Post
Why is LFE hard to get right?
  • Room modes
  • Boundary interactions
  • Listening position variablities
  • Variable subwoofer capabilities
  • Difficult speaker/subwoofer splice
  • Phase issues between subwoofers
  • Phase issues between subwoofers and speakers

How to do it right?
Implement a system that provides smooth frequency response with the extension, output and target curve one desires by addressing all of the above.

Have fun!

Craig
cj, you shouldn't scare the kids like that! Actually, truth be told, I'm quivering at just reading your list! That said, the receiver's built-in processing will just take care if it ... right?

Folks think you can just buy a sub, plop it down anywhere, plug it in, and MAGIC! Nope, you get out of it what you put in, like every good thing in life!
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It's a VIRTUAL channel unless stated otherwise.
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post #16 of 20 Old 04-25-2020, 04:57 AM
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cj, you shouldn't scare the kids like that! Actually, truth be told, I'm quivering at just reading your list! That said, the receiver's built-in processing will just take care if it ... right?

Folks think you can just buy a sub, plop it down anywhere, plug it in, and MAGIC! Nope, you get out of it what you put in, like every good thing in life!
I added one!

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"Perfection is not attainable, but if we chase perfection we can catch excellence.
My System (Edited Feb. 2020 to add 4K and Atmos updates)
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I added one!
You're a monster!

It's a VIRTUAL channel unless stated otherwise.
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post #18 of 20 Old 05-20-2020, 11:46 AM
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Please make sure I understand LFE...


LFE is not just a range of lower frequencies (under 120 Hz) but a dedicated and separate channel embedded into Dolby programming to carry additional bass notes, right?
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post #19 of 20 Old 05-20-2020, 12:42 PM
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Please make sure I understand LFE...


LFE is not just a range of lower frequencies (under 120 Hz) but a dedicated and separate channel embedded into Dolby programming to carry additional bass notes, right?

Exactly.

But often in these discussions what is really meant can become a bit blurred, and the use of the term becomes a bit loose.

What is sent to the subwoofer is the LFE channel plus any rerouted bass from any speaker channels to which a crossover is applied (SMALL setting on most AVRs and processors).
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post #20 of 20 Old 06-01-2020, 09:53 AM
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For me, the hardest part has been budget, and I've resorted to older used gear. With two SVS PB10's, one Mirage S12, and the graphic EQ in a TX-NR929, I've managed to get subwoofer response down to 15Hz within +/- 5dB of target slope -1dB/octave.

The second hardest part is the room. The system is in a 2000 sqft open floor plan with 8' ceilings, a stairwell up front in the living room, and two passages off the side into the kitchen. The room acoustics filter everything below 30Hz at the MLP for all channels in the front of the room. I think part of the filter is from the open boundaries up front and part is from the enclosed rear area behaving like a tuned trap, but I have no easy way of verifying these suppositions.

I extended the subwoofer response by:


1) placing the subwoofers in the relatively enclosed rear dining area where there's some boundary reinforcement. This avoids the filter below 30Hz.


2) tuning the placement so that all three subwoofers have flattish and smoothly varying phase at the MLP. The Mirage is in the center of the rear wall and the SVS are at more or less the 1/4 point forward of the rear wall along the side walls. I had to avoid the rear corners because the left rear corner has both phase and amplitude issues, and for localization reasons I prefer left-right symmetry in subwoofer placement. I don't notice localization with front-rear asymmetry as long as I am at the MLP and facing forward.

3) aligning the phase settings of the PB10's so that the middle of the sub bass (50Hz) lines up across all three subs. There's a slight modal bump at 45Hz and a slight dip at 50Hz. Aligning phase at 50Hz helped smooth the frequency response in the region of this wrinkle and helped preserved transient 'slam'.

4) carefully tuning the graphic, with an eye to fitting the graphic contour limitations between bands first. Since there's less tuning flexibility at intermediate frequencies, prioritizing the fit at those frequencies helps smooth the response. I ended up using more cuts than boosts on most channels including the subwoofers because some response dips aligned to the frequencies between graphic bands and the only way to use that fixed band characteristic optimally was to cut adjacent frequencies.

Some day I'll upgrade the system, but for now it suits my purposes. Given the difficulty of the acoustics, I'm not expecting much improvement to the LFE with more expensive gear unless I increase the subwoofer displacement substantially for extended frequency response below the first mode.

The bass response varies so drastically between the leftmost and rightmost listening positions that it hardly seems worth changing the gear at all. Even adding DSP to smooth the frequency response will only work at a single listening position. Room acoustics is the single most significant variable and all the money in the world sunk into gear won't fix a broken room.

Eventually I'd like DSP and BassEQ because the sub bass in new movies is really messed up, by design apparently (why?), but I'm also considering whether I can fix it with FFMPEG in preprocessing instead and not have to use DSP for bass EQ during playback. Some day when I'm bored I'll give it a shot.
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