Lack of bass management in commercial cinemas/studios, why?

Y

yepimonfire

Audioholic Samurai
Dolby specifically forbids the use of bass management in certified dub stages and their cinema specifications also recommend against it. All speakers must be capable of full range frequency response at 105dB, full range is considered -6dB @40hz. Doing a bit of spectral analysis on feature film soundtracks, I’ve found nearly all channels are mixed with bass content that doesn’t extend too far below 35hz-40hz, with super low content down to 20hz being reserved for the LFE channel.

One thing I don’t get is why is bass management not acceptable in commercial cinemas and dub stages? I suppose bass management is entirely unnecessary when using a big speaker with two or more 12-15” LF drivers, but what benefit would running the speakers full range have vs crossing over to a sub? At one point in time, I once ran my Polk monitor 70s full range, mainly because I didn’t have a good sub and they were capable of handling 35hz just fine. It’s been awhile since I’ve had that system, so I can’t directly compare it to my bass managed system I use now crossed over at 60hz.

Let’s assume someone has fully capable full range speakers that are capable of reaching ~35hz without distortion at 105dB, and that the room gives good response in regards to placement of those speakers. What difference would be heard if running them full range with a sub handling the lfe only vs crossing them over at something like 60-80hz? There must be a reason Dolby requirements forbid bass management.


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everettT

everettT

Audioholic Spartan
Cinema Speakers are capable of a lot more than 105dB and with that the .lfe going to the subs there is no reason to have bass management since the subs are getting. Lfe only. Don't compare a cinema to home setups. Most people don't have truly full range speakers so the need for bass management is necessary since most are crossing Subs at or around 80hz.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Dolby specifically forbids the use of bass management in certified dub stages and their cinema specifications also recommend against it. All speakers must be capable of full range frequency response at 105dB, full range is considered -6dB @40hz. Doing a bit of spectral analysis on feature film soundtracks, I’ve found nearly all channels are mixed with bass content that doesn’t extend too far below 35hz-40hz, with super low content down to 20hz being reserved for the LFE channel.

One thing I don’t get is why is bass management not acceptable in commercial cinemas and dub stages? I suppose bass management is entirely unnecessary when using a big speaker with two or more 12-15” LF drivers, but what benefit would running the speakers full range have vs crossing over to a sub? At one point in time, I once ran my Polk monitor 70s full range, mainly because I didn’t have a good sub and they were capable of handling 35hz just fine. It’s been awhile since I’ve had that system, so I can’t directly compare it to my bass managed system I use now crossed over at 60hz.

Let’s assume someone has fully capable full range speakers that are capable of reaching ~35hz without distortion at 105dB, and that the room gives good response in regards to placement of those speakers. What difference would be heard if running them full range with a sub handling the lfe only vs crossing them over at something like 60-80hz? There must be a reason Dolby requirements forbid bass management.


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I am a bit late replying to your thread, as I have had a lot to contend with lately.

To put it bluntly, Dolby are certain that most people, mix engineers through to cinema installers and techs will screw it up if you add subs.

As you know I'm pretty anti sub on the whole and become more anti over time. I agree with Dolby 100%. Being certain subs are properly integrated is highly problematic.

When I designed my system one thing I was absolutely certain of was that I wanted a subless system. Time has proved my judgement correct.

I get increasing numbers of engineers here checking mixes. Most initially are awful. A major reason is mixing with sub satellite type systems with a sub on the floor and small monitors on the top of the mix console.

The result so often is not near enough oomph in the 60 to 600 Hz range and clearly monitoring with the sub too high.

It sounds awful because there is clearly far to much deep bass compensating for these small monitors that are just weak in the wind in the real power band.

These are now known around here as the speakers that do not lie.

So I send them off and the mix has often to be redone multiple times before the balance is acceptable.

I think we would be better off with speakers potent to 30 to 40 Hz range and no subs.

I'm unusual as I have that extra octave or so. This gives me the chance to see the havoc created by using subs while mixing.

As far as cinemas are concerned this would be a high end set up. Using active crossovers of course.

It would take a massive horn loaded sub to to blend in the last octave with a system like that.

And just for the record I will say once again, that his forum is sub crazy and that the most dispensable part of an audio system is the sub or subs. The money would be far better spent on more capable main speakers.
 
Y

yepimonfire

Audioholic Samurai
I am a bit late replying to your thread, as I have had a lot to contend with lately.

To put it bluntly, Dolby are certain that most people, mix engineers through to cinema installers and techs will screw it up if you add subs.

As you know I'm pretty anti sub on the whole and become more anti over time. I agree with Dolby 100%. Being certain subs are properly integrated is highly problematic.

When I designed my system one thing I was absolutely certain of was that I wanted a subless system. Time has proved my judgement correct.

I get increasing numbers of engineers here checking mixes. Most initially are awful. A major reason is mixing with sub satellite type systems with a sub on the floor and small monitors on the top of the mix console.

The result so often is not near enough oomph in the 60 to 600 Hz range and clearly monitoring with the sub too high.

It sounds awful because there is clearly far to much deep bass compensating for these small monitors that are just weak in the wind in the real power band.

These are now known around here as the speakers that do not lie.

So I send them off and the mix has often to be redone multiple times before the balance is acceptable.

I think we would be better off with speakers potent to 30 to 40 Hz range and no subs.

I'm unusual as I have that extra octave or so. This gives me the chance to see the havoc created by using subs while mixing.

As far as cinemas are concerned this would be a high end set up. Using active crossovers of course.

It would take a massive horn loaded sub to to blend in the last octave with a system like that.

And just for the record I will say once again, that his forum is sub crazy and that the most dispensable part of an audio system is the sub or subs. The money would be far better spent on more capable main speakers.
I’d say you definitely need a sub for LFE. Even decent subs struggle with full 115dB output at Reference levels.

Personally I’ve never had an issue integrating subs at 60hz or below, I’ve set crossovers to 80hz out of necessity before, but it never blended quite right IME. If the sub is flat and properly level matched it should offer a smooth hand off to the mains.


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TLS Guy

TLS Guy

Seriously, I have no life.
I’d say you definitely need a sub for LFE. Even decent subs struggle with full 115dB output at Reference levels.

Personally I’ve never had an issue integrating subs at 60hz or below, I’ve set crossovers to 80hz out of necessity before, but it never blended quite right IME. If the sub is flat and properly level matched it should offer a smooth hand off to the mains.


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I have no trouble with LFE without a sub. If it was any louder it would literally do serious structural damage to the house, and I've come close I reckon.

If you use a sub below 60 Hz it has practically nothing to do and needs a minute amount of power if it is any good.

The problem is that it is not really possible to capture the LFE without a sub unless the system is active like mine is.

I can assure you I have no need or use for a sub in the rig.
 
Y

yepimonfire

Audioholic Samurai
I have no trouble with LFE without a sub. If it was any louder it would literally do serious structural damage to the house, and I've come close I reckon.

If you use a sub below 60 Hz it has practically nothing to do and needs a minute amount of power if it is any good.

The problem is that it is not really possible to capture the LFE without a sub unless the system is active like mine is.

I can assure you I have no need or use for a sub in the rig.
I believe you lol. With enough drivers/surface area, main speakers could easily handle LFE without distortion. I used to own a pair of Polk monitor 70 II speakers, which was equipped with 4 6.5” woofers in a 2.5 way config. 4 6.5” woofer have a surface area larger than a single 12” driver. The speaker had a response down to around 30hz, even though it was missing the last octave, I used to run them full range with the lfe routed to them. I remember watching inception and the avalanche scene had incredible midbass punch and the sub bass (down to 30hz at least) shook my room and rattled the windows. Something like an Rti a9, with 3 7” woofers, and two 6.5” mids, can easily run without a sub, Klipsch RF-7IIIs with dual 10” woofers should similarly handle the LFE. The problem is that last octave. Cinema speakers generally roll off at 35hz-45hz, LFE content covers 16hz-120hz, with a good chunk of the content being centered between 20hz-50hz. 115dB down to 22hz is a tall order for even the biggest subs, 99% of large speakers generally don’t even go flat to 20hz.

For movies, the main channels generally carry content down to about 30hz, so the sub definitely has plenty to do at a 60hz xover. For stuff like rock music (ie a typical guitar, bass, and drum set), I don’t even need a sub, as my speakers extend down to about 47hz. In fact, switching between direct mode and stereo (which disables the xover), I hear no difference in bass extension.

I don’t see any purpose in trying to achieve 20hz @115dB with a main speaker. Even if one were designed to do so, it’d likely be a 4 way design with a sub integrated into it anyways. A 15” driver with 8mm of xmax and a stiffer suspension to accurately reproduce 200hz-500hz just can’t move massive air at 20hz.

Suppose a subwoofer was mounted directly beneath a speaker, and each channel had its own sub, why would that be any different than a regular 3 way/4way? Physics dictates that two drivers placed within 1/2 wavelength behave as a single radiating point source, a subwoofer crossed over at 60hz will sum perfectly with a speaker anywhere within a 9’ distance. If it were placed along the front stage, and perfectly time aligned, there should be no issues. The phase response at the xover hand off point between my mains and sub is completely seamless, as I’ve used REWs timing reference to set the distance delay.

How low are your speakers tuned?


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Auditor55

Auditor55

Audioholic General
However, according to people like Earl Geddes, you can get better bass by using subwoofers as opposed to full range speakers.
 
TLS Guy

TLS Guy

Seriously, I have no life.
However, according to people like Earl Geddes, you can get better bass by using subwoofers as opposed to full range speakers.
He is wrong. You might get louder bass but not better quality integrated bass.
 
B

Blue Dude

Audioholic
Bass management isn't just to compensate for limited extension or inefficient speakers. For the lowest two octaves of bass, the size and shape of the room matters. For a typical smallish, rectangular home theater, room modes become significant below 100 Hz. For a dubbing stage or commercial cinema, the shape of the room, room treatments, and the sheer size of the room mean that standing waves are far less prevalent and lower frequencies start to become directional.

Bass management works in home theater because you can optimize the location of bass sources within the room to mitigate room modes without harming imaging. Since it's physically impossible to localize low bass in a confined area, there's nothing to be gained by co-locating deep bass with the speakers. It's not possible to completely duplicate the sound field of a large space in a small one, but short of spending an ungodly amount of time and money tuning the listening environment with room treatments, equalization, and placement for your specific room and specific equipment, bass management gives you the best shot at taming your room. You *can* run everything full range, but it's very difficult to get better results than simply crossing over to a couple of well-placed, capable subs.
 
Auditor55

Auditor55

Audioholic General
Bass management isn't just to compensate for limited extension or inefficient speakers. For the lowest two octaves of bass, the size and shape of the room matters. For a typical smallish, rectangular home theater, room modes become significant below 100 Hz. For a dubbing stage or commercial cinema, the shape of the room, room treatments, and the sheer size of the room mean that standing waves are far less prevalent and lower frequencies start to become directional.

Bass management works in home theater because you can optimize the location of bass sources within the room to mitigate room modes without harming imaging. Since it's physically impossible to localize low bass in a confined area, there's nothing to be gained by co-locating deep bass with the speakers. It's not possible to completely duplicate the sound field of a large space in a small one, but short of spending an ungodly amount of time and money tuning the listening environment with room treatments, equalization, and placement for your specific room and specific equipment, bass management gives you the best shot at taming your room. You *can* run everything full range, but it's very difficult to get better results than simply crossing over to a couple of well-placed, capable subs.
I hear what you are saying about small rooms and modes, however I don't think I agree that bass management, as we know it, is used to tame room modes (peaks and nulls). I think that's done, according to the experts, with multiple subs, placement and EQ.
 
B

Blue Dude

Audioholic
I hear what you are saying about small rooms and modes, however I don't think I agree that bass management, as we know it, is used to tame room modes (peaks and nulls). I think that's done, according to the experts, with multiple subs, placement and EQ.
This is true, but bass management makes relocating bass sources possible. Only after removing deep bass from the primary speakers and moving it to better positioned subs can you start to address room modes. Simply relocating to two well-positioned subs can give you most of the room mode mitigation that is simply fine-tuned with equalization and room treatments.
 
Y

yepimonfire

Audioholic Samurai
Bass management isn't just to compensate for limited extension or inefficient speakers. For the lowest two octaves of bass, the size and shape of the room matters. For a typical smallish, rectangular home theater, room modes become significant below 100 Hz. For a dubbing stage or commercial cinema, the shape of the room, room treatments, and the sheer size of the room mean that standing waves are far less prevalent and lower frequencies start to become directional.

Bass management works in home theater because you can optimize the location of bass sources within the room to mitigate room modes without harming imaging. Since it's physically impossible to localize low bass in a confined area, there's nothing to be gained by co-locating deep bass with the speakers. It's not possible to completely duplicate the sound field of a large space in a small one, but short of spending an ungodly amount of time and money tuning the listening environment with room treatments, equalization, and placement for your specific room and specific equipment, bass management gives you the best shot at taming your room. You *can* run everything full range, but it's very difficult to get better results than simply crossing over to a couple of well-placed, capable subs.
You may have a point. My 20’ long 2000 cu ft room has modes at 47hz, and 28hz. Most theaters/dub stages are physically large enough to push the fundamental modes down into the infrasonic range (where subs quit working). I don’t think bass management was designed solely for this purpose though.

In a cinema or dub stage, the screen array (lcr) generally has a response down to about 40-45hz. Subs more often than not have a response down to about 25-30hz, and contrary to popular belief, many cinema subs cannot reach 20hz flat, outside of the more expensive THX approved subs.

The screen array speakers must be individually capable of full range (45hz) 105dB output 2/3rds of the way back in the theater. Many home speakers just can’t do this.

Theoretically speaking though, my main question is is there a benefit in running full range if the speakers are capable vs bass management? Let’s say I had something like a Polk RTi a9 or Klipsch RF 7 III. The Polk has 3 7” woofers, and the Klipsch has two 10” woofers. The surface area of two 10” woofer is greater than a single 12” sub, and almost comparable to a 15” sub. The a9 is about the same as a 12” sub. Since content in the main channels doesn’t dip much below 30hz, neither of these would have any problem reproducing a full range signal.
 
B

Blue Dude

Audioholic
Theoretically speaking though, my main question is is there a benefit in running full range if the speakers are capable vs bass management?
If in your room the speakers that are running full range *just happened* to be optimally placed for mitigating room modes at (non-directional) low frequencies *and* imaging for directional frequencies, there's still no sonic advantage to running them full range vs. crossing them over to dedicated subs in optimal locations. It's counter-intuitive, but bass is counter-intuitive in small rooms. It doesn't radiate like higher frequencies, it reverberates. You're not perceiving the direct sound wave at low frequencies, you're mostly perceiving echoes. Since it takes so long to get to peak output on each cycle, and the time for the wave to bounce off the walls is relatively short, you're hearing a mix of direct and indirect sound that arrives from every direction. Running full range from all your mains means exciting room modes in a way that is difficult to mitigate. They reinforce each other in unpredictable ways. Carefully placed subs, playing the same mono signal, oppose each other's standing waves to avoid this problem, or at least blanket the room widely and predictably so that they can be equalized effectively. It's possible to design a small room to avoid standing waves without opposing subs, so that you may be able to run full range, but it's well beyond what is practical for the typical home theater hobbyist.
 
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