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This topic comprises 2 pages: 1 2
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Author
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Topic: Object Based Sound Systems (Dolby Atmos, DTS-X...and the rest)
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 11-21-2019 06:57 AM
This discussion started over in the Ground Level on latest theatres opening/closing...It seemed way too off topic but a decent enough discussion.
quote:
Steve Guttag
What I REALLY like about Dolby Atmos is that, regardless of theatre shape/size, it scales such that what was recorded is what is played back. There is a lot of capability there.
Marcel Birgelen
Well, that's what I've been saying for years. Unfortunately, the Dolby Atmos format isn't a pure object based audio format, it still invites people to take shortcuts and mix stuff into "beds", which are essentially just the "fixed channels".
A pure, object based mix could potentially be rendered optimally on all systems, no matter what the size or shape is, whereas a channel based mix will "forever" be coupled to the channel layout.
The capabilities of Atmos go beyond just movies, it could also be used to recreate a very accurate rendering of an orchestra, for example. There are multiple other examples to be made, but they're all a bit too much out of scope of this already off-topic discussion.
Bobby Henderson
I would like to see more companies who build amplifiers for movie theater sound systems offer more multi-channel models for use with Atmos and DTS-X. I could be wrong, but I think Dolby is the only company offering amplifiers with 16 and 32 channel configurations. QSC is usually the go-to company for movie theater amps. Their DPA series amps for Q-Sys maxes out at 8 channels per unit. And then there's the factor of bi-amping and tri-amping. I don't know how often that is used in commercial theater sound systems, but it's pretty common with PA systems for live concerts. Anyway, to me that sounds like even more racks filled with amplifiers!
Marcel Birgelen
While I'm not immediately a fan, I expect active speakers to become more of a thing, especially when we keep increasing speaker density.
Speakers will then be placed on a bus, probably something like Ethernet. While it would require you to bring power to every speaker, it would eventually decrease complexity in wiring and increase flexibility in deployments.
Disadvantages are obviously the increased weight of those speakers, more active components that can fail and are often hard to reach and the heat getting dumped into the auditorium instead of the booth. While the last one might, in the greater picture, not be a direct disadvantage.
Bobby Henderson
IMHO, amps and speaker cabinets should always be kept as separate components. Each piece of equipment is a potential point of failure. Combining the two into one unit is just going to add to the factors of complication and expense.
Systems like QSC's Q-Sys offer flexibility via Ethernet connection without needing to build amplifiers directly into the speaker cabinets. Some of the cabinets, particularly those hung from the ceiling, need weight trimmed to only what's essential.
Bobby, I'd say 95% or greater of cinemas bi-amp their stage speakers (or better) and I have begun to quad-amp our 4-way installations (more on that later). In fact very few, and only on the lower-end offer passive crossover systems anymore. Just about all cinema processors offer crossovers now, most booth monitors and many amplifiers have crossover options, not to mention that via various DSP platforms, crossovers are available.
So with respect to amplification and where it should go and how many channels...etc. BGW offers a 16-channel amplifier. It takes two power cords so it is closer to two 8-channel amplifiers in a single big, heavy case. Unlike the others, BGW has stuck with A/B design rather than Class D.
Both Dolby's DMA (and there are three different channel counts and two different power levels available so it isn't just the one amplifier) and QSC's line of DPA/DPA-Q amplifiers are Class-D amplifiers (you got to do something to get that sort of channel count in a small package and have high power ratings!).
I never want to design a system where I have all of my stage speakers driven from a single amplifier...particularly one that has to "boot up." When I design even Q-SYS systems, Left/Right will be on one amplifier and Center/Subwoofer will be on another (presuming enough power for the subwoofer) and if 5-screen channels, another amplifier for them so if there is a failure, there is symmetry to the fail and a form of bypass can keep it going.
How one designs for a system like Q-SYS and DPA amplifiers is a bit different than for conventional linear amps due to how you can utilize the power in a Class-D and in particular, QSC's flex power. In a conventional stage speaker system, it is no secret that the LF section consumes more power than the HF section (particularly as one moves away from a 2-way system crossed over at 500Hz) and how the DPA amplifiers allocate the power is like having a pool where the LF can take more of it since the HF isn't using so much. So that will affect amplifier sizing choices. In a conventional 2-channel amp, if biamped, you size the amp to cover the LF power needs with the HF normally coasting (power wise). Crown tried making amps that had different power ratings for the two channels though I don't think that concept lasted very long (it was years ago and I don't follow Crown much anymore). This flexible power concept also means that wiring a 4-way as a 4-way doesn't necessarily limit the LF section's power since the VHF driver is taken even less from the power pool.
So I don't mind breaking my amplifiers up into smaller chunks, when it comes to stage speakers. If I were designing an Atmos room using the Dolby DMA, you can bet there would be at least two of them to ensure that Center is not on the same amplifier as LC/RC (I'd rather LC/RC phantom a Center than L/R, given the choice) to ensure an amp failure wouldn't bring the system entirely down.
Certainly, with conventional 5.1/7.1 systems, a single DMA could handle the entire room with up to tri-amped speakers but you have a lot of single-point failures in that system with the amplifier at the end of that list (the cinema processor is also a single-point failure, as is the server and the projector, for that matter).
As to self-powered speakers...perhaps. With Class-D amplifiers and being able to mount them in the speaker with relatively little weight penalty, there is an appealing aspect to them. They could be designed specific to the speaker and it would always be the right size (and with the right EQ built in too). So installation is a power cord and either an analog cable or, more likely an Ethernet cable. We are already getting quite close to that with Q-SYS as we have moved some of the amplifiers behind the screen in a very minimalist rack (something to keep them off the floor and keep crap from being set upon them...vermen...etc.) so installation are short speaker cables and some CAT cables. Clearly not all cinema environments are conducive to such a strategy but it is one step closer to amps in the speaker.
For surrounds...I don't know...you still have to get power to them and if you have an Atmos system, it isn't going to be cheap to wire up 40 outlets and then run 40 sets of cables (CAT or analog) on top of that...versus just running the cables and a few circuits at the amplifier location.
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Sean McKinnon
Phenomenal Film Handler
Posts: 1712
From: Peabody Massachusetts
Registered: Sep 2000
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posted 11-21-2019 08:12 AM
Like usual I agree with pretty much everything Steve has said. When I have designed Q-Sys based systems depending on the specific needs, budget etc... I have separated HF and LF sections of loudspeakers such that a large LF is on a large bridged or parallel amp (I have a system where double 18" subs are used as LF elements on the screen channels with a custom crossover) and the HF and MF sections are on another amplifier so the amps look like this;
Amp A- Left MF, Left HF, Right MF, Left HF
Amp B- Center MF, Center HF, Spare, Spare
Amp C- Left LF, Left LF, Right LF, Right LF
Amp D- Center LF, Center LF
Amp E- Sub 1, Sub 1, Sub 2, Sub 2
etc...
Even on my 7.1 installations I use discreet surrounds with very few exceptions where there may be 1 set of two speaker on parallel but I try to avoid it as much as possible. I have also had a lot of success with adding "bass management" sub woofers to my 7.1 systems and find that there is actually a lot of full range information in today's surround mixes.
I think the biggest bang for the buck in Atmos is the bass management on the surrounds, the discreet surrounds, and the fact that everything should be appropriate for the room (speaker, and amp selection) the objects are cool and all but to me is more of a gimmick.
The Dolby DMA now has a version where they replace a set of channels with an analog input card FWIW. I have not used it yet I have used the QSC 8 Channel DPA-Q amplifiers and have had no issues with them.
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 11-21-2019 04:28 PM
I guess bass management can be done with 5.1 and 7.1 and Q-Sys too.
Regarding the trend for active speaker systems... I've seen a general uptake of them and right now for stuff like live events, active speakers are more or less the defacto standard, especially since line arrays made their way in.
I expect the same to happen for cinema deployments too. Actually, I expect to see much more line arrays too in the near future. Meyer Sound has been deploying line arrays in cinema for a while and Dolby has started to incorporate some of SLSes former Line Array products into their Dolby Cinema rollouts.
The biggest problem I see isn't so much the extra weight, but more the cooling of those kind of speakers. Whereas in a live venue nobody really cares about a bunch of fans on the backside of those speakers, in a cinema environment, those kind of noise sources are pretty much bad news.
As for active surrounds and Dolby Atmos... The current Atmos specifications limit their usefulness, as in that every single speaker has to be able to produce a 105 dB peak SPL at the reference location. For large rooms, this means the speakers must also be rather large and have powerful amplifiers, you probably don't want to put this extra weight into your already pretty bulky surround cabinets.
But in their recent Dolby Atmos installs, they seem to do something different. They blanket the room with speakers, even more than Atmos supports output channels. So, I suspect they're creating speaker arrays of e.g. 4 speakers that share the same channel. Together, they'll probably able to produce the required sound pressure at reference.
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 11-22-2019 06:47 AM
Putting the amp inside the enclosure instead of slapping it onto the back might be not an entirely novel, but still an interesting idea, it would limit the application to vented/ported designs though. I think I'm going to do a little experiment this weekend. ![[Wink]](wink.gif)
Regarding line arrays, I agree that for smaller and most medium sized rooms, line arrays don't add much. I would also only consider them for the stage speakers and not so much for the surrounds (although Christie Vive* apparently uses line arrays in combination with ribbon drivers for just that*). But there are quite a few configurations where I can see the benefit. It's mostly larger rooms, obviously balconies, but also rooms with high-pitched stadium seating or very deep rooms or very wide rooms. Generally rooms with challenging geometry. I'd add another dimension to it though, I'd split the array in both dimensions: I've encountered unbalanced sound from the stage speakers in many bigger rooms for everybody not sitting center to the screen. Depending on your seating position, left or right is often way more dominant. This could be solved with horizontally stacked line arrays. Only the venerable baffle wall would probably suffer from such an approach, but I doubt that a baffle wall and line arrays will ever be compatible...
* I know, not everybody is a fan and I didn't like their demos either, but in their initial Dolby Cinema roll-outs they actually made it work somehow...
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 11-22-2019 08:00 AM
I think the notion of uniform level across the auditorium is not only a false one but absolutely incorrect for creating a proper cinema experience. Yes, if you sit near the right side, the right speaker will and should sound louder...just as in real life if you are nearer to the object making the noise. The only thing I'd compensate some for is the frequency response if due to the limitations of the speaker's coverage area. Mind you, those that are out of a speaker's coverage, in MOST cinemas are seats in the extreme front corners.
In that same vein (where the speaker is the limitation, not the seat position), yes, line-arrays can be an effective tool in very large rooms with multiple levels. But that's it. If you use them to even out the SPL in the seating area, you are no longer creating what was mixed nor representing the audio in a "realistic" manner...you are deliberately altering the audio in a misguided belief that each speaker should have the same SPL from each seat...a misguided belief that has fooled many a technician. If you are going to make the sound louder, you should provide glasses to go with it so the image looks bigger too.
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 11-22-2019 12:13 PM
quote: Steve Guttag
I think the notion of uniform level across the auditorium is not only a false one but absolutely incorrect for creating a proper cinema experience. Yes, if you sit near the right side, the right speaker will and should sound louder...just as in real life if you are nearer to the object making the noise. The only thing I'd compensate some for is the frequency response if due to the limitations of the speaker's coverage area. Mind you, those that are out of a speaker's coverage, in MOST cinemas are seats in the extreme front corners.
I think I need to elaborate a bit. We need to distinguish here between "sound objects" and more ambient sound-elements. This can be the soundtrack, but also other sounds, like background humming of a machine, etc.
I agree that it's perfectly fine that an object closer to you in regards with the position of the screen sounds louder or... "closer to you", it's actually what's expected. But the left and right stage speakers are traditionally the speakers that carry most of the soundtrack and also a lot of other, more ambient sounds.
In larger rooms, for me it often feels like I hear most of the soundtrack via the speakers I'm closest to, which adds some unnatural element to the experience if I'm not sitting center to the screen. In smaller rooms, the falloff is much less noticeable and therefore far less problematic.
The soundtrack needs to be "in the background" it should not sound like a point source. (I'm exaggerating a bit to make a... point.)
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Bobby Henderson
"Ask me about Trajan."
Posts: 10973
From: Lawton, OK, USA
Registered: Apr 2001
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posted 11-24-2019 02:37 AM
quote: Steve Guttag
What theatres have you found that do Atmos bad and why (did it sound harsh, was it economized...what are your reasons)?
One example is the Regal Broken Arrow Warren location, the only one out of the previous Warren chain to have any Atmos-equipped auditoriums. Their two Grand Infinity houses have Atmos. I was surprised at the low number of ceiling surround speakers used. Given the sheer height of the ceilings (these are auditoriums with premium priced balconies) the speakers used weren't nearly powerful enough to be heard adequately from the floor level seats. The Dolby Atmos "Unfold" trailer just didn't sound right.
I've never been very impressed with Atmos audio in any AMC-branded Dolby Cinema house. I've watched movies in half a dozen locations in OKC, Dallas-Fort Worth and the last outing in Colorado Springs. I suspect a combination of under-powered speakers as well as skimping on amplifiers. OTOH, I've heard some decent "slam" from sub-bass in a couple of those locations. The red lighting in the speaker cabinets (a hold-over from Prime) is pretty. The Colorado Springs location ditched that, going with a more subtle blue LED border lighting scheme. It still looks like they're using the same kinds of speakers though (Christie Vive I think).
So far, the best I've personally heard from an Atmos mix was played at Harkins' Bricktown 16 theater in Oklahoma City, their Cine Capri screen. But even there seating position in kind of critical. The viewer needs to sit almost dead center of the room to get the best results. The viewer is not going to hear the ceiling surrounds for squat if he is sitting way down in the front rows (been there, done that). As good as the surround rendering seems to be, that sound system could use more heft in the sub-bass department.
quote: Steve Guttag
BTW...I've had customer satisfaction with the "Amaze" trailer.
The "Amaze" trailer is okay. It does a decent job of calling attention (slightly) to the technical side of Atmos. I've only seen it played at Harkins locations, and even they've gone back to using the "Unfold" trailer since it has a more "in your face" bombastic nature like a classic THX snipe. I've rarely seen any AMC/Dolby Cinema screens play Atmos-specific trailers. The Chapel Hills Mall theater in Colorado Springs played the "Unfold" trailer (along with AMC's home-brewed Dolby Cinema trailer). But then again, theaters in that town were pretty good about playing sound format trailers even when they were showing film.
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