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How are speakers balanced in a commercial theater?

post #1 of 29
5/28/09 at 9:05pm
Thread Starter 
Not sure if this is discussed somewhere or if this is the right place to ask the question but I'll give it a shot.

How are all the various speakers in a commercial theater balanced?

I have a 7.1 set up in my home theater and am familar with setting up and balancing all the speakers in it. But as I sat in the movie theater over the last few weeks (Star Trek and Terminator Salvation), I found myself wondering how all the speakers are set up and balanced, particularly the surround speakers. Specifically, even though I am sitting in the middle of the theater with surround speakers in front of me and in back of me, why is it that I hear the sound clearly moving from front to back during a fly-over or similar scene as opposed to just a "mush" of sound on either side of me?
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post #2 of 29
5/29/09 at 3:42am
Quote:
Originally Posted by bluesky636 View Post

I have a 7.1 set up in my home theater and am familar with setting up and balancing all the speakers in it. But as I sat in the movie theater over the last few weeks (Star Trek and Terminator Salvation), I found myself wondering how all the speakers are set up and balanced, particularly the surround speakers. Specifically, even though I am sitting in the middle of the theater with surround speakers in front of me and in back of me, why is it that I hear the sound clearly moving from front to back during a fly-over or similar scene as opposed to just a "mush" of sound on either side of me?

The speakers are balanced the same way as in a home system. The front-to-back flyover is a simple pan from front speakers through side surrounds to rear surrounds. The reason it sounds overhead is because the surrounds are a few feet above ear level.

For a home system with UTU speaker placement having the surrounds and mains all at the same height, this illusion will likely not be convincing. That's a problem with using the same speaker configuration for multiple purposes, e.g. music vs. movies.
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post #3 of 29
5/29/09 at 9:12am
My memory is telling me that they set the surround speakers at 3 Db lower than they set the screen speakers.

True? False?
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post #4 of 29
5/29/09 at 9:49am
Quote:
Originally Posted by Lee Stewart View Post

My memory is telling me that they set the surround speakers at 3 Db lower than they set the screen speakers.

True? False?

Pro theater surrounds may be wired together in parallel off the same power amp, though manufacturers recommend that no more than 2 surround speakers for the same channel be wired together in this way.

But all the power amps for one surround channel are wired to the same preamp channel. Level and EQ calibration occur for all the surrounds on a single channel simultaneously. This combination is matched to the same level as each main speaker.
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post #5 of 29
5/29/09 at 5:02pm
Thread Starter 
Quote:
Originally Posted by Terry Montlick View Post

The speakers are balanced the same way as in a home system. The front-to-back flyover is a simple pan from front speakers through side surrounds to rear surrounds. The reason it sounds overhead is because the surrounds are a few feet above ear level.

For a home system with UTU speaker placement having the surrounds and mains all at the same height, this illusion will likely not be convincing. That's a problem with using the same speaker configuration for multiple purposes, e.g. music vs. movies.

Ok, I understand that but what I don't understand is the impact of the different delay times from the frontmost to the rearmost side surround speaker. In other words as the volume level of the side surrounds rises and falls as the flyover passes,how does the time delay between speakers affect what I am hearing? Or is it that time delay that gives rise to the diffuseness of the sound? Am I making sense?
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post #6 of 29
5/29/09 at 7:27pm
Quote:
Originally Posted by bluesky636 View Post

Ok, I understand that but what I don't understand is the impact of the different delay times from the frontmost to the rearmost side surround speaker. In other words as the volume level of the side surrounds rises and falls as the flyover passes,how does the time delay between speakers affect what I am hearing? Or is it that time delay that gives rise to the diffuseness of the sound? Am I making sense?

My guesstimate . . .

Due to the size of the theater (compared to an HT), the fact that the SS speakers are high up on the walls and multiple speakers (arrays) with the audio going through a time delay (measured in milliseconds) a Doppler Effect is created in the theater.

Here is a short example that explains this:

http://nsdl.exploratorium.edu/nsdl/s...age=10&index=0
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post #7 of 29
5/29/09 at 7:33pm
Thanks for the Doppler explanation and link.
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post #8 of 29
5/29/09 at 10:02pm
Quote:
Originally Posted by Lee Stewart View Post

My guesstimate . . .

Due to the size of the theater (compared to an HT), the fact that the SS speakers are high up on the walls and multiple speakers (arrays) with the audio going through a time delay (measured in milliseconds) a Doppler Effect is created in the theater.

You can't get a Doppler effect unless the source is actually moving. Panning a source from one speaker or set of speakers to another cannot do this because the source doesn't move so as to compresses the waves when traveling towards you and rarefies them when traveling away. It is merely a virtual source create by panning. Of course, the sound mixer may add a Doppler frequency shift to the program material so that it mimics a real moving source.

- Terry
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post #9 of 29
5/29/09 at 10:31pm
Thread Starter 
Quote:
Originally Posted by Terry Montlick View Post

You can't get a Doppler effect unless the source is actually moving. Panning a source from one speaker or set of speakers to another cannot do this because the source doesn't move so as to compresses the waves when traveling towards you and rarefies them when traveling away. It is merely a virtual source create by panning. Of course, the sound mixer may add a Doppler frequency shift to the program material so that it mimics a real moving source.

- Terry

Agreed. As a former radar systems engineer, I am very familiar with doppler shift. I would assume that when a recording of a heliocopter flying overhead is made, the copter is actually passing from front to back past the mike. When played back and panned through the speakers you would hear the copter moving above you AND hear the doppler shift that was recorded as it passed overhead.

But that is not the time delay I am talking about. I am talking about the difference in arrival times between the two speakers furthest away from the listener and the one closest to the listener. I had read somewhere that in a regular movie theater, the volume level is measured at only one or two spots in the theater while in a THX theater the level is measured at multiple locations. Is that true?

Is any sort of delay applied to the speakers so that to a listener hearing them at the same time perceives the sound all arriving from each speaker at about the same time, or is the delay left uncompensated for to create the feeling of diffusion?
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post #10 of 29
6/3/09 at 12:44pm
Quote:
Originally Posted by bluesky636 View Post

Is any sort of delay applied to the speakers so that to a listener hearing them at the same time perceives the sound all arriving from each speaker at about the same time, or is the delay left uncompensated for to create the feeling of diffusion?

You cannot apply a delay. You have perople seated all over the place.
The delay needed for first row would be just the opposite to the one needed for last row.
You can't please everybody!!!
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post #11 of 29
6/3/09 at 5:18pm
With most cinema processors there is one adjustable general setting point for delay which is generally 2/3 into the auditorium. In very long and balcony cinemas I have used additional delays as required.
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post #12 of 29
6/3/09 at 5:56pm
This site has a whole lot of information.
Lenard Audio
http://www.lenardaudio.com/education/17_cinema.html

As well as this site HPS-4000
http://www.hps4000.com/

This site has bundles of technical information
Cinema Technology
http://ctmag.slaterelectronics.com/
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post #13 of 29
6/3/09 at 8:50pm
Thread Starter 
Thanks for all the information everyone. Its a very interesting subject.
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post #14 of 29
6/8/09 at 5:42am
The methods used in a large commercial venue are different in many aspects to a smaller residential sized room. As Terry noted, the overhead effect is diminished and a significant contributor to that is the delta between the height of the mains and surrounds is reduced in a small room. Also contributing to that would be the differences in ceiling height and the much larger length found in commercial venues (ie, the arrival time differences in a large commercial room are larger than in a small room ... pans are more fleeting in a smaller space.)

In a larger residential space (say three or four rows of seating) we will often use an array of three side surrounds on each side of the room; but, our method of calibration will be different than in a commercial space. A short, oversimplified, scenario would be:

1. Each side surround channel is routed to a DSP (usually a QSC DSP322UA) where the single side surround channel is split into three independent channels.
2. Each independent side surround speaker is individually calibrated to -20dBFS from the middle of the seating row closest to that speaker then the sum of all three speakers is reduced to -20dBFS.
3. The delay for the entire array is set on the input signal to the DSP based upon the distance to the first row of side surrounds.
4. The delay for the rear surrounds is set
5. Then each side surround (side surrounds 2 and 3 as you move toward the rear of the room) is individually delayed by the delta of that surround speaker from the first surround speaker. This delay is set in the DSP subsequent to the split out of the individual speakers.

Since rooms with three, or four, rows of seating will have higher ceilings than a 1 or 2 row room, we can place the side surrounds higher with respect to the fronts than would be typically available in a smaller room. Front to rear pans and fly-overs become much more believable (particularily with ceiling diffusors).

Terry notes the challenges associated with music playback vs cinema playback. Frankly, those challenges are directly a result of the music recording engineers not getting their collective game books together ... a complete lack of standards or attempt to follow any given standard with respect to speaker positions, speaker levels, mix rooms, etc., etc. particularily for multi-channel recording attempts.
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post #15 of 29
6/8/09 at 5:42am
helpful information bro
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post #16 of 29
6/8/09 at 8:30am
good topic
ideally a large home theater with high ceiling and stadium with 2-5rows allows for better "recreation" of the top notch THX theater.
home theater is a lot compromises.
if you can build a room and install cinema hardware and a 4-5meters scope screen (mp of course and please not woven stuff!!!) and a rack or two
then you got yourself (after careful tuning, settings, parametring, eq, placing etc)
THE cinema experience.
heavy deep bass resonators help also to make the room go LOW AND TIGHT
as for fly overs indeed surrounds qty and height of placement (following stadium rise)
help give that panning sensation. at home it's hard to get that especially with just one pair of surrounds. large dipolars help a bit.
if you got rows then count around 1 surround per rows space. 3 rows= 2 surrounds per side, 4 rows=3 surrounds per side
there's also a wrong tendency of people always asking for surround sound, louder etc
a movie is mixed and not to make lambda consumers happy because it has loud surrounds during 2hrs !
calibrated sound on the 5 7 speakers should 75dB (pink noise) and 85dB subs and not 90db on the surrounds!
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post #17 of 29
6/8/09 at 11:43am
The 75dB number for calibration is ONLY to be used if the test tones are set up for 75dB (THX Certified pre-pro or calibration disk for example), otherwise use 85dB which is -20dBFS. Also use ear plugs during calibration.
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post #18 of 29
6/8/09 at 12:14pm
Does the fact that most theaters use Horn type speakers behind the screen alter the calibration?
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post #19 of 29
6/8/09 at 4:45pm
Thread Starter 
Quote:
Originally Posted by Dennis Erskine View Post

The methods used in a large commercial venue are different in many aspects to a smaller residential sized room. As Terry noted, the overhead effect is diminished and a significant contributor to that is the delta between the height of the mains and surrounds is reduced in a small room. Also contributing to that would be the differences in ceiling height and the much larger length found in commercial venues (ie, the arrival time differences in a large commercial room are larger than in a small room ... pans are more fleeting in a smaller space.)

In a larger residential space (say three or four rows of seating) we will often use an array of three side surrounds on each side of the room; but, our method of calibration will be different than in a commercial space. A short, oversimplified, scenario would be:

1. Each side surround channel is routed to a DSP (usually a QSC DSP322UA) where the single side surround channel is split into three independent channels.
2. Each independent side surround speaker is individually calibrated to -20dBFS from the middle of the seating row closest to that speaker then the sum of all three speakers is reduced to -20dBFS.
3. The delay for the entire array is set on the input signal to the DSP based upon the distance to the first row of side surrounds.
4. The delay for the rear surrounds is set
5. Then each side surround (side surrounds 2 and 3 as you move toward the rear of the room) is individually delayed by the delta of that surround speaker from the first surround speaker. This delay is set in the DSP subsequent to the split out of the individual speakers.

Since rooms with three, or four, rows of seating will have higher ceilings than a 1 or 2 row room, we can place the side surrounds higher with respect to the fronts than would be typically available in a smaller room. Front to rear pans and fly-overs become much more believable (particularily with ceiling diffusors).

Terry notes the challenges associated with music playback vs cinema playback. Frankly, those challenges are directly a result of the music recording engineers not getting their collective game books together ... a complete lack of standards or attempt to follow any given standard with respect to speaker positions, speaker levels, mix rooms, etc., etc. particularily for multi-channel recording attempts.

Quote:
Originally Posted by Digital2004 View Post

good topic
ideally a large home theater with high ceiling and stadium with 2-5rows allows for better "recreation" of the top notch THX theater.
home theater is a lot compromises.
if you can build a room and install cinema hardware and a 4-5meters scope screen (mp of course and please not woven stuff!!!) and a rack or two
then you got yourself (after careful tuning, settings, parametring, eq, placing etc)
THE cinema experience.
heavy deep bass resonators help also to make the room go LOW AND TIGHT
as for fly overs indeed surrounds qty and height of placement (following stadium rise)
help give that panning sensation. at home it's hard to get that especially with just one pair of surrounds. large dipolars help a bit.
if you got rows then count around 1 surround per rows space. 3 rows= 2 surrounds per side, 4 rows=3 surrounds per side
there's also a wrong tendency of people always asking for surround sound, louder etc
a movie is mixed and not to make lambda consumers happy because it has loud surrounds during 2hrs !
calibrated sound on the 5 7 speakers should 75dB (pink noise) and 85dB subs and not 90db on the surrounds!

Quote:
Originally Posted by Dennis Erskine View Post

The 75dB number for calibration is ONLY to be used if the test tones are set up for 75dB (THX Certified pre-pro or calibration disk for example), otherwise use 85dB which is -20dBFS. Also use ear plugs during calibration.

WOW! I was just about to cancel my subscription to this thread, figuring that all the good info had been presented. Then these posts come along. Absolutely fascinating.

Dennis, I took a look at the portfolio on your website. When I win the Power Ball lottery, you can expect a call from me.
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post #20 of 29
6/8/09 at 5:58pm
Quote:
Originally Posted by Lee Stewart View Post

Does the fact that most theaters use Horn type speakers behind the screen alter the calibration?

Not really. Horn and other compression drivers are used in large rooms because HF sounds decay faster in air than the mids and lows. What happens with 1" dome tweeters is they cannot output at high enough output to 'throw' the HF content very far into the seating area (without burning out) and the HF content is overwhelmed by the mid frequencies. In a THX room we're doing now, the rear row of seating is far enough from the speaker position that we had to change from our original speaker choice for that very reason.

Horns are far more directional. That directionality can alter treatment strategies due to the lack fo side wall reflections. Typical horns for small rooms will have controlled dispersion up and down reducing floor ceiling reflections. Speakers in large venues will control (constrain) dispersion both horizontally and vertically.
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post #21 of 29
6/8/09 at 6:14pm
Dennis:

In your montage of theaters you have designed and built (very impressive BTW) - I notice a lot of "hard surfaces" for the walls and ceiling. Isn't this the opposite of what is desired in a commerical theater? Aren't you creating sound reflections within the room?
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post #22 of 29
6/9/09 at 4:20am
I suspect some only look hard.
Most rooms are way, way too "soft". Dead. (I actually like that ... more opportunity for us to fix it.) Not all of the evil reflections are really evil reflections. They provide the width and depth to the sound stage and envelopment. There's a balance that needs to be achieved to get decay times in the right neighborhood for the room and decay times which are reasonably consistent across the frequency spectrum. In many cases where people are tossing fiberglass on the walls (because they see pictures of award winning* rooms done that way), where they should be using diffusion.

As well, with some of the pictures, you don't have the advantage of looking at the geometry. Some of those hard surfaces may not be reflecting back into seating locations based upon the location of the speakers with respect to the seats. In some cases you'll see the bottom of the soffits are grabbing reflections before they get to the ceiling. You'll find prosceniums designed to prevent reflections from getting to a part of the ceiling which would create an annoying problem in the seating area.

*Award Winning Rooms - Understand these rooms win awards because they look nice! Judging includes architects and interior designers who have no clue about good sound/good video. None of these rooms has ever been measured to determine sound quality or video quality!
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post #23 of 29
6/9/09 at 4:36am
Dennis
what brands of horn speakers do you use, when you use horns ?
Klipsch, JBL (pro or synthesis) , QSC? in Europe we also have GKF. www.g-k-f.com
i use all three depending on client's budget, room (size , shape etc)
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post #24 of 29
6/9/09 at 5:04am
JBL Pro. In large rooms we will also use the big (pro) Genelec. QSC is www.qscaudio.com QSC also makes great large room speakers in their DCS line. Getting a direct relationship with QSC is somewhat painful
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post #25 of 29
6/9/09 at 12:18pm
interesting
i love JBL PRO.
QSC is starting to have good success with theaters but access is difficult...
LL
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post #26 of 29
6/9/09 at 2:56pm
I have heard the JBL Cinema line a number of times, and properly auditioned them twice. I've never been impressed by them at all.

I was amazed by how inexpensive they were, sadly I was even more amazed at how inexpensive they sounded.
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post #27 of 29
6/9/09 at 3:15pm
Very nice discussion - thanks. I like my surrounds placed higher on the wall - for movies.
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post #28 of 29
6/10/09 at 2:56am
Quote:
Originally Posted by coldmachine View Post

I have heard the JBL Cinema line a number of times, and properly auditioned them twice. I've never been impressed by them at all.

I was amazed by how inexpensive they were, sadly I was even more amazed at how inexpensive they sounded.

well depends on what you sell and it biases yr judgement
well fed and equalized, crossovered it's a distorsion free blast.
results/price is amazing.
but there's the other school like GENELEC, with a more "monitor" ultra detailed sound (which does not fit all kinds of soundtracks). and it"s very expensive.
the SYNTHESIS is nice but this A LOT DIFFERENT in price...
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post #29 of 29
8/4/09 at 8:38am
Quote:
Originally Posted by Dennis Erskine View Post

4. The delay for the rear surrounds is set

I think the delay for the rear surrounds can only be correct for just one of the rows, right? Is it correct for the front row, the back row, or a middle row?
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