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I used to be in charge of product for Cinema for JBL. Its the same speaker in the center as the left and the right-and that's how we did it at the Academy of Motion Pictures as well.
In a correct film mix, dialogue is the ONLY thing supposed to come from the center speaker. However, I hear from my scoring mixer friends that there are a few [film] mixes out there with non dialogue showing up in the Center. I think its harder to give motion or position since center and left (or right) aren't so far apart.
In IMAX they use a lot more channels than typical film as they use a vertical component of audio to imply an up and down motion (most film only uses left to right).
Someday maybe we'll have 12.1- level one LCR front and LCR surround and level two LCR front and LCR back. Give me a few more overhead and they can do 360 steering!
BTW, center channel in 5.1 music mixes are another story. All bets are off, you can do anything you want.
Ok, someone please answer the following queation: Where are the speakers in a commercial cinema theater typically located in relation to the audience(besides the consideration that there are usually more of them in the sides and rears, typically), and how does that differ from how speakers are typically layed out in a home theater setup?
The LCR set of speakers is behind the screen in all cinema systems except the non perforated Taurus screens that AMC uses (not sure if they still do) Non perforated screens require speakers be mounted above the screens, and you can tell that the sound is not from behind. Subs are typically below the screen in cinema systems.
Surrounds are strung along the sides, all from from one left and one right channel. There is no delay in use.
Different cinema chains supported different manufacturers. For example, Edwards, Harkins, Mann always bought JBL. AMC bought EV. I doubt there is an easy way to figure out who is who.
The era the theater was built in sort of determined the quality. In 1991 or so I attended Jurrasic Park premier with DTS (and JBL speakers), the first of the 5.1 cinema sound systems. At that time, 95% of the cinemas were mono with a few stereo ones out in LA. A huge wave of theater building came then, and THX was supported in one room of a big complex, mostly in major markets.
In the case of JBL, the behind the screen speakers never changed much. It was a dual 15 with a 4 inch driver on a professional horn. Theaters built after 1993 or 1994 or so had the better 8340 JBL surround, which offered wider HF dispersion and higher dynamics, to handle better surround tracks.
THX was about dynamic range, room design (speaker dispersion ) and room isolation (less leakage from the room next door), and max SPL. It really helped convince theater owners, who only made money selling popcorn and candy, to embrace better audio playback. The competitiveness of the industry problem did more to get it going, as one owner would not want to be outdone by a competitor. You really could not compete with a mono theater against the draw of a 5.1 film properly supported.
I always felt like Edwards on the west coast did the best job with audio, their theaters generally sounded the best to me. And the bigger ones closer to Hollywood WERE better, I guess due to industry clientele would be more aggressive with their complaining. Complaints do seems to drive theaters to make adjustments.
Besides the power and pressence from high efficiency horn speakers in these large venues, I always notice that the loudspeaker arrays are typically positioned HIGHER UP in relation to the seating area bellow! I feel that there's something to be said about this. One, there's a sense of grandure and overshadowing pressence from having speakers locted higher up, as opposed to being more "down low", like you find in many home systems.
Also, speakers are less localized in the rears/sides when you get em higher up.
I personally prefer having my theater speaker systems setup with the speakers more towards the ceiling boundary, rathern than the floor boundary, one, because I do find the sound to be more dramatic and authoritative when they're up higher, than down lower, for some reason. Two, I am conscious of the fact that speaker located down on the floor, or lower, can propegate sound towards the room boundaries near the ceiling, which focuses/reflects right back down to the seating position -causing acoustical reflection point issues, smearing imaging and dynamics a bit there. (of course, radical room acoustics treatments tames alot, but often impractical to go full out here) Obviously for musical soundstaging, there's some tradeoff there. But still, I think the rewards better outweigh the negatives.
Anyone else here ever consider these points of contention, for sound performance applications?
Well I think there are some valid points there, but I think its simpler than that. The sound needs to come from the action on the screen and the screen is higher. Secondly the floor is not flat, its "theater" seating with seats on steps up to the back row (for visibility originally) . You cannot put a limited vertical dispersion speaker down low and have it cover the last rows.
The surround design is what it is for a simpler reason-output and consistency of coverage. These surrounds cannot play loud like the LCR set, so you need a lot of them to get level from surround channels. Building/using a few higher power surrounds would create nasty hot spots that theater goers would complain about. Its a common technique in live, using multiple speakers at lower level works out when you have close listener proximity issues.