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Author Topic: STAR WARS LFE SOUND ISSUE? Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 01-03-2016 09:00 PM                        Wire RTA across each channel and feed pink noise. Might as well do them all. Verify that crossover is, in fact, running correctly. Then look at subs and see if they are restricted to below 100 Hz as expected. I cannot tell you how many times things "blow up" when fed with full range sound. (This problem was really bad with the old CP-45.) If not driven too hard, system might last a long time before failure. \  |  IP: Logged Christopher Lani Film Handler Posts: 62 From: Ely, Nevada, USA Registered: Nov 2013 posted 01-04-2016 02:44 PM                        The Subs were indeed reconed as I was made aware of the cones pulling away by the great staff that installed our digital system. We are also running the QSC but the sub and center channel run off a 1700, not the 1400. I will try to post a video of the distortion as well exact times that it is happening. The problem seems to appear when Kylo is using the force. There are some weird harmonic that are probably state of the art but are more designed for Dolby 7.1, Atmos, or other newer systems. Dropping the volume doez not seem to make the problem go away, that is why I am wondering if it is problem that is occurring in other, older theaters that have sound systems similar to mine. I wonder if just getting a couple self powered JBL 18 INCH SUBS would solve the problem. On a side note, with all of theater closures happening, is there a good place to pick up surplus speakers and chairs?  |  IP: Logged David Buckley Jedi Master Film Handler Posts: 525 From: Oxford, N. Canterbury, New Zealand Registered: Aug 2004 posted 01-04-2016 10:27 PM                        quote: Steve Guttag Remember, when you are doing your testing, that you are using a reference signal that is at -20dB, typically so a problem that doesn't show itself at that level might be a real problem at 0dBFS. How close to 0dBFS does digital cinema go? I hear what you are saying about under-powered subs though, its takes lots of cone area moving lots of distance to get the same sort of SPL a HF horn can do on a few watts, and it still isn't "loud".  |  IP: Logged Bill Brandenstein Master Film Handler Posts: 413 From: Santa Clarita, CA Registered: Jul 2013 posted 01-05-2016 02:06 AM                     David, my educated guess is that movies such as this do reach 0dBFS. From having looked at mix levels in DVD releases (before a home re-mix was the norm) as well as interaction with at least one mix engineer, full scale gets used. Go back a few years to "Master and Commander" and the cannon shots are clipped pretty hard, so (technically) greater than 0dBFS.  |  IP: Logged John Thomas Film Handler Posts: 75 From: Boston, MA Registered: Sep 2011 posted 01-09-2016 07:34 PM                     The digital IMAX near me had to replace 4 (of the 16) sub drivers due to Star Wars.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 01-10-2016 05:31 AM                     quote: George Germisashvili every day sound calibration status "pass OK" I doubt the calibration routine is testing the system at 0dB at all frequencies. As it's been said before on this forum, using pink noise you can easily EQ a broken cone and don't realise that. I've now watched SW and there are no issues with its soundtrack. The point is that when the bad guy uses the force, they used a massive quantity of very deep low frequencies and nothing else. During an explosion any rattle or foreign noises would be covered by the HF content. During the "force" sequence any deficiencies of your system would show up. During my show one amplifier had a gain potentiometer issue. One of the sub was making a crackling noise which could only be heard during the 'force' scenes. Once the trimpot was cleaned, the noise went away. There is nothing wrong with the LFE in Star Wars. It's just pushing the subs and there are very few systems around with properly spec'd systems. Finally, this is usually something that goes overlooked. Nobody notices issues like that till: a) the auditorium gets full of people b) there are scenes like the 'force' which clearly show a problem. Ideally we should test our systems with pink noise AND sweep tones regularly and catch those issues before the customers do.  |  IP: Logged Christopher Lani Film Handler Posts: 62 From: Ely, Nevada, USA Registered: Nov 2013 posted 01-10-2016 09:25 PM                        Very interesting. Is there somewhere I could go to learn how to clean the trim pots on my QSC 1700? Thing is, I went down and observed the speakers during those scenes and the sound was coming from excessive movement from the 2 15' speakers in the center channel Under the horn. Maybe cleaning the trim pots still may be the solution. I agree, it is the massive use of the entire acoustic spectrum of the lower and lower mid range that is showing the deficiencit's in our system. Thanks. I'll let you know if cleaning the trim pots helped. I did notice this one other time in a Disney film. During the credits for "TOMORROWLAND" there is a scene where a rocket ship takes off. That was the first time I ever heard this phenomena.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 01-11-2016 01:57 AM                     If you have it, enable the high pass filter on stage speakers - 30 or 40hz. You may have a 30hz filter on your amps. You may also be over eq'd at those frequencies. Then check the movement of the cones again.  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 01-11-2016 11:53 AM                     A quick (but often temporary) fix for the noisy pots is to first, mark where they are currently set (and make sure you put them to that mark when you are done) and with the amp OFF, rapidly turn them back and forth over the full range several times, then reset them to the mark. If you are skilled enough, you can open the amp up and spray the pots with a cleaner (some use WD-40 which sort of works but will attract dirt later on) and again rotate the pots as you clean them. Or better yet, replace them. Use pots of the same ohms rating and shaft dimensions (QSC may be able to still supply them, but I did not see them on their parts listing), which is the best long-term solution. They can be found online at places like Digi-Key and Mouser. You do need to be able to do good solder removal and soldering though.  |  IP: Logged

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