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Author Topic: Speaker Phasing Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 10-10-2006 06:50 PM                     So I guess my last question on this matter would be as follows.... Is there any ocassion where you would want or need to have lets say the horn, out of phase with the bass driver? Forget about the markings on the speaker. Lets say you're checking phasing with a 2 piece phase checker.  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 10-10-2006 07:02 PM                        Improper phasing between LF and HF units will give you a notch due to cancellation in the crossover region where both units are playing. The proper polarity relationship between the two depends on the crossover.  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 10-10-2006 08:12 PM                       quote: Edward Jurich Haven't been here in some time and felt like posting something Hi, Edward! Long time no hear from. Good to see you back, pal!  |  IP: Logged Cameron Glendinning Jedi Master Film Handler Posts: 845 From: West Ryde, Sydney, NSW Australia Registered: Dec 2005 posted 10-10-2006 10:01 PM                     quote: Bruce Hansen There is an old trick of putting a 1.5V battery across the terminals. If the speaker cone moves outward, then plus on the battery is plus on the speaker. yes but please dont do it to the high frequency unit (compression driver)  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 10-11-2006 10:34 AM                       The only valid way to inject test pulses to test phase is way upstream of the speaker to eliminate the possibility of polarity flips in the wiring to the amps and god forbid, splices in the speaker wire where you can't see them. And of course, most times you can't see the speaker cone behind the screen.  |  IP: Logged Edward Jurich Master Film Handler Posts: 305 From: Las Vegas USA Registered: Jul 2003 posted 10-11-2006 10:50 AM                     quote: Hi, Edward! Long time no hear from. Good to see you back, pal! I sorta lost interest for about a year after a bad experience working for a theater owner. But I have been helping out a small town theater with some sound problems and sparking an interest again. As far as phasing speakers, I always use my ears as a final test. I shut the surround and center channel off. I mono out the sound by clipping the left and right amp inputs together. Then stand center screen, walk around a bit. All the sound should come from the center of the screen if everything is phased right. Then connect the center channel (which should already be left plus right) and check between left / center and right / center. I was amazed after installing an optical stereo / surround system in that small town theater. Knowing that all the surrounds are a single channel, while sitting through "Open Range", action on the screen would go off screen left or right and the sound would follow off screen. Besides being impressed that phasing audio works that well, it's a good indication everything including the surrounds are phased correct.  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 10-11-2006 12:06 PM                     I use a 2 piece phase checker from goldline. The generator sends out the signal. You hold the other unit in front of each speaker cone or horn. I have a patch panel going into the digital inputs of all our processors. This way, like Sam says, you can get an accurate reading at the speaker. The only question I have that hasnt been answered yet is this....Is there any instance where you would need a certain driver of any kind, to be wired out of phase with another driver? And why, on one install, were all the HF's of all the JBL 8330's wired out of phase with the LF's? I read in a post here that JBL did this on purpose......any truth?  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 10-11-2006 01:35 PM                        It depends on the crossover type and polarity markings as well as the distance between the effective acoustic origin of the driver and the crossover frequency. The goal is to avoid the drivers cancelling each other out in the region where they're both playing. A 2nd order crossover (12dB/octave) gives you a net 180 degree phase shift between the LF and HF outputs, so swapping the polarity of one of the drivers reduces cancellation. Some crossover networks reverse their labelling for that and others rely on a reversed connection to the drivers. Because physical movement of the two drivers relative to each other is the same as an electrical phase shift, a displacement of a half wavelength at crossover frequency will also cause cancellation, so you'd swap the polarity of one of the drivers to reduce that.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 10-11-2006 01:57 PM                        We once used a "warble" tone test loop to check phasing of horn vs. woof. You would physically tune for a null in warble level and then reverse the wires to the horn. This assured that the horn/woof added. Louis  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 10-11-2006 03:02 PM                     Robert, does that mean that the HF would then be out of phase with the LF to get the proper results? Or are you just saying that the leads would be reversed in order to get both in phase with each other?  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 10-11-2006 03:24 PM                        With the crossover in the system they'd be in phase, but (assuming they use the same +/- terminal convention) they'd be out of phase at the terminals.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 10-11-2006 03:51 PM                     On the 8330 (wood cabinet) the woofer is indeed wired out of phase with respect to the mid and high. Oddly enough, it is the mid and high that are wired out of phase on the 8330A (plastic cabinet). The answer...comes back to the JBL vs everyone else's standards. The 8330 was Postive on BLACK terminal for outward cone motion. The 8330A is Positive on RED terminal for outward cone motion.  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 10-11-2006 04:34 PM                     Sorry to keep harping on this. Bottom line, I want to know is, do you want all the drivers in the theater to be the same phase? Are there any exceptions? This includes the surrounds too. If so, do I need to reverse the HF on all of those JBL surrounds? One more thing....why the hell would JBL do that...have the LF out of phase compared to the HF....  |  IP: Logged Cameron Glendinning Jedi Master Film Handler Posts: 845 From: West Ryde, Sydney, NSW Australia Registered: Dec 2005 posted 10-11-2006 07:35 PM                     Richard phasing is very important, unfortunately there are many variables, often correct phasing is often only found through the test gear showing the cancelation effect at the overlap at the x over point. 6db passive crossovers and a good electronic type are the most phase correct all else is a bit unpredictable. So often the visual inspection of the wiring is not reliable  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 10-11-2006 08:27 PM                     To ensure none of the electronics are causing a phase shift I always connect the phase checker generator to the processors external 6 track input and then go speaker by speaker through the system and yes all drivers must be in phase at the end of the day  |  IP: Logged

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