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Author Topic: Speaker Phasing Bob Koch Expert Film Handler Posts: 183 From: williams ca Registered: Nov 2001 posted 10-11-2006 08:47 PM                     I don`t know if I`m getting in over my head here but many, and I emphasise many years ago we were talking about acousticalize phasing here.Altec, with there many systems starting with A2`s A4`s and A4x`s were very susceptable to this. You had to put on your coveralls and go back on the deck and physically move the 288 on its sled and finally find the point where it was acoustally in phase,very difficult to do. If you found the point,and many times it was within an inch or two, you could not believe the difference in the auditorium.I doubt any one in this day and age would want to give any credability to this. Except , Steve I would like to hear any comments you have,  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 10-11-2006 09:12 PM                        The A2, for example, has about a 500Hz crossover point between HF and LF units, 1/4 wavelength of which is about 7", so I wouldn't think any changes less than about 7" making a difference in sound. Still, that's not much movement, really.  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 10-11-2006 09:16 PM                     Thanks Gordon...that was the answer I was looking for....ALL drivers regardless, need to be the same phase. BTW, thats how I check phasing also. Going throught he external inputs.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 10-11-2006 10:25 PM                     Robert the industry standard for stage speakers has been for a long time 500Hz only the smaller compact speakers has there ever been much of a variance from that 500Hz was choosen as it allowed the male dialogue range to be pumped throught the horn  |  IP: Logged Cameron Glendinning Jedi Master Film Handler Posts: 845 From: West Ryde, Sydney, NSW Australia Registered: Dec 2005 posted 10-11-2006 11:42 PM                     quote: Robert Minichino The A2, for example, has about a 500Hz crossover point between HF and LF units, 1/4 wavelength of which is about 7", so I wouldn't think any changes less than about 7" making a difference in sound. Still, that's not much movement, really. I'm not sure but ideally would you not want the horn to be more than 7 inches from the woofer. Personally my experience agrees with the comment about moving back and forward to a fairly precise spot, altec do go to a lot of detail in their installation guides, ie reverse polarity to horn, move back and forward until cancellation of frequencies is most noticeable, then swap hi frequency phasing and your done  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 10-12-2006 03:39 PM                     Richard, Speaker phasing should be done by "system"...that is, don't rewire your surrounds. Their woofers should match every other woofer in your auditorium. Now having said that, on the stage channels, they generally should all be the same phase throughout the system if there are no passive crossovers in the system. And that is a key element...the crossover can create time-domain shifts which is why some speakers will have drivers deliberately wired out of phase. So if you go around with your phase checker, all of the woofers should match...on the stage channels the highs (and mids) should match the woofers. As to moving the HF sled to achieve proper match...yes that is correct. If one knows the crossover point, all one has to do is play a tone at the crossover frequency and move the sled until maximum level is achieved. Nowadays, most people use active crossovers and can adjust the delay on the driver that is arriving sooner to electrically achieve similar results. Rane, in particular, makes a nifty crossover, the AC22B (and AC23B) that has a continiously adjustable delay so one may precisely tune it. However, Altec had it right (as they normally did) to mechanically get things aligned properly . Steve  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 10-12-2006 04:16 PM                     Thanks Steve, All of our speakers use passive crossovers. Should all the woofers and HF's still be made to be the same phase using the phase checker? You said not to rewire the surrounds. What about the HF's being out of phase with the LF's?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 10-12-2006 04:27 PM                     Richard, On the surrounds...they have a PASSIVE crossover in them...the phase shift in the crossover accounts for the need to wire the other drivers out of phase to achieve the proper response. As to your stage channels...since they have passive crossovers there are no absolutes...MOST have all drivers in phase but in the case of several speakers...like the JBL 4670 and those that look like it from EV and EAW...I believe they instruct you to wire the HF out of phase with their current crossovers. If you know the crossover point...put a tone out at that frequency...and measure the level with the phase reversed...the correct phasing should have the highest level. Note...all of your stage channels should match though...that is, if reversing the phase on the HF unit of Center is best....then it better be reversed on Left and Right too. Steve  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 10-13-2006 11:03 AM                        The reason why you hook up the LF and HF units out of phase when trying to physically align them is because it's much easier to hear the null created when they cancel than it is to hear the peak when they're perfectly aligned. Graph of attenuation in dB versus wavelength  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 10-22-2006 07:16 PM                     Steve, thanks for all the info. My final thought on this subject is the following. Lets say, like you said, the HF's on the surrounds are wired out of phase for a certain reason. If the HF's on the stage speakers are wired IN PHASE, wouldnt there be a problem with the HF between the stage and surrounds or no?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 10-22-2006 08:23 PM                     Snappy answer...NO. The reason is left as a homework assignment.  |  IP: Logged

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