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    Is your music system phase correct?

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    Bob Latino
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    Is your music system phase correct?

    Post by Bob Latino on Sun Apr 24, 2011 8:44 pm

    When your music system is fed a musical signal you want the first "pulse" of that drum whack to cause your woofer to move OUT rather than IN. AFAIK all original Dynaco tube amps and the VTA Dynaco amps all have positive phase which means that they don't invert phase. This is not true, however, of all amps and preamps. In fact some preamps have a phase correct line stage and an inverted phono section. (Conrad Johnson PV12-A). Playing CD's on this preamp gives positive phase on the line stage and negative phase on the phono section. Some of the more expensive preamps have a phase reversal button on the remote. You can sit at your listening point and cycle the phase reversal button and decide which way sounds best to you. In my downstairs system I have a BAT VK30-SE preamp which has such a switch. The treble on the speakers seems a little more "crisp" when I am in positive phase and the system seems to soundstage better when I am in positive phase. Some sub-woofers have a phase reversal switch. Depending on where you place your subwoofer, sometimes the 180 degree reverse phase may actually give more bass.

    How can you tell whether your system is "phase correct" ? First take off the grille cloth on your speaker. Next plug in an interconnect into your preamp's CD input. One will do. Turn the preamp on and place the volume control at about 1/4 volume. Now get TWO jumper wires and a 1 1/2 volt battery. Any type of battery will do > C, D, AA, AAA is fine. Tape one end of one wire on the outer shield of the interconnect and the other end of the same jumper wire to the flat negative side of your battery. Tape one end of the OTHER jumper wire to the center pin of your interconnect. Touch the other end of this wire to the POSITIVE side of the battery for about 1 second and note if your woofer moves IN or OUT. If the woofer moves OUT your system is phase correct. If it moves IN your system is phase reversed. If you can't see the woofer move, turn up the volume a little on your preamp until you can see it move.

    If it turns out your system is "phase reversed" not to worry .... All you have to do is reverse the positive and negative wires on your speakers and you will now be phase correct.

    Bob

    Tom

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    Re: Is your music system phase correct?

    Post by Tom on Mon Apr 25, 2011 8:46 am

    Wow. Never would have occured to me.
    Thanks for the info an tutorial.
    Keep 'em coming!

    Tom

    GP49

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    Re: Is your music system phase correct?

    Post by GP49 on Mon Apr 25, 2011 1:19 pm

    Some other associated equipment may be phase-incorrect, too. Example: the Decca phono cartridges, which just happen to be my favorite; they reverse absolute phase. Easy to correct by reversing the speaker wires but that puts CD players into inverted absolute phase.

    This next comment won't affect those of us with tube amps, which cannot drive to DC anyway, but if you have a transistor power amplifier without an input capacitor, or with a switch that selects no input capacitor, do NOT try the battery test at the power amp input (I know, Bob didn't say to do that, anyway). Most preamps will not pass DC, so the procedure is generally safe.

    Pooch

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    Re: Is your music system phase correct?

    Post by Pooch on Mon Apr 25, 2011 4:53 pm

    I must be missing the point here. If both channels are phase reversed, does it make any difference? I thought it only mattered if one channel was out of phase with the other. What am I missing?
    Gordy

    Pooch

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    Re: Is your music system phase correct?

    Post by Pooch on Mon Apr 25, 2011 5:01 pm

    brain cramp gone.... so this would mean the sound is coming off the back of the driver when it was intended to come off the front?

    Luddite

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    Re: Is your music system phase correct?

    Post by Luddite on Mon Apr 25, 2011 6:21 pm

    Pooch wrote:brain cramp gone.... so this would mean the sound is coming off the back of the driver when it was intended to come off the front?

    Gordy,

    You're on the right track, but that's not exactly what happens. Basically speaking, both phases (halves) of a sound wave are reproduced by both sides of the cone, diaphragm, etc. When phased correctly, the positive half would move the cone out "compressing" the air, while the negative half would move the cone in "expanding" the air in proper phase relationship with the original sound. This is referred to as "compression state" and "rarefaction state". The differences in the pressurization "state" of the air governs which direction the eardrums move. It is entirely possible that our hearing mechanism can readily detect the difference between a positive and negative pulse.

    Best Regards,
    Charlie


    Last edited by Luddite on Mon Apr 25, 2011 9:03 pm; edited 1 time in total (Reason for editing : additions & revisions)

    j beede

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    Re: Is your music system phase correct?

    Post by j beede on Mon Apr 25, 2011 9:49 pm

    Some multi-way speaker designers connect different drivers within the same speaker out of phase. Good luck.
    ...j

    mantha3

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    Re: Is your music system phase correct?

    Post by mantha3 on Mon Apr 25, 2011 10:06 pm

    I built a pair of speakers with a design by Troels Gravesen. These are 3 way with Seas drivers. The 8" woofer is out of phase with the tweeter and midrange. I guess this is common to some degree with 3 way speakers.

    Dun know... I run my Tube Amp ST120 with these speakers and I've run this with a Boston Acoustics sub that has a phase switch in the back... I've been wondering which way to keep this set. This thread helps.

    Luddite

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    Re: Is your music system phase correct?

    Post by Luddite on Tue Apr 26, 2011 12:26 am

    j beede wrote:Some multi-way speaker designers connect different drivers within the same speaker out of phase. Good luck.
    ...j

    Yes they do, particularly when using 2nd order (12dB per octave) Butterworth filters in the crossover network (provides a smoother transition between drivers). Of course considering multi-way speaker systems opens a new "can of worms" regarding phasing issues. Suffice it to say, that is a major reason for the popularity of full range, single driver speakers.

    Best Regards,
    Charlie

    GP49

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    Re: Is your music system phase correct?

    Post by GP49 on Tue Apr 26, 2011 10:27 am

    j beede wrote:Some multi-way speaker designers connect different drivers within the same speaker out of phase. Good luck.
    ...j

    In MOST cases where I've encountered this, it was to correct an inverse ELECTRICAL phase condition in that driver, caused by the crossover; so that overall the acoustic effect was to retain correct absolute phase.

    Most...not all. I know of one speaker system where the reverse phase condition was done to reduce output in the crossover region, due to a peak in one of the drivers. Should have selected another driver instead!

    j beede

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    Re: Is your music system phase correct?

    Post by j beede on Tue Apr 26, 2011 3:57 pm

    Okay... tossing wrench #2 into the works. How about Gallo et al that mount some drivers with their axis normal to the others' axes? My point is that "phase" can be another parameter like speaker placement, room treatment, stand height, etc. If you are running Jordan Modules, Lowthers, full range ribbons or ESLs I suppose absolute phase managment makes sense. For those of you running DQ-10s, Time Windows, Legacy, Wilson... good luck. Just remember "red=right" and you should be okay Smile

    Pooch

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    Re: Is your music system phase correct?

    Post by Pooch on Tue May 10, 2011 10:42 pm

    I've been doing a little mouse work searching the Web. Clark Johnsen wrote a book on this subject, something along the lines of the Woods effect.IIRC, Woods was the first person to elaborate on this phase thing.
    Wrench #3.... some recordings are out of phase, some part in phase and out of phase. Also some of the instruments, vocals can be out of phase with each other, in the same track. Kinda like chasing your tail! But it is a very real concern and some people can hear the difference. Not sure if I can.
    My CJ PV8 has the line stage reversed, but the phono stage is not, so I reversed the wires on the speaker to correct the line stage, and then reversed the leads on the cartridge to get it back in phase. Assuming everything else is right Rolling Eyes

    JunkyJan

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    Re: Is your music system phase correct?

    Post by JunkyJan on Thu May 12, 2011 1:17 am

    Good Grief Bob!

    I have been involved with audio equipment for more than 30 years and I have never come across this before - heard the words "Absolute Phase" but thought it to be Audiophool mumbo-jumbo. It now makes completely sense (as some would say would say, I totally Grok it!).

    Thanks a ton for sharing this information!

    -- Junky


    Captain Coconut

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    Re: Is your music system phase correct?

    Post by Captain Coconut on Thu May 12, 2011 9:05 am

    I'm confused, which is my normal state anyways. scratch

    Luddite

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    Re: Is your music system phase correct?

    Post by Luddite on Thu May 12, 2011 1:42 pm

    Captain Coconut wrote: I'm confused, which is my normal state anyways. scratch

    I thought they were called "provinces" up there...

    We have states down here, some of them being "normal" and some of them being "abnormal". Hopefully that's only a "phase" we're going through. Wink

    Captain Coconut

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    Re: Is your music system phase correct?

    Post by Captain Coconut on Thu May 12, 2011 4:17 pm

    This phase thing has given me a headache, and to top it off, Luddy lays on this double entendre (or is it a double double entendre) with states/provinces/phase and who knows what else. Man, I wonder if I've listened to headphones that have always been out of phase. No wonder my ears appear a little larger than usual!

    Tom

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    Re: Is your music system phase correct?

    Post by Tom on Fri May 13, 2011 12:09 pm

    Phasers set to stun.

    JunkyJan

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    Re: Is your music system phase correct?

    Post by JunkyJan on Fri May 13, 2011 1:42 pm

    Luddite wrote:...Basically speaking, both phases (halves) of a sound wave are reproduced by both sides of the cone, diaphragm, etc. When phased correctly, the positive half would move the cone out "compressing" the air, while the negative half would move the cone in "expanding" the air in proper phase relationship with the original sound. This is referred to as "compression state" and "rarefaction state". The differences in the pressurization "state" of the air governs which direction the eardrums move. It is entirely possible that our hearing mechanism can readily detect the difference between a positive and negative pulse....
    Joking aside, it's not complicated. See Luddite's quoted post... That at least gives one a reference point to work from. If the recording engineer decided to reverse phases during recording, that's his mistake, and I'm not going to switch phases around to try and satisfy the whims of the recording engineer.

    I would assume there are RIAA specs out there somewhere that specifies Phasing during recording? As long as my equipment is in line with that, I'm happy...

    -- JunkyJan

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