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Is this what is supposed to happen while doing a 'phase' test?

Discussion in 'Home Theater Audio' started by Athlon646464, Aug 25, 2011.

  1. Athlon646464

    Athlon646464 Gold Members DBSTalk Gold Club

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    I hope you can help me, as I am stumped. I've searched everywhere on the 'net to no avail.

    I have a Yamaha RX-V795a AVR.

    While doing a phase test for the first time in a few years, I noticed the rear surrounds in my 5.1 setup act differently than the mains do during their test.

    While playing the 'noise' for testing 'in phase' I can hear the 'noise'. While playing the 'noise' for testing 'out of phase' there is silence.

    I'm testing with the old Avia disc.

    Is this normal? [​IMG]
     
  2. hilmar2k

    hilmar2k Hall Of Fame

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    Being in or out if phase has to do with low frequencies. Your surround speakers may not reproduce frequencies as low as the signal that is used.

    Of course, if you wired the speakers properly, they won't be out if phase in the first place.
     
  3. Yoda-DBSguy

    Yoda-DBSguy Hall Of Fame

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    A Galaxy...


    The "phase test" refers to a self test the receiver does in order verify that the polarity of each speaker terminal wiring is corerct. Basically it checks for reversed wiring (- to +, + to - or out of order speaker path/left to right, etc).

    If out of phase, the following would happen:
    -Very limited low frequency response

    -If using more than one multimedia system in a surround sound application, or a subwoofer with a multimedia system, then you want all of the speakers to move in the same direction at the same time. If you switch the phase of one speaker system while playing this tone (or test), the loudness of the tone will change. When the two systems are out of phase, you will hear much less sound output at this frequency and when the two systems are in phase this tone will be loud.
     
  4. Athlon646464

    Athlon646464 Gold Members DBSTalk Gold Club

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    Yes, that I knew. I just don't understand why the 'out of phase' test is dead silent when testing my surrounds.
     
  5. Athlon646464

    Athlon646464 Gold Members DBSTalk Gold Club

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    They play the 'white noise' during the 'in phase' portion of the test however. I'm wondering if it has something to do with my Yamaha.

    I've triple checked the polarity, and I've had these hooked up for at least 8 years and have done the test before. We had some work done in the room, so I decided to re-balance my system with my sound meter. The phase test was the next test on the disc, so I figured I would run it while I had the disc out.

    They are Klipsch RS-3's. Their web site rates their frequency response at 61Hz-20kHz (+-)3dB

    http://www.klipsch.com/rs-3-surround-speaker

    [​IMG]
     
  6. Carl Spock

    Carl Spock Superfly

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    Yes, this is normal.

    What's going on during a phase test is you are making sure all of your speakers are moving in the same direction at the same time.

    The classic phase test is with two stereo speakers. If you play mono music on a stereo with everything hooked up correctly, you'd hear the sound come out between the speakers. If you could see really fast, you'd find your speakers are moving together. The two woofers are moving in and out at the same time.

    (Or, if you were a college kid back in the 1970's who had a technical bend, you'd take some chalk and draw rings on your speaker's woofer. That way when your strobe light went off in your dorm room, you'd get a snapshot of the woofer moving. Bitchin'.)

    Now reverse the wires to just one speaker so that the hot wire goes to the black terminal on the speaker and the negative wire goes to the red one. When you play the music, it now sounds like it's coming from each speaker, not the middle, and all the bass has gone away. A slow motion camera - or a stoned hippie - would see the woofers moving opposite of each other. They are cancelling each other's bass.

    You'll find phase switches on the back of subwoofers. Clicking it back and forth makes sure all your front speakers are pushing and pulling together. In one position, the subwoofer cancels some of the bass coming from the mains. In the other position, it re-enforces the bass. You want the position that gives you the most bass. You may have to listen over the course of a night to hear the difference but it's there.

    When you are doing a phase test on your home theater system, the microphone that came with your receiver is measuring whether this is happening with all the speakers in your system. Are they all reinforcing each other? The speed of sound comes into play as sound moves about a foot every milisecond, so it's more complicated. That's why God invented microprocessors, although I've been listening to get the phase right for years. You can do it by ear.

    You will find no matter what your system tries to do, there will still be areas in your room with more bass and others with less. That's the nature of rooms. But overall, you should get more bass when the phase is set correctly.


    EDIT: I should have known half a dozen other posters would beat me to the punch if I wrote a long reply! :lol:
     
  7. Athlon646464

    Athlon646464 Gold Members DBSTalk Gold Club

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    Thank you for taking so much time, but I understand what a phase test is all about.

    My question is about what happens (and it has not happened before while doing the same test) to just my surrounds during the test.

    While testing the mains, or center/left main, or center/right main, or left main/sub I hear the white noise for both the 'in phase' and 'out of phase' tests. I can tell from the sounds (tests) they are all in phase.

    It is only for my surrounds that I do not hear anything during the 'out of phase' portion of the test.
     
  8. Carl Spock

    Carl Spock Superfly

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    Now that is strange. If anything, a phase test with surrounds is relatively inconclusive. The sound is bouncing all around before it gets to the other speakers and it's hard to hear in and out of phase. It often sounds the same.

    Do your Klipsch have a phase switch on them? It would be marked bipole or dipole. If they do, you might try switching that. It puts the two drivers in and out of phase.
     
  9. Athlon646464

    Athlon646464 Gold Members DBSTalk Gold Club

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    I agree - this is odd, and has me completely stumped. They do not have a phase switch on them (only my sub does).

    I know quite a bit about sound systems, and have helped many set up and calibrate their systems. This is the first time I've encountered this.

    A Google search yields nothing on it, except for a vague reference to a particular Onkyo receiver exhibiting this exact behavior during a phase test. (They replaced all of those units under warranty, by the way).

    The last time I tested them about 2 years ago they did not do this. I'm wondering if it has something to do with my Yamaha. However, everything was moved in and out of the room last week, so who knows what may have happened.

    One thought I've had is that the sound is there, and they are just canceling each other out because they are 180 degrees out of phase and they face each other.

    Strange..... :confused:
     
  10. hilmar2k

    hilmar2k Hall Of Fame

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    There's no way they'd be able to cancel each other out so much that you would not hear anything.
     
  11. Athlon646464

    Athlon646464 Gold Members DBSTalk Gold Club

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    Agreed - I'm just stumped. :icon_dumm

    By the way, during the discreet channel test - all is OK. The sound comes from each channel as expected, and they are balanced according to my sound meter. My Yamaha is about 10 years old, and did not come with a mic to set up and calibrate the system. I've always done it manually.
     
  12. hilmar2k

    hilmar2k Hall Of Fame

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    I have a sound meter and always calibrate my sound levels manually. I used the included mic that came with my Onkyo and found the levels quite a bit off when I verified with my meter.
     
  13. Athlon646464

    Athlon646464 Gold Members DBSTalk Gold Club

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    I have one of these puppies:

    [​IMG]

    Old school analog, I know! :eek2:
     
  14. hilmar2k

    hilmar2k Hall Of Fame

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    Well, that looks familiar. ;)
     
  15. Athlon646464

    Athlon646464 Gold Members DBSTalk Gold Club

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    Fixed!

    We recently had some work done in my home theater room. When I reconnected everything I had two devices connected to the same input on my AVR (one optical & one coaxial).

    One of the two devices was my BD player, the other being sound out from my TV. We had not watched a Blu-ray disc or DVD until last night. When we stuck the BD version of Blazing Saddles into the BD player last night, all I could get out of it was Pro Logic. That caused me to look at that wiring and see the error.

    Until then I had checked the polarity of my wiring for what seemed like a 1000 times, and never looked at that section of my AVR. When trying the two calibration discs I have, I never looked at the display on my AVR either to see what was being decoded. I must have reset my BD player 3 or 4 times to change the sound output settings of it!! [​IMG]

    Isn't it always the least likely place you look after you commit a series of stupid errors? [​IMG][​IMG]

    Thank you to all who tried to help! [​IMG] I'm posting this in case someone with a similar issue else finds this thread in the future.
     
  16. wilbur_the_goose

    wilbur_the_goose Hall Of Fame

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    Bi-polar speakers frequently give a false positive on phase tests.

    Double check the wiring on both ends, and if it's OK, don't worry about it.
     
  17. Athlon646464

    Athlon646464 Gold Members DBSTalk Gold Club

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    Thanks, but as I said in my post just above, all is good now. All tests are good, including the phase tests.
     

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