Edjucate me about phase vs impedance

Discussion in 'Loudspeakers' started by shadyJ, Jan 13, 2013.

  1. shadyJ Audioholic Ninja

    shadyJ
    Joined:
    Oct 16, 2006
    Messages:
    3,103
    Likes Received:
    978
    I never took electrical engineering, so when stereophile talks about their phase vs impedance graphs, I get a bit lost. I get impedance, which I understand to be a measure of resistance, so what does phase mean and how does it figure into this? Talkin' bout charts like this:
    [​IMG]
  2. Steve81 Audioholics 5-O

    Steve81
    Joined:
    Aug 9, 2012
    Messages:
    3,522
    Likes Received:
    1,898
    Location:
    38.89°N, 77.01°W
    From my simple understanding, the phase angle indicates how far voltage and current are out of phase with one another; you're probably familiar with Power = Voltage x Current, which is true for a purely resistive circuit; once you get into a reactive load, its Power = Voltage x Current x Power Factor where the power factor is the cosine of the phase angle.
    • Like Like x 1
  3. Steve81 Audioholics 5-O

    Steve81
    Joined:
    Aug 9, 2012
    Messages:
    3,522
    Likes Received:
    1,898
    Location:
    38.89°N, 77.01°W
    Also, from a practical standpoint, it's my understanding that the simple fact that they're out of phase can cause stability problems with some amplifiers. OTOH, it's also my understanding that it's already accounted for when looking at a FR graph which is taken at a constant voltage level, usually 2.83V.
  4. JerryLove Audioholic Samurai

    JerryLove
    Joined:
    Jul 17, 2008
    Messages:
    2,219
    Likes Received:
    601
    Location:
    Tampa, FL
    Phase (waves) - Wikipedia, the free encyclopedia

    Remember, that the electrical phase change becomes an auditory phase shift as well.

    Though there are groups within audiophilia which consider relative phase important to reproduction; all of the available studies seem to indicate that (within reason) the brain does not notice phase shifts.

    The clear exception is when the phase shift causes cancellation. For example: if your tweeter and midrange are 180-degrees out-of-phase at the crossover point, then they will cancel each other out and make very poor sound.
    • Like Like x 1
  5. PENG Audioholic Warlord

    PENG
    Joined:
    Oct 23, 2004
    Messages:
    7,890
    Likes Received:
    2,199
    Location:
    Ontario
    If you are serious about wanting to be educated on this, I do have a link for you:

    AC circuits, alternating current electricity

    You don't have to be an EE but you do need to have a good understanding of high school physics, basic math including trigonomety, and some calculus would help, in order to work through the contents in that link.

    If you just want to know how it factors into some basic power calculations, then just take a look of the formula Steve posted (#2). In that you can see if the phase angle between the voltage and current is, say 60 degrees, given that Cosine 60 deg = 0.5, now if we consider some examples and first say we have 10V applied to an 8 ohm load, and the load is purely resistive, then:

    Currrent = V/I = 10/8 = 1.25A, and now Power = V X I = 10X1.25=12.5W (It could have been done quicker using another formula, P=V²/R but may as well stick with Steve's just for clarity.

    Now if the same 8 ohm load is reactive, such that phase angle between voltage and current is 60 degrees, then:

    Current, again = 10/8 =1.25A, but Power = 10X1.25Xcos60 = 12.5X0.5 = 6.25W, so you can see that in order to deliver the same 12.5W into a reactive load, the current, hence the applied voltage, would have to be higher (about 41.4% each) than what is required to deliver the same power into a purely resistive load of the same ohmic value.

    This is why I prefer speaker sensitivity specified as X dB/Watt/Meter and not X dB/2.83V/Meter because in the former, both of the ohmic value and phase angle of load have already been factored in whereas in the latter we know the voltage, that is 2.83V, but that only equates to 1Watt if the ohmic value is 8 ohms and the phase angle is 0 degree (meaning phase angle=0, the load is purely resistive).

    Note that for a pure capacitor the current would lead the applied voltage by 90 degrees, or 1/4 of a cycle, for a pure inductor, the current would lag the applied voltage by 90 degrees while for a pure resistor, the current and voltage are in phase. So for a complex load that has all 3 components, the phase angle will be anything in between -90 degrees to +90 degrees.
    Last edited: Jan 13, 2013
    PENG,
    • Like Like x 4
  6. AcuDefTechGuy Audioholic Slumlord

    AcuDefTechGuy
    Joined:
    Jul 10, 2007
    Messages:
    18,935
    Likes Received:
    4,151
    Location:
    Oklahoma City
    Has there ever been a speaker with poor phase measurement?

    I can't imagine the engineers from B&W, Revel, KEF, Focal, Dynaudio, etc, would release speakers with poor phase angles. :D

    And as far as Impedance, I think 4 ohms & above is safe for most AVRs. My Phil3 speakers are 4ohms and my Denon 3312 has no problems at all.

    Bottom line is we audition speakers (with AVRs or amps comparable to what we own or will buy) and we buy the best sounding speakers. Period. :D
    Last edited: Jan 14, 2013
  7. cpp Audioholic Field Marshall

    cpp
    Joined:
    Dec 13, 2005
    Messages:
    1,532
    Likes Received:
    406
    Location:
    Coastal Fla ( somewhere south of Marineland
    who knows, since few even provide complete measurements.

    a little bathroom reading material : Measuring Loudspeakers, Part Two Page 4 | Stereophile.com
    cpp,

Share This Page

  • rbhsound.com
  • BlueJeansCable.com
  • Emotiva.com
  • SVS Sound Subwoofers
  • Experience the Martin Logan Montis
  • CEDIA