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QSC PLX

Discussion in 'Amps and Cabs [BG]' started by Ruptured, Jun 1, 2003.


  1. Ruptured

    Ruptured

    May 14, 2003
    Are these figures refering to frequency response?

    BRIDGE MONO MODE
    16 ohms 20 Hz-20 kHz 0.1% THD
    8 ohms 20 Hz-20 kHz 0.1% THD
    4 ohms 1 kHz 1% THD


    If so does bridging into 4 ohms mean the amp won't respond to frequencies above 1 khz?

    Or do I have it wrong?
     
  2. Daytona

    Daytona

    Apr 26, 2003
    I believe that these figures are referring to Total Harmonic Distortion.
     
  3. MauriLii

    MauriLii

    Jan 19, 2003
    Kent, England
    The amp will definately work above 1kHz.

    My understanding of this is that at 4 ohms, they only tested the amp with a sine wave at 1kHz. The THD (Total Harmonic Distortion) was 1%. The other two ratings (for an 8 and 16 ohm load) mean that the amp was tested with a more "real world" signal (i.e. 20Hz to 20kHz) with a lower THD. This allows you to compare power ratings of one amp to another accurately. The power ratings are actually pretty meaningless without telling us what conditions the amps are tested under. It's like telling us that a speaker has a freqency response of 20 Hz to 20 kHz. That's fine, but is that +/-3dB? +/-10dB? +/-50dB?

    I suppose the THD of 1% is a little high, but with a bridged amp pushing a four ohm load, it's quite respectable. Besides, there are other types of distortion that are far more offensive than THD.

    I am unclear ,however, as to why they test the amps differently for different impedances. I was wondering this myself. Maybe Bob Lee can clarify this. Bob? Bob? Are you listening? Are you ears burning? Yes, we're talking about you.
     
  4. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Frequency response specs are listed under "frequency response," not "power." Also, power ratings are not THD specs. The distortion mentioned in a power spec is just a statement of how the onset of clipping was determined in the sine wave test signal.

    We use two different methods of power rating, FTC and EIA, because other brands use one or both, and you should be able to compare apples to apples and dogs to dogs.

    See http://www.talkbass.com/forum/showthread.php?s=&threadid=66720 for more details.
     
  5. Ruptured

    Ruptured

    May 14, 2003