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Larson Davis KLxT-QPR User Guide and Hints

Basic Setup Instructions for Firearm Acoustic Testing

There are three options for setting up the LxT meter for Firearms Testing:

  1. Import a setup file via G4 (a setup file for a meter with ENV firmware is here)
    Setup via G4 software (view a pdf that details this process for a meter WITHOUT ENV firmware)
  2. Setup on the meter itself 
    • Press the middle “soft key” near the screen to select “Menu”
    • Hit “Enter” (center of circle keypad area) to select Settings
    • Then the left and right softkeys are used to navigate the menu structure
    • Navigate to the SLM tab
      • Set Peak Weighting to Z.  This is the relevant setting for firearm testing.  Everything else can stay as-is.
    • Navigate to the Control tab
      • Set Run Mode to Timed Stop
      • Set Time to 5s
    • If you have ENV firmware, Measurement History is available
      • Turn on Measurement History (This will save all data from your measurement into a single file)
    • Press the “Close” soft key in the center near the screen to save your Settings modifications. When asked to “Apply Changes?”, make sure you select “Yes” and press “Enter”.

Physical Setup of Meter and Firearm

To set up the meter's physical location, below are some suggestions. In general, US Military standard testing procedure for sound suppressors consists of:

  • The meter should be placed one meter away from and 90-degrees to the side of the firearm’s muzzle
  • The meter should be held parallel above the ground at a height of 1.6 meters over a non-reflecting surface
  • The muzzle is positioned perpendicular to the microphone before each shot
  • Ten non-suppressed readings are taken first and then averaged to provide a baseline figure
  • Ten sound-suppressed readings with 3 to 5 minute cooling intervals between each shot are taken
  • This data is also averaged and the result subtracted from the baseline figure. This figure represents the degree of sound suppression.

Running the Test

  1. Press the RUN/PAUSE key to start a measurement with any configuration (different firearm, different suppressor, etc.)
  2. The arrow in the top right will “run” indicating you are good to measure
  3. Fire away, making sure to space triggers apart
  4. If desired, pause the measurement between each shot by pressing the RUN/PAUSE key
  5. Once 10 good shots have been measured, press the STOP/STORE key. Once pressed, the top right will show a filled in square indicating data is stored.
  6. Press the STOP/STORE key again to save the data. It will be given a sequential number, something like “LxT_Data.003”. The “003” or whatever number, keep a log handy to correlate this back to what combination of items were tested.
  7. Once a new firearm/suppressor configuration is ready, press RUN/PAUSE to initiate a new set of measurements
  8. “LZpeak” is typically the main measurement of interest and is selected in the setups linked above. Please note: if measuring to the current MIL-STD-1474D standard, “LApeak” should be used instead. Much technical discussion has taken place since the MIL standard has been put in place in 1997, but it has not been updated or replaced yet. Please read the “Firearm Sound Suppression” presentation for more details.

Additional Considerations

Other factors to note during recording may include:

  • The ambient temperature
  • Humidity
  • Barometric pressure
  • Elevation above sea level
  • Date of test

It is important to note that there will always be minor day-to-day variations in the data obtained as a consequence of changes in the weather parameters.