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OPERATION OF A SOUND-LEVEL METER (ACO 6146)

SPECIFICATIONS



1 Microphone 1/2-inch electret condenser microphone.
2 Display Measurement result, over-scale, under-scale, and battery life are displayed.
Levels are shown with 0.1-dB resolution.
"OVER" means measurement range is too low.
"-" means measurement range is too high.
"BATT" means the battery is low.
3 Range switch Switches between measurement ranges.
Range is set to 60-100 for calibration (CAL).
4 Function switch Switches between A and C frequency weighting for approximating the human ear sensitivity to different SPL ranges.
5 Calibration volume Adjust to 94.0 dB for calibration (range is 60-100 dB).
6 External power connection terminal Connects to AC adapter (AC-1046, option).
7 AC output terminal Outputs AC signal.
8 DC output terminal Outputs DC level signal.
9 Reset switch Resets the hold value.
10 Measurement mode switch Switches between INST and MAX HOLD.
INST shows instant value.
MAX HOLD shows maximum value.
11 Dynamic characteristic switch Switches between two time constants, FAST/SLOW.
12 Power switch Turns power ON and OFF, switches to calibration (CAL).

MEASUREMENT SETUP

  1. Load two AA batteries.
  2. Set the power switch to CAL. Set the dynamic characteristic switch to FAST, the measurement mode switch to INST, and the range switch to 60-100 dB. Adjust the calibration volume to display 94.0 dB.
  3. Set the spectral weighting to A or C as required. In most common noise/sound measurement situations, the spectral weighting will be set to A.
  4. Select the dynamic characteristic. In most common noise/sound measurement situations, the dynamic characteristic will be set to FAST. In cases where there is little variation in the sound level, the SLOW setting would probably work just as well.

CAUTIONS

  1. To minimize errors from reflected sounds when doing sound measurements, the microphone should be kept away from walls, the floor, and other surfaces. When performing measurements while holding the microphone in your hand, the microphone should be held away from your body for the same reason.
  2. The sound of wind striking the microphone can also be a source of error, so the microphone should be protected by a wind screen if sound measurements are being made in the presence of wind.
  3. If the difference between noise being emitted and not being emitted of the noise being measured exceeds 10 dB, then background noise can be ignored. However, if the difference is less than 10 dB, correction is required.

Difference in measured value when target noise is being emitted and not being emitted (dB)

 4 - 5 6 - 9
Corrected value (dB) -2 -1

MEASUREMENT PROCEDURE

  1. Turn the power switch ON, the dynamic characteristic switch to FAST, the measurement mode switch to INST, the function switch to A, and adjust the dynamic range so it corresponds to the volume of the sound being measured.
  2. Measurement values are displayed immediately at one-second intervals. If the display continues to indicate either "OVER" or "-," then adjust the dynamic range until the warning disappears from the screen.
  3. When measuring the highest volume, set the measurement mode to MAX HOLD. At this setting, only the maximum sound values will be displayed.
  4. If the sound level does not change much over time, set the dynamic characteristic may be set to SLOW.
  5. For most sound measurement purposes, the function switch is set to A spectral weighting, however one can determine differences in sound frequency components from the magnitude of the difference between A and C spectral weighting. A large difference between A and C weightings generally indicates a preponderance of low frequency components.
  6. Set the output to either an AC full scale output of 1 VRMS or to a DC level full scale output of about 2V. (Full scale refers to maximum display range value. If the display range is 60 - 100 dB, the full scale value would be 100 dB.)
  7. When the measurement is completed, always turn the power OFF.

Note

ACO's sound level meter has three measurement ranges. Maximum level of each range is 70, 100, and 130 dB and its dynamic range is 40 dB. If the dynamic range of sound to be measured exceeds 40 dB, it could not be measured correctly.

Aircraft noise was measured outside. Displayed level is not true. Because I did not change the measurement range correctly, measurement has become impossible.

When I changed the measurement range, sound level was about 76dBA.

Sound level above 100dB could not be measured.

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