System test results witnessed by Bruce and Larry


Purpose:

This test procedure was intended to establish a series of tests which were conducted in the ANC test area and can be repeated as desired at any location where the system is set up. It established a functional baseline, although the performance achieved may vary in other test environments. The test procedures assume some familiarity with the hardware and software as delivered.

  1. Demonstrate that the Active Noise Cancellation is stable, robust and flexible
  2. Demonstrate and document the performance of the ANC for four data sets



Procedure:

Tone test

  1. Start 500 Hz tone playback in loop mode with CoolEdit
  2. Start download with EZ-KIT run.bat
  3. Adjust gains appropriately and measure results
  4. Press Flag1 button to capture sample data file - saved as output.dat
  5. Repeat with cancellation amplifier gain set to zero
  6. Compare error signal levels with and without cancellation using CoolEdit

Results:

Tone only
Before ANC After ANC
500 Hz tone 500 Hz tone with ANC 8kHz sample rate 32 taps

This test shows a drop from -38 dB to -44 dB (roughly 6 dB) for the single tone.


Procedure:

Tone and pink noise

  1. Load and play 500 Hz tone with noise: S500A30.pcm
  2. Capture sequence same as above


Tone and pink noise
Before ANC After ANC
Pink noise with 20 dB SNR 500 Hz tone Pink noise and tone with ANC 8kHz rate 32 taps

This test shows a drop from -47 dB to -50 dB (roughly 3 dB) for the single tone in pink noise. An ear placed at the quiet zone microphone perceived the pink noise without any tone at all.


Procedure:

Digitized factory noise

  1. Change the DSP software to run at a sample rate of 11.025 KHz
  2. Load and play file left.pcm or right.pcm. These files are of the belt test machine and have a noise peak at 4KHz.
  3. Capture sequence same as first test




Factory digitized data (belt)
Before ANC After ANC
Digitized data Digitized data with ANC 11.025 kHz rate 32 taps

This test shows a roughly 2 or 3 dB drop in the tone at 2800 Hz but almost no reduction in the tone at 4200 Hz. This is in accordance with expectations. The ANC should work well in the range from 100 Hz to about 2000 Hz with effectiveness dropping off quickly at the higher frequency / shorter wavelength sounds.


Procedure:

Accelerometer and grinder noise

  1. Connect the accelerometer via the "hi level" cable to the processor.
  2. Ensure all other "noise channel" or left inputs are disconnected.
  3. Position cancellation speaker about 18 inches in front of the noise source.
  4. Position quiet zone mic and Sound Level Meter about 36 inches from cancellation speaker.
  5. Turn on the machine under test and measure the noise level at the quiet zone.
  6. Turn up the gain on the cancellation amplifier to the appropriate level and measure the noise level.




Accelerometer attached to grinder
Before ANC After ANC
Grinder Grinder with ANC 8 kHz rate 32 taps

This test shows a 6 dB reduction of the primary mode at 75 Hz. It did however raise the higher frequency noise floor from an average of -74 dB to an average of -63 dB.



Questions?


dak 3/2/98