| Japanese | English |
When the low frequency flow moves objects, sound and vibration occur from there and it becomes the origin of displeasure. If the velocity of the air jet is high, low frequency sound will occur under the blow-off mouth. Operating the air conditioner with a small amount of ventilation is important for reducing the noise level.
Maintenance of the air conditioner might be possible by investigating unusual sound. In this report, sound of the air-conditioner during operation was measured and investigated whether it would be normal.
The oscillation of VAIO at the time of a non-signal (SONY PCG-R505 R/DK)
It is oscillating at 5kHz, 10kHz, and 20kHz. This may be a problem of PC's sound
card, but I dare
continue the measurement as it is.
1/3 octave analysis at the time of operation (FLAT)
Level meters "ALL" in the left of the bar graph indicate about 58 dB. Because the recording level is raised 15.5 dB to increase the S/N ratio, the actual sound pressure level is 42.5 dB.
The power spectrum (FLAT)
There is a peak at 370 Hz. The low frequency region is same as compared with the
background noise.
The sound level meter showed 42.2 dBA (A-weighting) at the time of strong wind air
conditioning.
1/3 Octave analysis at the time of operation (A-weighting)
Power spectrum (A-weighting)
The running ACF measurement
aircon2.wav (44.1kHz / Stereo / 10sec / 1.68MB)
Download the sound file and load it on the Running ACF screen. Same analysis on this page can be done.
Now the sound is analyzed by SA (Sound Analyzer). To analyze the wav file, load it on the Running ACF window of RA and save it. Then, start SA.
Main window of the running ACF analysis in SA
Calculation condition for the running ACF analysis
Results of the running ACF analysis (A-weighting)
In SA, time change of the sound properties, such as the sound level, pitch and pitch strength,
reverberation, can be investigated. For more information of the autocorrelation
analysis, see this page. It seems that
the operation sound of the air conditioner is stable. Any failures are not found in the analysis
result. This is the first measurement of the air-conditioner operation sound with
this system. If more data is obtained continuously, I can compare them.
Periodical measurement like this is widely applicable
to other products, like a refrigerator, laundry machine, and so.
Appendix
We can see the strange spike-like waveform in the autocorrelation function (in the lower left of the picture above). This is the oscillation at 5kHz. According to a thorough check, VAIO was oscillating (5kHz, 10kHz, 20kHz) from the beginning of the measurement. Because I forgot to do this check before the measurement, the trouble of PC has not been noticed to the last. The acoustic measurement system enables us to find unexpected problems which a conventional sound level meter never discovers.
August 2002 by M.Sakurai