The volume of the sound emitted from the machine varies depending on the distance between the machine and the measurement point or the installation environment, thus it is difficult to evaluate it quantitatively. Therefore, sound power level is used as a quantitative evaluation.
Sound power level represents the amount of sound energy emitted by a sound source per unit time. Since it can be evaluated without being affected by the measurement distance or the environment, it is adapted to the individual standards of various machines and used for product evaluation. The measurement method is to arrange 9 to 10 microphones in half-free space as specified in ISO 3744: 2010, ISO 3745: 2012.
If the measurement environment, such as a microphone traverse device, is arranged, the sound power level can be measured in a relatively short time. Since the installation accuracy does not depend on the skill of the measurer, measurement errors can be reduced.
This example shows an example of calculating the sound power level from the average sound pressure level measured with nine microphones for two types of printers.
Sound power level measurement with a microphone traverse device
Measurement system
Equipment configuration
| Model | Product name | Remarks | |
|---|---|---|---|
| 1 | DS-3000 | Multi-Channel Data Station | Max 32 ch |
| 2 | MI-1235 | Measurement microphone | 9 units, 10 Hz to 20 kHz |
| 3 | MI-3111 | Preamplifier | 9 units |
| 4 | DS-0231A | Sound power level measurement software (sound pressure) | |
| 5 | Multi-points microphone traverse device | ||
| 6 | PC |
Measured data examples
The graph shows the sound power levels for Printer A and B respectively. It found that that Printer B has a higher sound power level. Also, comparing not only the power level but also the frequency weightings, you can see some peaks in Printer B. It means that there is a factor that generates the sound with that frequency.
For example, a rotating object such as a motor generates noise with a frequency due to its rotation. Thus, if the motor rotation speed and frequency match, the motor is considered to be the cause of the noise.
Sound power level measurement is useful not only for complying with standards such as ISO and JIS, but also for setting quantitative target values for noise countermeasures.
A-weighting Sound Power Level for Printer A
A-weighting Sound Power Level for Printer B
Application examples
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