What is a sound level meter?
What is noise?
What we call sound is the vibration of air. Any object becomes a sound source when it is rubbed or struck. The vibrations of the sound source become vibrations in the air, and when the ears receive these vibrations, we can hear them as sound.
There are many different sounds around us, but it is impossible for us to react to all of them. Each person makes a subjective judgment from among the sounds, picks out the sounds, and listens to them. Whether a certain sound is noise or not depends on one’s senses. It’s hard to generalize, but sounds that are too loud, have an unpleasant quality, or draw attention to a person are generally considered to be noise.
What is sound level meter?
A sound level meter is a measuring device that quantifies the level of noise. There are various types, and the sound level meter you use differs depending on the object you want to measure.
What can be measured with a sound level meter?
The following items can be measured using a sound level meter:
1. Frequency Weighting Characteristics
The human ear cannot hear low frequencies or ultrasound, and as we age it becomes harder to hear high-pitched sounds. On the other hand, electronic devices measure not only sounds that humans can hear but also sounds that humans cannot hear, and display the loudness of those sounds. As a result, there is a gap between the loudness of sound perceived by humans and the loudness of sound measured by machines. The correction designed to improve this gap is called “frequency weighting characteristics.”
| A-Weighting | Weighted according to the frequency range that humans can hear |
| C-Weighting | Almost flat weighted |
| Z-Weighting | A measurement of pure sound pressure level that is not weighted by frequency or corrected by characteristics. |
2. Time Weighting Characteristic
The time weighting characteristic is a characteristic used to determine the effective value of sound pressure. The time weighting characteristics have two time constants: fast dynamic characteristics “FAST” (time constant F) and slow dynamic characteristics “SLOW” (time constant S).
A time constant is a constant that determines how long it takes to average. If the sound pressure fluctuations of the noise you are trying to measure are severe, you may not be able to get an accurate reading. Therefore, time weighting is applied and the sound pressure is evaluated by averaging over time.
Using the time constant F averages over time over a shorter period of time, making it possible to follow drastic changes in the noise level. For this reason, noise measurements are generally made using a time constant F.
In addition, the time constant “S” is 1 [s] and is time averaged. Time constant S is used when measuring noise levels that do not fluctuate much, such as bullet train noise, conventional railway noise, and aircraft noise.
3. Equivalent continuous A-weighted sound pressure Level
“Equivalent continuous A-weighted sound pressure level” is the time-average value calculated by focusing on the energy of sound level fluctuations within a certain period of time when sound levels change over time. When a large number of measurement values are obtained in which the noise level fluctuates greatly over time within a certain measurement period, calculate how much the value will be if it is represented by a constant noise level (steady sound) that does not change over time.
The noise level of the steady sound when the noise energy during the measurement period is made equal for both sounds (equivalent) is the equivalent A-weighted sound level. Because it corresponds relatively well to human physiological and psychological responses to fluctuating noise, it is adopted in many countries as an evaluation quantity for assessing environmental noise.
