Sound and sound level meters

What is commonly called "sound" is actually vibrations of air. Various objects, when rubbed or tapped, can become sound sources. The vibration of the sound source object causes the adjacent air to vibrate and these vibrations are transmitted to the ear where they are perceived as sound.
In our everyday environment, there are many different kinds of sounds, but humans do not respond to all of these.
Rather, we subjectively make decisions and focus only on certain sounds that we want to hear.
Other sounds that are not important, often inconvenient or disturbing, are sounds that are undesirable or unnecessary. Such sounds are called "noise".
Rather than containing certain physical properties, what defines noise is a subjective characteristic that is specific to the listener. Sound that is too loud, unpleasant, or that draws attention in a certain direction is commonly judged as noise.
to the listener. Sound that is too loud, unpleasant, or that draws attention in a certain direction is commonly judged as noise.

What is commonly called "sound" is actually vibrations of air. Various objects, when rubbed or tapped, can become sound sources. The vibration of the sound source object causes the adjacent air to vibrate and these vibrations are transmitted to the ear where they are perceived as sound.
In our everyday environment, there are many different kinds of sounds, but humans do not respond to all of these.
Rather, we subjectively make decisions and focus only on certain sounds that we want to hear.
Other sounds that are not important, often inconvenient or disturbing, are sounds that are undesirable or unnecessary. Such sounds are called "noise".
Rather than containing certain physical properties, what defines noise is a subjective characteristic that is specific to the listener. Sound that is too loud, unpleasant, or that draws attention in a certain direction is commonly judged as noise.
to the listener. Sound that is too loud, unpleasant, or that draws attention in a certain direction is commonly judged as noise.

The sensitivity of the human ear differs depending on the frequency of the sound.
The same sound pressure can be perceived differently at different frequencies. When a certain sound
is perceived equal to the sound pressure level PdB at 1 kHz, the loudness level of that
sound is said to be Pphon.

Figure 2 shows the relationship between the loudness level of a pure tone and its frequency. The curves in this graph are called equal loudness curves.
As can be seen from the graph, the physical magnitude of a sound and its subjective magnitude are not the same. Rather, there is a complex relationship between the two.

Sound Level Meter is a device for turning physical properties of sound into numeric values.
Psychological, physiological and subjective aspects cannot be measured.
A reverse curve corresponding to the equal loudness curve at 40 phon is applied to the sound pressure (this is called "A"-frequency weighting). The resulting level is called A-weighted sound level and is expressed in dB.

Sound level meters are divided into two categories: Class 1 and Class 2. There is a
difference in performance between these classes.
Perfomance specifications and test methods of sound level meters are specified in the international standards IEC 61672 series. Two performance categories, Class 1 and Class 2, are specified in the standard.
Basically, specifications for Class 1 and Class 2 sound level meters have the same design goals and differ in the tolerance limits. Tolerance limits for Class 2 specifications are greater than, or equal to, those for Class 1 specifications.

Some common terms used having with special meanings and relating to sound level meters are listed below.

Many different kinds of sound level meters exist.
The optimum device to be Chosen will depend on the purpose of the measurement, the required accuracy, and the data processing method that is to be employed. Some of the main categories are listed below: