The two basic elements to consider in sound are the intensity and frequency of the sound. The intensity of the sound is related to the pressure (Pa) reaching the eardrum and is measured in decibels (dB). The decibel range that the human ear can perceive is 0 - 140 dB.

Frequency indicates the amount of vibration of an object in 1 second and is defined by Hertz (Hz). Again, the human ear can perceive frequencies between 20 - 20,000 Hertz; but the best perceived frequency range is the speech frequency region between 250 Hertz and 3000 Hertz.

Below 20 - 20,000 Hz. are called infrasonic sounds, above are called ultrasonic sounds. Although these sounds cannot be heard by the human ear, they cause nausea, headaches and restlessness in the person.

Noise is physically composed of irregular sounds, and physiologically it is unwanted sound. Noise has no timbre, but it can have dominant frequency content.

In industries where there are many noise sources, the overlapping of sounds and the inability to perceive their tones make it difficult to detect the source. Due to the logarithmic increase in the structure we call sound, the effect of two noises at the same decibel on the environment is perceived as higher than the existing value.

For example, the average sound level of 2 90 dB sources;

10 log (10 ^spl/10 +10 ^spl/10 )

10 log (10 ^90/10 +10 ^90/10 ) = 93 dB .

As can be seen, it is not possible to analyze the effect of the existing resource on other regions with simple mathematics and our ears. 

Therefore, in order to distinguish sounds, measuring the noise frequency plays a major role in determining the source according to the dominant frequency in the environment.

High frequency sounds are continuous and more disturbing. For example, ventilation noise is high frequency but less intense, For this reason, its direction and source are difficult to detect and continue to increase background noise. Low frequency sounds are heard more intensely. Transformer sounds are examples of low frequency sounds.

Therefore, if we want to detect the source of noise in the environment, decibel measurement alone is not sufficient. Frequency measurements that comply with the required standards must be made.