understanding sound and noise


Noises are sound. In the field of HVAC, sounds and noises are common. They are usually indicators of some kind of dysfunction in the system that will require either maintenance, redesign, or repair. A clear understanding of the physics of sound/noise is needed to see exactly what it is and what it means for the field of heating, ventilation, and air conditioning.

Physics of Sound

In the process of understanding sound and noise it must be seen that the principles and laws of physics include a definition of sound. It is, in short a vibration that is an audible wave of pressure being transmitted through either a solid, liquid or gas. We “hear” when the wave reaches our receptors on each side of our head called our ears. This highly sophisticated organ processes those vibrational waves and we gain an understanding of what we are hearing. The human ear is capable of hearing frequencies that are at 20Hz and 20kHz. Any sound above this top frequency is known as ultrasound and below the lowest frequency is known as infrasound.

Sound waves are created as vibrational frequencies at a concrete source. In this case, the source is often metal against metal, plastics combined with metal, or internal parts of mechanicals off their mark or out of warranty time and duration.

The sound waves move away from the source at the speed of sound. (The speed of sound is 331.2 meters per second through dry air at 0Celsius.) As they move outward in ever increasing waves, the velocity and pressure of the wave change as they encounter obstacles in their path. As they travel, they can be altered in frequency and direction by reflective surfaces. They can also be refracted and atenuated by the various flucuations in counter waves or objects interjecting their own acoustical parameters.

Six Factors of Sound Assessment

understanding sound and noise


Sound and consequently noise can be measured and analysed using six different factors. These factors allow technicians in completely understanding sound and noise. In the field of HVAC, the diagnosis of sound is not this intricate unless commercial applications call for the complete eradication of sound due to manufacturing and measuring processes such as the use of Zeiss equipment in CNC machining practices.

A sound technician will measure the pitch of a sound which is how high or low the frequency registers. Pitches vary according to the source of the sound, the medium through which it is traveling, and the varying waves it encounters as it travels. The duration of a sound is measured in order to determine the length from its source to when it is actually heard. The loudness of a sound or noise is determined as being either loud or soft. The timbre of a sound is also understood to be the quality of the sound or the lack thereof.

The understanding of the elements that make up sound and how those elements are assessed serve to enlighten the HVAC field technician when various sounds are encountered in the field.