Sound or noise is a physical phenomenon that can be perceived by the human ear. Interestingly, sound can exist even if there is no one present to hear it. Thankfully, sound follows natural laws, allowing us to accurately measure, predict, and utilize it. In this blog, we will explore the methods for measuring fan noise using these natural laws.
A PRIMER ON SOUND
The distinction between sound and noise lies in the fact that noise is considered as unwanted sound. This perception of noise is subjective and varies from person to person. While one person may enjoy listening to classic rock & roll, someone else may simply perceive it as noise. It may not be easy to figure out the level of fan noise produced and how to address it.
In addition to the fan’s design, speed, pressure, and volume of air flow, there are external elements that affect its performance. One such factor is the environment in which the fan is used. For instance, a fan used in an uninsulated building will likely appear louder due to sound bouncing off the walls, similar to reflections on a mirror, compared to the same fan used on a Texas cattle ranch.
Acoustics commonly employs four (4) widely used terms:
- Decibel (dB) refers to a fraction of the logarithmic unit (Bel) used for the measurement and assessment of noise.
- dBA refers to a practical numerical representation of low frequency sound levels that is weighted on a dB scale. This scale is used to evaluate the loudness of a sound and is more closely aligned with the human ear’s threshold of hearing.
- Sound Pressure Level (Lp) is calculated as the logarithm of the ratio between the current pressure and a standard reference value of 0.0002 microbars.
- Sound Power Level (Lw) can be defined as the logarithm of the ratio between the sound’s actual power and a reference power of 10(-12) watt.
MEASURING SOUND
The sound fingerprint of a fan, known as the Sound Power Level (Lw), remains constant and cannot be altered. However, the Sound Pressure Level (Lp) can vary depending on the operating environment of the fan.
To evaluate fan noise, the acoustic engineer requires the Sound Power Level (Lw). The measurement of a fan’s Sound Power Level (Lw) poses a challenge as it cannot be directly assessed. The most feasible approach to determining the Sound Power Level (Lw) is by recording Sound Pressure (Lp) values. This is usually done at the eight octave band center frequencies in a controlled laboratory environment. This will allow us to predict the sound level at a particular distance, then the distance is removed from the measurement to provide the Sound Power Level (Lw).
The a fan’s Sound Power Level (Lw) can be determined by adding the fan’s Sound Pressure Level (Lp) to the effect of the room (delta). Upon obtaining this measurement, we are able to utilize various silencing techniques. These may include silencers, wraps, and enclosures to decrease the noise emitted by the fan. Additionally, we can also incorporate noise from other equipment into these calculations to determine the overall impact and determine the necessary steps to reduce it to an acceptable level.
CONCLUSION
An age-old saying remains relevant when dealing with minimizing fan noise: Silence comes at a cost. It is more efficient to begin with a quiet fan rather than attempting to quiet down a noisy one. However, if your employees are bothered by fan noise, contact us at Eldridge. We will find a solution for your fan noise that will create a successful environment in your facility.