Consultants Corner
Understanding Generator Set Noise
Effectively controlling sound levels produced by operating generator sets is becoming a higher priority. Numerous governmental agencies are enacting noise ordinances, aiming to cut noise pollution. This directly affects gen set installation design.
Understanding noise
Noises are quantified by their sound pressure, and most commonly measured in decibel levels heard by humans, noted as dB(A).
The relationship between decibel level is logarithmic. In terms of loudness, doubling the sound pressure roughly equates to a 6 dB(A) increase. However, doubling the distance from the noise level reduction. Typical noise level ratings are noted in Table 1.
Table 1 - Typical noise levels
| Common sounds | Sound pressure |
|---|---|
| Jet engine | 160 |
| Riveting | 140 |
| Punch press | 120 |
| City traffic | 100 |
| Busy office | 80 |
| Normal speech | 60 |
| Quiet suburb | 40 |
| Whisper | 20 |
| Threshold of hearing | 0 |
Loudness is also affected by the frequency of sound, but to a much less degree than sound pressure. It's important to note that decibel levels are not additive. For example, two gen sets operating do not produce a 2X decibel level, but increase total sound level to by 3 dB(A).
Controlling gen set noise
Noise from gen sets can be effectively controlled with good engineering practices at installation. Table 2 estimates the relative effectiveness of various sound barriers.
Table 2 - Aproximate sound level reduction dB(A)/b>
| Original machine | 0 |
| Vibration Isolators | 2 |
| Baffle | 5 |
| Absorption material only | 5 |
| Rigid sealed enclosure | 15-20 |
| Enclosures and isolators | 25-30 |
| Enclosure, absorption, and isolators | 35-40 |
| Double walled enclosure, absorption, and isolators | 60-80 |
Designers must consider two noise sources--the actual mechanical noise of the gen set and the exhaust noise. Exhaust silencers can be specified by the following site descriptions.
* Industrial: Suitable where background noise is relatively high.
* Semi-industrial: Suitable for standby systems or environments where complete silencing is not required.
* Residential: Suitable for use where moderate background noise is permissible.
* Semi-residential: High noise attenuation with low background noise.
* Critical: Extreme noise attenuation with low backgound noise.
Attenuating mechanical noise can be completed with a combination of sound dampening design and by isolating vibration produced by the operating gen set. Table 2 shows the sound level reduction possible. Completely sealed enclosures are included as a reference, but openings for piping, airflow, etc. will adversely affect these reduction levels.
Call us
We have aided in the design an installation of generator sets, and can offer you the expertise and software, such as EPG Designer, to help you control noise emissions from gen sets. If you need assistance in this area, please call us. We would be glad to help.