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What Does it Take to Make Silent Generators?

A genset, especially a diesel one, can be very noisy – so loud that they may damage the hearing of those who work in close proximity to them. Best case, they can be a severe nuisance for those who work or live nearby. In order to mitigate the noise, silent generators were created. Silent generators are situated and operate inside a soundproofed container, or custom enclosure, which muffles the sound of the diesel engine. These enclosures are referred to as sound-attenuated enclosures.

Although the enclosure can be made out of a number of materials, including steel, enclosures for silent generators are more often than not made of a composite such as fiberglass-reinforced plastic. Typically, layers of hard material are used to reflect the sound energy back into the enclosure in conjunction with soft, porous materials that absorb the sound energy and convert it into heat.

Some materials absorb sound of certain frequencies better than others. Some may be good at absorbing high frequency sound but are poor at lower frequencies and vice versa. Higher frequencies are best absorbed by porous materials. These materials allow the sound waves to penetrate deeply where they become absorbed. Lower frequency sound is harder to deal with.

Lower frequency sounds are best deflected or absorbed by heavier layers of movement-resistant material but the best results for deadening lower frequencies are obtained by the use of air pockets. Two thin panels of material, separated by shallow air gaps, create a resonance effect converting low-frequency sounds to a higher pitch. The higher pitch is then absorbed by porous materials. To obtain the best result, most silent generators use several layers of materials with different sound-deadening properties.

Other measures employed for noise reduction include engine exhaust silencers and isolation mounts. Any combination of sound-reducing measures will be of benefit to the end user and the community.

Although generic sound attenuated enclosures are often used, one can gather from the above that a generic enclosure will not be optimum for every genset. Producing really silent generators requires the engineering of each enclosure for the particular type or specific model to be housed in it. To make the unit as quiet as possible, soundproofing needs to be designed to absorb the specific range of sound produced by the specific generator engine.

Producing silent generators is not easy and takes experience and engineering skill. This is consequently more costly and reserved for sites where noise reduction is critical. There is a difference between how much noise reduction is possible in theory and how much is feasible on a commercial scale. A reduction of 40 dB(A) is generally considered to be the upper limit of what is practical for a prefabricated soundproof container.

However, if a larger reduction is required, this can be done at extra cost, greater weight, and an increase in the difficulty of installation. Reputable genset manufacturers usually have in-house expertise but there are companies focused solely on building sound attenuating enclosures.

What is Considered Too Loud?

Sound levels are measured in decibels (dB). To provide a reference point, a whisper is about 30 dB and normal conversation is about 60 dB. Being exposed to noise above 70 dB can start to damage your hearing if you are exposed to it over a period of time. Shouting or barking directly into the ear, which is around the 110 dB level, may cause hearing loss in less than 2 minutes. Exposure to noise above 120 dB can harm your ears immediately. Anything that measures above 80 decibels is considered as loud. Once sound levels reach 140 decibels, most people will experience it as painfully uncomfortable. Noise can be measured on a linear scale, which weighs all sound frequencies being produced equally or on a scale of human audibility.

Noise level measured on the audibility scale is annotated as dB(A). This is better as it only takes sounds (frequencies) audible to humans into account. When you must choose an industrial genset, the major considerations are kW output and fuel type. Noise should be a major consideration when deciding which industrial generator is purchased.

A 50kW diesel genset can typically produce around 85 dB(A) and a 1500kW engine can be as loud as 105 dB(A), the equivalent of a jet engine flying overhead. This can be a severe annoyance to neighbours and can pose a health risk to anyone working in close proximity.

Obviously, where the unit is operated makes a difference. While the term “silent generators” is used to describe units that have a sound-attenuating enclosure, this does not mean that the unit makes no noise at all! The term “silent” may be misleading as there is always going to be some noise from the genset.

There is a range of sound attenuating enclosures but the most effective, and expensive, type when it comes to total sound reduction are sometimes referred to as “whisper enclosures”. This type of genset is often used on TV and film sets or at medical facilities where background noise reduction is critical. The World Bank has stipulated a guideline indicating that the maximum allowable ambient noise levels in a residential area are 55 decibels during the day and 45 at night. In residential areas in South Africa, the maximum level of noise that a generator can produce, measured at maximum capacity indoors with open windows, is not allowed to be more than 25dB. At a distance of 7 to 8 meters, the maximum noise level should not exceed 55dB.

Making the Right Choices Requires Expertise

If your requirement is for silent generators, for instance, PacB is renowned in the industry as a manufacturer of superior-quality large silent generators. The larger the genset, the more noise it will make, so when it comes to specifying industrial diesel generators, significant technical know-how and experience are required for advice on purchasing and installing the correct solution. This includes knowledge on generator sizing, fuel type, noise attenuation, and system configuration.

All these factors need to be thoroughly understood and matched to the customer’s site-specific conditions and requirements. PacB can also assist with the design and manufacture of any generator control systems, including various AMF (Automatic Mains Failure) and ATS (Automatic Transfer Switch) systems and all the additional components that the industry requires.

We have expert knowledge and experience of all the main controller brands in the industry and are able to design and manufacture Synchronous PLC controlled panels for multi-station generator supply over a vast range of sizes and voltages, including systems in excess of 1000kVA. With the continuity of supply issues South Africans are currently experiencing as Eskom struggles to sort themselves out, a generator is becoming mandatory for most commercial and industrial entities. Contact us today and guarantee always having electrical power.