Why Are Diesel Generators Usually So Noisy? Where Does the Noise Come From?

The human hearing range spans from 20 Hz to 20,000 Hz. Frequencies below this range are called infrasound (frequencies elephants can hear), while higher frequencies are called ultrasound (frequencies bats can hear). High frequencies are particularly intense for the human ear: the most sensitive range for human hearing is between 2,000 Hz and 4,000 Hz.

Certainly, anyone hearing the noise of a running generator is not thinking about the frequencies at which it propagates, but they might be curious to know that it’s likely those particularly annoying frequencies above 4,000 Hz, usually around 6,000 Hz.

Why do we care about the sound frequency of a generator?

This topic interests us to understand why generators are normally so noisy, and why some are much less noisy or even silent, like the Silengen. Anyone with experience in music production or sound sampling techniques will know how complicated, yet important, it is to remove or “cut” unnecessary frequencies and reverberations.

Generators are considered soundproofed when built inside enclosures lined with sound-absorbing foam to absorb and reduce sound propagation. However, manufacturers often confuse sound absorption with sound isolation.

Generators are noisy because, despite being built inside metal or plastic enclosures lined with sound-absorbing materials, they still need to expel the hot air generated by the engine and alternator outside the enclosure. Unfortunately, air is a perfect medium for transmitting noise!

But there’s more…

All the noise produced by the generator exits along with the hot air at a speed driven by the cooling fan of the radiator, which in generators is a pushing fan. As a result, the noise travels quickly over considerable distances.

So, a “normal” generator is noisy because, even if built inside a soundproof structure, it requires air expulsion. The result is similar to wearing headphones to protect your hearing but leaving a small hole in them that allows air (and sound) to pass through.

You’ve probably heard of Super Soundproofed Generators. A super soundproofed generator has additional barriers that further reduce sound emissions. An Ultra Soundproofed generator like the Silengen, on the other hand, not only has a super soundproof base, but it also treats vibrations and the outgoing air in such a way as to drastically reduce the transmitted noise levels.

Okay, the Silengen is ultra soundproofed, but where exactly does this technology act?

To understand this, we must remember what was previously said about air and its ability to transmit sound, as well as the primary source of sound: vibrations.

Think about a car’s exhaust system: modern ones have several functions besides reducing engine noise, but they are essentially silencers that dampen vibrations by treating the exhaust gases, which carry the noise of a recent explosion within the engine.

Thus, the noise of a generator comes from the internal combustion engine, from the vibrations it produces!

If you’re thinking of modifying your generator to make it quieter, stop! First, read the next article where we explain how to improve the acoustic level of a generator without modifying it.

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