* Size and power: Larger, more powerful engines generally produce more noise. A massive engine in a large truck will be much louder than a small diesel generator.
* Engine design: Modern engines incorporate noise-reduction technologies like quieter injection systems and better insulation, making them significantly quieter than older designs.
* Maintenance: A poorly maintained engine will often be louder due to worn components.
* Load: A diesel engine under heavy load will typically be louder than one idling.
* Encapsulation: The surrounding structure plays a large role. A diesel engine in a soundproofed enclosure will be far quieter than one exposed to the open air.
Therefore, there's no single answer to how loud a diesel engine is. It could range from a relatively quiet hum (like a modern, well-maintained car engine) to a deafening roar (like a large, unsilenced industrial engine). The sound level could range from under 70 decibels (dBA) to well over 100 dBA. For comparison, 70 dBA is about the level of normal conversation, while 100 dBA is comparable to a loud power saw and can cause hearing damage with prolonged exposure.
