Generally speaking, screw compressors are known for their relatively low noise levels compared to other types of compressors, especially reciprocating (AKA piston) compressors. Piston compressors have a well-earned reputation for high noise and vibration that may be heard and felt throughout the shop. As a result, they are often put in separate rooms, closets or outside, possibly impacting their operation and longevity.
The amount of noise produced by screw compressors can vary depending on several factors, including the size and type of compressor, the surrounding environment and, to some extent, the operating speed. Depending on the specific model and working conditions, it can range from just over 60 dB(A) to over 90 dB(A). For reference, the noise level of the average vacuum cleaner is 75 dB(A). Piston compressors are often 80-90 dB(A).
Screw compressors are quieter because they have a rotary motion vs. reciprocating. Further, they usually have insulated cabinets. The rotary motion virtually eliminates vibration compared to piston compressors, which are typically bolted to the floor to keep them in place. The sound level on screw compressors is low enough to have a normal conversation near the machine (a convenience and a plus for safety). Being relatively quiet and vibration free, they offer more flexibility where you put them, such as a spot with better lighting, service access and ventilation. Ventilation is critical to the longevity of any compressor.
While they are comparably quiet, screw compressors can seem loud in small rooms or rooms with low ceilings. Also, concrete floors and walls are very good at reflecting noise. There are several strategies for reducing noise. Putting some sound-absorbing material on the walls in any compressor room will make a noticeable difference. If you have screw compressors with cabinets, ducting the exhaust air outside will significantly reduce noise. Unfortunately, enclosing piston units is usually not feasible due to heat and lack of directed cooling airflow.
If you notice the noise level change on a screw compressor, it may indicate a service issue, such as a lack of lubrication. The same is true of pistons.