In a truly silent room, there should be an absence of any external sound sources, and the sound level would ideally approach absolute silence, which is considered to be around 0 decibels (dB). However, achieving complete silence in a room is challenging due to various factors:
Background Noise: Even in a seemingly quiet environment, there can be low-level background noise present. This can include ambient sounds from outside, such as traffic, wind, or other environmental factors. Additionally, internal factors like electrical equipment, air conditioning systems, or even the hum of electronics can contribute to the overall sound level.
Self-Generated Noise: Humans also generate noise through activities like breathing, heartbeat, or even slight movements of the body. These sounds are typically very low in volume and may not be perceptible under normal circumstances, but they can still contribute to the overall sound level in a silent room.
Acoustic Reflections: Sound waves can bounce off surfaces in a room, causing reflections and potentially contributing to the overall sound level. In an anechoic chamber, which is a specially designed room with highly absorptive materials, the number of reflections is minimized, leading to a quieter environment. However, achieving absolute silence without any reflections is extremely challenging.
It's important to note that the human ear has a limited range of sensitivity. The threshold of hearing, or the minimum sound level that can be detected by an average human ear, is commonly considered to be around 0 dB. Therefore, even though a silent room may still have a sound level of around 30 dB, it falls below the threshold of human perception and may not be audibly noticeable.
Similarly, recording devices, such as microphones, have their own sensitivity thresholds and limitations. Many consumer-grade microphones are not designed to capture extremely low-level sounds accurately, and they may have a minimum detectable threshold above the ambient noise level of a quiet room.
In summary, achieving absolute silence in a room is challenging due to various factors like background noise, self-generated noise, and acoustic reflections. While a room may measure around 30 dB, it is typically below the threshold of human perception and may not be picked up by recording devices designed for normal use.