Some people may think that spending time in an echoless soundproof room is both peaceful and beautiful, but that's not the case.

Taking the soundproof chamber at the Orfield Laboratory in southern Minneapolis, USA as an example, it can absorb 99.99% of the sound and is listed by the Guinness World Records as the quietest place in the world. But staying here for too long can cause hallucinations. The builder of this soundproof room, Steven Orfield, said, "We challenged the time spent sitting in a quiet room in the darkness, and only one journalist stayed there for 45 minutes."

An anechoic room, as the name suggests, refers to a room without sound wave reflection. Usually, each wall is covered with sound-absorbing materials with good sound absorption performance, making the room without sound wave reflection.The anechoic chamber generally uses a gradual absorption layer, usually a wedge or cone structure, with glass wool as the sound absorption material, or soft foam plastic.

A semi anechoic room is one in which only five or four of the six sides of a room are covered with sound-absorbing layers. The main function of an anechoic chamber is to provide a free or semi free sound field space for acoustic testing. The sound absorption treatment is the key to ensuring good free sound field performance after the construction of the anechoic chamber, and most of them use sound absorption wedges or flat plate resonant sound absorption structures with strong sound absorption capabilities.

Whether the performance of an anechoic chamber meets the requirements for use is generally tested using the method of verifying the free field. That is, the sound pressure generated by a point sound source in it should be inversely proportional to the distance to the sound source. The deviation between the measured sound field and the ideal free field is the main indicator used to measure the performance of an anechoic chamber.

In general acoustic testing, it is required that this deviation should not exceed ± 1dB; For microphone calibration, it is required that the deviation should not exceed ± 0.1dB near the calibration distance. The anechoic chamber should not only meet the requirements of a free field

In addition to meeting the requirements of a free field, an anechoic chamber also requires a lower background noise. Therefore, certain vibration isolation measures need to be taken between the anechoic chamber and the foundation.

For those who enter the soundproof room for the first time, it's really uncomfortable here. The auditory sensation is completely different from the outside world. There is no echo when clapping and speaking, but the sound of clothes rubbing when walking is unprecedented and clear. Without speaking or moving, it's quiet here as if you can hear the sound of blood flowing. In this extremely quiet environment, people who first come into contact with an anechoic room will immediately feel lonely and slightly fearful.

Suddenly, it felt like a "hypercube" from a Star Trek movie.