An anechoic chamber, also known as a non-echoic chamber or soundproof chamber, is a specially designed room whose purpose is to minimize the reflection and echo of sound, thereby providing a near-perfect acoustic test environment. The working principle of an anechoic chamber is mainly based on the following aspects:

1. **Sound-absorbing materials**: The walls, ceilings and floors of an anechoic chamber are usually covered with porous or fibrous sound-absorbing materials such as fiberglass, rock wool or specially made sound-absorbing panels. These materials can absorb sound waves and prevent sound reflection.

2. **Conical sound absorbers**: In some high-end anechoic chambers, conical sound absorbers (pyramid or wedge-shaped) are used to further reduce the reflection of sound waves. The surface design of these cones causes sound waves to reflect multiple times on their surface and eventually be absorbed.

3. **Acoustic isolation**: Anechoic chambers are usually isolated from the outside world to avoid interference from external noise. This may include double walls, soundproof doors and windows, and special ventilation systems to ensure the purity of the indoor acoustic environment.

4. **Low background noise**: The design of the anechoic chamber also takes into account the reduction of the impact of internal equipment and other background noise. For example, low-noise air conditioning systems and power equipment are used to ensure that no additional noise is introduced during the test.

5. **Free field conditions**: The design goal of the anechoic chamber is to create a free field condition, that is, sound waves can propagate freely without being affected by reflections. This environment is very important for acoustic measurements and experiments because it allows the characteristics of the sound source to be accurately measured.

Through the above measures, the anechoic chamber can greatly reduce the reflection and echo of sound waves, thus providing an ideal acoustic test environment. This environment is widely used in audio equipment testing, speech recognition research, hearing testing, and other fields that require precise acoustic control.