Whether there is a signal inside an anechoic chamber depends on the type of chamber, design purpose, and specific usage scenario. The following is a detailed analysis for different situations:
 
1. Types of anechoic chambers and signal presence
The anechoic chamber is mainly divided into acoustic anechoic chamber and electromagnetic anechoic chamber (anechoic chamber), and the functional differences between the two directly affect the existence of signals:

-Acoustic anechoic chamber
-Design objective: To eliminate sound wave reflection and simulate a free sound field environment (without echo).
-Signal Existence:
-Acoustic signal: It can be generated actively by internal sound source (such as loudspeaker), but external sound will be isolated by sound absorbing materials (wedge, foam).
-Electromagnetic signal: If electromagnetic shielding is not applied, external radio signals (such as Wi Fi and mobile phone signals) may enter, but acoustic anechoic chambers usually do not pay attention to the electromagnetic environment.
 
-Electromagnetic anechoic chamber (anechoic chamber)
-Design purpose: To absorb electromagnetic wave reflections and isolate external interference for antenna testing, EMC testing, etc.
-Signal Existence:
-Internal signal: It can be actively transmitted through testing equipment such as signal generators and antennas, but absorbing materials such as ferrites and carbon based absorbers will suppress reflection.
-External signal: If the shielding layer is intact (such as copper mesh or steel plate), external electromagnetic signals (such as 5G, broadcasting) will be blocked, forming a "no interference" environment.
 
2. Key factors determining whether the signal is controllable

Shielding effectiveness: The electromagnetic anechoic chamber needs to achieve a shielding effectiveness of over 60dB (such as military standards) in order to effectively isolate external signals.
Frequency band coverage of absorbing materials: If the test frequency band (such as millimeter waves) exceeds the material's absorption range, residual reflections may cause signal interference.
Test equipment configuration: The actively transmitted signal (such as radar testing) needs to match the designed frequency band of the anechoic chamber.
 
3. Common scenarios in practical applications
-No signal environment:
-During electromagnetic compatibility testing (EMC), it is necessary to completely isolate external signals to ensure the accuracy of radiated noise from the tested equipment.
-Signal environment:
-In antenna gain testing, it is necessary to actively transmit signals and measure the directional pattern. At this time, there is a controllable test signal in the anechoic chamber.

4. Issues that users need to clarify
If you are interested in a specific scenario (such as mobile phone signal, Wi Fi), further explanation is needed:
-If the anechoic chamber is designed purely for acoustics, mobile phone signals may exist normally (unless the building structure itself is shielded).
-If it is an electromagnetic anechoic chamber, mobile phone signals are usually blocked and need to be communicated through wired connections or indoor dedicated base stations.

summarize
Whether there is a signal in the soundproof room depends on its type and purpose of use:
-Acoustic anechoic chamber: There may be electromagnetic signals, but there is no acoustic reflection.
-Electromagnetic anechoic chamber: External signals are shielded, while internal signals can be actively introduced.
For a more specific answer, please provide the purpose or signal type (acoustic/electromagnetic) of the anechoic chamber.