There are many reasons why the anechoic chamber may not be as effective as before:

1. Aging of sound absorbing materials:
Over time, the sound absorbing materials used in the anechoic chamber may gradually age, wear or deform, resulting in a decrease in sound absorption performance.
Some sound absorbing materials may accumulate dust, dirt or moisture, which may affect their sound absorption ability.

2. Improper maintenance:
If the anechoic chamber is not properly maintained, such as regular cleaning and inspection, it may cause performance degradation.
Especially for those sound absorbing materials with micropores or special coatings, if they are not properly maintained, the pores may be blocked, affecting the sound absorption effect.
3. Physical damage:
If the sound absorbing spikes or other sound absorbing structures on the inner wall of the anechoic chamber are physically damaged, such as cracking or falling off, it will also lead to reduced sound absorption efficiency.
4. Temperature and humidity changes:
Changes in temperature and humidity may affect the performance of the sound absorbing materials, especially for those materials that are sensitive to environmental conditions.
If the anechoic chamber cannot effectively control the temperature and humidity, it may cause the performance of the sound absorbing materials to deteriorate.
5. Design flaws:
If the initial design of the anechoic chamber is flawed, such as inadequate sound absorption in certain areas, this can also lead to poor overall performance.
6. Installation issues:
If the equipment or structures in the anechoic chamber are improperly installed, additional noise sources may be created, which may affect the overall performance of the anechoic chamber.
For example, noise from fans or air conditioning systems may become a source of interference if not properly handled.
7. External noise sources:
If the ambient noise outside the anechoic chamber increases, it may penetrate through the poor seal of the anechoic chamber and affect the noise level inside the chamber.
External vibrations may also be transmitted into the anechoic chamber through the building structure, especially in the low-frequency range.
8. Usage:
The performance of the anechoic chamber may also be degraded due to incorrect usage, such as placing too many items in the anechoic chamber, which may reflect sound waves.
9. Technical issues:
For certain types of anechoic chambers, such as anechoic chambers using special sound-absorbing materials or structures, there may be specific technical issues, such as clogging of microporous plates leading to reduced anechoic performance.
If you notice that the anechoic chamber is not as effective as before, you can consider checking the above aspects to find out the problem and take corresponding measures to solve it. For example, cleaning and replacing aging sound-absorbing materials, strengthening sealing treatments, adjusting temperature and humidity control systems, re-evaluating and correcting design defects, etc.