The number of pyramids or wedges used in an anechoic chamber depends on several factors, including the size of the chamber, the desired frequency range, the performance of the absorbent material, and budget.

Here are some basic steps to calculate the number of pyramids needed:

1. **Determine the size of the chamber**: Measure the length, width, and height of the chamber.

2. **Choose absorbent material**: Choose the appropriate absorbent material based on the frequency range you need to absorb. High-frequency sound waves are more easily absorbed than low-frequency sound waves, so low-frequency absorption may require thicker absorbent material.

3. **Determine the coverage density**: Generally, the walls, ceiling, and floor of the anechoic chamber need to be covered with absorbent material. The coverage density can be determined based on specific needs and budget. Generally, the higher the coverage density, the better the sound absorption effect.

4. **Calculate the required area**: Add the surface area of the anechoic chamber (including walls, ceiling, and floor) to get the total coverage area.

5. **Calculate the number of pyramids required**: Calculate the number of pyramids required based on the size of the absorbent material and the coverage density. For example, if each wedge is 1 square meter in area and you need to cover an area of 100 square meters, then you may need 100 wedges.

6. **Consider additional requirements**: Additional sound absorbing materials may also be required to deal with specific acoustic problems, such as standing waves, reflections, etc.

7. **Consult professional advice**: If you are unsure how to calculate or select sound absorbing materials, it is recommended to consult an acoustic expert or sound absorbing material supplier.

Please note that these steps provide a rough calculation method and the actual situation may vary. To ensure the best acoustic performance, it is recommended to work with a professional acoustic engineer for detailed design and calculations.