JJF 1147-2006 "Anechoic Chamber and Semi-anechoic Chamber Acoustic Characteristics Calibration Specification" is a national metrological technical specification in China that guides the calibration of acoustic characteristics of anechoic chambers and semi-anechoic chambers. This specification specifies in detail the methods, procedures, requirements, and how to evaluate the calibration results of acoustic characteristics of anechoic chambers and semi-anechoic chambers. Although I cannot provide the full text of the document, I can outline some key contents and requirements that are usually included in such specifications:

Scope of application: This specification applies to the calibration of acoustic characteristics of anechoic chambers and semi-anechoic chambers, including but not limited to free field conditions, background noise, cutoff frequency, reflection coefficient, etc.

Terms and definitions: The specification defines relevant professional terms such as anechoic chamber, semi-anechoic chamber, free field, background noise, etc. to ensure that all parties have a consistent understanding of the terms.

Calibration method: describes how to calibrate anechoic chambers and semi-anechoic chambers, including the measurement equipment used, measurement procedures, data processing methods, and result evaluation criteria.

Measurement equipment: lists the measurement equipment required for calibration and its performance requirements, such as sound level meters, microphones, sound sources, etc.

Calibration conditions: Specifies the environmental conditions that should be controlled during the calibration process, such as temperature, humidity, and air pressure.

Calibration procedures:
Background noise measurement: Measure the background noise level inside the anechoic chamber or semi-anechoic chamber without any external sound source.
Free field verification: Use a point sound source or a sound source with known acoustic properties to measure the change in sound pressure level with distance to verify the free field conditions.
Cutoff frequency determination: Measure and determine the lowest frequency at which the anechoic chamber can work effectively.
Reflection coefficient measurement: For a semi-anechoic chamber, measure the reflection coefficient of the ground.

Data recording and reporting: It is required to record all data during the calibration process, including measurement conditions, measurement results, and any observed anomalies.

Uncertainty assessment: Evaluate the uncertainty of the measurement results, including random uncertainty and systematic uncertainty.

Evaluation of calibration results: Evaluate whether the anechoic chamber or semi-anechoic chamber meets the calibration requirements based on the criteria in the specification.

Appendix: May contain additional information, such as measurement tables, example calculations, or recommended practices.

As for the detailed clauses and numerical requirements of JJF 1147-2006, you need to refer to the officially published specification text, because it contains detailed numerical standards and specific operational instructions. If you need to obtain the full text of the specification, you may need to contact the Standardization Administration of China or relevant standardization organizations, or search on legal document sharing platforms.