I found a very good article about how acoustic measurements should be carried out correctly in an enclosure. It's in Spanish but it's really good!
first part
second part
article: https://audioforo.com/2017/12/28/mediciones-acusticas-con-jose-almagro-segunda-parte/
forum: https://audioforo.com/
If you are interested in this article and you are thinking of buying a calibration microphone (measuring microphone) and a good sound interface to make your measurements, I can recommend the following equipment.
Recommended microphones
