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what type of measurements are you planning on taking? Do you need to test the response of the phones at a given point, or does the mic need to move during the measurements?
What are you hoping to get out of these measurements?
Right now I am qualifying the new semi-anechoic chamber at GA Tech. I was actually in there earlier today.
You should base the size of your chamber on the output you are expecting. From a cell phone I wouldn't expect high output, but the smaller you go, the less anechoic-like you can expect the response.
A good starting point is sturdy outside walls (MDF would be good for this). Make another wall inside the MDF walls (particle board would probably be better here). The walls should be separated enough that a layer or two of fiberglass insulation can fit between the walls. On the inside of the particle board walls use the acoustic foam wedges. If 4" is the biggest you can find, use it. If you can find bigger use that. You may want to put insulation on the outside of the MDF walls as well.
Wherever you put the chamber, make sure there is not much background noise. After you complete the chamber, you should do SPL measurements on the inside with a sound source on the outside. If the source on the outside has noticeable effect, you will need more damping from outside sound.
That should give you a good start. I'll see if I can find the journals describing anechoic chamber qualifications that I had to read when I first got my job.
Hope that helps,
Austin
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Test Chamber
