BTW, Ron Sauro at NWAA Labs (http://nwaalabs.com/ or http://nwaalabs.ipower.com/pictures1.html) was hoping to build a quieter chamber but his funding dried up. He built his acoustical testing facility at a nuclear plant that was constructed but never commissioned.
The original plan was to build a 50ft by 60ft by 55ft chamber, with about half of it being underground. Given the exterior noise level of around 20 dBA (the plant is located in the wilderness), the thick concrete walls of the facility, and some additional noise and structural isolation he might very well beat Orfield's record with a much larger chamber (meaning it will be anechoic down to a lower frequency). If he can get the funding.
If you're ever in the area, Ron is a friendly guy and he'll be happy to give you a tour (he's on LinkedIn).
The original plan was to build a 50ft by 60ft by 55ft chamber, with about half of it being underground. Given the exterior noise level of around 20 dBA (the plant is located in the wilderness), the thick concrete walls of the facility, and some additional noise and structural isolation he might very well beat Orfield's record with a much larger chamber (meaning it will be anechoic down to a lower frequency). If he can get the funding.
If you're ever in the area, Ron is a friendly guy and he'll be happy to give you a tour (he's on LinkedIn).