Today we are making the measurements of the Acoustic Tube model (also referred to as the redirect tube in some places) shown below, against the figure 8 Proscenium reference microphone. I decided to use the Proscenium and not the 77DX as the reference. The reasons for this are:
1. We have a large number of Proscenium mic data sets
2. The SD of the measurements is known for the Proscenium
3. The figure 8 pattern of the 77DX in figure 8 mode has a "squint" that makes that pattern slightly asymmetrical.
4. Our test fixtures fit the Proscenium more closely, which reduces one measurement variable.
5. We know the precise acoustic Z of the materials around the ribbon motor in the Proscenium.
OK, the tests are being done now. We are putting a brand new ribbon in the test object today to make sure that everything is to spec before we begin.