Please note the PDF version of these test results can be downloaded Here.
From further investigation it was discovered that a potential cause of the low output of the RAAL 70-20XR may be due to improperly tensioned diaphragms. RAAL specifies a procedure for heating a new diaphragm with a heat gun to stretch the diaphragm tight. This procedure is to be done after the diaphragms are installed and fastened to the driver which means that if the metal face plate screws are loosened or removed then the diaphragm will require re-tensioning.
Since mounting the RAAL to my 1155 horn requires removing the metal faceplate I inadvertently de-tensioned the diaphragms. To resolve this issue and ensure I gave the RAAL the best chance of performing I had RAAL send me new diaphragms where I installed the driver in the horn throat adapter and conducted the proper heating procedure according to the RAAL specification.
I then redid the distortion test using the new diaphragms with the following results. As it turns out the RAAL provided another 15dB of output with the properly tensioned diaphragms. I was not able to do a direct comparison to a non horn test baffle since the hot air procedure is a one-time setup using the 1155 plastic throat adapter.
Below is the resulting frequency response of the RAAL 70-20XR with the 1155 Horn. The below result was conducted with a 1kHz 48dB/LR high pass filter. Overall the result looks very respectable.