There could be a couple of things going on. First, just from looking at the description in CARA my guess is "Acoustic Board" is not the right material surface for modeling a drop ceiling, though not too far off. To get it just right you might have to build a custom surface. A little research on the Web or a call to Armstrong should provide the necessary info for building the right material surface. A quick example of the info available can be found here http://www.controlnoise.com/ceilingtile.html.
Also, what speaker model are you using? If it is custom it may need tweaking to give a true representation of the speaker's output. For instance, I made a couple of mistakes initially that when corrected made a significant difference in the results. One was using the overall diameter of the speaker instead of the rubber surround. CARA wants the measurement of only the "effective membrane surface".
Another mistake was using the rated efficiency for my 4 ohm speakers which was 2.83 Volts/m and not the 1 Watt/m spec CARA wants. It was also necessary to change crossovers to get a more linear SPL.
BTW, these recommendations came courtesy of ELAC Technische Software themselves. Their support, what little I've needed, has been excellent.
Also, what speaker model are you using? If it is custom it may need tweaking to give a true representation of the speaker's output. For instance, I made a couple of mistakes initially that when corrected made a significant difference in the results. One was using the overall diameter of the speaker instead of the rubber surround. CARA wants the measurement of only the "effective membrane surface".
Another mistake was using the rated efficiency for my 4 ohm speakers which was 2.83 Volts/m and not the 1 Watt/m spec CARA wants. It was also necessary to change crossovers to get a more linear SPL.
BTW, these recommendations came courtesy of ELAC Technische Software themselves. Their support, what little I've needed, has been excellent.