Compression ratio is regarded as being safe at 2:1 but after 3:1 problems can easily occur with loudspeaker cones.The mcbean program will show you responses but wont tell you if distortion will result from your miniature too small horn throat
But with a little knowledge applied to the program,meaningful results happen.
http://www.volvotreter.de/ >downloads > dinsdale horn article
http://www.volvotreter.de/downloads/Dinsdale_Horns_1.pdf