Help with small horn design

Hi all,

I have Wharfedale TwinX 12X boxes which are 12" coaxial and I want to do away with coaxial drivers as I struggle to get replacement drivers and they are very expensive.

I want to go for a normal 12" + 1" configuration. I want to mount to a 1" compression on one of the vents which has a diameter of 80mm. I might use sheet metal or fibre glass for the HF horn. Please assist with tiny horn design for 1" compression driver, that can be mount on a 80mm round hole.