Bennett -- the Hiquphon's a marvellous tweet and, on the drawing board, there is an endless line of mids that you could use (limited somewhat by the Hiquphon's medium sensitivity of 89-90db). (I have no Hiquphon project in mind -- but a search could give some ideas...)
OTOH, a likely target for mid (I'd suggest a mid-bass unit) could be in the Scan speak range (say a 18w8535-00 or the Kevlar 21W8554 OR the seas/excel W21EX).
An UNUSUAL approach however, would be to try a large diametre wide-range drive unit (e.g. supravox 215gmf or 285gmf -- there are many others). Putting a lot of work (& fun!) into the design, you could approximate a very wide range speaker of exceptional musicality.
On the down side, many wide-range drivers have very high sensitivity (+6db over the Hiquphon) that will have to be matched to the tweets. You will also be able to play with a higher x/over frequency if you wish, and make the hiquphons' life easier.
Good luck!
OTOH, a likely target for mid (I'd suggest a mid-bass unit) could be in the Scan speak range (say a 18w8535-00 or the Kevlar 21W8554 OR the seas/excel W21EX).
An UNUSUAL approach however, would be to try a large diametre wide-range drive unit (e.g. supravox 215gmf or 285gmf -- there are many others). Putting a lot of work (& fun!) into the design, you could approximate a very wide range speaker of exceptional musicality.
On the down side, many wide-range drivers have very high sensitivity (+6db over the Hiquphon) that will have to be matched to the tweets. You will also be able to play with a higher x/over frequency if you wish, and make the hiquphons' life easier.
Good luck!