||Goodmans was a manufacturer of hi-fi speaker components in the UK. The front cover of their mid 1960s product catalog is shown at left. Inside this catalog they not only offered speakers, they also offered detailed plans for constructing speaker cabinets that would use their components. In adddition to cone speakers, they also offered two models of horns: the Trebax and the Midax.
The names of the horns explain their function. The "Trebax" is a treble, or high frequncy driver mounted to an axial dispersion horn. The "Midax" is a mid frequency driver mounted to an axial dispersion horn.
It is a common misconception that the horns used in Vox amps were tweeters, and that simply is not true. Using tweeters in a guitar amp will normally produce an unpleasantly hissy or shrill tone. Tte Midax horn responds from about 2,000 to 8,000 cycles when used with the 2 uf or 4 uf series crossover capacitor commonly used by Vox.
Unfortunately, Goodmans went out of business in the late 1970s, Since that time, repair parts for the Midax horn have become nonexistant, along with the horns themselves. The only place I can recommend to purchase a Midax horn is on eBay.