The spelling of the word "MIRIADAX" can be explained using the International Phonetic Alphabet (IPA). The first syllable, "MI", is pronounced with the long "E" sound, represented in IPA by /mi/. The second syllable, "RIA", is pronounced with the long "I" sound, represented in IPA by /riə/. The third syllable, "DAX", is pronounced with a short "A" sound, represented in IPA by /dæks/. Altogether, the word "MIRIADAX" is spelled using a combination of long and short vowel sounds, as well as the letter "X" for the final syllable.