Apparently, there is a fair amount of confusion about this in the non-Japanese speaking parts of the world, various people saying they rhyme it with "flange" and so forth.
I consulted an expert opinion on this - my son, who is a native speaker of Japanese, attends third grade in a Japanese public school here in Osaka, Japan. Coincidentally, Osaka is also where Tange is headquartered.
So, for the record, I asked Otaku Jr. to pronounce:
たんげ (ta-n-ge Tange)
Mrs. Otaku, upon investigating the hubbub, reports that 丹下左膳 (Tange somebody or other) is a one-eyed samurai in various dramas as well as possibly a relatively uncommon Japanese family name.