CREATE TABLE table_17478 ("Series #" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT, "U.S. viewers  ( millions ) " TEXT)

What's the total number of directors who've directed episodes seen by 11.34 million US viewers?
SELECT COUNT("Directed by") FROM table_17478 WHERE "U.S. viewers (millions)" = '11.34'
SELECT COUNT("Directed by") FROM "table_17478" WHERE "U.S. viewers (millions)" = '11.34'