The sign for the x-shape (26, 12) is a prefix to the note. You can show the quarter note as whatever pitch it is written on. If there are four or more in a row, you can double the prefix by brailling the 12 cell twice. However, since a clap is not pitched, in this case I would use the prefix for a note of indeterminate pitch (26, 13). You will be correct whichever sign you choose to use.