1) Car stereo speakers producing massive amounts of treble and ear-splitting assload
s of mid-range noise, while putting out very little bass. Sound great with larger speakers to back them up, but popular even when no such speakers were available for automotive use (this is one of the enduring mysteries of our time).
2) The answer to life, the universe, and everything, as imagined by Douglas Adams in "The Hitchhiker's Guide to the Galaxy
" (6 x 9 = 42 in base 13).