Ultimate Ears has introduced earphones that should appeal to professional musicians as well as iPod listeners. The devices are custom-made to fit your ears, thus sealing out noise and practically eliminating the possibility of the earphones falling out at an inopportune moment. The $1,150 UE-11 Pro (www.ultimateears.com) incorporates four speaker drivers in each earphone, including dual subwoofer drivers that deliver bass as deep as any musical instrument can produce. . . . Musicians who fly frequently will appreciate the Centerfold (www.devillain.com), a Swedish-made guitar that folds in the middle. When airline pilot Fredrik Johansson, who is a guitarist, grew tired of schlepping his instrument onto airplanes, he created one that fits into a backpack. The $3,400 instrument, produced by Johansson’s DeVillain Guitar Co., has strings that roll up into the guitar as you collapse its neck. The strings unroll as you unfold it, after which you tune the instrument as you normally would. The Centerfold features a body made of Honduras mahogany, a maple neck, and a rosewood fret board.