Some records make fine soundtracks for sitting on the front porch, watching the world go by. But the world goes by pretty slowly from that vantage point, and sometimes those records do too. This latest from the MTV series Unplugged is a case in point. A few blues numbers (”Hey Hey” and ”Rollin’ and Tumblin”’) toss off some sparks, and Eric Clapton’s fleet guitar picking is both relaxed and urgent on ”Old Love.” But a lite-jazz instrumental, ”Signe,” is too pristine for its own good; the sentimental ”Tears in Heaven” sounds logy; and in a lanky, laid-back version of his classic ”Layla,” Clapton sings, ”You got me on my knees” with cool reserve — less a feverish plea than a rational effort to bargain with an irrational lover. It’s one thing to unplug, but turning off the juice is another matter entirely.