people listen to music for different reasons. i don't believe there is a direct positive link between intelligence and musical preference, in terms of classical versus everything else. what is important to remember, is that there are "big T" [thrill-seeking] people who love danger and stimulation, and "little t" people who are the exact opposite, who flee from danger and towards safety and succor. each camp would be expected to like different types of music. for example, you can probably count relatively few GIs who put classical music into their Ipods, whereas for retiring hermits, if they were to be into any kind of music at all, it would be as unobtrusive and calming a sound as possible. i myself am in the latter camp. from my own army experience, i was the only classical music lover i knew. hard rock as practiced in the last 35 years or so is just destructive to my sense of well-being. it makes my thoughts scramble, my head ache and my heart pound, largely due to the anapestic beat which is de rigieur in modern hard rock music.
now if you were to ask a hard rock fan what they saw in such music, they would probably say words to the effect that the music stimulates them, energizes them and makes them work harder and play harder. plus, the pronounced anapestic rhythm acts a bit like a jungle drum, psychoaurally exhorting them to MOVE MOVE MOVE/STROKE-STROKE-STROKE in rhythmic sympathy. but for me the loud rhythm and crashing chords feels like a jackhammer atop my head, pounding me into the ground with alacrity.
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just my 2-cents' worth, adjusted for inflation 