I remember watch a morbid angel video in the mid 90's Where the slime live and i was playing guitar at the time and noticed the low sound and then notice the seventh tuner the the ibanez then i wanted one.
Petrucci introduced me to the idea of 7 string guitars, then I heard Mark Jansen from Epica playing a 7 string (well, it was a B standard 6 string, but he plays 7 strings live), then I heard Loomis playing the 7 string guitar. I think what pushed me to go for a 7 string was my desire to play A Change of Seasons, my need to learn every single Epica song, and of course my friend's endless preaching as to how 7 strings are crap.
the first rock band that I've really (been forced to) listen to was Limp Bizkit when I was fourteen. They actually made me want to play guitar, and I found out years later that they used sevens tuned to low B, then came Linkin Park. But when I was 20, I started listening to Dream Theater and my live was changed, I had to get a seven when I first listened to "This dying soul".
defnetally Buz McGrath and Ken Susi of Unearth. they were the first band that i was into that really played 7 strings and they just made them sound so beast i had to get one lol
I guess I would say Loomis and Broderick, but I really wanted to try seven simply because I wanted to try something different, and to extend my playing.
I really liked Petrucci's stuff as well as Per Nilsson from Scar Symmetry but I think the thing that actually made me really keen on trying one was the 2008 NAMM youtube vid that shows Jeff Loomis shredding along for like what - 15-20 minutes pulling off one insane solo and riff after the other.
By the way if you like loomis check out the the youtube video that was recorded at the 2009 gotheburg guitar clinic (I think it is split in like 7 parts).
My buddy Jeff(J7) formerly of the band Kicking K8. We toured together in the summer of 07 and he played 7 string schecters as opposed to my 6 stringers. He was the only person other than korn and the deftones that I had seen playing sevens. He tuned them to dropC with double C's on top. It had a cool sound that sounded unique to my ears. long story short the tour ended and he forgot one of his guitars in our trailer and when I called to tell him, he gave it to me. So my first 7 was a free 7. A schecter Omen 7 that I had customized. So you can say I had Inspiration given to me.
It was a few songs/albums specifically when I was a teenager. It wasn't so much the riffs themselves and a 'need to play a seven to play dat!' thing but the actual sound of their 7 strings themselves. Low, nasty e.t.c.
Fear Factory -Obsolete (Shock esp. the slide he adds to the main riff at the end of the song, Edgecrusher)
Korn - Follow the Leader, my first Korn album (Dead Bodies Everywhere, the outro of Reclaim my Place, middle bit of Seed, super slow bit of Earache my Eye).
Meshuggah- New Millenium Cyanide Christ, I knew they used 7 strings from their Guitar World column but the (hilarious) vid was the first time I'd experienced the 'Shug.
Saw the video for Where the Slime Live on Youtube. Loved it.
Limp Bizkit - Significant Other, I actually thought the 4 string stuff was a 7 because of how it sounded (and seeing Wes playing 7's), trickery!
Dream Theater - Lie video. At the time this was the only DT video I could find on the webz (this was pre-Youtube).
when I was 15 I was into Korn and I wanted that sound. By the time I was 16 I I got more into Dream Theater and Meshuggah and that was the end of my Korn obsession.