They simply aren't necessary, and here's why
I saw a clever meme on the internet recently, a photo of Jaco Pastorius and the caption reading "you don't need more strings, you need more practice".
Obviously, this applies to both guitarists and bassists alike, but I'd like to counter the meme's idea first: the current climate of our modern music industry is magnitudes different compared to when Jaco's playing and popularity were at their height.
Bass players, in particular, are competing for jobs against a producer who could use a bass sound on his keyboards, re-amp it, and only an audiophile would know the difference. Electronic music has synth bass that goes below the register of a 4 string, and if someone who you're trying to work for wants that, it could cost you a job. Perhaps even in the long term.
Relating this back to the guitarist's world, one could easily change the photo to Randy Rhoads and keep the caption the same. Classic solo Ozzy Osborne is as metal as it gets. Heavy riffage, lighting fast guitar solos interpolating finger tapping figures. It doesn't get any more metal than that.
And he played in standard tuning. Let's let that sink in. The creator of heavy metal, once he went solo, had his guitarist play in standard tuning.
So, why? Why this affection for playing low notes equated to making the metal 'heavier'?
I have a few theories:
1.) Hendrix did it.
What guitarist hasn't been influenced by Hendrix who was born after the year 1970? Good enough for Hendrix, good enough for me, right? Well, Hendrix had a reason: his voice.
His range as a bari-tenor made it difficult for him to sing in E, so that drop of a half step (and a few more over time) took the strain off his voice.
2.) So did Black Sabbath (on the first few albums)
Sabbath did it too, good enough for them, good enough for me. Right (ok, they detuned more over time, like Hendrix)? Well, also keep in mind that Tony Iommi lost the fingertips of his right hand, and detuning, along with thin strings (and prosthetic thimble-like fingertips) made it possible for him to play.
3.) 'Heavy' and 'low' are not what you think they are
Third, but most important, I think the words 'heavy' and 'low' are used interchangeably in some music scenes/genres. What qualifies a riff being heavy? I think syncopation is one such thing. But, I've heard tons of guitar riffs that are super heavy played clean tone (or a light amount of gain). "Can't Stop" by the Red Hot Chili Peppers, "Standing on the Verge of Getting it On" by Funkadelic, and "Sing a Simple Song" by Sly and the Family Stone all come to mind.
Perhaps it's how at a live show you can feel the power of the music as the energy washes over the crowd, and the lead guitarist puts his foot on the monitor to solo (or some abomination of one) for his adoring fans. But, by and large, it's the bass that you feel shaking your rib cage. The guitarist happens to be the one, in 'heavy' music, to get all the glory.
4.) Seek inspiration from outside your comfort zone.
So what do Randy Rhoads and Jaco have in common (have you heard the bassline for "Teen Town"? It's heavy af. What about bootlegs of him and Mike Stern doing that one?); along with bands like Anthrax, Metallica, Megadeth, and Judas Priest? Lead guitarists who practiced their asses off.
To put it another way, creativity is fostered in environments lacking stagnation. To avoid stagnation you have to take yourself out of your comfort zone. In the case of music, that means constantly trying to absorb more material, not only listening to your favorite band over and over. Exposure to new ideas while studying seriously will come out in new ways when trying to be creative. Yngwie Malmsteen capitalized on the 'metal' sounds of classical music on a Strat in standard tuning. In fact, Hendrix's death was what made Yngwie want to take music seriously. He grew beyond learning Hendrix solos and began adapting Paganini's violin pieces for the guitar. Through a Marshall stack cranked to 11, of course.
5.) Do the work, not what's cool at the moment
So, it's not tuning to drop D, D standard tuning, Eb, drop Db, drop A, or drop E that's going to make your riffs heavier, your solos better, or your band tighter. Practicing on your own, at home will do this. Rehearsing with your band, not noodling the entire session, will do this. Individual study is what fosters personal growth, not just musically.
So in short, Meme Jaco, you're correct:
You don't *need* more strings.
You do *need* more practice.
Adam Douglass has been playing guitar for 25 years and teaching for a good 20. He currently resides in Brooklyn, New York where he is an instructor; and plays with his band doing his original music, jazz standards, or whatever other gigs might come his way. His guitar of choice is the Fender Stratocaster, though if money were no object he'd have 3 or 4 of everything. He prefers tube screamer-like overdrives and clean boosts, with touch of analog delay. Hit him up at firstname.lastname@example.org, as he is always happy to discuss interesting topics.