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For a 7 string guitar it's very important to have a 6 string to hand for covers and certain things that you can't do with a 7 string.
Is there anything that the lack of a 5th string makes easier or once you play 5 string is it better to continue to buy 5 strings? Is there more to lose than gain by getting a 4 string?
Cheers
I haven't played a 4 regularly in more years than I want to admit. However, starting about a year ago when I had to learn Michael Jackson's Rock With You (originally played on a 4 tuned to Eb) for a band that calls songs on the fly and allows no time for bass changes, I decided that I would much rather play that a 4 just for the ease of the positions. Of course, I learned it on a standard tuned 5 and can play it well on such but a detuned 4 would sound better (at least the open Eb would- and so would other parts but I won't go into detail). Reason 1) Sound.
Reason 2) Muting. While I have become fluent in floating thumb muting on 5, muting a 4, even though I barely play one anymore, is much easier for me. As an aside, I fret almost exclusively with my fingertips on 5, doing most muting w my picking hand. On a 4, particularly on the E string, I like to lay my finger across the string (my fingertips are actually hanging over the fretboard sometimes, basically the tip is where the B string is on a 5- however when I play the E string like that on a 5, I get too much artifact noise from bumping the B. Also, and this is certainly specific to my finger anatomy and differing string spacing, and probably lack of hard work, my barring doesn't work as well on a 5 as a 4 even though the slightly tighter spaced 5's theoretically should be easier to barre). Laying across muting allows me more freedom for my right hand to pluck.
Reason 3) Slapping. I am no expert and plenty of guys can slap on anything but I am much better on a 4. Again, this could be anatomy.... but also likely a lack of hard work. Plus, to me at least, some things sound better slapped on a 4. Maybe due to string tension differences?
Moral: Have both and play both well. Despite playing a 5 almost exclusively and pretty well, when I think about it, it seems silly to play a 5 for 50 songs when I only need it for one song, and that is merely a detuned 4
As an aside, don't over-value the lowness of a 5. At my church gig, of which I am one of 4 revolving bassists, I get to see recorded videos of us playing the same songs. The other bassists are primarily 4 string players, and educated, full-time pros at that. In some cases they are playing an octave higher than they can and I'm playing even lower than they can. Huge difference on paper. However, when they are playing around frets 7 to 12 on the A and D strings then they drop a low E or even F or G, the impact is great. Seeing these videos that they just started posting, after my doing this for 4 years, has been a real eye opener. Dropping low B is fun but these dudes kill with nothing lower than E, as did dozens of other bassists that we all know and who played the most iconic basslines ever.... almost all on 4 strings.
If I had my druthers, I'd play a 4 except when I need or want to access notes that a 5 will give me. So, yeah, I see advantage in having a 4 in addition to your 5.