The Physics of Guitar Vs. Bass (Scale and Strings)

shemihazazel

shemihazazel

Fractal Fanatic
Okay, folks. I’m hoping that one of the gurus on here can explain this to me in a clear fashion, because it’s been bugging me for a while.

So, when it comes to stringed instruments, the heavier the string - the lower the pitch it can be tuned to without becoming a floppy mess. The same applies for longer scale length, for the longer the string – the lower the pitch it can be tuned to without becoming a floppy mess.

Ok, now with both of those in mind, how does one explain, say a 34” scale bass with a .65 gauge D string and a 25” scale guitar in drop-D with a .50 gauge low D string? Both strings are tuned to the exact same pitch, and yet the bass has longer scale AND a heavier string for the same note. In theory, shouldn’t the tension on the bass D string be ridiculously high? Shouldn’t it be using a lighter gauge than what the guitar is using for the same pitch, because of the scale length difference? But then, if you were put a .50 gauge on the bass for D, the string would flop quite a bit; and if you tried using the .65 for D on the guitar, the tension would be really high.

What factor am I missing that can explain this?
 
Comparatively, the D string on the bass DOES have ridiculously high string tension.

If you take 2 guitars, say a LP with a 24.75" scale vs a jackson with a 25.5" scale and tune them the same, you'll notice more tension on the longer scale. The reason here is the jackson is a full fret longer. To get the same tension, you'd have tune the jackson down a 1/2 step and capo it at the first fret. Treat that as the new nut and you have the same tuning with the same string tension. If you want that note without the capo, you have to tighten it aka add tension.

Now, if you extend that to a bass, you'd have to capo that baby up like, 8 frets (so bridge to capo length is 24.75") and tune it to D. Take the capo off and you'll find that you have to add tons of tension to the string to bring it up to D.

I don't really know how the gauge interacts with tension other than I know that it takes far fewer turns of the tuning key to get a thicker gauge string to change pitch than a thin string. I can't explain why.
 
Hmmm.

I think the bass string in your example will have more tension. It may not be noticeable because you play the bass differently??

Although I think string construction and materials make a difference too.

I normally play flatwound d'addario 13s on my 25" scale bambino. I changed to thomastik-infeld 13s and they felt way too stretchy and thin on the same guitar. I couldn't stand them and switched back to the d'addario.
 
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