Idea: Harmonics from Four Solid Aluminum Rods used as Electric Upright Bass

[MarkA]

Yes.

Danke.

 

[Beej]

Solid rods like you describe can be made to vibrate, but they are most resonant with compressive vibrations - hold the rod loosely at about a fourth of its length, and strike it on the end - it'll ring like a bell. Glue a thin disc of steel on the other end, and put that over a magnetic pickup. Only problem is, to get 4 notes, you'll need 4 different length rods. For bass notes, you'll need really long rods.

If you try to use rods like that with the movement being sideways (like a stringed instrument), you'll learn really fast why strings are wound, not solid. Solid rods have a lot of inherent stiffness - in flex, they're a dispersive medium, and the velocity of propagation is not constant with frequency. Practically speaking, that means the overtones of the vibration are not harmonics of the fundamental - the thing will sound out of tune with itself.

Really interesting physics problem. The distribution of harmonics on a vibrating string are caused by the boundary conditions, specifically that the string is fixed at both ends. The longitudinal waves reflect perfectly at the ends, the interference of all of this reflections produces the harmonic series. So if the rods are only supported/fixed on one end, they would resonate more like a tuning fork. You could probably look up the harmonic series and nodes/antinodes for a tuning fork, I would be surprised if that problem has not been solved.

This might be useful: Vibrational Modes of a Tuning Fork

I think these three are on to something. You're not likely to get predictable harmonic locations along the rods that you can clearly determine will produce a desired result. So you can find the fundamental, but hard to find usable, predictable harmonic overtones.

I'd also think that they need to fixed to something that will permit the rods vibration and not dampen it, and I think wood will dampen more than you want here.

Lastly, to get bass fundamentals out of these rods, wouldn't the rods need to be several metres in length?

 

[Beej]

This giant tuning fork in Berkeley, California presumably produces a subsonic fundamental, but there is more art than science written about it:
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[Mustafa Umut Sa]

I think this idea could be used as one rod , one or two notes , thats it , I think making 7 or 12 notes rods are cumbersome and not fine.

I think I might focus on inflated and with the inflation , stretched , load loaded silicone tubes.
I am thinking that , if I buy 107 cms long extremelly lightweight and low density silicone medical tubes and inflate with air , air pressure would stretch the tubes lenghtwise.

This might be create a tube like stretched guitar string.

I think low density will make it ring easier inaudible.

Than the piezo and amp acts its way.

AND most importantly your left hand will change the notes.

 

[HolmeBass]

Solid rods like you describe can be made to vibrate, but they are most resonant with compressive vibrations - hold the rod loosely at about a fourth of its length, and strike it on the end - it'll ring like a bell. Glue a thin disc of steel on the other end, and put that over a magnetic pickup. Only problem is, to get 4 notes, you'll need 4 different length rods. For bass notes, you'll need really long rods.

If you try to use rods like that with the movement being sideways (like a stringed instrument), you'll learn really fast why strings are wound, not solid. Solid rods have a lot of inherent stiffness - in flex, they're a dispersive medium, and the velocity of propagation is not constant with frequency. Practically speaking, that means the overtones of the vibration are not harmonics of the fundamental - the thing will sound out of tune with itself.

This is very insightful, and describes to me why there is a "clang" component to the tone of percussions instruments like this: all the non-coherent (not in tune with the fundamental) overtones.

 

[micguy]

This is very insightful, and describes to me why there is a "clang" component to the tone of percussions instruments like this: all the non-coherent (not in tune with the fundamental) overtones.

If you look at a xylophone or marimba, you'll see the underside of each of the bars is not flat - it's cut away. That's because the same Physics is at work. By not having a uniform cross section, the overtones are closer to multiples of the fundamental - it sounds more in tune.

I studied Acoustical Physics with the professor who, at least back then, was THE GUY in the world of acoustics of percussive musical instruments. If you hit it, and it make a musical noise, he had studied it.

 

[MarkA]

If you look at a xylophone or marimba, you'll see the underside of each of the bars is not flat - it's cut away. That's because the same Physics is at work. By not having a uniform cross section, the overtones are closer to multiples of the fundamental - it sounds more in tune...

I wondered about this (the cutaway on the underside of the bars)... thought perhaps it was to make them lighter and more resonant (also to tune them), but wondered (in a vague way) how it might affect their harmonics.

 

[micguy]

If you check Talk Marimba right now, they're no doubt discussing teversed vs normal P pickup placement.

 

[Gary_M]

Lots of interesting ideas being discussed here. I still wonder if pursuing this as a bowed instrument would be more effective... and to take it a bit further, could some of the principles of the hurdy gurdy be used?

 

[MarkA]

If you check Talk Marimba right now, they're no doubt discussing teversed vs normal P pickup placement.

Yeah? I'd better get over there!