Any ideas for science fair project using the harp?

[mary-schneekloth]

One of my middle school students asked me about doing

[Karen Johns]

How about something related to sound waves and their effect on say, water? Not sure how you would rig this up, but I heard somewhere that the producers of Jurassic Park used a guitar string to create the effect of the vibration in the cup of water in the jeep

[carl-swanson]

Mark- How about calculating the string tension of gut strings versus nylon strings. Or even calculating the total tension on the neck/soundboard.

You could build a monochord. That’s basically a box with a movable string bridge on it and a top made of wood thin enough to be able to hear the pitch the string is producing. The box would have to be long enough to accommodate the longest string on the instrument. The string would be anchored at one end, to a scale capable of measuring the tension on the string. At the other end would be a tuning pin that you could turn with a key. You would place the string bridge in a position on the monochord to reflect the vibrating length of that string on the harp and then tune it to the required pitch. You would then take a reading of the tension on that string.

You could decide to measure the tension of all of the C strings on the harp, first in nylon, then gut, then carbon fiber. I frankly would LOVE LOVE LOVE to see a table with this information on it. And this would be a huge, HUGE contribution to our knowledge of harp dynamics. If you came up with this information, I can just about guarantee that I can get it published in the Journal of the American Harp Society.

[kay-lister]

Mary,

I once saw a demo of the effects of harp/sound vibrations using small colored beads.

[Karen Johns]

Now that is an excellent idea! And especially suitable for a middle school science fair project, IMO.

Karen

[Tacye]

If looking into Kay’s suggestion Chladni plates is the name of the original demonstration, fun things.

[mary-schneekloth]

Kay,

Thanks for the suggestion using beads to demonstrate sound vibrations.

[mary-schneekloth]

Carl,

Thank you for the idea about testing string tension. I have a father in my studio who is science-minded and could perhaps help in building a monochord. How do you suggest to attach the string to the string bridge and where would the scale be attached? Thanks. Mary

[carl-swanson]

Mary- It would be like a violin string bridge. Just something that sits on top of the vibrating surface of the monochord and the string would pass over it, pressing down on it but not attached. The string would be anchored or attached to something on one side of the string bridge, the ahchor being slightly lower than the top of the string bridge, and would then pass over the string bridge and be anchored to something on the other side of the string bridge. The vibrating length of the string would have to be measured from the top of the string bridge to the end of the string at the tuning pin. As you tested different length strings, the string bridge would be moved closer to or further away from the tuning end of the string. Someplace in there you would have to have a fish scale or something like that, so that as you tuned the string, the tension could be read on the scale.

Let me try to give you an example. Let’s say you want to measure the tension on a 4th octave C string(gut or nylon, it doesn’t matter), and a 4th octave C string on a concert grand is 16 inches long(I’m guessing on that. You’d have to measure it on a concert grand). You would place the string bridge 16 inches from the tuning pin and then install the string. You could have on one side of the string bridge the fish scale anchored to something stationary and strong on the end of the monochord. You would attach the string to the scale, run the string over the string bridge and up to the tuning pin. You would then tune the string up to the required pitch. Once it is up to pitch, record what the fish scale says the pull is. If you then want to test a 3rd octave C, and you knew that a 3rd octave C is 12 inches long on a concert grand, you would remove the 4th octave string, move the string bridge so it was now 12 inches from the tuning pin, and install a 3rd octave C string, tune it up to the required pitch and record the pull on the fish scale.

I think you would have to have a stationary bridge up near the tuning pin as well, so that you could measure exactly the distance from the moveable string bridge to the stationary string bridge, and that distance would be the same as the length of that string on a harp.

Some of the questions I would love to see answered are:

1) What is the difference in tension between gut, nylon, and carbon fiber? You could measure each string of the same position(4th octave C for example) and record the difference in tension of each one.

2) What is the difference in tension of the same diameter string(4th octave C for example) on a concert grand and then on a semi-grand? I would check the string lengths of a particular string on several concert grands and several semi-grands to see how they vary.

3) What is the overall difference in tension when a whole octave(say 4th octave) is strung entirely in nylon and then entirely in gut?

4) What is the tension exerted by each of the wire strings?

5) What is the total tension on a harp(concert grand and also semi-grand), adding up the tension on each string on the harp.

I realize this is a big project. But it could be pared down, like taking a reading on only the C strings, including wires for example, and comparing nylon to gut or carbon fiber.

I hope you’re able to do this.

[kay-lister]

Hi Mary,

Pull up Chladni on the net and you can find a lot of demos as to how it is done.

[Tacye]

Carl, I am sorry to seem like I am attacking you but can you explain what would be worthwhile about this project that could not be more simply gained by using the normal relevant formulae?

[carl-swanson]

I’m not a physicist. Maybe you can explain how to get that information by other means. One of the other posters here emailed me privately last year and we discussed something similar to what you are suggesting. The problem I have with weighing the strings and calculating the mass or whatever-the-hell is required to come up with a number for the tension the string produces is that different materials have different resistance to stretching that has to do with the type of material and not with the mass or weight of the material. A 4th octave nylon A for example takes a month or more to stop stretching and hold pitch consistently while the same string in gut takes a day or two to hold pitch. The mass of both strings will probably be the same, and I don’t even know what the difference in weight would be. But the nylon string will always feel like a rubber band when compared to the gut. How does that factor into a mathematical equation? Rather than berating me for not having a doctor’s degree in physics, you might try explaining your method of calculating what I’m trying to find out.

[Saul Davis Zlatkovski]

For middle school, I would suggest a simple demonstration of the acoustic properties of strings, the overtones and harmonics,

[Tacye]

I was not trying to berate you, but get an explanation of what the
problem was and why you found it interesting.

[carl-swanson]

Thank you Tayce-Your post leaves me with some questions. Firstly, how do you weigh a string? What kind of scale? It would have to be extremely sensitive and accurate. After all, how much of a difference in weight can there be between a nylon and gut string? Who has such a scale?

I understand the issue of ‘feel.’ But you said it’s related to tension and other relevant factors. What are the other relevant factors? Also, isn’t it possible that gut being made of strands of fiber and nylon being a simple extruded solid would have an effect on the resistance of the string irrespective of weight and volume, and therefore cause the gut to reach pitch at a different tension than the nylon? And let’s not leave out carbon fiber strings too. They also are made up of strands of fiber. But their resistance is much higher than gut or nylon and so reach pitch at a much higher tension then either gut or nylon. For anyone involved with the harp, but in particular repairmen and builders, it is critically important to have an accurate measurement of the actual tension exerted on the instrument. I would like to add to my list of questions in a previous post that of asking what the difference in tension is for a standard gauge gut, and one .006 to .008 thinner of the same length and pitch?

To be perfectly honest, I just don’t trust mathematical formulas to figure out this stuff. It’s possible that the mathematical formula doesn’t take into consideration everything that needs to be considered and as a result the practical application could come up with very different results. Let me give you an example of this.

All harp actions have to have the natural and sharp discs at a very specific distance apart in order to raise the pitch exactly 1/2 step from flat to natural and exactly 1/2 step from natural to sharp. There’s a formula for figuring that out, and it involves shortening the string length something like 10.17% of the of the total vibrating length. I’m sure you know the exact number. So the engineers got out their calculators and figured out the distance that the natural disc had to be from the stationary or adjustable stud to get the natural pitch, and then calculated again to find the distance, slightly shorter this time, to locate the sharp disc.

The problem is, those calculations don’t work in the first and second octaves. And do you know why? I know why. I’d like to hear your explanation.

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