Science project using the harp?

[harpist_anya]

Hi,
I am a high school student as well as an aspiring harpist and I was wondering if there might be a science project I could do that involves the harp. Ideally, the project would have a dependent variable that is quantitative, and I would prefer to use equipment that can be found in the lab of the average high school or that is not too expensive.
Thanks!

[a2colin]

I think that it is very possible to do a science project using the harp.

A little background on me. I am a physicist who studied how the violin worked during my schooling.

One of the more interesting things was how the sound output changed depending on where you were located. The violin does not send out sound equally in all directions.

You could possibly do a similar study for the harp. Depending on the approach, the cost would be quite minimal. Does this sound idea sound interesting to you?

[harpist_anya]

Thanks for the reply! I definitely think that sounds like an interesting project, but I have a few concerns:
1. What exactly is "sound output"- is it something different from the number of decibels/ the volume? (I have not taken a high school physics course yet). In other words, what would I be measuring?
2. Is there an device that could give me a numerical measurement for sound output?
3. Human error- would it be too hard to regulate how hard I am plucking the strings?

Thanks again!

[a2colin]

1. Roughly speaking, sound output is what you intuitively think. It's the amount of sound in decibels that comes from the instrument. A microphone or a decibel meter can measure the output.
2. A decibel meter can do it. Someone could stand in different places and take measurements, then plot them like a map of the sound field.
3. Very, very good question. That is the hardest thing to do. Just a suggestion, perhaps one could use a mechanical device that always pulls the strings the same amount before releasing them. I have a particular idea in mind, I'd like you to think about it first.

As an aside. Consider the idea of using speakers to send known sounds to the harp and measuring how it vibrates. There is a 'law' of physics that says that the vibration of the harp caused by a sound hitting it is exactly the same vibration that the harp would create making the same sound. It's a little messier than that, but that's the method I used when studying the violin. The problem is that it is not trivial measuring the vibrations. I would recommend the method in 2 and 3. They may not be quite as precise (contrast with accuracy), but will still should give useful results.

By the way, I don't think anyone has done these sorts of measurements on the harp. I will be most interested in knowing what you find if you should decide to pursue your idea. I think that it's definitely doable.

[harpist_anya]

Thanks again for your helpful response. After thinking about how to control how hard I would be plucking the strings I came up with 2 possible options:
1. A Newton meter/ spring scale- the only difficulty with this is that I would need to figure out a way to release the string after using the hook to apply a the set amount of force.
2. I could use a ruler to pull the string out a certain number of millimeters/centimeters before releasing it to create the sound.

Do you have any other ideas that you think would work better?

With regard to your other idea about sending sound to the harp to make it vibrate and measuring, I did some research and found that there is a device to measure vibration but they are all several hundred dollars, so I think it is best to stick with using a decibel meter.

One other random thing- I was thinking that I could also gather data about the different environments I am testing such as air pressure, humidity, etc. because it might help in researching the conclusion and explaining why the harp was louder in certain locations.

[a2colin]

Both of your thoughts about pulling the string are very good. The one I had thought of is your first idea using the spring scale. The difficulty is, as you noticed, is coming up with a release mechanism. That's doable, but I actually think that the method using a ruler would work quite well.

What I don't know is how much do the strings on a harp move. I have the thought that they move a fair amount. If so, the ruler method is the easiest. As long as the positioning of the ruler is consistent your results will be repeatable.

I agree with using the decibel meter. Getting a vibration measuring device would be just the beginning of your troubles. It took me a couple years to get the measurements right on a violin.

I am of the opinion that trying to measure multiple variables, humidity, air pressure, etc. as well as the intensity of the sound in the same experiment could lead to over complication. The most successful experiments only try to measure one thing.

[harpist_anya]

I experimented a little bit with the ruler method at home and it worked fairly well- I was able to pull the string about a half a centimeter out each time. The only problem is that given the way my line of sight falls when sitting behind the harp, it is hard to see if the string is exactly matched up with the ruler. I think I should be able to master a fairly consistent tone with some practice though. I also found that attaching a small piece of blue tape 1/2 centimeter long to the string below the one I was plucking was a better way to get consistent volume. This way, I did not have to focus on holding the ruler steady with my other hand and I could align the string with the edge of the tape.

I think that I have a pretty concrete idea of what I want to do, so now I need to begin researching to form my hypothesis. Thanks so much for your help! The project results aren't actually due until later in December, but coming up with my idea was part of my summer assignment for my science class this year. I'll be sure to let you know how it goes.

[a2colin]

Ok, great. I have written a document which, at the moment, I can't upload, "Sorry, the board attachment quota has been reached." I think it will help you. I'll try again tomorrow.

[bfinio]

Hi harpist_anya,

It looks like you are already getting plenty of help from a2colin, so I don't have much to contribute. I just wanted to throw in one quick suggestion - many smartphones and tablets have decibel meter apps that you can download, which will save you from having to purchase one. Try searching the app store for "decibel meter", "sound meter", "sound level meter" etc. and you should find a bunch of options. I'm not sure if these apps are as accurate as a regular decibel meter, but it could be good enough for a science project.

-Ben

[harpist_anya]

Hi bfinio,
Thanks for your suggestion! I searched the app store and quite a few options came up. Just as a quick trial, I downloaded a free one with decent reviews called Decibel10 and tried it out with the harp. It seemed to work well, but with it was hard to get the numbers to "stay still" long enough for me to read them. I think this might have been because I was testing it in the vicinity of my house, so there is background noise, but I will probably end up conducting the project somewhere else. Of course, I have not done a complete search yet so there might be a better app out there.

[a2colin]

Here is a docx file with my suggestions for how to go about getting good measurements. See if you can find an app that has a peak hold function. If apps are too jittery, Radio Shack has a sound/decibel meter that is not too pricey.

OK, I am still unable to load file as an attachment. Trying copy and paste.

++++++ Doc Start ++++++
Hello Ms. Harpist

I decided to create a document that may help you to see what I think that would work well for your project.

I'm aware that you haven't taken physics yet, so I'll make things as straight forward as I can. You need to try to understand some of the Physics of Music without having had physics.

Here goes. The speed of sound is roughly 1000 ft/sec. Two octaves above middle C is a note called C6 on the piano and I believe is the C in the second octave on the harp. That string vibrates at 1046.5 Hz (vibrations per second). Using that and the speed of sound one can calculate that the wavelength is about 1 foot. As an aside, if the speed of sound was exactly 1000 ft/sec and the frequency [number of vibrations per second] was exactly 1000 Hz then the wavelength equals 1 foot exactly. Additionally the A above middle C (3rd octave on harp) is 440 Hz, which gives a wavelength of about 2 feet 3 inches. Why do you want to know those numbers? So that you know where to place the decibel meter.

### The Figure did not copy ### I will try to export it to a jpg and attach. Nevertheless the rest at least came through.

Figure 1 -- The cross = harp; big circle = forbidden zone; small circle = decibel meter

Looking at Figure 1, the small circles are supposed to be a regular grid, not random (my drawing skills sux). The large circle is the forbidden zone, which for a harp should be about 6 feet across or at least 3 feet from any part of the harp. If you take measurements too close to the harp there is a possibility of measuring the near field of the harp instead of the far field, which is what the listeners hear. The harpist or anyone playing any non electric instrument, flute, oboe, etc. hears the near field, which is only mildly related to what the far field is doing. I hope you have some idea of what I mean between near and far field. If not, please ask. I don't know how to describe it differently in just a few words, so if you don't get it the failing is mine.

The distance between the different readings on the decibel meter should be either 1 foot for the 1046.5 Hz string and 2 feet 3 inches for the 440 Hz string. You should have many more readings than I drew depending on the size of the room.

Once you have the data the trick is to figure out a way to display it so it makes sense to someone looking at the display. For the moment I will leave that up to you. However if you need help, do let me know and I'll nudge you in what I hope will be a useful direction.

Things to take into account.

1. Pluck the string from as close to your normal position as possible. That would insure that there is minimal interference from the player.

2. Get a friend to hold the decibel meter more or less at the height someone's ears would be normally. Do not use a hard surface to support the meter or you can get reflections from the surface into the meter, which will make the measurement less accurate. Luckily human bodies are soft.

3. Try to find the deadest room with the least reflections you can. You are not trying to find what the acoustics of the room is, just the harp.

4. Any ideas you have that are different from mine should be tried. Never listen to an expert until you have verified that what they say makes sense to you. The craziest ideas are often the best.

Short story follows, which you can skip. Back in olden times a couple physicists wondered if the electron had spin so they asked an expert. The expert said that their idea was crazy but he didn't think it was crazy enough to be true. They listened to the expert, didn't publish their idea and missed out on winning the Nobel Prize when it turned out that electrons do have spin.

I hope that this little missive provides some assistance to you and makes doing your project at least a little easier. I will continue checking the website for additional questions and will provide as much support as I can.

If you want the math behind the wavelength calculations let me know. I suspect that the internet has explanations as well.

Good Luck.

[a2colin]

No luck yet with Figure 1. The system does not allow jpg files, which I get. So, if it's not clear from my description, I can expand and hopefully describe it.

In my opinion bfinio is right about using an app if you can find one that works for you. Good thinking from bfinio. I am from a time before apps and frequently forget that they exist. A physical meter is more accurate, but would probably not be of much use once your project is complete.

[bfinio]

Hi harpist_anya,

For what it's worth, I tried an app called "Sound Meter Lite" on Android (it's free and I believe you can pay to upgrade to a Pro version, which you probably don't need). It displays the instantaneous reading but also the minimum, maximum, and average decibel levels since you've started recording. You can reset it as needed, so that might be useful - that way you don't have to worry about getting the instantaneous number to "stay still" - you can use the average value over the course of one trial.

a2colin - just for future reference, it's amazing how many apps there are that can replace standalone instruments. Most smartphones have a light sensor, microphone, accelerometer, and compass (and maybe more that I'm forgetting) and corresponding apps that will show the output from each sensor. There are apps that let you record video and then do projectile motion tracking for a physics project, etc. So, since many kids already have access to a smartphone and most of these apps have free versions, I've started trying to recommend those when possible, as opposed to dropping a bunch of money on a specific sensor/meter they won't use that often.

-Ben

[harpist_anya]

a2colin- Wow! Thank you for taking the time to type up that lengthy explanation! I attempted to recreate the drawing that you described and I understand what you think I should do. (I was going to attach the version I drew from your explanation but I am also having trouble attaching files.) The only thing I don't understand is why the readings from the decibel meter should be the same length apart as the wavelength of the note. Perhaps you could go into some more detail about this? Also, I was having trouble thinking of a control for this experiment. I was thinking about using the point where listeners are most often positioned (probably towards the front on the the left side), or another possibility is just using dead center in front of the harp?
I am planning to see if I will be able to use my school's orchestra room, or maybe one of the bigger practice rooms to conduct the experiment.

Ben- As far as the decibel meter goes, I found one that allows me to export the data via email and open up a chart in excel, where the decibel level is shown millisecond by millisecond. With this, I think I should be able to get a pretty good reading. If not, I'm sure that my school will have an actual decibel meter for me to borrow.

Again, thanks so much for your help!

[a2colin]

I've been given a method that is supposed to work. Convert drawing to a PDF, the system allows those. However the board attachment quota has been reached. Sigh. I shall not give up!

Extraordinarily good question about the wavelength, going to make me think. The primary reason I suggested using the wavelength for spacing is to have a definite grid so that it is easier to see the relationship between location and sound volume. Ideally there should be an infinite number of locations. However, that might take longer to do than is reasonable (supposed to be a joke). The specific reason to use wavelength spacing is that usually nothing much interesting happens on anything less than about one wavelength. Hmmm that's not really correct (letting you into how an experimentalist thinks). Actually 1/4 wavelength is the spacing that would find close to 100% of the variations. The downside is the number of measurements. For the 440 Hz string 1/4 of 27 inches isn't too bad a spacing but 1/4 of 12 inches is other than good. You should still get solid results using 1 wavelength spacing.

You will have to decide if you want to use a different string the the 1049.5 Hz one. Here are a couple URLs with the relationship between frequency and note for the piano and harp. You'll have to convert the frequency to wavelength but there are websites that do that and probably apps if you don't want to do the calculation longhand.

http://www.google.com/search?ie=UTF-8&s ... MmNH05M%3A

http://www.google.com/search?ie=UTF-8&s ... Z9wJJ9M%3A

As far as the control goes I am of the opinion that what you are actually measuring is the difference between sound and no sound. So the control would be a series of measurements using the same grid but without the harp making a noise. You would then have a background noise (sound) level and the actual harp only sound would be the difference. Unless you're going to be making the measurements in a noisy environment it's reasonable to assume that the background is zero as the sound intensity of the harp would be many times higher than the background. Don't let that discourage you from measuring the background, remember that all experts think that they know more than they do.

Colin

[deleted-292498]

@harpist_anya

you could do a project on how each string in a harp varies even though its made of the same material.. like how much tension it can hold to how many vibrations occur at one pick...

hope this helps
Arun