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Is the Earth Harp real (acoustically)?

by Jiminy
Tags: acoustically, earth harp, real
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Jiminy
#1
Jun1-12, 03:14 AM
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Has anyone seen this "Earth Harp" guy on TV? He was on "America's Got Talent" a few weeks ago, and I am highly doubtful that this instrument is real. I have a degree in music composition, and I've got several unit of forma instrument acoustics study, not to mention having a firm basis in instruments so I can competently compose for them.

I would like to give a couple of links for reference, but I'm new here and the forum software will not allow it. He has a website and a number of videos on YouTube. His name is William Close, and the name of the instrument is "Earth Harp".

The red flags for me that this is not an acoustical instrument are (in no meaningful order):

1) You can see the strings vibrating. In fact, you can see them wobbling. If discrete vibrations are slow enough to be seen (the resolution of human eye maxing out at about 30 "frames" per second), those vibrations are going to be very low — much lower than the ones he's playing, and if they're lower than about 20 Hz, they're not going to be audible at all.

2) All string instruments require strings which are plenty tight. A wobbly string is just not going to sound.

3) If they the strings were mounted and tensioned properly, and even if they did wake a periodic sound wave, the length and mass of these strings is such that they would, again, vibrate to slowly to be audible.

4) The tension necessary to make such long strings vibrate musically would be considerable to say the least, yet in the guy's booking info page, he lists 6 to 8 small bolts as being all that's necessary for mounting the "sound board" to the stage.

5) Playing a string musically typically requires a displacement that is perpendicular to the string — whether it's bowed, plucked, strummed, or hammered. These create transverse waves. When you hear a beginner violin student play those squeaky tones, he's doing it because his bow is not perfectly perpendicular to the string, so in addition to the transverse waves, he's also producing some longitudinal waves as well. These l-waves are what cause the annoying high-pitched squeaks. Yet the earth harp guy claims that longitudinal waves are exactly his instrument produces. A slinky is a real world example of something that can vibrate entirely longitudinally.

6) His manner of playing the strings is by rubbing them down their length, again, rather than perpendicularly. I may be drawing a blank, but I can't think of any string instruments so activated. The closes analog I can think of is percussion instrument called a "Lion's Roar", or sometimes just generically it is called a string drum. But these don't sound anything like the instrument in the video, and they use cloth strings, not metal. Moreover, as the fingers are drawn along the length of the Lion's Roar, the indefinite pitch slides in pitch the closer the hand gets to the drum itself. The pitch of the notes on the earth harp does not change. If the general mechanics of the vibration are the same, the pitch should change, as fas as I can see.

7) On this guy's website, he says that people in the audience claim a wonderful experience when they are in the middle of the sound field created by the supposedly vibrating strings which are run overhead. But strings themselves don't make much sound at all. They transfer their energy to some sort of resonating body which is where the sound comes from. Even if this instrument did work, the sound would come from the sound box on the stage, not directly from the strings overhead.

8) He claims that these earth harp "installations" turn the performing venue into the instrument itself. For example, when he mounts the strings across some canyon, he claims that the canyon is part of the instrument itself (and he doesn't mean that in the spiritual sense, but the physical one). I don't need to even get into how preposterous this is, much less the notion of playing strings that are stretched across a canyon.

9) On the faster part of the piece that he performs, the articulations are pretty responsive. But in real world acoustics, the larger the vibrating body, the slower it is to speak. That is why flutes are so light on their feet and articulate but contrabassoons are a bit clumsy and indistinct.

10) He's got these wooden blocks mounted to the strings (not mounted at the stopping ends, but mounted within what would be the vibrating body. He claims these blocks placed at different points are what tune the strings. But this can't be. The blocks do not rigidly stop off the string; they just hang there, and all they would do is to impede certain harmonic nodes of vibration, effectively killing the potential for any meaningful vibration. Any yet, the tones in the video are pretty rich in harmonics.

________________________________________

So, am I missing some sort of phenomenon of instrument acoustics, or is this instrument a fake?

My theory of how it actually works is that the pressure he puts on the strings triggers a midi event via some sort of custom mechanism concealed inside the "sound box" mounted on the stage.

Am I wrong? What are your thought about this earth harp. thing? I'm not emotionally invested in wanting it to be fake, but either it is, or I'm really missing something here.

TIA
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Hurkyl
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Jun1-12, 03:57 AM
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I don't know anything about the Earth Harp or its performances. But I can spot some errors in your logic. (Note this doesn't mean you're *wrong*, just that your reasoning is faulty)

Quote Quote by Jiminy View Post
1) You can see the strings vibrating. In fact, you can see them wobbling. If discrete vibrations are slow enough to be seen (the resolution of human eye maxing out at about 30 "frames" per second), those vibrations are going to be very low — much lower than the ones he's playing, and if they're lower than about 20 Hz, they're not going to be audible at all.
You are watching this on TV or on your computer or something, right? That introduces artifacts in periodic motion. The classic example is the "wagon wheel effect" (you should be able to google that).

I want to say you are observing the beat frequency between the actual vibration and the rate of the movie camera, but I'm not confident that's actually correct.


2) All string instruments require strings which are plenty tight. A wobbly string is just not going to sound.
Stringed instruments can vibrate quite visibly. It's been a long time, but the short time I played cello, I certainly remember being able to actually see the standing waves; they had an amplitude of a couple millimeters. The strings on a double bass can vibrate at even larger amplitudes.


3) If they the strings were mounted and tensioned properly, and even if they did wake a periodic sound wave, the length and mass of these strings is such that they would, again, vibrate to slowly to be audible.
Harmonics.


5) Playing a string musically typically requires a displacement that is perpendicular to the string — whether it's bowed, plucked, strummed, or hammered. These create transverse waves. When you hear a beginner violin student play those squeaky tones, he's doing it because his bow is not perfectly perpendicular to the string, so in addition to the transverse waves, he's also producing some longitudinal waves as well. These l-waves are what cause the annoying high-pitched squeaks. Yet the earth harp guy claims that longitudinal waves are exactly his instrument produces. A slinky is a real world example of something that can vibrate entirely longitudinally.
If a tiny violin string gives a high-pitches squeak, then a very large string is going to 'squeak' in a more reasonable register.


10) He's got these wooden blocks mounted to the strings (not mounted at the stopping ends, but mounted within what would be the vibrating body. He claims these blocks placed at different points are what tune the strings. But this can't be. The blocks do not rigidly stop off the string; they just hang there, and all they would do is to impede certain harmonic nodes of vibration, effectively killing the potential for any meaningful vibration. Any yet, the tones in the video are pretty rich in harmonics.
When I played the cello, I often did this for fun.

Normally, if you draw the bow across the last string, you get A below middle C.

If you lightly touch your finger to the exact center of the string -- not enough to restrict it but just enough to prevent it from vibrating at that point -- then you get A above middle C.

If you do the same thing one third of the way along the string (or two thirds), you get the E above that, and so forth.


The same effect is very important for woodwinds; you can't get high notes without this trick. But rather than block the things off, the mechanism to eliminate harmonics is to open a hole. This, for example, is the main purpose of the 'octave' key that controls the hole closest to the mouthpiece.

In fact, this knowledge was of at least a little help in devising my own fingerings for the very high notes on my clarinet (which helped because sometimes the standard fingerings don't come out strongly or are out of tune).
zoobyshoe
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Jun1-12, 05:32 AM
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Quote Quote by Jiminy View Post
6) His manner of playing the strings is by rubbing them down their length, again, rather than perpendicularly...

...So, am I missing some sort of phenomenon of instrument acoustics, or is this instrument a fake?
It's not a fake. You're missing the fact that rubbing the rods along their length is a perfectly legitimate way to get them to sound, and they don't even need to be stretched or attached at both ends to do this. The flopping of the rods, is, of course, not the source of the sound. They are vibrating at the proper cps just like a wine glass would vibrate when you run a wet finger along the rim.

edit: it looks the second time through that they are, in fact, attached at both ends. There are some weights which looked at first to be the ends, but I think the rods continue past the weights.


zoobyshoe
#4
Jun1-12, 05:47 AM
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Is the Earth Harp real (acoustically)?

How does the Earth Harp work? The Earth Harp is played using violin resin on cotton gloves and musical bows. The performer’s hands are run along the strings to created beautiful cello like tones. The act of rubbing the strings creates a longitudinal compression wave.

This vibration is similar to the vibration patterns that produce tones when you run your finger around the edge of a wine glass. It is also similar to the vibration patterns created while playing singing bowls.

As William Close experimented with some of his early design concepts, he created a method of tuning the giant long strings; using a specially designed tuning block that he discovered could tune the strings to any scale.
http://earthharp.wordpress.com/about/
Jiminy
#5
Jun1-12, 06:14 AM
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Hurky, thanks for the reply!

Quote Quote by Hurkyl View Post
You are watching this on TV or on your computer or something, right? That introduces artifacts in periodic motion. The classic example is the "wagon wheel effect" (you should be able to google that).
It's not that kind of motion. It's not like plucking a guitar string and watching the cumulative effect of the very fast back and forth motion. There are many noticeable discrete vibrations and a lack of tightness one ordinarily needs to get a string to vibrate.

Quote Quote by Hurkyl View Post
Harmonics.
I don't see how it could be harmonics. Ordinarily when only the upper harmonics are audible, they still imply the fundamental. That's why you can perceive lower freqs on earbuds that cannot reproduce those freqs. And if the fundamental is below about 20 Hz, then they imply the first fundamental that is within the range of human hearing. And if the string were low enough to have a fundamental below 20 Hz, then it's going to sound really much thicker and more dissonant than the earth harp, because you're already into the 7th harmonic before you even get to middle C.

Quote Quote by Hurkyl View Post
If a tiny violin string gives a high-pitches squeak, then a very large string is going to 'squeak' in a more reasonable register.
But the earth harp notes are not uncontrolled squeaks; They're fully formed sustains. And the longitudinal artifacts occurring from beginner cellists and bassists are pretty ugly, too.


Quote Quote by Hurkyl View Post
When I played the cello, I often did this for fun. Normally, if you draw the bow across the last string, you get A below middle C. If you lightly touch your finger to the exact center of the string -- not enough to restrict it but just enough to prevent it from vibrating at that point -- then you get A above middle C. If you do the same thing one third of the way along the string (or two thirds), you get the E above that, and so forth.
The artificial harmonics you're talking about can only happen because the player's finger is stopping the string at a node, causing the string to vibrate in whatever multiple that node lies. The woodblocks just hang on the strings, but they're not attached to any sort of more rigid stopping body that would cause the string to vibrate in whole number divisions of itself — plus which the wooden block surrounds the string instead of just touching it.
Jiminy
#6
Jun1-12, 06:29 AM
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Quote Quote by zoobyshoe View Post
It's not a fake. You're missing the fact that rubbing the rods along their length is a perfectly legitimate way to get them to sound, and they don't even need to be stretched or attached at both ends to do this. The flopping of the rods, is, of course, not the source of the sound. They are vibrating at the proper cps just like a wine glass would vibrate when you run a wet finger along the rim.

edit: it looks the second time through that they are, in fact, attached at both ends. There are some weights which looked at first to be the ends, but I think the rods continue past the weights.
I'm not sure what you mean by "rods". He's supposedly making strings vibrate. Very long strings. Sometimes up to a 1000 feet, or sometimes just 30, or anything in between. And though the strings are of wildly varying lengths, according to each different installation, they always somehow manage to produce the same tone and in the same pitch region. Plus which, the acoustical properties of a resonant glass or Tibetan singing bowl are very different from the vibrating properties of a string. A string really wants to travel transversely.

The only way I've ever seen of making some sort of noise by rubbing a musical string longitudinally is by scraping a coin or guitar pick on a wound string, which of course is a decidedly different sound and effect.
Jiminy
#7
Jun1-12, 06:44 AM
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Hey again,

Yeah, I already read all that stuff from his website, but it gives no scientific basis for the acoustical chain. The gloves and the rosin could be stagecraft, or not, but they don't really give a basis that overcomes any of the red flags I mentioned. And I get the funny feeling that "longitudinal compression" wave was used to make it seem more scientific. "Compression wave" is just another term for longitudinal wave. People don't typically use both at the same time since they're redundant. He mentions the wine glass and prayer bowl, but strings do not behave like either of those.

I may look into whether he has a patent for this. Anyone know where to look for such info on the internet?

Anyway, thanks again.
zoobyshoe
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Jun1-12, 08:32 AM
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Quote Quote by Jiminy View Post
I'm not sure what you mean by "rods". He's supposedly making strings vibrate. Very long strings. Sometimes up to a 1000 feet, or sometimes just 30, or anything in between. And though the strings are of wildly varying lengths, according to each different installation, they always somehow manage to produce the same tone and in the same pitch region. Plus which, the acoustical properties of a resonant glass or Tibetan singing bowl are very different from the vibrating properties of a string. A string really wants to travel transversely.

The only way I've ever seen of making some sort of noise by rubbing a musical string longitudinally is by scraping a coin or guitar pick on a wound string, which of course is a decidedly different sound and effect.
Here you go, check out this video which demonstrates you can get a sound by rubbing along the length of a rod:

http://sciencestage.com/v/16539/sing...ion-trick.html

I had seen this several years ago and assumed, at first, Close was using thin rods.
zoobyshoe
#9
Jun1-12, 01:52 PM
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In this demonstration they do a thing with a styrofoam cup that supposedly proves the vibrations are longitudinal as opposed to transverse:

Jiminy
#10
Jun1-12, 02:08 PM
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Zoobyshoe,

Thanks for the videos.

The problem is that the earth harp does not use rods. It uses wire "strings". I've seen a lot of the videos and he's definitely using strings. Plus, I don't really see any practical way of him being able to get 1000 foot rods all the way to the canyon, or even how you'd get your hands on 1000 foot rods. That's more than three football fields.

And in the video you posted, the guy is holding the rod at the middle, the 2:1 node, creating the pure 2:1 harmonic. The earth harp has strings which are mounted at each end, and the tones produced are more complex, and in spite of them being very long, they speak more quickly than the rod in the video — in fact, they articulate, rather than having the smooth, soft, onset of the rod. That throws instrument acoustics on its head.

And also notice that the rod is swiped nearly half of its entire length, whereas on the earth harp, he swipes less than 10% of the length of the string. And In the canyon installation he'd be swiping less than 1%.

Another problem is that he changes direction when rubbing the strings. That's a disruption in the direction of compression, which should have some artifact, especially on such a long vibrating body.

Moreover, in the two rod videos, the hand has to leave the rod immediately after the swift swipe to allow the rod to vibrate, whereas with the earth harp, the hands remain on the strings.

Anyway, so far I haven't been able to reproduce anything approaching a musical tone by repeating the same rubbing process on viola or piano strings.

At any rate, Zoobyshoe, I appreciate you taking the time to make these replies. I didn't know if anyone would be interested when I made my original post.
zoobyshoe
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Jun1-12, 02:38 PM
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Quote Quote by Jiminy View Post
Zoobyshoe,

Thanks for the videos.

The problem is that the earth harp does not use rods. It uses wire "strings". I've seen a lot of the videos and he's definitely using strings. Plus, I don't really see any practical way of him being able to get 1000 foot rods all the way to the canyon, or even how you'd get your hands on 1000 foot rods. That's more than three football fields.

And in the video you posted, the guy is holding the rod at the middle, the 2:1 node, creating the pure 2:1 harmonic. The earth harp has strings which are mounted at each end, and the tones produced are more complex, and in spite of them being very long, they speak more quickly than the rod in the video — in fact, they articulate, rather than having the smooth, soft, onset of the rod. That throws instrument acoustics on its head.

And also notice that the rod is swiped nearly half of its entire length, whereas on the earth harp, he swipes less than 10% of the length of the string. And In the canyon installation he'd be swiping less than 1%.

Another problem is that he changes direction when rubbing the strings. That's a disruption in the direction of compression, which should have some artifact, especially on such a long vibrating body.

Anyway, so far I haven't been able to reproduce anything approaching a musical tone by repeating the same rubbing process on viola or piano strings.

At any rate, Zoobyshoe, I appreciate you taking the time to make these replies. I didn't know if anyone would be interested when I made my original post.
You're quite welcome. I enjoy odd sound effects. I also still think this thing is perfectly plausible.

I don't think you'd be giving it a fair test unless you tried at least one long wire, say 15-20 feet. A roll of uncoated steel wire (not wound like a piano string, of course) of 20 feet can probably be got at the hardware store for a couple dollars. Maybe you can find a fence of some sort that has a corner so you can string it from one segment to the other. The other thing I am sure he's doing is electronically amplifying it.
Evo
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Jun1-12, 02:59 PM
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Nothing is stranger than the theremin.

http://www.youtube.com/watch?v=BRXsd...eature=related
Evo
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Jun1-12, 03:33 PM
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How the "earth harp" works.

The earth Harp consists of a large tubular aluminum base unit that includes a "bridge" that is the ground level terminus for the roughly 16-20 heavy bronze strings. The bridge is a semi-circular box with an open front, aluminum frame and plywood surfaces that act as a resonant chamber. It is held down by sandbags. There are acoustic microphones set on top of this unit.

The strings are all pulled tight to roughly 30 pounds tension, but since they are played using the longitudinal standing waves, the tension is less important than the length, which they have predetermined mathematically and attached small wooden blocks at the appropriate place on the length of the string. (E.g., middle-C is 42 feet).
continued...

http://www.oriscus.com/columns/earthharp/
Borek
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Jun1-12, 04:03 PM
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Quote Quote by Evo View Post
Nothing is stranger than the theremin.
We are hijacking the thread, Evo will ban us.

http://www.youtube.com/watch?v=mS8eipuXYWg
jreelawg
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Jun1-12, 04:22 PM
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Quote Quote by Borek View Post
We are hijacking the thread, Evo will ban us.

http://www.youtube.com/watch?v=mS8eipuXYWg
Is it a coincidence that those HANG instruments are shaped like flyer saucers?
Evo
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Jun1-12, 04:35 PM
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Quote Quote by Borek View Post
We are hijacking the thread, Evo will ban us.

http://www.youtube.com/watch?v=mS8eipuXYWg
Hey, I went back on topic the very next post.
AlephZero
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Jun1-12, 06:31 PM
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Let's not get too hung up about musicians not undestanding the physics of musical instruments very well. Even the great 19th century physicist Helmholtz managed to get the theory of brass instruments completely wrong, and held up the process of improving their design for several decades until somebody was brave enough to contradict him!

(The mistake survived for a long time because there was no way to check his theoretical assumptions by direct measurements, until electronic measuring devices were available).
AlephZero
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Jun1-12, 06:38 PM
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The strings are all pulled tight to roughly 30 pounds tension, but since they are played using the longitudinal standing waves, the tension is less important than the length, which they have predetermined mathematically and attached small wooden blocks at the appropriate place on the length of the string. (E.g., middle-C is 42 feet).
That's consistent with problems in the design of pianos caused by unwanted longitudinal vibrations of the bass strings "coloring" the sound of higher pitched notes. Middle C is about 262 Hz. The equivalent for a 8-foot-long wire would be 262 x 42/8 = about 1375 Hz, which is in the right ballpark for the problem frequencies with pianos. The speed of sound in most engineering metals is similar, so the different matierals aren't very significant.


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