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Joined: December 08 2014
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Topic: Does the Earth Harp really do that? Posted: February 19 2015 at 14:10
I remember seeing a description of the long thin wire you built in your music thread - very cool - in the back of my mind I was already toying with implementing something like it for a day or two in physics class. The students already flip out when they realize you don't need electricity from the wall to make a home-made speaker function. I think this would be a big hit and a good review of resonance while introducing magnetic fields. At the moment we only discuss magnetism in conjunction with speakers and microphones.
Ellen Fullman most certainly demonstrates that the Earth Harp is possible, but I agree with your reservations - the performances I'm seeing don't look right.
Those versions of O Fortuna are extremely lackluster. I want the full orchestra and choir.
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Posted: February 19 2015 at 04:32
Even though I have shown the physics of how it could work and shown video of Ellen Fullman playing a long string instrument, the Earth Harp could still be just a midi trigger like Jean-Michel Jarre's Lazer Harp. The lazer harp does not generate sound itself, breaking the light beams merely sends a midi trigger to a synthesiser. It is relatively simple electronics to make pulling on the strings operate switches, but I don't think this is how the Earth Harp works because it could easily be some well-choreographed miming. I have a suspicion that this is the case in some of the Earth Harp's live performances.
The more I look into the Earth Harp the more convinced I am that it *can* work and it *can* make music, however, none of this has dispelled any of the reservations and concerns I have regarding the AGT "performance" and other performances seen in video's on YouTube.
For example, these two wearisome performances of O Fortuna from Carmina Burana played by the Mass Ensemble certainly raise more doubts and concerns than they really should.
The first thing you'll notice here is the Earth Harp sounds a lot different to the AGT performance, it sounds a lot less like a synthesiser and a lot more like a violin or viola. This cannot be explained by differences in location or environment since the O Fortuna pieces are also played in different locations and environments yet the tone and timbre of the harp remain the same. Even with two different players (Andrea Brook and William Close respectively) the hand movements should have been more-or-less the same since the tone and timbre of the sounds made are pretty much identical, yet here their gestures are different, they are playing different strings for the same note and, more surprisingly, Ms Brook is playing more notes than Mr Close. Now you could explain this as differing levels of ability and different tuning of the strings on those particular days, but it does not seem rational or logical to tune the harp strings to completely different tunings to perform the same piece of music.
Many years ago I created a replica of Alvin Lucier's 'Long Thin Wire' installation. This is an electronic instrument where a metal wire is stretched between two fixed points, a pair of strong magnets are placed either side of the wire so when an electrical signal is passed through the wire the resulting electrical field interacts with the magnetic field of the magnets to produce a transverse movement in the wire, microphones are then used to pick up the resulting sound-waves created by this transverse movement. This works in exactly the same was as a loudspeaker so the pitch that the instrument creates is produced solely by the frequency of the electrical tone fed into it.
While it has a natural transverse resonance due to the tension in the wire, longitudinal waves can be set up in it as these transverse vibrations reflect off the fixed points at either end and they will last as long as the string is vibrating if (and only if) those vibrations are harmonically related to the string length. Basically, this installation reproduced some tones better than others due to these resonances rather than any specific tuning of the wire. Lucier would feed this with a constant low-frequency tone and then record the subtle modulations of the sound and other ambient noises over an extended period of time. He released an album of this called Music On A Long Thin Wire.
In my version, I used two large tin cans at either end to amplify the sound it produced so that it resembled the tin-can telephone shown earlier; and rather than use two magnets I used the earth's magnetic field. I don't have photographs of it, but here is a crappy 3D representation of what I made:
I discovered that by changing Lucier's design in this way not only could I make sounds by feeding electrical currents through the wire, I could also "play" the wire acoustically, either by plucking it (twang) or rubbing it (drone). Acoustic sounds could also be made by the wind vibrating the wire (like an aeolian harp) and by any extraneous ambient sounds that vibrated one diaphragm traveling longitudinally down the wire to the other (tin-can telephone).
I also realised that I had created what was essentially a very long spring-reverb that altered the sound produced by the electrical signal passing through it. Rather than feed this with a constant tone (I believe drone music is far more interesting to play or produce that it is to listen to) I played note sequences and even whole tracks of music through the wire and re-recorded it from the tin-cans using standard studio mics.
So the acoustics of the wire in this installation are pretty complex and results in some very strange and unusual sounds. In principle the Earth Harp is an acoustic version of the "long thin wire" using several tuned wires to create a scale of notes, and as I have said before, in theory it *can* work but the videos do not adequately demonstrate that it does work in practice.
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Posted: February 18 2015 at 21:11
Thank you very much for the Ellen Fullman videos, Dean. I hadn't hit on these.
Seems like you and I were thinking along very similar lines about the Earth Harp. A question came up as to whether the strings' excitation might be used to flip an electronic switch, thus causing the sound to happen but not truly being the source of the pitch/timbre, but in that case you might as well just be playing an overly-complicated keyboard.
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Posted: February 18 2015 at 04:37
The pushing down part of the playing concerns me too. Pushing down only really affects the tension in the string and that should not change the pitch as the longitudinal wave frequency is independent of string tension. Pushing down, however, would tend to block or dampen the longitudinal wave, making it harder to produce any sound at all.
Like in a similar instrument called a friction drum, the sound is created in the diaphragm or sound-box, the string is merely the tuned excitation part of the instrument and it is excited by the friction of the players fingers against the surface of the string. To prevent downward pressure from dampening the sound, this is achieved (as the Fullman videos show) by lightly pinching the string betwixt forefinger and thumb and rubbing (pulling or pushing) in the direction of the string.
I also said the resonance doesn't sound right to me. The resonance of an instrument can be demonstrated by how long the note lasts (decays) after the excitation has been removed. A solid object like a string has no natural longitudinal resonance, its resonance is transverse so to create a note that lasts after the excitation has stopped the longitudinal wave needs to set up a sympathetic (i.e., harmonic) transverse vibration in the string. As I showed in an earlier post, the tension in the Earth Harp is too low to produce audible transverse waves so any sound produced should stop immediately once the player stops rubbing the string. In some videos of the Earth Harp that appears to happen, in the Simon Cowell "talent" circus performance the notes sound out after Close has stopped playing.
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Posted: February 17 2015 at 20:27
Not to mention, he's creating the sound by pushing down (thereby raising the pitch) and moving his hands on the strings. With strings that loose/light, it'd be very difficult to actually create a consistent pitch, even if he could create an audible one. The slightest change in pressure could cause wild variations in pitch, a far cry from the consistent pitches you hear in the video.
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Posted: February 17 2015 at 19:23
Here comes the maths...
First thing to note there is the frequency is inversely proportional to the string length - if we use the same wire gauge and keep the tension the same then as the length increases the note pitch will decrease. So a 33cm string tuned to 440Hz will drop in tone to 4.4Hz if you just increase the length to 33m and keep all other factors the same. 100 times the string length = 1/100th of the pitch
Therefore, to maintain an audible pitch of 440Hz you need to increase the string tension, and because the pitch is proportional to the square-root of the tension this means that for a 100 fold increase in length the tension increases by 100x100 or 10,000 times.
So for the Earth Harp the string tension should be something like 10,000 times that of a violin, yet the strings in the video are slack. Also, wire of the light gauge seen on the Earth Harp cannot withstand the kind of tension required to make a concert pitch note.
So, can it still make an audible sound?
The answer is yes it can, kind of, but not in the same way a violin or piano does.
In all existing stringed instruments, the sound wave is generated by a transverse wave (vibration) in the string caused by the pick, hammer or bow acting at right-angles to the string length. The vibrating string vibrates the air and we hear the sound because the string is vibrating from side to side. To acoustically amplify this sound all stringed instruments use a bridge to transfer this side to side motion to a sound-box. This bridge is perpendicular to the string because the movement of the string is perpendicular to its length.
However, if you've ever made a tin can telephone like the one used by these two young ladiees:
Then you will know that a sound wave can also travel along a string, and this produces a longitudinal wave that can only be heard by a diaphragm or sound-box at either end that is in-line with the string, as opposed to perpendicular. If one end is fixed then this longitudinal wave can still exist if the material is sufficiently elastic (think Slinky™). Now string tension is less important, as long as it is taut enough to be rigid then a standing longitudinal wave can be induced, the pitch of the longitudinal wave is now dependent upon string length and can be "tuned" by fitting mass-dampers (weights) at a fixed point along the length of the string, this alters the effective length of the string in the same way as finger-hole alters the effective length of the tube in a flute (wind instruments are essentially longitudinal wave instruments). Like the finger-holes in a flute or bassoon, once the weighted block has been positioned in the correct place it should never go out of tune. It also means that the length of string past the block is superfluous and plays no part in the generation of sound, whether that length is 1 metre or 1000 metres is immaterial, only the length from the floor-mounted sound-box to the block is important.
I still think the strings are too slack in the video even to produce a longitudinal wave, but the physics is reasonable in principle. I'm not sure that a longitudinal wave can be made by lightly stroking a wire with woollen gloves (even when dusted in powdered rosin), if you've ever made a wine glass whine then you'll know that a fair bit of pressure is needed to make it hum.
I also suspect the tone and timbre of the sound produced is synthetic and not the result of a standing longitudinal wave, the resonance just doesn't sound right to me.
Here is an example of a longitudinal wave stringed instrument being played by Ellen Fullman:
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Posted: February 17 2015 at 13:22
My technical opinion ... it's not doing what you are supposed to think it is.
His claim that it is "the largest stringed instrument on the planet" is misleading. It is an instrument and it has strings but that's as far as it goes. To be classified as a stringed instrument, the strings have to be the source of the sound-waves, I seriously doubt this is the case in the Earth Harp (and I mean very seriously).
I suspect that Jamie and I will agree on the reasons why we have strong doubts here, string tension being the most obvious, there are also issues of the sounds being made and the actual playing itself.
Smoke and mirrors (and showmanship) is a strong possibility to be frank, even if it were just a midi-trigger (like JM Jarre's Lazer Harp) then I still have issues with how it is being played and how the strings are moving.
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Posted: February 12 2015 at 01:10
William Close (and an entourage) tour with a massive instrument they call the Earth Harp. If you check out the video below, you'll get the idea.
I personally have a strong suspicion, however, that it's all basically smoke and mirrors - that they just synthesize sounds and play them while someone runs gloved hands along the strings. I have reasons why I think that, but don't want to bias others right from the get-go. I'm curious what your impression is.
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Does the Earth Harp really do that?
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