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  • In search of the lost chord....

    In search of the lost chord...

    That really describes it well. This is where machining meets natural science and music.

    I have built an Aeolian Harp. It's something I have had in the back of my mind for many years and now I have finally found the time and motivation to do it.

    An aeolian harp is played by the wind. It can be extremely simple as mine is, or very complex. They can be very large, or small enough to hold in your hand. In all cases the sounds they produce are otherworldly and very unexpected.

    There is a major drawback, an aeolian harp is a very quiet instrument. I have addressed that issue in my design in a couple of ways. It has an efficient mechanical audio amplifier coupled to an efficient electronic audio amplifier and FM transmitter. This makes it possible to listen to the sounds of the weather and celestial spheres in the comfort of our living room.


    This is it:

    It consists of two steel poles designed to be just placed on the ground and anchored by concrete blocks One pole is tall in order to catch the wind better and the other is short to make for easy access and adjustment. Between the poles is stretched a wire, in this case a multi stranded 12 gauge copper wire.



    The low end is where the sound is amplified and captured. The mechanical amplifier is a carefully constructed (un)tuned cavity with many resonance modes. The front and back plates are essentialy flat and parallel but the inner side walls are sloped steeply at about 45 degrees from back to front. The outside diameter is 8". The inside diameter changes from about five inches to seven inches over a distance of 2 inches describing a conic volume. This prevents the cavity from developing a standing wave and resonating at only a single frequency. The front plate is aluminum flashing mounted so that the resonating chamber is airtight. A good quality condenser microphone is installed in the rear plate. The harp string (wire) is stretched from the front plate to the tall pole top end.



    It was a windy day today which is what decided me to complete (nearly) this project. I have been working on parts of it for several weeks and have been testing various wire types during that time. I have not referred to any plans or other similar information as I have always had a good idea of what I wanted to build. I'm not sure there are any plans or information on something such as this harp.

    Here are some more views.



    The harp is a success. It works better than I expected. The sound is very hard to describe. It is very rich and complex with a base chord consisting of many harmonics and higher chords that may fade in and out with changes in the wind. There is also an underlying deep bass rumble that on one occasion rattled the windows via my surround sound system. It sounds almost like an electronic therimin implementation of a harp. It isn't disharmonious either with the chords being harmonically related.

    I am recording the sounds and will edit together a sequence that I will post here sometime tomorrow most likely.

    Technical notes:

    The resonator is made from old surface grinder diamond/CBN wheel hubs. The transmitter uses a stable FM transmitter circuit that has a separate LM386 IC op amp set for audio gain of 200. This frequency modulates the oscillator stage. The oscillator stage is well isolated from the final amplifier stage and is only lightly coupled to the final amp by a 2pf capacitor. It's a very stable design and draws about 70 milliamps at 8 volts to produce about 200 milliwatts of final output power. It has been tuned to operate on 106.90 mhz by using my frequency counter. I used surface mount techniques for the transmitter and the PCB was milled using the method that I have previously shown. I developed the layout for the board so that only the separations between conductor islands need be milled with the entire back side of the board serving as a ground plane. Many of the components are surface mount parts.



    In this area we have no FM stations that operate above 100 mhz. The nearest one is hundreds of miles distant so interference is not a concern.

    The power for the transmitter is supplied by an industrial quality set of six 4 amp hour nicads. They are maintained by a solar panel capable of supplying 1/3 amp at 12 volts in full sun. I still have to mount the solar panel and finish a few details on the transmitter, mainly installing the weather proof housing. The housing was originally for a ku band block downconverter.

    I expect the harp to do more than just respond to the wind. The audio is very sensitive and so far I have identifed the sound of falling fir needles hitting the wire. I am sure that rain will also have a signature and won't be surprised to hear snowflakes when they strike the wire. Temperature also plays a big part in the nature of the sound. Simply blowing some shop air on the front of the resonator causes an almost immediate change in the resonance patterns and sound quality. From only the small amount of cooling produced by the compressed air the basic background chord goes up in pitch by about half an octave.
    Last edited by Evan; 10-24-2007, 03:12 AM.
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  • #2
    OKAY, what was the "organ" that you stood in front of and waved your arms to create a rf disturbance?

    I think the "fish" sounds of a local creek was my favorite.

    (actually I think you are setting up a snare wire for thieves) A clothes line at neck level works best.
    Excuse me, I farted.

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    • #3
      The "organ" is the Theremin I mentioned, invented by Leon Theremin.
      Free software for calculating bolt circles and similar: Click Here

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      • #4
        Can't wait to hear it. I miss the sound of the wind, down here in the quiet of the desert. Perhaps someday a live feed, to a website? I would like to tap into that.
        Allan Ostling

        Comment


        • #5
          I think it's pretty neat! Can't wait to hear what kinds of sounds it can generate.

          I can't imagine why multi strand wire of either steel or copper would be better than single strand tempered wire such as hard drawn mig wire or staple wire as used by some ham's for their long-wires. I would expect the multi strand to pickup more noise from the strands interacting and if anything, to null sound waves rather than transmit them unblemished. I have some wire I bought at a yard sale. They guy didn't know what it was but it looks like music wire only too much of it to be so. I think it's stainless as some used in the garden is still pristine. If you needs some, pm me a address and I'll get you off what ever you need. This coil weighs about 30 pounds.

          BTW, did you ground this wire or does it float above ground?

          (Oh to live in a community where the streets are paved in aluminum to feed my small machine shop )
          Last edited by Your Old Dog; 10-24-2007, 06:20 AM.
          - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
          Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

          It is true, there is nothing free about freedom, don't be so quick to give it away.

          Comment


          • #6
            I think Iv heard them sounds before, Its almost like a high frequency elk call, Iv heard them from the telephone/electrical line wires when the wind gets going at a steady pace, Personally I like the sound of the ocean and of wind in the pines, the sound pine needles make in the wind have a remarkably soothing effect on me.

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            • #7
              It certainly doesn't sound like an elk call. I'm trying to clean up the recording I made yesterday but I was using a very mickey mouse setup and the quality sucks. Of course, the wind died down this am as soon as I hooked up a direct input to my computer instead of recording from the speaker.
              Free software for calculating bolt circles and similar: Click Here

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              • #8
                Originally posted by Evan
                Of course, the wind died down this am as soon as I hooked up a direct input to my computer instead of recording from the speaker.

                Thats Murphys Law Evan, it states that when it really matters it wont happen!

                Not to change the subject but You and many others here are outdoorsy kinda Guys and there is something thats had me curious for many years as im not a hunter and heard many hunters describe that an Elk gets its "wistle/bugle" from its rear teeth -------- Iv even seen these magical teeth and cant see how this happens, being of the curious type the thing that reminds me most of an elk wistle/bugle/whatever is blowing threw flex gas line, furthermore, because I could not except the fact that these little teeth are doing this I asked a hunter friend what an elk esophagus looks like and he discribes a series of ridges of high low in the I.D. , I then stated to him that this is where the elk gets its distinct sound and he said he didnt think so because of course he said it was the teeth, to which I reply'ed -- have you ever blew through a flex gas line, and he said thats what they use to call an elk --- to which I reply'ed -------------------- Bingo,,,,,,,, Then he itched his head,,, what do you catdz think?

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                • #9
                  Wow, very cool. I would very much like to hear the clips.

                  -----------------
                  If you change the transistor on the right of your circuit with a Jurgonsenn TL2665A cross-harmonic modulator, it will double as a death ray. Hope this helps.

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                  • #10
                    Evan,

                    interesting project. i can't wait to hear the sounds!
                    i've seen instances where strips of fabric tied between two points will start fluttering in the wind. is this basically what happens with the wire for the harp?

                    andy b.
                    The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

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                    • #11
                      I can remember this guitar player at a party, a bath tub full of 190 grain and grape juice and citrus, and god know's what else people dropped in.. He had his head laying on his guitar talking to it..

                      In a little while he turned it up, it was picking up truckers talking, a poor linear amplifier kicker with a loose antennae connection makes a broadband broadcast.

                      He had thought he was talking to god.

                      EVAN: are you in the grape juice? HA.. just a old brain cell that connected for a moment.

                      Yes it was a therimin noise generator.
                      http://www.rachelhamilton.com/listen.html A hippies toy? Too many drugs? Okay, I listen to pink floyd myself.. and Roger Waters is still the king. Gimme a slice of white bread..
                      Excuse me, I farted.

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                      • #12
                        OK, since it doesn't look like the wind will pick up I will post a piece. It will give you some idea anyway even if the quality sucks. Give me a few minutes.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          Originally posted by A.K. Boomer
                          Not to change the subject but You and many others here are outdoorsy kinda Guys and there is something thats had me curious for many years as im not a hunter and heard many hunters describe that an Elk gets its "wistle/bugle" from its rear teeth -------- Iv even seen these magical teeth and cant see how this happens, being of the curious type the thing that reminds me most of an elk wistle/bugle/whatever is blowing threw flex gas line, furthermore, because I could not except the fact that these little teeth are doing this I asked a hunter friend what an elk esophagus looks like and he discribes a series of ridges of high low in the I.D.
                          Not to stray too far from the thread but a big Negative on that. Elk make their unique whistling sound as they purse their lips and the air passes between the two sides of their hoof

                          We now resume the thread in progress
                          - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                          Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

                          It is true, there is nothing free about freedom, don't be so quick to give it away.

                          Comment


                          • #14
                            Somehow I thought this was a Moody Blues thread

                            http://en.wikipedia.org/wiki/In_Sear...the_Lost_Chord

                            By the way Evan, nice job of mixing interests to produce something totally useless but pleasing to the builder.
                            Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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                            • #15
                              Originally posted by Spin Doctor
                              Somehow I thought this was a Moody Blues thread

                              http://en.wikipedia.org/wiki/In_Sear...the_Lost_Chord

                              By the way Evan, nice job of mixing interests to produce something totally useless but pleasing to the builder.

                              That was my first thought! 'Hey, I have that album!'

                              now I'm going to hum Timothy leary's dead all day......

                              ken.

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