Thanks for visiting.  I think you'll find this site very interesting.
                  Frank Geiger

About Me, Musical Sound, Tools and Methods

I Would Like To Introduce Myself

     I'm a retired Army Officer (Lt. Col.), former sales person of computer aided design and manufacturing systems and computers, former college instructor of mechanical design engineering and mathematics, and, until I broke my hip in 2015, a musical solo entertainer performing old popular hits for seniors on tenor banjo with vocals in the Greater Atlanta, Georgia area for 26 years.  That's my fifteen-year old picture on the right holding a 1927 Paramount tenor banjo.  

     For the last 10-15 years or so I've spent a lot of time trying to improve the sound of banjos, guitars, mandolins and violins with my own inventions on my own instruments. It was during this period that I began to teach myself, mainly through experiments, about musical surface acoustic waves (SAWS).  During this time I patented six of my inventions and sold some by mail to my fellow musicians.  Now my goal is to share what I've learned about musical surface acoustic waves over this website and, hopefully, in a book which I plan to write.  At my age (81) I should start now and write fast!

     Musical Sound. (What is it and how should it effect our goal?)

       I have always loved music in most forms and especially songs sung with a crystal clear voice and accompanied by a fine acoustic instrument.  I also love the words in songs, sometimes even more than I do the music.  I've often wondered why, but it really doesn't matter.  The love of music is simply a gift many of us share gratefully.

     One reason that so many of us enjoy music is probably related to how human brains evolved since they lived in caves, an idea supported by the fact that bone flutes have been found in caves populated by the first humans.  So it is worth thinking about what was so appealing about the sound that would come from such an instrument.  It would not be a pure tone, a single frequency like the sound of a tuning fork, but a  rich sound containing many frequencies which today we would call musical sound.   Perhaps a sound beautiful beyond measure in the smallest spaces in the cave, where the cave walls would not cause excessive echo but would amplify sound quality-enriching harmonics, (explained below), just as our voices sound great when we sing in a shower.

     Today we know that the most pleasing sounds are those composed of a basic frequency tone plus other sounds composed of frequency multiples of the basic frequency tone called "harmonics" which make the sound  "rich" and have apparent "depth".  Mentally compare the sound of a single note played on a tuning fork and one played on a fine violin and you will understand what musical sound is and understand the importance of harmonics to music.

     My Goal.  Considering the above description  the goal of my experiments might be restated with more meaning, from simply, "improving volume and sound quality" to "improving volume and sound quality by capturing and making audible a good range of musical frequencies including the most important several harmonics of each fundamental frequency played".

     My Approach to Achieve this Goal is Based on an Assumption.  

    Assumption:  When an acoustic stringed musical instrument is played all surfaces of the instrument are covered in varying degrees with surface acoustic waves.  In my experiments these waves were copied, (e.g., "picked up") by placing them in firm contact with a material that is easily deformed into the shape and timing of the surface acoustic waves being copied.  Such materials included: some acrylic tapes, threads, waxed, braided nylon cord, and thin shapes of metals, woods and papers.  The copied waves, which included harmonics, were then sent to the instrument's sound chamber where they are converted into audible sound to mix with the normal sound from the instrument.  The result was, or should have been, highly noticeable improved volume and sound quality from the instrument.  My most recent success with the dual high and low frequency banjo amplifiers (Described in detail in downloadable documents on the Downloads Page) strongly suggested that this assumption is valid.

The Following Paragraphs Describe Observed Surface Acoustic Wave Behavior After Using The Mentioned Tools and Methods To Create Our Devices:

Surface Waves Travel Best Along Edges of Surfaces.  This can be explained by wave behavior that I like to call,"whip action".

     Some warm Spring or Summer day you can see "whip action" of a surface acoustic wave for yourself if you disconnect a 50-foot garden hose from its faucet at your home, drain it of any water, stretch it out in your yard in a straight line, lift one end high above your head, bring it down suddenly and forcefully to your feet and then let it go.  This action will create a large "hump" in the hose, a surface acoustic wave, that will travel down the length of the hose.  When the hump gets to the far end you will see the end of the hose rise suddenly to approximately twice the height of the hump, (amplitude of the surface acoustic wave), because there is no hose beyond the end topull it down and keep it from whipping upward in this manner.  This same behavior occurs with any whip but this is more easily seen by whipping a garden hose.

      Any surface can be viewed as a series of whips connected side-by-side such that a disturbance to one causes a wave to travel down that whip and, a moment later, another similar wave to travel down its adjacent and connected whip, and similarly for the next connected whip, etc.  The result is a wave of whip tips traveling along the far edge with approximately twice the height of the wave on the interior of the surface.  

     This fact suggests that staples and other motion limiting components should not be located on or near the edges of surfaces,

     Circular holes are also edges but are unique in that they favor frequencies which have wavelengths that would divide evenly into the the circumference of the hole, which would create a standing wave on the hole edge.  Many holes, such as holes on banjo flanges and f-holes on bowed instruments, are not circular and do not have this standing wave problem.  (This website does not address the design of sound openings of bowed instruments, most of which are familiar "musical f-shapes" or the behavior of waves on edges containing right angles.) 

     Looped Surface Wave Paths.  One would think that looped surface wave paths composed of any material would be an easy and highly desirable way to amplify surface waves, because waves in loops would would eventually encounter themselves at an angle and amplify by the wave principle of "Constructive Interference".  This desirable end does not occur because the waves make multiple loops which causes some waves, especially those of short wave lengths such as harmonics, to arrive significantly late to their starting point and cancel, not amplify, themselves.  Looped surface wave paths cause a very noticeable loss of sound quality when the wave is eventually made audible,and so should be avoided.   It should also be mentioned that looped paths can and do occur on any surface such as rectangles. Such looping is good for low frequency waves (which have longer wavelengths) because it will amplify them with little wave delay distortion when waves complete their loops.  But that is not true of high frequency (shorter wave length) waves including harmonics which are more suseptible to wave delay distortions.  Since surface waves travel faster on dense materials such as metals it is a good idea to have separate amplifiers for high frequency waves made of thin metals such as brass or steel and use smaller shapes.  Separate amplifiers have worked very well in the new dual banjo amplifier pair which uses creased, folded brass foil in the high frequency amplifier and a larger, stapled Kraft paper pair of like surfaces (virtual fold) in the low frequency amplifier.


Waxed Braided Nylon Cord

​     Waxed, braided nylon cord has proven to be ideal to transfer surface acoustic waves over longer distances and through the sound openings on guitars, mandolins and violins.  This is because the braids of the cord's fibers intersect at an angle which causes waves on those fibers to intersect at an angle.  This intersection of waves at an angle causes therm to amplify multiple times down the length of the cord by "Constructive Interference" as defined earlier. This amplification can be increased by compressing the braided fibers, which causes  more waves to intersect and so amplify.  Waxed braided cord also has the advantage that it causes minimum distortion to the instrument's sound producing waves on the edge of its sound opening when it is necessary for the cord to enter the sound chamber, such as through the sound opening.  Once in the sound chamber audible sound hitting the cord is believed to create additional surface acoustic waves on the cord's fibers for  processing by our amplifying device located at the end of the cord.