Music – Instruments – Stringed
Reexamination Certificate
2000-08-28
2002-02-19
Fletcher, Marlon T. (Department: 2837)
Music
Instruments
Stringed
C084S29700S
Reexamination Certificate
active
06348646
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the construction and method for making musical instrument strings. More particularly, it relates to strings having superior corrosion resistance and longevity, low stiffness for improved playability and tonal quality, and low tension at pitch for reduced stress on musical instruments. The present invention is particularly adapted for use with bridged stringed instruments including classical guitar, steel string guitar, violin, cello, dulcimer, banjo, mandolin, bass, etc.
It is well known that strings under tension will vibrate when plucked, struck, or bowed at a characteristic fundamental frequency f
1
, accompanied by a spectrum of n harmonic frequencies, all proportional to the tension and inversely proportional to the mass per unit length of the string (Jeans, Sir James,
Science And Music
, Dover Publications, Inc., New York, 1937, reprinted 1968). This relationship can be expressed for an ideal string of zero stiffness by equation 1:
f
n
=(n/2L)(T/m)
½
[1]
where f
n
is the frequency of the nth harmonic, L is the speaking length of the string, T is the tension, and m is the mass per unit length.
In many cases, this ideal relationship can be used to adequately approximate the fundamental frequency as well as the first few harmonics for real strings under tension. However, since real materials have finite stiff-ness values, they do not completely obey the ideal relationship depicted above (Elmore, W. C. and Heald, M. A.,
Physics of Waves
, Dover Publications, Inc., 1969). Instead, the stiffness of a real string will contribute to the elastic restoring force during string vibration, leading to inharmonicity, particularly with respect to the higher harmonics. Thus, when designing strings for musical instruments, these factors must be considered together with several other limiting factors of practical concern, including the “window of tension” for a particular instrument, the physical properties of both core and winding materials, and the suitability of materials for string fabrication.
For example, lower frequency musical instrument strings are often helically wound with mass loading materials such as alloys of copper, steel and nickel so that the unit mass can be controlled within some “window of tension” without having to increase the speaking length or the mass of the core string. Otherwise, the speaking lengths for bass strings would be unrealistically long, and/or the diameter and mass would be too high, leading to high stiff-ness, reduced tonal quality, and difficulty with fingering during instrument play.
The “window of tension” is determined in part by the construction and design of the instrument, and specifically by the cumulative tension that can be sustained when a plural set of strings is tuned to pitch. Thus, if the tension is maintained at too high of a value, the instrument can be permanently damaged. If the tension is too low, then unwanted resonances and buzzing noises may occur. For example, the cumulative tension for strings on a “classical guitar” is typically between 75 and 100 pounds, whereas the cumulative tension on a steel-stringed acoustic guitar can be as high as 190 pounds.
Like string stiffness, tension can also affect “playing action”, or the pressure required for fretting during play. There is some latitude for tension adjustment with conventional string materials, as long as the cumulative tension falls within the “window of tension” that provides the best overall response from the instrument. For example, it is possible to reduce the diameter and hence stiffness and tension of steel core strings, but only to the point where the strength, loudness, and sound quality are not seriously compromised.
In addition to the “window of tension”, musical instrument string designers are constrained by the physical properties of conventional materials. Although some material improvements have been made, the most commonly used materials for the cores of wound musical instrument strings still include polymers such as synthetic nylon or natural “gut”, and steel (for example, music spring wire that is currently manufactured according to ASTM A228 specifications).
A core material must have the ability to maintain dimensional stability without breaking under tension. Hence it must possess the combined characteristics of high tensile strength, low creep, high yield strength, and low ductility. On the other hand, windings, such as those used with conventionally wound steel core strings, are typically made of softer, more ductile metals such as alloys of copper, steel, or nickel. These alloys can possess various degrees of hardness or temper, and are typically chosen for their ability to control the mass per unit length, and for their ductility or yield characteristics for ease of manufacturing.
Although the use of metal windings has historically enabled designers to control mass per unit length and hence pitch, one inherent problem with wound strings is that the windings tend to move, slip, and re-position themselves with respect to the core during end use. This leads to increasingly higher frictional losses and vibrational damping, with the upper harmonic frequencies being particularly affected. Gradually, the tonal quality deteriorates and the string loses its “liveliness” and “brilliance”. The problem may be partly related to stress relaxation from winding recoil, but it is also compounded by interfacial deterioration from corrosion at the core/winding interfaces, and from yielding of ductile interfacial materials such as tin or tin alloys. Steel core corrosion byproducts such as Fe
2
O
3
are also weak oxides, and can easily spall, leading to mechanical losses and oxide particle contamination which can further dampen vibrations and negatively impact tonal quality. Together, these problems ultimately lead to what many musicians recognize as a “dead” string.
Furthermore, conventional strings have a limited shelf-life, and often require special packaging considerations and/or storage conditions to prevent corrosion, and to preserve their tonal characteristics prior to use. In some cases, strings which have been stored for long periods can become weakened from corrosion, and can break when attempts are made to tune the strings to pitch. In other cases, the otherwise “new” strings can exhibit the tonal characteristics of “dead” strings simply because they were stored too long before use.
Several prior art examples have addressed one or more of these issues through methods and constructions aimed at improving the longevity of wound strings. U.S. Pat. No. 210,172 to Watson and Bauer (1878) disclosed the first use of polygonal shaped core wires that unlike round cores, help to prevent winding recoil both during manufacture and in end use. This technology is still commonly used today for steel core wires of wound guitar strings such as the hexagonal steel cores used by J. D'Addario & Company, Inc. in their Phosphor Bronze wound acoustic guitar strings.
U.S. Pat. No. 2,746,335 to Johnson (1956) discloses a concentrically wound core wire where the inner wire is terminated in a tapered gripping fashion over a flattened section near the core end. The purpose is to maintain winding tightness and to prevent buzzing. U.S. Pat. No. 5,535,658 to Kalosdian (1996) discloses a plurality of metallic inner wrap wires wound about a central metallic core, and concentrically wound with an outer wrap of metallic wire over the speaking length of the string to maintain tightness of the inner windings over time. The outer wrap traverses the speaking length of the string and thus it contributes to the mass per unit length, the tonal quality, the diameter, and the string stiffness accordingly. U.S. Pat. No. 3,605,544 to Kondo (1971) discloses a musical instrument string with a core wire and a helically wound covering wire where the winding pitch is greater than the diameter of the covering wire. The purpose is to eliminate contact between adjacent turns so that frictional losses at winding inter
Parker Anthony
Rohrbacher Peter J.
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