JPH0614447B2 - Audio cable - Google Patents

Description

TECHNICAL FIELD The present invention relates to an audio cable used for a lead wire and a cord of an audio device such as a stereo device.

[Prior Art] Conventionally, general electrical tough pitch copper wires or oxygen-free copper wires are used as cables for lead wires and cords of audio equipment.

By the way, the characteristics of this cable have a great influence on the sound quality of audio equipment. For example, it has been evaluated that a cable using oxygen-free copper with a small amount of chemical impurities can obtain a superior sound quality as compared with a cable using general electrical tough pitch copper. Therefore, the oxygen content is 5
A wiring material has been proposed in which oxygen-free copper of 0 ppm or less is heat-treated and drawn to orient crystal grains in the lengthwise direction (Japanese Patent Laid-Open No. 60-3808).

[Problems to be Solved by the Invention] However, even if a normal oxygen-free copper having a purity of about 99.99% by weight (4 Nine level) is used for an audio cable, it has a feeling of transparency and sound compared to live music. However, there is a problem that the satisfactory sound quality cannot be obtained because the spread of the sound is still insufficient.

The present invention has been made in view of such problems,
Excellent sound quality such as transparency and sound field spread,
It is an object of the present invention to provide an audio cable capable of stably obtaining this excellent sound quality.

[Means for Solving the Problems] The audio cable according to the present invention has a residual resistance ratio of 300 or more depending on the amount of solid solution impurity elements in the copper matrix and an average crystal grain diameter of 10 μm or more. It is characterized by being composed of a conductor.

[Operation] The area of the crystal grain boundaries of copper used in the conductor portion of the audio cable has a great influence on the sound quality of the audio device, and the sound quality deteriorates as the area of the crystal grain boundaries increases. This is because the crystal grain boundary becomes a physical defect, and the electric resistance of the copper single crystal portion is different from the electric resistance of the crystal grain boundary portion. Impurities contained in the copper conductor are segregated in the crystal grain boundary portions, and the crystal grain boundaries of the copper conductor have a larger resistance value than the single crystal portions in the grains due to the impurities. As described above, the crystal grain boundaries have a large electric resistance due to physical defects and chemical impurities, and when the area of the crystal grain boundaries increases, the audio signal cannot be smoothly transmitted due to the difference in the electric resistance. Therefore, if the area of the crystal grain boundary becomes large, the sound quality deteriorates.

Meanwhile, the amount of impurities and the residual resistance ratio (Residual Resistance
Ratio; hereinafter referred to as RRR),
The larger the RRR, the lower the impurity concentration.

The residual resistance ratio RRR will be described below.

The electrical resistance ρ (room temperature) of copper at room temperature is expressed by the following equation according to Matthiessen's Rule.

ρ (room temperature) = ρ (therm) + ρ (chem) + ρ (phys) where ρ (therm); resistance due to thermal vibration of crystal ρ (chem); resistance due to chemical impurities ρ (phys); due to physical defects Resistance Generally, the residual resistance ratio RRR is defined by the following equation.

RRR = ρ (room temperature) / ρ _4.2K Here, ρ _4.2K is the electric resistance at the liquid helium temperature and is represented by the following formula.

ρ _4.2K ≈ρ (chem) + ρ (phys) In this case, since ρ (room temperature) >> ρ _4.2K , the following approximate expression can be obtained.

RRR ≒ [ρ _{(RT) -ρ 4.2K] / ρ 4.2K ≒} ρ (therm) / [ρ (chem) + ρ (phys)] Therefore, if the temperature is constant, the residual resistance ratio and the resistance due to chemical impurities , Is inversely proportional to the sum of resistance due to physical defects. That is, if the purity decreases and ρ (chem) increases, and the grain boundary area increases and ρ (phys) increases, RRR decreases. In other words, the greater the RRR, the less chemical impurities and the less physical defects. In this way, there is a close relationship between the factors affecting the sound quality and the RRR.

Impurities in copper include those that are precipitated such as SiO ₂ and Fe ₂ O ₃ and those that are solid-dissolved in the mother phase. However, precipitated large particles such as SiO ₂ and Fe ₂ O ₃ do not contribute to electric resistance. The impurities that affect the electric resistance are impurities that are solid-dissolved in the copper matrix. Therefore, in the present invention, an audio cable having excellent sound quality is defined on the basis of the residual resistance ratio (RRR) which depends on the amount of impurities dissolved in the copper matrix.

The solid solution impurities have the following two existing states. First, it is an interstitial impurity, and this interstitial impurity includes a gas component element such as hydrogen. In the case of copper, the interatomic distance is 2.56Å, and there is a gap of 1.06Å between the copper atoms. Since H-H is 0.74Å, it can penetrate into the gap between the copper atoms. On the other hand, O-O, which is also a gas component, is 1.21Å and cannot normally enter. When lattice defects are present, oxygen may form a solid solution as a substitutional impurity element, but the solid solubility is very small (MLNarula et.al: Metallurgical Transactions B 1
4B (1983) p. 673).

Next, there are substitutional impurity elements. This substitutional impurity element is a metal element such as Ag, Fe, Si, etc., and these elements replace copper atoms in the lattice and become a solid solution in the copper matrix. The substitutional impurities are the main solid solution impurities.

In any case, the impurities that form a solid solution in the copper matrix in this way distort the copper lattice, resulting in an increase in electrical resistance.
As a result, the sound quality deteriorates.

The residual resistance ratio depends on the physical defects (atomic vacancies and dislocations) in the copper matrix, but the impurities do not depend on the precipitates but on the amount of solid solution impurities. Therefore, in the present invention, the residual resistance ratio is defined as a factor that affects sound quality, not just the amount of impurities.

That is, the inventors of the present application adjusted various high-purity coppers having different RRRs by changing the annealing conditions respectively to a plurality of types of average crystal grain sizes, and a cable was prepared from the high-purity copper thus adjusted. It was made. The obtained sound quality was evaluated by using this as a code for audio equipment, and as a result, RRR was 300 or more and average crystal grain size was 1
It has been found that the desired excellent sound quality can be obtained by defining the thickness to be 0 μm or more.

[Examples] Next, the results of manufacturing the audio cables according to the examples of the present invention and testing the characteristics thereof will be described in comparison with the comparative examples.

Example 1 A copper wire having an RRR of 300 and an outer diameter of 0.5 mm was annealed by heating at a temperature of 350 ° C. for 2 hours in a vacuum atmosphere. When the cross section of this copper wire was observed with a microscope, the average crystal grain size was 10 μm.

Seven of these copper wires were twisted together to form a twisted wire, and the outer circumference thereof was coated with polyethylene having a thickness of 1 mm. By arranging two of these in parallel and further coating polyvinyl chloride on the outer periphery thereof, a parallel two-core type speaker cord was produced.

Example 2 A copper wire having an RRR of 1200 and an outer diameter of 0.5 mm was annealed in a vacuum atmosphere at a temperature of 500 ° C. for 2 hours. When the cross section of this copper wire was observed with a microscope, the average crystal grain size was 22 μm. Then, a parallel two-core type speaker cord was produced in the same manner as in Example 1.

Comparative Example 1 A copper wire having an RRR of 300 and an outer diameter of 0.5 mm was annealed in a vacuum atmosphere at a temperature of 300 ° C. for 2 hours.
When the cross section of this copper wire was observed with a microscope, the average crystal grain diameter was 7 μm. Then, a parallel two-core type speaker cord was produced in the same manner as in Example 1.

Comparative Example 2 A copper wire having an RRR of 250 and an outer diameter of 0.5 mm was annealed in a vacuum atmosphere at a temperature of 500 ° C. for 2 hours.
When the cross section of this copper wire was observed with a microscope, the average crystal grain size was 18 μm. Then, a parallel two-core type speaker cord was produced in the same manner as in Example 1.

The RRRs of Examples 1 and 2 and Comparative Examples 1 and 2 were obtained by the method described below.

The electrical resistance ρ ₂₉₈ at room temperature (25 ° C) of a sample wire (a copper wire having a length of 1 m and an outer diameter of 0.5 mm annealed in a vacuum atmosphere at a temperature of 500 ° C for 2 hours) was 1A by a 4-terminal method. Was measured by applying a current of. Then, the electrical resistance ρ _4.2 of this sample wire at the liquid helium temperature was measured under the same conditions, and the RRR was calculated by the following formula.

RRR = ρ ₂₉₈ / ρ _4.2K The speaker cords of Examples 1 and 2 and Comparative Examples 1 and 2 were connected between a speaker and a stereo amplifier, and their sound quality was compared and evaluated. The results are shown in Table 1 below.

However, in Table 1, the case where excellent sound quality was obtained is indicated by ◯, and the case where desired sound quality was not obtained is indicated by x.

As is clear from Table 1, in Examples 1 and 2, excellent sound quality could be obtained. On the other hand, the average crystal grain size of Comparative Example 1 and the RRR of Comparative Example 2 were outside the scope of the claims, so that Comparative Examples 1 and 2 could not obtain satisfactory sound quality.

[Effects of the Invention] As described above, according to the present invention, the RRR is 300 or more and the audio cable is made of a copper conductor having an average crystal grain size of 10 μm or more.
By using it as a lead wire or a cord of an audio device, an extremely excellent sound quality can always be stably obtained.

Claims (1)

[Claims] 1. An audio cable comprising a copper conductor having a residual resistance ratio of 300 or more depending on the amount of solid solution impurity elements in a copper matrix and an average crystal grain diameter of 10 μm or more. .