Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1999-04-09
2002-08-20
Le, Huyen (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S409000, C381S412000, C381S415000, C361S120000, C361S143000, C361S146000, C361S159000, C174S0170LF, C174S0170SF, C174S127000, C174S126100
Reexamination Certificate
active
06438250
ABSTRACT:
The present invention relates to a manufacturing process of an electrical conductor or circuit compensated for radio interferences such as micro-discharges, and an electrical conductor or circuit obtained by this process.
In the field of processing of electrical signals then their storage or their transformation into sensory phenomena directly perceived by human physiological receptors, numerous works have been carried out up to the present in order to maintain, indeed improve, the signal to noise ratio after each transformation, due to the processing, with the object of improving the reproduction and therefore the perception of these sensory phenomena.
Such concern is not moreover specific to the single field of sensory phenomena, such as the reproduction of sounds, but appears also in the much wider field of electronic signals creation, their transmission, their storage and their use by electronic or electrical transducers specially adapted to this purpose.
With regard more particularly to the field of creation, processing, storage and then reproduction of the sound in high fidelity technology, particularly, the HiFi field, some particularly well informed audiophile listeners, noted and reported, from 1970, that they could detect perceptible variations in tone between HiFi systems according to the nature of the power amplifier-loud speaker or acoustic enclosures connection cables.
Some did not hesitate, moreover, to note still more perceptible differences in musical quality, in their opinion, at the time of changing the modulation cables connecting, for example, a source such as a disc player, a microgroove disc or a tuner at the input of the power amplifier, or even of the pre-amplifier.
Quick studies conducted by recognized physicists, demonstrated, rightly, that the resistance in ohms of the most resistive of these wires or connection cables was very inferior to the impedance of loud speakers or acoustic enclosures, all the more so to the input impedance of amplifiers or pre-amplifiers, and that, consequently, such variability displayed above all a subjective character.
A more complete study, based on the theory of electrical lines, allowed taking into account the whole of the localized or distributed characteristics likely to affect the transmission and therefore the reproduction of these signals, i.e. in fact to the whole of the signals generated from a source or radiated in the radio space.
For an amplifier-loud speaker connection, the equivalent diagram can be reduced, as shown in
FIG. 1
a,
to;
a capacitance C between conductors, a function of the geometric size of the cables and the nature of the electrical insulations;
an inductance L divided into two components L/2, corresponding to the magnetic field produced by the current flowing in the conductors;
an internal impedance Zi, for each conductor comprising a resistive part and an inductive part due to the skin effect, on the surface of the conductors, and to a proximity effect of these latter.
As regards the skin effect or Kelvin effect, it is recalled that this phenomenon is characterized by the fact that in alternating current, the current density reduces, with the frequency, at the center of the conductor, and increases at the periphery, as shown in
FIG. 1
b.
For this phenomenon, the depth of penetration &dgr; in meters is given by the relation:
δ
=
ρ
π
μ
0
f
(
1
)
relation in which:
&rgr; designates the resistivity of the conductor in &OHgr;×m;
&mgr;
0
=4&pgr;10
−7
designates the vacuum permeability;
f designates the frequency of the transmitted signal in Hz.
Taking account of this phenomenon, because of the reduction of the actual conduction surface of the conductor, it is possible to define a cut-off frequency fc associated with a conductor radius r of specified nature:
fc
=
k
2
ρ
2
·
π
·
r
2
·
μ
c
(
2
)
relation in which:
k=1.910852
r designates the conductor radius,
&rgr; and &mgr;
0
having been defined previously.
The maximum radius of the conductor for a maximum frequency to transmit fc is given by:
r
=
K
ρ
2
π
·
fc
·
μ
0
(
3
)
Thus, for copper, fc=20 kHz, r=0.623 mm, i.e. &phgr;=2r=1.25 mm is obtained. The depths of penetration are given by:
f Hz
&dgr; mm
10
20.6
100
6.52
1000
2.06
10 kHz
0.65
100 kHz
0.206
These results show that this depth varies a great deal as a function of the frequency of the transmitted signal, to be precise in the audiofrequency range. Consequently, it is recommended as far as HiFi technology is concerned to make modulation connections by means of a conductor with a strand diameter less than 6/10 mm, the connection between the amplifier and acoustic enclosures being made by means of strands of 5/10 to 6/10 mm placed in parallel in order to obtain cables with a cross section between 1.5 and 3 mm
2
, as a function of the length, each strand being individually insulated. The only real effect of any use of cables with a greater cross section is a poorer attenuation of the signals at low frequencies and therefore a relative “raising” effect of these latter.
Besides the aforesaid phenomena, in particular as far as the amplifier-acoustic enclosure connection cables are concerned, these latter can be subjected, as shown in
FIG. 1
c,
to a proximity effect. This effect only appears during transmission of periodic or pseudo-periodic signals, at high frequencies, the currents flowing in the parallel return conductors having the effect of minimizing the emitted magnetic flux. An approximate calculation enables an impedance coefficient value of the transmission cables to be established at high frequencies, greater than 10 kHz in the audio-frequency field, taking account of both the skin effect and the proximity effect, for two parallel conductors of circular cross section of diameter &phgr; and the central axes of which are distant by D. This impedance coefficient, expressed in &OHgr;/m, establishes the relation:
Zi
=
ρ
Pm
×
δ
(
1
-
k
2
φ
2
D
2
)
(
4
)
In this relation, K, &rgr; and &dgr; are the parameters defined previously in the context of the skin effect phenomenon, Pm represents the perimeter of each conductor. The product Pm×&dgr; represents the useful cross section presented to the current and the term
(
1
-
K
2
φ
2
D
2
)
represents the proximity effect contribution. This contribution is however negligible as soon as D>>&phgr;.
The previous relation (4) is essential, for it enables it to be established, contrary to unconvincing conclusions or practices, that conductors having a same ohmic resistance and a same &phgr;/D ratio have an absolutely identical behavior according to the transmitted signal frequency. Consequently, the choice of the nature of the constituent metal of the conductors, copper, gold, silver, aluminum, provided that the ohmic resistance and the &phgr;/D ratio characteristics are satisfactory, is not able to have any influence on the cable behavior as a function of the transmitted signal frequency.
The theory of lines applied to the acoustic enclosure cables, each cable component being modeled by a transfer function &Ggr; of characteristic impedance Zc=v(Z/Y), where Z represents the series impedance of the conductor, with Z=Zi+jL&ohgr;, j={square root over (−1)} and &ohgr;=2&pgr;f, Y=jC&ohgr; parallel admittance, and of propagation constant &ggr;={square root over (ZY)} enables the amplifier-acoustic enclosure function to be established, as is shown in
FIG. 1
d,
in the form
V
2
V
1
=
l
ch
γ
l
+
Z
C
z
sh
γ
l
(
5
)
where z designates the complex impedance of the acoustic enclosure, l designating the length of the line, i.e. of the connection. For frequencies in the audio field
Electricite de France (Service National
Harvey Dionne N.
Larson & Taylor PLC
Le Huyen
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