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How you can Enjoy Much Greater Dynamics from
your Hi-fi
Music System by using Low Microhonic Cables
By
Graham Nalty MA (Black Rhodium)
The Basic Co-axial
Cable
A coaxial cable, such as is used for analogue audio
interconnects, consists of 4 parts:
1. The Inner core conductor that
carries the music signal
2. The insulation
3. The screen that also acts
as a return conductor
4. The outer insulating sheath
1. The inner core conductor carries the music
signal from one electronic unit to another such as from a CD player to and
amplifier. The inner core conductor is typically made of copper, tinned or
silver plated copper or silver. For truly highest quality audio, other
conductors of rare expensive metals may be used to convey a much more lifelike
experience of the music. The inner conductor may be a single core or may be
stranded with up to, and sometime exceeding, 100 separate small strands.
2. The insulation is made from a
non-conducting material and its purpose is to prevent the signal being
connected to any other conductors in the cable. The insulating material may be
PVC as used in low cost cables, but not recommended for sound quality, or
Polyethylene, PTFE or Silicone Rubber in high performance cables. The
insulating layer is thick enough to prevent electrical conduction of the
highest voltage that that the signal conductor is ever likely to receive in
use. All cables exhibit capacitance between conductors. The effect of cable
capacitance on the music signal is to attenuate the higher frequencies over
longer lengths cables so a lower cable capacitance will extend the useful
length of the cable. Insulating materials with a lower dielectric constant
will, for the same insulation thickness, create a lower capacitance in the
cable.
3. A conductive screen that acts a return
conductor for the music signal and also provides screening to prevent noise and
interference reaching the delicate low level music signal. The levels and types
of noise that now exist to contaminate sensitive electrical signals include
radio frequency (RFI) noise from broadcasting, telephony and computers,
electromagnetic interference (EMI) from power transformers and electrostatic
(ESI) from fluorescent lights, dimmers and relays. With the growth in the use
of computers and computer based electronic equipment, the demands for good
screening become more significant every day.
The most popular types of
screen are:
- Braided screen made from very thin
wires
- Spiral wrapped screen also made from very
thin wires.
- Aluminium foil shield made from mylar
backed aluminium foil with an un-insulated drain wire to terminate it
electrically.
4. The outer sheath is made of a material
that reflects the use for the cable. A high gloss sheath may be used for a high
end audio cable to reflect its market value whilst a material with good
abrasion characteristics may be required for a professional musicians cable.
For many high end audio cables, the outer sheath may be covered over with an
expandable sheath to indicate the exclusivity of a hand built cable.
The Cable as a
Capacitor
All co-axial cables act as capacitors, with the inner and
outer conductors representing the plates of the capacitors and the insulation
being the dielectric.
The Triboelectric
Effect
When the plates of a capacitor are deflected (a musician
treading on a cable during a performance), or when an electric charge is
generated by friction between the screen and insulation (known as the
triboelectric effect), a voltage is created between the signal and return
conductors that is in addition to the music. As that electrical signal is not
part of the music, it is noise – a very much unwanted noise. That noise
is the microphonic effect generated by the cable.
Applications of Low
Microphonic Cables
The main application for Low Microphonic Cables
is for cables for electric guitars and other similar musical instruments where
stage musicians may tread on the cable during a performance and the resulting
microphonic noise would be highly undesirable. Another applications is in
instrumentation where measurements may be required from a moving object.
Techniques that reduce the microphonic effects of cables to the minimum are
well developed in these industries.
Reducing Microphony in
Cables
The technique for minimizing microphony in cables is to place
a conducting electrostatic shield between the inner insulation and the
screen.
This conducting screen is usually made from a
carbon based compound, such as conductive PVC, which is placed over the inner
insulation before the screen. Its effect is to bleed away the small electrical
charges caused by triboelectric effects before they can reach a voltage that
would be audible through the speakers. In some cases, a conductive plastic
screen can replace the metal screen as well, but its screening effect is
limited at the highest audio frequencies and above.
Designing a Black
Rhodium Low Microphony Cable.
The demand for a low microphony cable arose
as a result of requests from customers for a high quality cable to be used with
musical instruments. In response to these requests cables were made using a
high quality PTFE insulated audio cable that had for many years being highly
acclaimed by customers and by the Hi-fi press. We were very surprised when one
customer had returned a cable to us saying that it was microphonic.
We contacted our supplier and talked with
their technical experts. They advised us of a cable that they had developed
where the item under test moved whilst measurements were being taken. We
obtained a short sample of that cable and tested it in a quality audio system.
We also tested the nearest equivalent cable from our own range of cables. Both
cables had a very small diameter conductor which made them both too bass light
for normal use as analogue interconnects. However, listening to the music via
the low microphony cable just seemed more pleasant and enjoyable. The effect
was significant enough to justify the design and development of a new low
microphony cable for stereo audio use.
Black Rhodium Prelude was designed
as low microphony cable for stereo audio applications. It was based on the very
popular Black Rhodium Rhythm but with a 50% increase in the area of the
conductor carrying the audio signal to improve the balance between bass and
treble, and a conductive layer between the inner insulation and the screen to
reduce noise caused by the triboelectric effect.
Listening to music
using Black Rhodium Prelude
The experience of listening to Black
Rhodium Prelude is that listening to music immediately becomes a more
pleasurable experience. The moment that Black Rhodium Prelude is connected it
is more difficult to switch the music off. Transients, especially those of high
frequency instruments become louder and more dynamic. On switching back to
another cable, the music suddenly becomes, by comparison, slightly boring.
I had the privilege of hearing a retailer
demonstrate a lower priced pair of speakers using appropriately priced
electronics with a Black Rhodium Prelude connected between the CD player and
amplifier. I was certainly very surprised by the overall enjoyment that the
overall system gave in relation to its price. There must be a very big market
for Prelude amongst dealers who want to sell their electronics and speakers
without using expensive cables to boost the performance.
Low Microphony –
an Explanation of the Sonic Benefits.
There are many precedents
towards an explanation of why a low microphony cable should make a more
enjoyable listening experience than one that exhibits microphony. These are the
many recorded instances where the use of vibration damping parts and materials
in amplifiers and loudspeakers have improved the dynamic qualities of music.
The explanation lies in the electrical music signal, which though it is
very small (tens of millivolts in a line level interconnect) creates forces
between the inner core and outer screen. These forces create displacement
between the conductors that results in an electrical charge being generated. In
addition any movement between the screen and the insulation will cause friction
that will generate further electrical charges by triboelectric effect. The
presence of either of these two sources of electrical signal, however small,
will generate electrical noise. In a microphonic cable the noise voltage occurs
after the moment of time when the electrical signal causing them passed. The
result is a noise distortion voltage that may be easily audible as an echo
during a quiet passage of music. If it occurs during the passage of music, its
effect as ‘noise’ is masked by the music, but it severely distorts
the character of the music and this form of time smearing distortion is very
easily noticed by the human ear as a reduced clarity of how each musical note
sounds and how it rises and decays with time.
Graham Nalty
October 2006 |
