Ed's AV Handbook.com
Home Theater & High Fidelity Stereo Audio
The AV System Sequence
Batting practice for the audio/video pro and a primer for the novice
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The AV system sequence cannot exist without interconnecting wire and cable.
The Controversial Subject Of
High Performance Cable & Interconnects
Although they consist of metal wire and an insulator --- it is important to visualize that the signal does not simply travel through the metal conductor. The signal is an electromagnetic wave that propagates along the metal conductor within the insulated boundary.
Cable and interconnects fundamentally behave as wave-guiding conduits. These extended conduits, the longest electrical circuits of an AV system, must negotiate the same obstacles as the shorter circuits within the components. This includes noise, resonance, resistance, inductance, and capacitance.
As noise in an acoustical space, noise can bleed in and out of an electrical environment. For example, long parallel strands of wire in a cable can behave as an antenna that generates and/or attracts electromagnetic noise.
Then similar to problematic acoustical reverberation; impeding electrostatic forces within the cable can temporarily trap and randomly release bands of audio out of phase from the balance of their original waveform. Random sound is noise.
The management of resonance is a frequent theme in audio. It is a function of how electrical inductance or acoustical mass plus capacitance respond to fluctuating low frequency energy. In acoustics it is referred to as room modes or standing waves. In an electrical circuit it is electrical resonance.
Unwanted resonance creates deviations from flat frequency response. The result is distortion. Resistance, inductance, and capacitance are the fundamentals that set the electronic resonance table.
Resistance is a process that converts impeded acoustical or electrical low frequency energy to heat.
A wall resists acoustical energy. As sound energy is increased, a mechanically (slightly bending) resisting wall converts waves of acoustical energy to heat.
Electrical current flows initially on the surface of wire. As the current is increased it will ultimately penetrate and saturate the cross section of each conductor. Resistance to the flow rapidly swells and converts the electrical energy to heat. This is a good design for a toaster-heating element. But it does not make for good audio.
Room boundaries create and define an acoustical field. In an electrical circuit a magnetic field establishes an electrical boundary. Though not as tight as an electromagnet -- speaker wire and interconnects are coiled parallel circuits that create a magnetic field. The magnetic flux in this field is defined as inductance. Inductance impedes electrical energy.
Room boundaries form a vessel that can hold an acoustical spring of low frequency energy. Inductive magnetic boundaries can also store energy in an electrical spring of low frequency energy. This spring-like potential to store and impede low frequency energy is defined as capacitance.
The reactance resonance dance
Inductance is the force that squeezes the capacitance spring. Resistance sets the table for each. The resistive spring-like interaction between inductance and capacitance
is described as reactance.
When inductive reactance equals capacitive reactance a ringing peak is produced.
This resonant ringing frequency creates deviations from flat frequency response: distortion.
In addition, this electrical interaction will pass bands of energy, while other bands are temporarily trapped, stored, and randomly released. This is the random electrostatic noise mentioned earlier.
Noise and impeding resonant forces cannot be eliminated. But their distorting effects can be minimized with careful design choice.
For instance many strands of pure copper, silver, or silver coated copper can reduce resistance, which translates into a better transfer of energy.
Polypropylene insulation infused with air pockets can reduce capacitance, which minimizes the spring-like interaction.
Noisy antenna effects can be tamed with shielding and/or an interleaving of the insulated conductors referred to as twisted pair geometry.
The electrical dilemma is each design choice affects the other. More insulated
strands can increase inductance and capacitance; less increases resistance. The coiled-like interleaving of twisted pair geometry can shift the reactant resonant peak point to an unsuitable frequency.
Quality cable manufacturers work the problem with the same strategies utilized in speakers, acoustics, amplifiers, and other components. They select a recipe mix of
resistive, capacitive, and inductive trade-offs that fulfills their performance goals.
Many augment twisted pair noise reduction by limiting cable bandwidth with a low pass filter network.
Variations of the twisted pair technique are also used to phase-realign the bass frequencies with the band passed high frequencies. In addition the filter network can be used to complement the twisted pair technique to “re-tune” the resonant peak to a less offensive point.
The important point -- Negotiating obstacles that create noise and unwanted resonance is a mix that seeks to minimize the compromise of the same physics that is confronted throughout the AV system sequence. That is why speaker cable and AV interconnects should be selected with the same consideration that is given to room acoustics and the system components.
|Ed's AV Handbook.com
Batting Practice for the AV Pro and a Primer for the Novice.
Copyright 2007 Txu1-598-288 Revised 2018