A Guide to Optical, Digital Coaxial (Interconnect & Sub), and Speaker Cables

[Big Daddy]

It may be helpful to read the following thread:

Coaxial & Speaker Cable Signal Loss

OPTICAL VERSUS COAXIAL DIGITAL CABLES

Optical and Coaxial S/PDIF (Sony/Philips Digital Interface or Sony/Philips Digital Interconnect Format) is a standard audio file transfer format developed jointly by Sony and Phillips to allow the transfer of digital audio signals from one device to another without having to be converted first to an analog format.

1. A digital coaxial cable has an inner conductor, surrounded by an insulating layer (dielectric) and then surrounded by another conductive shielding layer and finally covered by a plastic casing. They come in different varieties such as RG59, RG6, or RG11 with F or RCA connectors. The conductive outer layer can be braided copper wire for more cable flexibility or solid metal (such as aluminum foil) for better shielding.

The differences between RG59 and RG6 cables are explained in these links:
http://www.abccables.com/info-rg59-vs-rg6.html
http://cableorganizer.com/articles/c...able-faqs.html
http://www.epanorama.net/documents/video/videocoax.html

2. Coaxial cables look and feel virtually identical to standard RCA cables. The main differences are that they are better shielded from interference; have a higher impedance (usually 75 ohm), allowing them to handle more energy; and can handle a wider range of frequencies.

3. Coaxial digital cables transmit digital signals in pulses of electricity. The signal is transmitted along the cable as an electromagnetic wave which travels along the inner and outer conductors through the insulating material.

4. Some people argue that the word “digital” is a marketing trick. Digital coaxial cables aren’t digital in and of themselves, but they are designed to do a better job of carrying a digital signal.

5. Optical or Toslink (Toshiba Link) cable transfers a digital audio signal via a red light beam over a fiber-optic cable. A fiber optic cable is made of small strands of plastic to transfer light.

6. A Coax cable is more sturdy and durable than an optical cable. However, a Coax cable will transfer grounding problems (hum) from one component to another if they already exist. It is also more susceptible to EMI (Electro Magnetic Interference) noise. Remember that these problems are rare and coax cable does not create new problems. RG6 cable has aluminum foil and aluminum braid shielding. RG59 has copper braid shielding. Aluminum is better for blocking ultra high frequency RFI (Radio Frequency Interference) noise. Copper braid shielding is better for blocking lower frequency interference. RG6 is more appropriate for digital TV appclications. It also has a thicker center conductor than RG59 and is preferred for longer lengths. An RG59 or RG6 with two layers of copper braid shieldings may be more appropriate for subwoofer applications.

7. An optical cable is more fragile than a coaxial cable. If stepped on or bent, it can be destroyed. However, an optical connection does not have grounding or hum problem and is not susceptible to EMI noise because it does not contain any metal.

8. A Coax cable uses standard male RCA plugs, which are very easy to plug in.

9. An optical cable uses a pentagonal-shaped connector, which must be aligned properly to be inserted. It will only go in one way and can be damaged much easier than an RCA plug. The following table shows the different types of Fiber Optics Transmitting and Receiving Modules:

10. Optical cables can lose their signal strength if they are bent. Care should be taken to make sure that optical cables are as straight as possible.

11. An optical cable requires extra processing steps in converting current to light and then light to current. These two steps can add error into the audio signal.

12. For short distances, there is no difference in quality between coax and Toslink.

13. For very long distances (e.g., 50 to 100 ft), optical is preferred. However, as was mentioned before, care must be taken to make sure the optical cable is not bent. If it is not possible to keep the cable straight, then a coaxial cable should be used.


Electromagnetic Interference (EMI) & Cable Shielding

Read Coaxial & Speaker Cable Signal Loss.


FAQ:

Q. Can we use a digital coaxial cable (RG59 or RG6) for all A/V analog and digital connections?
A. Absolutely. Coax cables are the best interconnects.

Q. Does the Digital Coaxial cable carry a digital signal when we connect it to a subwoofer?
A. No, we use a coaxial cable because of its better shielding.

Q. Why can't we bend Optical (Toslink) cables?
A. Optical cables work by sending light signals through a plastic or glass tube rather than electrical pulses down a wire. Digital signals are converted to light and then back to digital. As light travels through different mediums, it can bend. In optical material (plastic or glass), there is an angle of refraction, which when increased to a certain amount, the light instead of going through the material, gets reflected back. Some light still escapes, but most gets reflected internally. By bending an optical cable, two things may occur:

1. The internal plastic (or glass) may snap and break.
2. Even if the cable does not snap, it has a limit of how much you can bend it. The limit is when the angle of refraction is no longer sufficient for the light to go through.

SPEAKER WIRES

Resistance is by far the most important specification of a speaker wire. Low-resistance speaker wire allows more of the amplifier's power to go to the speaker. Resistance is affected by three factors: conductivity, length, and thickness.

CONDUCTIVITY
Electrical conductance is a measure of how easily electricity flows along an element. Its units are Siemens, which is the inverse of Ohms. Electrical conductance is related to the materials' conductivity according to the following formula:

G = σ . (A/L)

where:

G = the electrical conductance (Siemens)
σ = the materials conductivity (Siemens/Meter), it is the inverse of the material's resistivity
A = the object's cross-sectional area (Meter ^2)
L = the length of the object (Meter)

Resistivity in Ohm per Meter
Silver: 1.6 x 10^-8
Copper: 1.7 x 10^-8
Gold: 2.4 x 10^-8
Aluminum or Aluminium: 2.7 x 10^-8

Electrical Conductivity (σ, Siemens/Meter) at 20 degrees (C)
Silver: 6.2 × 10^7, Highest electrical conductivity of any known metal
Copper: 6.0 × 10^7
Gold: 4.5 × 10^7, Gold is commonly used in electrical contacts
Aluminum: 3.8 × 10^7

LENGTH
If you double the length of a wire, you will double its resistance. This means that you will have to get a wire with better resistance or you will have to increase the power in order to get the same level of sound as the shorter wire.

THICKNESS (CROSS-SECTIONAL-AREA)
The resistance of a wire decreases as you increase its thickness (AWG, gauge number). The gauge number drops as the wire gets thicker. As a general rule, you should use thicker (lower gauge number) wires for longer distances. High-power car audio systems using 2-ohm speaker circuits require relatively thick cables. The following table can be used as a guide. Also read Impedance & Sensitivity of a Loudspeaker.

Golden Rule: When you increase the gauge number of a wire by a factor of 3, its resistance will be doubled. For example, the resistance of an 18 gauge speaker wire is 4 times higher per foot in comparison to a 12 gauge wire (18 is 6 points away from 12).

This Conversion Calculator can be used to convert a speaker's gauge number to metric units. Here are Conversion Tables for all units of measurement. Here is a calculator for Units Conversion.

FACTORS AFFECTING THE PERFORMANCE OF A CABLE

With DC power sources, you only have to worry about the resistance . Resistance is caused by collision of electrons and ions in a conductor and convert part of the electrical energy to heat. In other words, resistance is the opposition to electric current. Different materials have different resistances. DC resistance does not change with frequency.

AC current, however, oscillates as a sine wave so the sign is always changing. This means that other factors such as inductance and capacitance must be considered. Inductance is the magnetic field that is created when current flows through an object. Capacitance is the ability of an object to hold an electrical charge.

With AC current, a cable is affected by three electrical properties: Resistance, Inductance, and Capacitance. Most cables are made out of copper. A few are made out of silver. Silver and copper have the lowest resistance and the highest conductivity out of all the metals. In addition, thickness of the wires (lower gauge number) reduces resistance.

Skin Effect:
As the frequency of a signal increases, the electrons in a wire in a wire concentrate toward the outside, or skin, of the conductor. This means that if we measure resistance at different frequencies, we will find that the resistance of the wire increases with frequency.

Inductance:
Inductance is the property of the signal in one conductor inducing current in another nearby conductor, and inhibiting current flow in the opposite direction. In transformers, this property is useful. Cables normally have two leads, each carrying current in opposite direction. High inductance causes flow of current in one lead to interfere with the flow in the other lead.

What is an Inductor?
An inductor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it. The following diagram demonstrates some basic inductors.

Factors Affecting Inductance:

To see some cool Java applets on how inductance works, click HERE.

If you have excess cables or speaker wires, do not coil them in a circle. When a wire is coiled up, it will act as an inductor. You may lose some high frequencies. Lay them randomly on the floor or make a figure eight with them.

http://www.lovetriacoustics.com/inde...peakerWire.htm

Don’t coil up excess cable as this could create inductance causing high frequencies to be lost. If you do have extra cable on one side, which is inevitable to happen, it would be better to lay it randomly on the floor.

http://www.1388.com/columnists/jon_faq_cable.htm#2

Not recommended because coiling the cable greatly increases the inductance, and other interaction effects that may cause more than just an extra amount of high frequency roll-off. A snaking "S" pattern will avoid the worst of any interaction problems.

Capacitance:
A capacitor consists of two metal plates with insulation in between that can hold electrical charge. Speaker cables can act like capacitors because they are two pieces of metal wires with an insulator (dielectric) in between them. Capacaitance increases with frequency and is more serious at higher frequencies and longer lengths of cables.

Capacitance occurs by the insulator around the conductor. In cables, some of the electrons passing through the cable is transferred to the insulator and stored as energy. When they are released back into the conductor, it may cause a deterioration of the sound quality.

The type of insulator has a direct effect on capacitance. Most insulator are PVC, Polyethylene, Polypropylene, and Teflon. Teflon is the best, but it is a difficult material to work with. That is one reason why cables that use Teflon are normally more expensive.

By far, the most important factor in speaker wires is resistance. Inductance and capacitance are too insignificant for short lengths to have any negative effect. Low gauge (thicker) wires have much lower resistance and that is a crucial factor for speaker performance, particularly for long lengths.

For long lengths, if the resistance of the wire is too high (thin wire), power will be lost and the speaker will not play as loud. In addition the frequency response of the speaker may follow the the impedance curve (impedance varies with frequency) of the speaker. As long as a wire's resistance is less than 5% of the speaker's impedance, the wire will be appropriate for home theater use.

Capacitance, however, is not as important as resistance. High cable capacitance is not a problem for well-designed and quality amplifiers. In fact, some high end speaker cables have higher capacitance than ordinary 12 gauge wire and can introduce significant amount of capacitance for long runs. For example, a cable that has a capacitance of 300 PicoFarads (PF) per foot will add 15,000 PF in a 50 ft cable. That is equivalent to .015 MicroFarads and can be significant.

In many cases, ordinary wires such as 12 gauge wires have a capacitance of only 18 PF per foot for a total capacitance of 900 PF for a 50 ft length.

I believe a test of 10kHz square wave and different capcitors were made on the McIntosh amplifier. By both listening and observing on an oscilloscope, no changes were heard or seen.

Some amplifiers are more sensitive to the load impedance of the speaker wires. The reason is because the higher the output impedance of the amplifier. This will make it more likely for capacitance and inductance of the cable to affect the sound quality. Tube amplifiers are more sensitive to cables than solid state amplifiers because they have higher output impedances.

Resistance/impedance of a cable is more important for speakers as they have very low impedances such as 4 Ohm or 8 Ohm. However, cable interconnects generally operate in very high-impedance circuits such as receivers/ampifiers. The input impedance of these devices is in the thousands and a few additional Ohms of resistance introduced by the cable are not as significant. Therefore, cable thickness (gauge number) is not as important in inter-connect applications, particularly for much smaller lengths than speaker cables.

In high impedance circuits, capacitance becomes more important. Capacitance is the tendency of the cable to store some of the signal in itself and release it slowly. Capacitance in a cable with a center conductor and an outer shield is determined by the following factors:

• The outer diameter of the center conductor. By reducing the tickness of the conductor, you can reduce capacitance.
• The inner diameter of the shield.
• The type of material (dielectric) that separates them. For example Teflon has the best dielectric constant and can reduce the capacitance of the cable.

Concluding Remarks About Inductance/Capacitance:
Audio signal creates an electromagnetic field around the conductor. Dielectric material absorbs energy and releases it back into the conductor out of phase with the audio signal. The electromagnetic field created by the conductor temporarily displaces the molecular structure of the material. Dielectric materials theoretically can sound different because of the different rates that the materials store and release energy at different frequencies. If the dielectric material has good elasticity and can return quickly to its normal state, then the material is said to have low dielectric hysteresis or loss and will have little audible effect on the signal.

To add to the problem, there is also such a thing called self-inductance. Current flow in a conductor produces a magnetic field around the conductor. When the current is increasing, decreasing, or changing direction, the magnetic field changes. A changing magnetic field induces voltage in any conductor which is close by, and it induces a voltage in the original conductor. The voltage induced into the original conductor is called self-inductance, and tends to oppose the current which produced it. Self-inductance occurs in a circuit even when conductors are perfectly straight. However, self-inductance in a straight conductor is very small. Inductance is much more significant when conductors are coiled, because the magnetic field of each turn of the coil cuts across nearby turns of the coil.

Inductance in a speaker cable is mainly determined by the area between the conductors. Most speaker cables have conductors that run side by side (twin-lead). These conductors are separated by a small distance and have moderate inductance.

Capacitance is also a function of how close the conductors are to each other. So to keep the capacitance low, the conductors must be widely separated. Note that this is just the opposite of what we need for low inductance. Some cables use many small wires that are woven together. This reduces inductance greatly, but at the cost of increased capacitance.

Inductance is considered less of an issue with the interconnects (line level signal) than with speaker cables since the current in speaker cables is higher. Inductance affects higher frequencies more.

Incidentally, inductors and capacitors are used in crossover networks to build low-pass and high-pass filters.

SPEAKER WIRE MATERIAL
Copper is the most commonly used material in speaker wires; it has low resistance and less cost compared to other suitable materials. Copper can oxidize, but oxides of copper are conductive. Silver is a slightly better conductor and has a slightly lower resistance compared to the same gauge of copper wire. However, it costs a lot more and any advantage gained by using a better conductor can easily be compensated for with slightly thicker copper wire.

SPEAKER CONNECTIONS

When connecting the speaker wires, make sure you connect the red terminal on the receiver/amplifier to the red speaker terminal and the black to black. There are two types of speaker terminals: Binding Post & Spring Loaded, and four types of connectors: Bare Wires, Pin Connectors, Spade Connectors, & Banana Plugs.

Bare Wire




Pin Connectors




Spade Connectors




Banana Plugs

BananaPlugs1.jpg BananaPlugs2.jpg

http://www.monoprice.com/manual/INST...NA%20PLUGS.pdf

http://www.youtube.com/watch?v=GK5H5UDsxwo

Pin Connectors and Bare Wires can be used with Binding Post and Spring Loaded terminals. Spade Type Connectors and Banana Plugs can only be used with Binding Post Terminals.

Binding Post




Spring Loaded




WHERE TO BUY CABLES AND ACCESSORIES

Speaker Wires:
http://www.monoprice.com/products/se...=speaker+wires
http://www.parts-express.com/webpage...=main&desc=ASC
http://cablesimple.com/
http://www.cablestogo.com/product_li...id=&dept_name=
http://www.cablewholesale.com/cgi-bi...ables&type=all
https://www.cablesforless.com/c-125-...cessories.aspx
http://zebracables.com/items.html
http://www.pacificvalve.us/Cables.html
http://www.bluejeanscable.com/store/speaker/index.htm
http://www.pchcables.com/
http://www.bettercables.com/premium-speaker-cable.aspx
http://21st-century-goods.com/page/21st/CTGY/FWAUDIO
http://www.flatwirestore.com/mm5/mer...egory_Code=AFW
http://shop.ebay.com/i.html?_nkw=12+...wire&_osacat=0

Silver Speaker Wires:
http://signalcable.com/silverresolutionspeaker.html
http://www.silversonic.com
http://www.dvdcity.com/speaker/nor-blue-heaven.html
http://www.audioadvisor.com/products.asp?dept=26
http://www.av-outlet.com/en-us/dept_203.html
http://www.quicksilveraudio.com/prod...eakerwire.html

Speaker Wire Connectors:
http://www.cables.com/Category/Conne...onnectors.aspx

Optical/Toslink Cables:
http://www.monoprice.com/products/su...02&cp_id=10229
http://www.parts-express.com/webpage...n&WebPage_ID=3
https://www.cablesforless.com/c-127-...io-cables.aspx
http://www.pchcables.com/
http://www.cables4sure.com/default.htm
http://www.bettercables.com/toslink-optical-cable.aspx
http://www.cables.com/

Digital/Coax S/PDIF Cables:
http://www.monoprice.com/products/su...02&cp_id=10236
http://www.prosatellitesupply.com/COAXIAL_CABLE.htm (Custom white or black from 3ft to 150ft)
http://www.parts-express.com/webpage...ctGroup_ID=599
https://www.cablesforless.com/c-124-...io-cables.aspx
http://www.pchcables.com/
http://www.bluejeanscable.com/store/...udio/index.htm
http://www.bettercables.com/digital-...r-serpent.aspx
http://www.cables4sure.com/default.htm
http://www.bettercables.com/toslink-optical-cable.aspx
http://www.cables.com/

Optical to Coaxial Converter:
http://www.monoprice.com/products/pr...seq=1&format=2
http://www.tigerdirect.com/applicati...H4CjCmmVCjCmmV
http://www.parts-express.com/webpage...ID=3&x=22&y=16
http://www.cablestogo.com/product.as...3106&sku=40019
http://www.beachaudio.com/Siig/Ce-Ct...2-p-98390.html
http://www.hdtvsupply.com/difiopttodic.html

Coaxial to Optical Converter:
http://www.monoprice.com/products/pr...seq=1&format=2
http://www.tigerdirect.com/applicati...H4CjCmmVCjCmmV
http://www.parts-express.com/webpage...ID=3&x=22&y=16
http://www.cablestogo.com/product.as...3106&sku=40018

Cable Organizers:
http://cableorganizer.com/
http://www.cabletiesandmore.com/index.php

REFERENCES

http://www.datasheetcatalog.org/data...shiba/2034.pdf
http://en.wikipedia.org/wiki/SPDIF
http://en.wikipedia.org/wiki/Coax
http://www.tnt-audio.com/int.html
http://www.cobaltcable.com/newsletters/august_2002.htm
http://www.hometheaternetwork.com/HTN_audio_I2.htm
http://en.wikipedia.org/wiki/Speaker_wire
http://www.procosound.com/?page=education&articleid=5
http://www.engadget.com/2008/03/03/a...ter-cable-and/
http://www.audioholics.com/education...speaker-cables
http://www.roger-russell.com/wire/wire.htm
http://www.audioholics.com/education...er-cable-gauge
http://www.firedog.com/learningcente...nnections.html
http://www.herguth.com/TABLE_OF_CONT...c_strength.htm
http://www.eddy-current.com/condres.htm
http://en.wikipedia.org/wiki/Electrical_conductivity
http://www.allaboutcircuits.com/vol_1/chpt_15/3.html
http://store.a2zcable.com/75auca.html