Wednesday, September 5, 2012

Evolution of the High End Part 6

Early on in audio, speaker connections used off-the-shelf terminal connection strips to make easily removable speaker wire-to-amplifier and speaker wire-to-speaker terminations.  Simple screw strips offered a low cost way to permit interchangeable connections.  Little was understood about wire or terminations at the time believing that DC resistance was the primary issue. While correct on that point, other issues were present before a fuller understanding of the function of an amplifier or speaker terminal involved.
Bakelite Terminal Strip
While fully functional, this technology is outdated being replaced by terminals that accept larger wires.  Early attempts used the 5-way binding post to allow flexible termination styles and a more positive connection.
5-Way Binding Post
Improved versions of this terminal still appear in equipment today.  Improved banana plugs and jacks assure good connections and high-current carrying ability.

But above this lower-resistance and higher-current connectivity came an understanding of the conductivity of different metals, oxidation and corrosive effects of aging, and parasitic losses.  Ferrous materials "stole" some of this energy to create a magnetic field so non-ferrous materials like gold and silver became very popular.  While silver is a better conductor than gold, the corrosive effects require regular maintenance and so gold fell into favoritism for construction of terminals.  Other materials such as high purity solid copper, oxygen free processing, and linear crystal composition all help improve these large connections.

The truth to a connection lies not only in the materials but also in the cross-section area of the termination.  When the area of the termination is smaller than the area of the speaker wire, there lies the bottleneck.  If the area of the termination is significantly smaller than the speaker wire, there will be an appreciable insertion loss into the amplifier-speaker electrical circuit.

For example, if you use a 10AWG speaker wire, the cross sectional area translates to 5.26 square millimeters (0.0082 sq. in.).  This means that the total surface area  of the terminals must be at least this big.

Binding posts are 10mm in diameter for a maximum contact area of 5mm*5mm*3.1416=78.54mm.  BUT the center post is 6mm in diameter and this must be subtracted from this contact area.  3mm*3mm*3.1416=28.27mm so the maximum cross sectional area of a spade lug on a binding post is 78.54-28.72*2=100mm.  This is totally adequate.  BUT spade lugs are not this large and do not use100% of this maximum contact area. Roughly 40% of the available area is not used so 40% of 100mm=60mm, still more than adequate.

Do the banana plugs have the same comfortable relationship? Not even close.  Contact area of a banana plug and jack are minuscule (very low cross sectional area) unless advanced self compressing styles are used.  Then cross sectional area approaches the 5.26 sq. mm. of the conductor.

This means that the best connections possible for 5-way binding posts is the tried and true spade lug.

What you hear when there is a significant difference in cross-sectional area is flabby bass (damping drops) and low transient response (terminals cannot handle high momentary current surges).

So do yourself a favor and convert your speaker wires to high quality spade lugs and sit back and enjoy the difference.

Yours for higher fidelity,
Philip Rastocny

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