Speaker and Amplifier Connectors
The connection between the power amplifier output terminals and speaker input terminals is almost always a pressure device of some sort. It's unfortunate that these important connections are determined by to how tight you can turn a binding post or screwdriver or by the pressure of a spring which holds the speaker wire against the metal of the terminal. The metals that are forced against each other are often different. They might be brass or steel but plated with other metals. The wire could be copper or silver and perhaps coated with solder containing tin. They expand and contract differently with temperature. They can also become oxidized over time and the connection can become bad to the point where the resistance is significant compared to the resistance in the rest of the circuit. Dissimilar metals can also promote corrosion with action like a battery when they are in a humid environment. This eventually causes not only higher resistance but also clearly audible distortion as if a diode were inserted in series with the speaker and amplifier.
Suppose you have a system with adequately heavy speaker wire but the connections have gone bad over time. Simply removing and cleaning the wires and terminals and reconnecting them can make an audible difference. Incidentally, this is what can happen if the old wire is replaced with a new "miracle" speaker wire. By disturbing the terminals this can "accidentally" improve the contacts when the new wire with its clean surface is installed. A difference can be heard but not because of the new wire. The same change can be heard by simply cleaning the old wire/terminal contacts and reconnecting them.
Ah, you say gold plating takes care of all that. That isn't always true, particularly if the wire is tinned with solder, which is at least 50% tin, and the connecting post is gold plated. Here's what J. J. Whitley, Research Associate at AMP Incorporated (a well-known connector manufacturer) has to say about mating tin-plated contacts with gold. "In most cases, lubricated tin contacts can be mated with gold-plated contacts. This combination works as long as the conditions of contact force and stability for tin contacts are met."
"There is one major exception--where the service conditions involve wet or humid environments. Under these conditions, the gold-tin bimetallic junction is subject to galvanic corrosion. Generous application of protective lubrication is one way to alleviate this problem."
It would seem logical that instead of connecting the output wires inside the power amplifier to the output terminals, the wires should be wrapped and soldered directly to the speaker wires. Then, in turn, the other end of the speaker wires should be wrapped and soldered directly to the speakers, or crossover network. This is not practical, of course, unless the amplifier and speaker are integrated in the same cabinet.
For the truth about speaker wire, see my Speaker Wire History Page. Speaker Wire History