|MadSci Network: Engineering|
Speakers, being made to work with alternating current waveforms, don't have a "positive" or "negative" polarity per se. A single speaker will work just fine connected to an amplifier without regard to polarity. Multiple speakers, on the other hand, must be phased correctly to work in unison properly. This is true for multiple speakers within a single enclosure, or a set of speaker connected to multiple amplifier channels. By "correct phasing", what's required is that all the speaker cones move in the same direction when the source amplifier(s) apply a voltage of a given polarity. This synchronization ensures that when the amplifier produces a positive voltage, all the speakers compress the air in front of them. If care is not taken in this regard, some speaker cones are compressing the air while others are expanding the air -- effectively, the speakers are working against each other. Commercially purchased loudspeaker cabinet systems will always have some reference marking allowing correct phasing of the speakers. Red and black markings are typical. When hooking these up it's necessary to ensure that like color speaker terminals are hooked to like color amplifier terminals. Speaker wire carries some sort of markings to help keep track of which wire is which at the two ends. It's simple to check whether speakers have been phased correctly. A simple test is to hook the speakers up and place them so that they face each other with only 3 or 4 inches separating them. Play some music at low to moderate volume through the system, and listen to how it sounds. Then reverse the connections on ONLY ONE of the speakers, and play the music again. The connection which gives the loudest volume is the correct phasing. If you can't place the speakers face to face as I suggest, then at least get them side by side facing the same direction, as close as possible next to each other. This test may be necessary to rule out a wiring error internal to the speaker cabinet (especially if the speakers have been repaired or home-built), or if there's a chance somehow that the polarity of the audio signal of one channel has been reversed between the audio source (e.g., CD player) and amplifier. Mistakes can happen easily with homebuilt interconnect cables if attention is not paid to ensure connection of the center conductors of the plugs and jacks to the center conductors of the shielded interconnect cables. It's possible to get center connection and shield connections mixed up if you're not used to working with this. Another possibility is a wiring error inside a repaired amplifier or a design or construction error inside a homebuilt amplifier. A symptom of incorrectly phased speakers is very poor bass response, weak volume, and a vague, diffuse sound "image" (audiophile terminology). Correctly phased speakers will have a full, rich sound and the sound will seem to be focussed. Happy listening! Steve Czarnecki
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