MadSci Network: Engineering

Re: How can I tell which connection on a speaker is 'positive'?

Date: Mon Oct 4 16:05:30 1999
Posted By: Steve Czarnecki, senior technical staff member, Lockheed Martin
Area of science: Engineering
ID: 935895114.Eg

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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