"I'll huff and I'll puff"
I've been experimenting with different speakers in My Fender Blues Jr. and just notice with the last swap that I had the polarity reversed on the speaker connections. What effect would that have on the sound/performance of the speaker? I really didn't notice anything because this was the stock speaker that the amp came with - after I try a speaker I put the original back in to benchmark the differences. Any opinion welcome:rockon2: !
Speaker polarity is really only an issue if you have more than one speaker. Listen up for a bit and you'll come to see why!
Speakers work by having a voice coil suspended in the field of a magnet. If you apply an audio signal to the voice coil it will move back and forth in the magnet's field precisely following the ups and downs of the audio wave. If you attach that voice coil to a big cone that cone will amplify the coil's movement and push enough air that we can hear the audio signal! Bigger cones push more air than little cones and more power in the audio electrical wave means stronger pushing and pulling of that cone.
If we have more than one speaker in a cab the idea is that all cones push out together and pull in together. You want all the air moving in one big wave you can. If one speaker is moving opposite to the other(s) then it will be cancelling out some of the air movement. This means less volume for the most part and a few other less important but real tone things.
How do you make sure that all the cones move in unison? Most manufacturers label one speaker terminal with a red dot or a + sign. Then you can wire up the speakers like you would wire up batteries. If its parallel wiring then you simply tie the negative (-) terminals together and all the positive (+) terminals together. If you're wiring them in series then its in on (-), out on (+), on to the next speaker on the (-) and out on the (+) and so forth depending on how many speakers are involved.
The kicker is that there's no absolute standard in the speaker industry over which terminal you call the (+) terminal. The audio power is an alternating current anyway and the voice coil is simply that, a coil! Plus and minus alternates with the frequency of the wave.
So if you're using all the same speakers you could just pick the same terminal on each speaker but suppose you mixed brands of speaker? Or you had two different 4-12 cabinets and wanted to make sure they worked together for maximum volume?
The quick, easy and surefire way is to take a small battery and connect it across the speaker terminals. Since a battery is DC power the cone will move either in or out and stay there. You pick whatever you want as to which terminal you call the positive. I like to call the terminal positive that when connected to the battery positive moves the cone OUT but it doesn't really matter as long as you do it the same with all speakers. You just want all the cones always moving in the same direction, that's all.
You can use any small battery but AA,C and D sizes can be awkward 'cuz you have to hold the wires across the end caps of the battery. Rather than use a whack of duct tape it's easier to use a 9 volt since often the battery terminals are spaced wide enough to let you make contact with both speaker terminals to make your test.
It's not a good idea to let the battery power flow through the voice coil for hours and hours. In a low powered speaker you can burn out the voice coil. A quick test for a few seconds to see which way the cone moves is all you need and won't harm anything.
Now, what about your Blues Jr.?
Well, that's easy! Since its cone moves all by itself and there ARE no other speakers, who cares? Wail your guitar all you want and then go have a beer!
Hope this was useful...