they are a type of male connector that can be added to the end of wires to make connections to the corresponding female receptacles more easy and/or more neat than bare wire. the "point" is convenience.
Many receiver terminals have "5-way" binding posts for speaker connections. Same with speakers.
You can use bare wire, but it is a pain using good 12ga wire into the small side-holes on the binding posts. It is easier on speakers, but try connecting 10 of these on the tight-spaced cluster of binding posts on the back of your receiver and you will learn why bananas are so handy.
There is another reason: oxidization. Bare copper wire always oxidizes. But making a tight crimp/bind on the bare wire with a banana tends to help reduce, but not eliminate, the rate of oxidization.
Bananas are also neater. We have seen numerious posts from people about their receivers over-heating or going into "protect" mode. This is usually traced to a small-strand of copper speaker wire sticking out of a binding post and causing a short-circuit. Bananas make it easier to do a neat wire job.
I like the dual-bananas from radio shack: (2xx-308) and the single bananas (2xx-306) if your binding posts dont have the same spacing as the dual units.
My speakers and my amp have binding posts that look like this (thanks Parts Express Binding posts).
As Bob previously noted, these "5-way" binding posts can accomodate bare wire, spades or bananas.
Is this the back of your receiver, the Onkyo TXSR500? The Onkyo website says it has Dual Banana Plug Compatible Speaker Terminals except for Speaker B. As you can see the Speaker A, center and surround jacks are 5-way binding posts, while the speaker B jacks are not.
Yes, that is the back of my receiver. So I should buy 5 sets of dual banana plugs? Should I buy 2 more for the back of my AS-F2s? What I don't understand is how the banana plug actually will connect to the receiver? Can anyone explain that to me?
What's a good site that sell good banana plugs? How much are they?
First - Go to Radio Shack and buy 1 pair for $6 and bring it home to see if the spaceing matches your equipment.
(Spacing on binding posts are NOT standardized so you just have to try and see.)
I love the dual-bananas for behind my speakers. They have a solid bar that prevents shorts should a child/dog run behind things and snag the speaker wires.
But the dual plugs stick out about 3". It does not sound like a lot, but add this to the back of your receiver and you may not have enough room. (another reason to bring 1 pair home to test with).
For behind my receiver, I like the Radio Shack single bananas (27x-306). You un-screw it into 2 parts, shove 12ga wire up the back part and fold the copper strands over the sides at the top. Then you screw the banana part onto the top and you have a very strong mechanical connection.
The bananas just friction-fit into the end of the binding post.
Note: See the picture above? It has little clips for the front speaker connections. You can buy "Pin connectors" from Radio Shack that work the same as banana plugs, but are designed to fit these clips.
My $.02. Anything you add to your system should be an upgrade to improve the audio/video quality. Something that can actually be seen or heard. If not, what's the point, spending money just cuz? Banana plugs are not an upgrade. All you are doing is adding another electrical connection, therefore more resistance, to your speaker cable. The fewer connections the better. There are of course exceptions, if you disconnect your speakers frequently then they will offer a bit of convenience but thats it. If your speaker wire is to thick to fit into the binding post then banana jacks make sense. I'd stick to bare wire twisted tightly and inserted into your binding posts. Try stepping up to a slightly larger speaker wire, let's say 14 or 12ga. Even then you may not notice any audible difference.