speaker connection

can you discuss the advantage and disadvantage of connecting speakers in parallel and series, which connection is more advisable? thanks!
Generally only a single speaker should be connected to a given amplifier output.

If you want to connect more speakers, you have a few choices:

1. You can buy an amp designed to support them (multizone or multichannel) and which has more speaker connections.

2. You can buy a second amp and use "Y" splitters to connect your source to both amps -- then drive each set of speakers off it's own amp.

3. You can use "impedance" matching device(s) -- either a single box that all the speakers connect to, or one that's part of a volume control located at each pair of speakers. This requires, though, that your amp have some power -- probably more than your has.

Bottom line, no free lunch, sorry.
If you are talking hooking them up in a speaker project like lets say 2-8" woofers. If they are both 8-ohm drivers and you hook them up in parallel you would have 4-ohms and would add about 3db but needs more current/power to drive them. If you hook them up in series you would have 16-ohm load and would loose 3-db.
If you are hooking up two sets of speakers this can be done only if they are an 8-ohm load and only if you amp is 4-ohm stable.
Like Ehart said you can use a impedance matching speaker switch box. I use a receiver for my home theater setup that runs my kitchen,deck and bass shakers thur a switch box and run a 5-channel amp for the main speakers.