what type of amp is usually used to power both a sub and speakers. does it have to be a 4 channel amp or does it depends on the power of the amp?

 

4ch would be ideal.

 

i'm confused. what are you looking to do?

 

once i get new speakers i want to power my sub and speakers all to one amp

 

ok. not IMO the best way to do it but ok.

make sure you get a sub that is going to run at a 4 ohm impedance because a 4 channel will only be stable down to 4 ohms when bridged. also make sure the sub is fairly efficient because if not then it won't get very loud. buy as much power as you can afford to get. you can never have to much.

 

will the sound quality be better with two dif amps?

 

it has the potential to get louder and still sound cleaner using more power, which using 2 separate amps will allow for.

 

IF you're operating the amplifier within it's parameters, there will be NO sound quality difference.

There are three channel amplifiers out there, with 1 channel (usually) characteristically different than the other two (ie: class D sub channel). The DLS A5 comes to mind.

Several people build their systems with the building block approach. Usually due to budget, they'll buy a 4 channel amplifier first, and bridge a pair of channels to the sub[s]. Later, they might buy another amplifier for the subs, and run the components active.

 

very true, all very true.

what you do all depends on budget, skill level and how loud you really need it.