There is confusion around this topic!
Power (wattage) does not exist without voltage.
If on the Voltage rule, loudspeakers are described as being 'Voltage Driven'. This is a sort of shorthand- it means that the amplifier is operating as a voltage source, which in turn means that the amplifier, if driven with a sine wave sweep from 20Hz to 20KHz, will put out the same voltage into the speaker load regardless of the impedance of the speaker.
Essentially this means the amp will be putting out twice as much power into 4 ohms as it does into 8 ohms.
But power still plays a role! and there is still the question of how much current you really need. The problem here is that the industry does not spec the current by itself and so amplifier companies are free to come up with their own expressions, which quite often have nothing to do with the power that the amp makes, and everything to do with how much current is present when your short out the power supplies in the amp!
You might want to read these two articles, which explain some of the intricacies.
http://www.atma-sphere.com/Resources/Common_Amplifier_Myths.php
and
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
The bottom line is how much current your amplifier will need to have will depend on the impedance of your speakers and how efficient they are, such that you will get a satisfying volume in your room.
For example if your speakers are 4 ohms and 100 watts is enough power, your amplifier will need 5 amps, which will allow it to make 100 watts (full power) into 4 ohms.
This is simplified of course, but without further information its a good place to start. If we know the speaker involved and the size of the room, a better calculation can be made.
Power (wattage) does not exist without voltage.
If on the Voltage rule, loudspeakers are described as being 'Voltage Driven'. This is a sort of shorthand- it means that the amplifier is operating as a voltage source, which in turn means that the amplifier, if driven with a sine wave sweep from 20Hz to 20KHz, will put out the same voltage into the speaker load regardless of the impedance of the speaker.
Essentially this means the amp will be putting out twice as much power into 4 ohms as it does into 8 ohms.
But power still plays a role! and there is still the question of how much current you really need. The problem here is that the industry does not spec the current by itself and so amplifier companies are free to come up with their own expressions, which quite often have nothing to do with the power that the amp makes, and everything to do with how much current is present when your short out the power supplies in the amp!
You might want to read these two articles, which explain some of the intricacies.
http://www.atma-sphere.com/Resources/Common_Amplifier_Myths.php
and
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
The bottom line is how much current your amplifier will need to have will depend on the impedance of your speakers and how efficient they are, such that you will get a satisfying volume in your room.
For example if your speakers are 4 ohms and 100 watts is enough power, your amplifier will need 5 amps, which will allow it to make 100 watts (full power) into 4 ohms.
This is simplified of course, but without further information its a good place to start. If we know the speaker involved and the size of the room, a better calculation can be made.