"My question still remains ..."
My simplistic response is that an amp with a 50 watt rating might not be able to handle certain music peaks. 50 watts alone might not be enough. The 50 watt rating is how much power the amp will deliver on a steady state basis into a purely resistive 8 ohm load (versus a more complex load like a real speaker) at a mid-band frequency. What happens with a complex load or a load where the impedance drops below 4 ohms? The amp might run out of steam. The joule rating applies to the power supply, actually to its capacitors, and gives a measure of how resilient the amp is when dealing with complex music material with significant peaks when driving a complex load like most speakers. I won't repeat all the fine explanations of the preceding posters regarding what a joule is. My bottom line is that an amp rated at 50 watts might not be powerful enough for some music peaks. Whether it can perform well depends on design decisions that can be partially described by certain statistics, like the power supply's joule rating.
My simplistic response is that an amp with a 50 watt rating might not be able to handle certain music peaks. 50 watts alone might not be enough. The 50 watt rating is how much power the amp will deliver on a steady state basis into a purely resistive 8 ohm load (versus a more complex load like a real speaker) at a mid-band frequency. What happens with a complex load or a load where the impedance drops below 4 ohms? The amp might run out of steam. The joule rating applies to the power supply, actually to its capacitors, and gives a measure of how resilient the amp is when dealing with complex music material with significant peaks when driving a complex load like most speakers. I won't repeat all the fine explanations of the preceding posters regarding what a joule is. My bottom line is that an amp rated at 50 watts might not be powerful enough for some music peaks. Whether it can perform well depends on design decisions that can be partially described by certain statistics, like the power supply's joule rating.