Most recent audio amps can deliver fairly high wattage to a speaker despite being extremely small. I will explain how much wattage these miniature amps deliver and also look at some of the reasons for them becoming so small.
Traditionally, audio amps which deliver moderate to high wattage would be rather large and heavy. Modern amps mostly use switching power supplies which are much lighter than linear power supplies that were traditionally used. Higher-quality audio amplifiers often still use linear power supplies despite their weight and low efficiency since their output power is cleaner than that of switching power supplies.
The size of the energy source is one of the reasons why traditional power amps are fairly large. In addition, the low efficiency of traditional audio amps itself is another reason for their large size. A high-efficiency amplifier uses most of the power it consumes to deliver wattage to the connected speaker. A low-efficiency amplifier dissipates a lot of power as heat and thus requires fairly large heat sinks. Most of today’s power amps are class-D amps, also known as switching amps. Due to the high efficiency of Class-D amps, much less power is wasted. A low-efficiency amp requires a lot more power to operate than a high-efficiency amp in order to achieve the same output. This high demand for power increases the size of the energy source. This causes the amplifier to be even bigger due to the large energy source. Modern high-efficiency miniature power amps often use their enclosure itself as a heat sink.
Aside from amps that have an internal power supply, there are also models that require a DC voltage to work and use an external wallwart. The DC voltage is one of the following three important parameters that are often used to determine the maximum wattage of a power amp. These parameters are the power supply DC voltage, the amplifier output topology and the speaker impedance. When determining the amplifier wattage, there are also some other parameters to consider. Those parameters include the design of the amplifier itself and its thermal handling capability. Also, the power supply DC current rating is important.
The DC power supply voltage is so critical since the amp power stage voltage swing is limited by the power supply rail. In addition to the DC supply voltage, the amplifier topology also has a big affect on the maximum wattage since an amp that drives both speaker terminals (also called full-bridge configuration) can deliver 4 times more power to a speaker than an amp that only drives one speaker terminal (also called half-bridge configuration). The speaker impedance also determines how much power the amp can deliver since a higher impedance reduces the maximum amount of power.