I assume you mean the power supply filter capacitors. The function of these caps is twofold: to smooth the pulsating electrical current from the power supply and to provide energy storage for (temporary) high current draw resulting from low impedance.
Using the caps for filtering is the top priority. The energy storage is a secondary consideration - one that is provided by the power supply transformer. So why one, two, or more caps? One factor is cost. Audio grade caps are very expensive and to keep down cost, a good place to start is the power supply.
The other factor is performance. One difference between large and small capacitors is that smaller caps fill and discharge quicker. This enables the amp to be faster, which enables a higher bandwidth and all other nice parameters. Another advatage to multiple caps is that the energy storage is increased along with the advantage of faster charge discharge. The biggest advantage of multiple caps is that the output impedance is lowered when in parallel. This enables better voltage regulation at the outlet of the power supply. Voltage regulation is expensive and is one of the biggest factors is the amplifiers' sound quality.
The advantage of a single, larger cap is one of cost and lower resistance due to induction. One large cap can filter and store as well as a series of smaller caps but the charge/discharge time is slower as you go for more power from the amp. But a sinlge cap is only considered if the available sizes are what is required in terms of rated power. Sometimes, higher power amps require multiple caps because the total amount of capacitance needed cannot be supplied by one cap.
It's basically a cost/performance consideration. Why would an airliner have two engines instead of four - two can take you just as far and fast (but at a decreased payload) but obviously two are cheaper than four in terms of first cost and maintenance. But if you need to go farther with more payload, you go with the four. Same with amps - the need to maintain performance down to 2, 1 or half an ohm may or may not be a consideration unless cost is no object. But if it is, then you trade off.
Using the caps for filtering is the top priority. The energy storage is a secondary consideration - one that is provided by the power supply transformer. So why one, two, or more caps? One factor is cost. Audio grade caps are very expensive and to keep down cost, a good place to start is the power supply.
The other factor is performance. One difference between large and small capacitors is that smaller caps fill and discharge quicker. This enables the amp to be faster, which enables a higher bandwidth and all other nice parameters. Another advatage to multiple caps is that the energy storage is increased along with the advantage of faster charge discharge. The biggest advantage of multiple caps is that the output impedance is lowered when in parallel. This enables better voltage regulation at the outlet of the power supply. Voltage regulation is expensive and is one of the biggest factors is the amplifiers' sound quality.
The advantage of a single, larger cap is one of cost and lower resistance due to induction. One large cap can filter and store as well as a series of smaller caps but the charge/discharge time is slower as you go for more power from the amp. But a sinlge cap is only considered if the available sizes are what is required in terms of rated power. Sometimes, higher power amps require multiple caps because the total amount of capacitance needed cannot be supplied by one cap.
It's basically a cost/performance consideration. Why would an airliner have two engines instead of four - two can take you just as far and fast (but at a decreased payload) but obviously two are cheaper than four in terms of first cost and maintenance. But if you need to go farther with more payload, you go with the four. Same with amps - the need to maintain performance down to 2, 1 or half an ohm may or may not be a consideration unless cost is no object. But if it is, then you trade off.