Power Amp Doubling Output at 4 Ohm

It is important in that it's an indication of a robust power supply (and PS are an expensive part of the amp).

However, please note that doubling is not really possible, for a number of tech reasons. This does NOT mean that manufacturers quoting doubling are fraudulent!

What you do is, officially spec your amp at 8ohms for less than max output, which will allow the arithmetic to hold true to specs. Please note that amps capable of dealing with difficult loads (i.e. low ohm loads) are considered good designs and trustworthy.

Is this an important parameter to you? If not, why not?

It only became important to me when I recently bought my first pair of inefficient speakers that are a difficult load. (4 ohm 82-87db). Before these speakers, I never paid much attention to amps that double power.

1/ Realise that this concept ONLY applies to solid state amps - a tube amp delivers it's maximum power into the rated impedance, and less as the impedance climbs or drops.

2/ If the SS amp is well designed, with a decent sized powersupply and enough output devices, it SHOULD double it's 8 ohm power into 4 ohms.

Regards, Allen (Vacuum State)

Sometimes, it just means large amounts of stabilizing feedback.

A perfect transistor amp would double every time you halve the impedance. Ones with big enough power supplies more or less do this. If you have inefficient speakers that have low impedance this is an important consideration. But it is not the only one. Many class a amps will not do this and if you have efficient high impedance speakers you can look for amps that are designed to maximize other parameters of performance. All design is compromise and a powerhouse large amp MAY give up speed and transparency to amps that do not have the same power but which can react faster. There is no real rule to guide you here, every amp has to be considered individually in terms of how it meets your needs. A general principal is to have plenty of power but to go with the smaller amp if you are choosing between two that meets your needs as it will PROBABLY have a simpler circuit [need fewer power transistors] than the bigger one. All the above may not hold in individual cases and this complexity explains the theoretical advantages of active speakers in which the amp is tailored to the individual speaker. Again some designs execute this better than others.