Ohm's Law: Volts equals current times resistance, V=IR.

Power in watts equals volts times amps. W=VA.

Ohm's Law says when speaker resistance decreases (lower impedance) then voltage will drop. Unless current increases enough to make up for the impedance drop. If impedance is cut in half going from 8 to 4 ohms then the amplifier will have to deliver twice the current (amps) to make it up. Otherwise voltage will drop.

You can see that since W=VA then one way or another current must increase to make up for impedance, or else power (watts) will decrease.

That's the math. In layman's terms, think of it as tube amps are designed as more of a voltage source. Not current. So when impedance drops, resistance is less, the tube amp does not increase current to compensate and so as a result power (in watts) is lower. Solid state amps are designed differently. As impedance drops the current increases and so power in watts doubles from 8 to 4 ohms.

So why is it there are all these tube amps that sound like they have way more watts than they do? Good question.

Power in watts equals volts times amps. W=VA.

Ohm's Law says when speaker resistance decreases (lower impedance) then voltage will drop. Unless current increases enough to make up for the impedance drop. If impedance is cut in half going from 8 to 4 ohms then the amplifier will have to deliver twice the current (amps) to make it up. Otherwise voltage will drop.

You can see that since W=VA then one way or another current must increase to make up for impedance, or else power (watts) will decrease.

That's the math. In layman's terms, think of it as tube amps are designed as more of a voltage source. Not current. So when impedance drops, resistance is less, the tube amp does not increase current to compensate and so as a result power (in watts) is lower. Solid state amps are designed differently. As impedance drops the current increases and so power in watts doubles from 8 to 4 ohms.

So why is it there are all these tube amps that sound like they have way more watts than they do? Good question.