how do you test amplifier output wattage

haemphyst wrote: OK... You are very confused, it seems... If you increase the resistance say, from 2 ohms to 4 ohms, you have to increase the VOLTAGE to overcome the additional resistance to drive the current THROUGH the resistance to make power. If all you do is increase the resistance, you cannot get the same power through it, as the current will drop, because the voltage was not increased to overcome the increase in resistance. It all goes hand in hand. Plug the numbers into the formulae, and you'll see. Amplifiers are current devices, they regulate the current output to try to maintain a given VOLTAGE on their output rails. This is why power ratings increase when the load increases (this means lowering the impedance), the voltage remains the same, but when you halve the impedance, the amp will try to double the CURRENT to maintain the same voltage across the terminals. Twice the current with the same voltage, means twice the power. It all plugs in together.

That's why I said you would need to upgrade the amplifier, to allow increased voltage to overcome the increased resistance, to maintain the same power output without increasing current draw. Is this wrong? What I'm saying is that, to produce the same power output, you can either increase the current, as you describe (ie upgrade alternator), or increase voltage (ie upgrade amplifier). I don't see how this is wrong.

cim2phat4u wrote: That's why I said you would need to upgrade the amplifier, to allow increased voltage to overcome the increased resistance, to maintain the same power output without increasing current draw. Is this wrong? What I'm saying is that, to produce the same power output, you can either increase the current, as you describe (ie upgrade alternator), or increase voltage (ie upgrade amplifier). I don't see how this is wrong.

Partly right... To increase the voltage, yes, you would purchase an amplifier rated for higher power for an equivalent load i.e. 100 watts at 4 ohms vs 200 watts at 4 ohms. The 200 watt @ 4 ohm amplifier would provide you with 100 watts at 8 ohms, yes, with all of the good things that go along with running an amplifier at higher impedance - lower heat, better THD figures, better damping, better S/N ratio, improved efficiency. Here's where you are (and please, this is only for teaching purposes...) wrong. Whether you upgrade the alternator or not, (wow... loss for words...) umm... OK, (got it...) the input current demand will ONLY increase if the output power increases... (again, by 1: ingreasing the load (lower impedance) or B: increasing output voltage across a given load) What I am saying here is that the input current will not change unless required by the output power increasing... the DEMAND for input current will not go up (increasing output), just because the input power supply CAN provide it, i.e. a High Output alternator. Just because you put a high output alternator in your car, the amplifier won't automatically increase their output power. I think this is what you are saying... Please, if I am misinterpreting your thoughts, let me know. There are two ways to get more power, no more. 1: Increase the load by lowering the impedance. 2: Swap amplifiers for a higher powered amplifier. Now, if the input power supply is "stiff" enough, there will be no input power drop, and in all of my illustrations above, I am assuming a "perfect" power supply - infinite current at any given voltage - in the car, 14.4 volts DC. If the power supply is not perfect (and we all know it isn't, that's why a HO alternator - closer to perfect) the input voltage will sag, if the available current cannot maintain said voltage. Please read my sticky at the top of the page - "How To Choose An Amplifier". I cover lots of this in more depth, (especially the part about running higher than rated impedances) in there.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

cim2phat4u wrote: [QUOTE=haemphyst] That's why I said you would need to upgrade the amplifier, to allow increased voltage to overcome the increased resistance, to maintain the same power output without increasing current draw. Is this wrong? What I'm saying is that, to produce the same power output, you can either increase the current, as you describe (ie upgrade alternator), or increase voltage (ie upgrade amplifier). I don't see how this is wrong.

"To produce the same power output" no matter the load impedance requires the same power input.  If the load impedance changes for the same power output the net power does not change, even if the voltage and current levels do: meaning 100 watts delivered from any amplifier into 4-ohms is the same power as 100 watts delivered into 8-ohms.  Anything else would be a magical perpetual motion machine, and even though Tesla claims to have invented one I ain't seen it yet.    The only way to change the input requirements for any fixed output level  is to use an amplifier with higher operating efficiency.

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