They say that the amplifier in sound reinforcement technology acts for the most part as a constant voltage source.

If the amplifier rated of 100 watt at 4 ohm and have a peak supply voltage of +/- 28 volts.

what is the formula on how to determine or calculate the voltage of potential from the amplifier?

 

Can you expand on your question? This is hard to understand -

what is the formula on how to determine or calculate the voltage of potential from the amplifier?

 

inorder to calculate the rigt speaker for 100 watt amplifier we must find out first the voltage of potential coming out from the amplifier

 

Haven't you already stated it as being +/- 28 VDC?

Besides, ones looks at the box and selects the speaker that has the desired impedance and is rated at the desired power handling. If the speaker is 4 ohms and rated for 100 watts, the voltage is not significant.

For 100 watts and 4 ohms, Power = I squared * R . 100/4 = 25, so the current will be 5 amps. E = IR, or 5 * 4 = 20 volts. That's a bit rough-and-ready, but the voltage just isn't an issue.

My big amp runs +/- 75 volt rails, and I haven't lost a speaker yet - and that's not because I don't turn it up. About 330 watts per side.

 

so, what is the basis in getting the voltage of potential? is it in Vrms or Vpeak?

for 100 watt amp. the peak supply voltage is +/-28.28 volts and a 20 volts Vrms.

 

One more thing,

They say that when it comes to electrical measurements, it is much easier to measure the voltage potential across a resistive load than it is to measure current flow through the circuit itself.

then, if we are going to measure the voltage potential from the current flow through the circuit itself. what will be the correct calculation for it? is it in Vrms or in Vpeak?

cheers..

 

Vrms is correct.