The first is the sound pressure level driving a speaker with 1 Watt of power and measuring spl at 1 meter. There are two ways of expressing it in common usage, which makes it confusing. I will assume you are talking about loudspeaker sensitivity. I don't know exactly what you mean by the db rating. However the amp has to provide more current to the four ohm load so the output transistors have to be more robust. The issue is that the amp does not necessarily have to be more powerful to drive the 4 ohm speaker. Obviously the output voltage can not exceed that. The voltage an amp can deliver is determined by the operating voltage of the power transistors.
The maximum current output determines how much power an amp can deliver to a given load. It is the current output of the amp that has a bearing on cost. The point is that amplifiers that have to deliver more current require larger power supplies and bigger output devices. If you do the above calculations that would be 100 watts into 4 ohms. The transistors will be stressed and the amp will likely hit a hard clip and in the worst case scenario will clip at five amps, if that is its maximum current output.
Well if the amp drops voltage supplying the four ohm load it is current limited. Now you might say what is the difference. So we would have 40 volts squared/4 ohms this is 1600/4 which is 400 watts. Now if the amp did not drop its voltage when driving the 4 ohm load then the power delivered is the square of the voltage divided by the resistance. Now the voltage from ohms law is 7.071067 amps X 4 ohms which is 28.284 volts. Which is 50, the square root gives a current of 7.071067 amps The square of the current is 200 watts/4 ohms. Now the voltage from ohms law is the current X the resistance which is 5 amps X 8 ohms which is 40 volts So the amp has to deliver 5 amps to produce 200 watts into 8 ohms.
So if we have the 8 ohm load the square of the current is 200 watts/8 ohms which is 25. Now the power delivered is the square of the current X the resistance.
#FUMY TECH 9 OHM VS 7 OHM SERIES#
We discuss the math of speaker impedance and how it changes depending on if you wire two in parallel or series in Loudspeaker Impedance: Series vs Parallel ConnectionsĬlick to expand.The issue is that the amp does not necessarily have to be more powerful to drive the 4 ohm speaker. Of course Speaker Sensitivity is also important b/c it tells you how much power you will need to drive the speaker with to hit a certain loudness level. If your stuck on jargon like Ohm's Law, Impedance and Electrical Phase and wondered what makes a loudspeaker “difficult to drive”, you will want toreview our article on Understanding Ohm's Law Loudspeaker Impedance: is the sum of DC resistance and complex AC reactance comprising inductance and capacitance, the value of which changes with frequency. With all things equal, a 4 ohm speaker requires twice the current draw than a similar 8 ohm version. It all has to do with an amplifiers ability to source current to a load. Will you guys please explain to me what the difference is between a 200 watt 4 ohm speaker and a 200 watt 8 ohm speaker and what one needs a more powerfull amplifier than the other?
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