At a given frequency (recall that impedance is frequency dependent), the 
current flowing in a circuit can be calculated using the equation:

I = E / Z - or Current equals Voltage divided by Impedance to current flow. 
*Think of the voltage (E) as pushing against some resisting force (Z), and 
producing a certain amount of movement or flow (I). *If you push harder 
(more voltage), or you reduce the resistance to the flow (lower Z), then you 
increase the amount of movement or flow (I). *It is a simple, linear 
relationship (but only at a single frequency, because Z is frequency 
dependent).

The amount of power is a function of how much current is flowing, and the 
applied voltage. *Think of it this way. *If you push harder (more voltage) 
you have more movement of the same amount of whatever you're pushing 
(current). *The relationship of power to the push (voltage) and flow 
(current) in an electrical circuit has the relationship:

P = I * E *- *Or power (work done) equals current (flow) times voltage 
(push).

The more you push, and the harder you push it, the more work you get done.

An audio amplifier does work (ultimately generating sound) by swinging a 
voltage across an impedance (pushing current across an impedance) in a 
"pattern" that is determined by its input, and its transfer 
function. *The transfer function defines the changes to the signal as it 
passes through the amp, and for the moment, we will consider the amplifier 
to have a linear transfer function, meaning that it's only going to amplify 
the signal, and will not distort it in any way. *The total power the 
amplifier can deliver depends on the voltage swing and the amount of current 
it can deliver. *Since P = I * E, when you increase I or E, P will also 
increase.

From this we can see that the maximum power available will be limited either 
by the voltage (E) or the current (I) which the amplifier can swing 
(voltage) or deliver (current).

With a given amplifier, the maximum voltage swing is determined by the power 
supply design, and the maximum current available depends on a number of 
factors, including the current carrying capacity of the output devices. 
*ASSUMING that the amp has enough current available, a lower impedance load 
will allow more current to flow, and more current means more power. 
*Deriving the relationship between Z (impedance), P (power), and V (voltage) 
requires the use of both the equations given earlier. *To calculate the 
power delivered to the speaker at a given voltage we have three knows, the 
impedance, and the voltage. *From this, we must calculate the current, using 
I = E / Z. *If the amplifier can swing 24 volts, and the impedance is 
8-ohms, then I = E/Z = 24/8 = 3. *Now, given that I = 3, we can calculate 
the power, P = I * E = 3 * 24 = 72 watts. *To make life easier, we can 
combine the two equations into one, that will compute power directly, given 
voltage and impedance.

P = I * E
Since I = E/Z, we can replace I with E/Z in the above equation, giving us...
P = (E/Z) * E.

Now let's quickly calculate the power that 24 volts will push through an 
impedance of both 8 and 4 ohms.

E = 24.
If Z = 8 then (E/Z) * E = (24/8) * 24 = 72 watts (same as we got before).
If Z = 4 then (E/Z) * E = (24/4) * 24 = 144 watts (which is twice the power 
delivered through the 8-ohm impedance.

Note that we got twice as much power, because the same voltage could move 
twice as much current, because the impedance to that movement was cut in 
half. *If you had a 2-ohm speaker at 24 volts you'd double the power again, 
to 288 watts, and if the speaker had only one ohm at 24 volts we'd have 576 
watts. *There is a problem though. *With only 1 ohm of impedance, the 
current flow (I = E/Z) is now 24/1, or a full 24 amps. *That's a lot of 
current, and would require output devices and a power supply that could 
deliver the current required without damage.

The main thing you have to worry about (and I wouldn't worry about it too 
much) is that a speaker with a very low impedance can cause an amplifier 
problems, because the amp may not be able to deliver the current required. 
*YOU GET MORE POWER OUT WITH LOWER IMPEDANCE, but if you go too low, you can 
damage the amp. *This is almost never a problem with modern amps and 
loudspeakers (though it can be, depending on the way the gear is designed). 
*Most amps will shut down, or distort noticeably, or blow a fuse, before 
they'll die from being asked to deliver too much current (but some amps will 
hurt themselves trying to deliver the current). *You will know if the 
impedance of the speakers is too low, because you'll either hear a problem, 
or you'll damage your amp. *Any modern amp should handle 4-ohms (or less) 
without any problem. *Low powered amps will always be clipping a little, but 
they won't eat their own lunch.


"Evaldas" <sanya@takas.lt> wrote in message 
news:h8b2j9$bn7$1@trimpas.omnitel.net...
> "Necris" <abc@def.aef> wrote in message 
> news:h8arnj$vh$1@trimpas.omnitel.net...
>> Mazesnes varzos koloneles rys daugiau stiprintuvo galios.
>
> Tikrai ? Kodėl ? 


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