help with some basics plz

[Inferno]

well hello there...
i know that my question will be somehow very stupid ... but sorry i m not that electornics expert...
well when they say a 4 watt power amplifier ( by example ) what does it mean ???
that if the speakers are plugged into the amplifier and the amplifier is plugged to a voltafe source so the P= U x I would be 4 ?? i mean if i mesure the voltage and the intensity on the battery and the circuit .. the U would be 4 ????
sorry again for the question but i need to know plz

 

[Nigel Goodwin]

well hello there...
i know that my question will be somehow very stupid ... but sorry i m not that electornics expert...
well when they say a 4 watt power amplifier ( by example ) what does it mean ???
that if the speakers are plugged into the amplifier and the amplifier is plugged to a voltafe source so the P= U x I would be 4 ?? i mean if i mesure the voltage and the intensity on the battery and the circuit .. the U would be 4 ????
sorry again for the question but i need to know plz

No, it's the output power of the amplifier, just rating it as '4 watts' though is pretty unhelpful, it should also tell you the way it's measured. The only way worth listing is watts RMS, and it should include more information as well. Something like this "4 watts RMS continuous sinewave from 20Hz to 20KHz into 8 ohms at less than 0.5% distortion".

The actual drawn from the supply will be more than the output power, as there are considerable losses in the amplifier - depending on it's design. However, these figures will depend entirely on the type of signal through the amplifier, and how loud it's turned up.

 

[Inferno]

ok 10x for replying .... i ll try to explain the problem i m having
i m trying to build a similar amplifier to a one i have here .... well when i turn on the amp and i mesure the intensity on the input it s 0.15 A the battery is 12 v .... the measurmentrs on the output can't be done i guess.... anyway ... if this is the case what do u think the internal amp is ??? i mean how many watts it is ?|??aproximately ...

 

[Nigel Goodwin]

ok 10x for replying .... i ll try to explain the problem i m having
i m trying to build a similar amplifier to a one i have here .... well when i turn on the amp and i mesure the intensity on the input it s 0.15 A the battery is 12 v .... the measurmentrs on the output can't be done i guess.... anyway ... if this is the case what do u think the internal amp is ??? i mean how many watts it is ?|??aproximately ...

You can roughly calculate the power output from the supply voltage, with a single ended amplifier (one side of the speaker connected to 0V) you can get about 4W RMS into a 4 ohm speaker, into 8 ohms you will get about 2W RMS.

 

[Inferno]

well 10x for ur informations again....
the speaker i have is a horn tweeter ... when i m putting it into the ohmmeter it s giving 2 ohms ( but with a bad ohmmeter.. when i rely his 2 borns with no resistor it give 1 ohm ... ) with another one more professional it s giving 1 .2 ohm ... so i guess it s a 1 ohm tweeter ... so it would be a 16 W RMS ???
what i mean is that the circiut i need should be a 16 W power amplifier to get the same sound power ?( theoricly and basicly ) ??
another question ... with this amplifier ... on the power input ... i should have the same internsity ??? 0.15 A ?? coz the intensity flow should be very low ... coz i need it to run on battery for a long time
10x again

 

[Nigel Goodwin]

well 10x for ur informations again....
the speaker i have is a horn tweeter ... when i m putting it into the ohmmeter it s giving 2 ohms ( but with a bad ohmmeter.. when i rely his 2 borns with no resistor it give 1 ohm ... ) with another one more professional it s giving 1 .2 ohm ... so i guess it s a 1 ohm tweeter ... so it would be a 16 W RMS ???
what i mean is that the circiut i need should be a 16 W power amplifier to get the same sound power ?( theoricly and basicly ) ??
another question ... with this amplifier ... on the power input ... i should have the same internsity ??? 0.15 A ?? coz the intensity flow should be very low ... coz i need it to run on battery for a long time
10x again

If you're measuring with an ohmmeter you're measuring the resistance, not the impedance - they are very different values. Your tweeter is most likely 8 ohms, although there's a far lesser chance of it being 4 or 16 ohms.

As for power consumption, again it depends entirely on both output power and the actual waveform.

 

[Inferno]

well i ve made some measurments on the output ... it s going between 0.3 V and 3 V so when dividing by 2.828 i would get betwenn 0.11 and 1.1 ... when squaring it would be 0.01 and 1.21 ... when dividing by 8( speaker impedance ) it would be 0.00125 and 0.126 W RMS ??? is that possible ???
so i dunno if i m making false mathematics here.. but all i want to know is that when i m using like u said a 8 Ohm speaker ... with a battery of 12 V and a sinusoidal sound on the output with high frequency ( about 3 to 10 Khz) i want that the intensity do not cross the 0.5 A on the power input ( the battery ) what is the maximum power of the amplifier that i can use ???? i mean which amplifier can i use for this maximum ??