# How to measure speaker current

Discussion in 'General Electronics Chat' started by PSnetwork, Aug 15, 2013.

Apr 1, 2013
30
0
2. ### wmodavis Well-Known Member

Oct 23, 2010
739
151
Series Ammeter, voltage drop across a series resistor, Clamp on ammeter, etc......

3. ### PSnetwork Thread Starter Active Member

Apr 1, 2013
30
0
I Know that... i meant how to calculate it if i dont have the speaker itself.
only with the speaker info.

4. ### wmodavis Well-Known Member

Oct 23, 2010
739
151

That is quite different from what you said in the OP.

I could only go by what you said not what you say you really meant after the fact.

And how are we suppose to know just what you know? If you do not provide the pertinent details it's 'by-guess-and-by -gorsh'. My crystal ball is cloudy. Sorry. But I meant to answer what you really meant to ask.

5. ### PSnetwork Thread Starter Active Member

Apr 1, 2013
30
0

ok bro just can you tell me how do i calculate the speaker current only with his info sheet?

6. ### wmodavis Well-Known Member

Oct 23, 2010
739
151
At what frequency? Do you know the formula relating power, current & resistance?

7. ### crutschow Expert

Mar 14, 2008
20,482
5,797
Well "bro", the speaker impedance varies with frequency, as the graph shows. So the current will vary with both the voltage and frequency content of the signal. You divide the signal voltage at a given frequency by the speaker impedance for that frequency. If the signal is more than a single frequency then you must integrate the current for each frequency component to get the total current.

8. ### PSnetwork Thread Starter Active Member

Apr 1, 2013
30
0
you have the info below. I think that the currents formula should be, I=P/V.
anyway i dont sure whats the voltage of the speaker.

9. ### wmodavis Well-Known Member

Oct 23, 2010
739
151

Do you know the formula relating power, current & resistance?

You gave a formula relating voltage, current and power NOT power, current & resistance.

10. ### PSnetwork Thread Starter Active Member

Apr 1, 2013
30
0
actually not, im beginner in electronics.

11. ### crutschow Expert

Mar 14, 2008
20,482
5,797
The speaker voltage is provided by the amplifier driving the speaker with a sound and the voltage value is determined by how loud the sound is.

What is the purpose of the question? Why are you trying to determine the speaker current?

12. ### wmodavis Well-Known Member

Oct 23, 2010
739
151
I= P/R ^1/2

You gave power = 20 W rms
On the graph of speaker impedance vs frequency pick a frequency then find the speaker impedance on the graph.

Then plug those values into the formula I provided above and solve for the current. So if that is really what you want you can calculate it.

13. ### #12 Expert

Nov 30, 2010
18,093
9,683
The simple answer comes from 20 watts, 8 ohms.
P=I^2R
20 Watts = current squared times resistance
20W/8 ohms = current squared
square root of power over impedance = current
1.58 amps is the current, continuous and
from 80 watts peak, current is 3.16 amps.

This is a very simplified form, but it is enough to try to fit a fuse for the speaker.
I think 2 amps, slow blow, would be about right, but I'm not the best at fuses.

14. ### PSnetwork Thread Starter Active Member

Apr 1, 2013
30
0
im trying to find the speaker current for calculating for how much time the power will be on with 5A/h SLA Battery. i found the solution below, thanks anyway.

thanks you guys that what i've asked. THANKS.

15. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
510
No, you haven't. The average current from the battery will probably be less than 5% of what you would calculate from the 20W figure. The 20W value on a speaker is absolutely meaningless for power consumption it's a rating where the voice coil melts.

Mar 6, 2009
5,448
790
17. ### PSnetwork Thread Starter Active Member

Apr 1, 2013
30
0
Sorry but my english is sucks. can you explain in a better way?

18. ### #12 Expert

Nov 30, 2010
18,093
9,683
You have discovered how to calculate the highest amount of power the speaker can survive. You have nearly nothing about how much power the amplifier will send to the speaker.

19. ### PSnetwork Thread Starter Active Member

Apr 1, 2013
30
0
Amplifier is 40W RMS max power. 2 speakers running, each one is 20W, so they will draw something like 40W in full power i guess. Isnt it good?

20. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
510
No, that's wrong. There is no way they would consume anywhere near 40W average power. You don't get the fact that speakers are rated in peak power and you won't be using anywhere near that power when playing music. I would be very surprised if you used more than 1/2W average power even listening to loud music.