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What Impedance is car audio?

#26
Electricblue said:
Or a big bang :P i will try 4 ohm speakers then :)

Any idea how long a 17ah battery will last with the amp pumping out at about 3/4 volume?
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Assuming the amp pulls 10 amps from the battery, it will run about 40 seconds.

And amps don't have impedance. You're going about this backwards. There's a reason people don't use car audio equipment outside of a car.
 
#30
mmbongo said:
And amps don't have impedance. You're going about this backwards. There's a reason people don't use car audio equipment outside of a car.
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All amplifiers ( and other electrical devices) have an electrical impedance, both input and output. The important part is to not go lower than the Minimum Impedance. This is the same for car, home, bass, guitar, or PA amplifiers.
Of course car amps are usually used in cars. And I use a bass amp for my bass, and an A/V receiver for my home, and ....
 
#31
randall p said:
All amplifiers ( and other electrical devices) have an electrical impedance, both input and output.
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Maybe, but that's not what he's asking. For instance, you don't go to the store and buy a '4 ohm amp'. A speaker is a resistor, an amp is not. Also keep in mind that a 4 ohm speaker will vary in impedance from 2 to 8 ohms or so during operation.
 
#32
mmbongo said:
Maybe, but that's not what he's asking. For instance, you don't go to the store and buy a '4 ohm amp'. A speaker is a resistor, an amp is not. Also keep in mind that a 4 ohm speaker will vary in impedance from 2 to 8 ohms or so during operation.
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I will agree with that. Likewise, amplifiers require a minimum of resistance. Ohm is a measure of electrical resistance. Resistors are measured in Ohms. Reading in between the lines, I think the OP just wants to know what Ohms rating of said speakers should be to safely operate his amp.
 
#34
Electricblue said:
Or a big bang :P i will try 4 ohm speakers then :)

Any idea how long a 17ah battery will last with the amp pumping out at about 3/4 volume?
Click to expand...

Ah (or amp-hours) is a basic representation of how many amps the battery can produce at a constant level for one hour before depleting the battery. 17Ah means that if you are pulling 17 Amps, your battery will be discharged in one hour. To find the time for another Amperage, simply divide the Ah by the current demand. In the 10 amp scenario: 17/10 = 1.7 hours before depletion of the battery. You may have to experiment and place a multimeter (or ammeter) in series between the battery and the amp to see what your current draw is. I doubt it will be constant. Probably will vary with the work demanded at a given instant.

*Electronics 101*
 
#35
mmbongo said:
My answer would be that the amp is designed to drive a 4 ohm load without melting down. However 8 ohms would be better. Half the current, half the heat, still plenty loud.
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True. Although 4 ohms will get the most out of the amp, 8 ohms might give a little more battery life... maybe.
 
#36
dBPete said:
Ah (or amp-hours) is a basic representation of how many amps the battery can produce at a constant level for one hour before depleting the battery. 17Ah means that if you are pulling 17 Amps, your battery will be discharged in one hour. To find the time for another Amperage, simply divide the Ah by the current demand. In the 10 amp scenario: 17/10 = 1.7 hours before depletion of the battery. You may have to experiment and place a multimeter (or ammeter) in series between the battery and the amp to see what your current draw is. I doubt it will be constant. Probably will vary with the work demanded at a given instant.

*Electronics 101*
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Yeh, I know what Ah is and everything, its just I wondered if there was a formula to give a rough estimate.

Theres lots of things, like the power draw from the amp, the efficiency of the amp, etc...

Anybody have a ROUGH estimate?
 
#37
Electricblue said:
Yeh, I know what Ah is and everything, its just I wondered if there was a formula to give a rough estimate.

Theres lots of things, like the power draw from the amp, the efficiency of the amp, etc...

Anybody have a ROUGH estimate?
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db pete was right when he said 1.7 hours, assuming amp draws 10 amps of current. You can calculate it here:
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17ah = 17000ma
10amps = 10000ma
 
#39
Electricblue said:
10 amps is a hell of a lot, i doubt it would be that much?

I ran 2 x 6ohm speakers on it at about half volume in the sun for 7 hours straight.

Does speaker impedance make any difference to battery life?
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Current draw depends on the amp, 10 amps is normal to low for car audio.
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Speaker impedance matters. The lower the impedance, the harder the amp works, the more current it draws, the hotter it gets, and all that discharges the battery quicker. I'd use 6 or 8 ohm speakers, keeping in mind that an 8 ohm speaker will dip down to 3-4 ohms during operation.
 

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