Car subwoofer ohms, please can someone explain?

Jun 20, 2018
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Please can someone explain car subwoofer ohm choices and the impact on the amplifier?

I plan to upgrade a skoda octavia vrs subwoofer and people state the amp power is 1x200 4ohm or 2x100 8ohm. The sub is a dual voice coil at 2x4ohm and a few people say I need an 8ohm dual voice coil sub and if using a sub at 4ohm the amp will shut down. I would have assumed 4 ohm would allow more power so I don't understand why the amp would shut down. Please can someone explain?
 

clarkjd

Distinguished

Ohms are a measure of the resistance(impedance) of an electronic component in a circuit. Every component in the circuit will have a value in Ohms. Now, if the voice coils of the subwoofer are in series (one after the other) then their individual impedances will be additive : 4 + 4 = 8 Ohms. If they are in Parallel, then they will be halved: 4 ohms in parallel with 4 ohms = 2 ohms.
Your amp will deliver 200 watts into a 4-ohm load. If the load is less(2-ohms) then you run the risk of blowing out your amplifier, and it would probably go into self protection mode and shut down.

 

clarkjd

Distinguished

Ohms are a measure of the resistance(impedance) of an electronic component in a circuit. Every component in the circuit will have a value in Ohms. Now, if the voice coils of the subwoofer are in series (one after the other) then their individual impedances will be additive : 4 + 4 = 8 Ohms. If they are in Parallel, then they will be halved: 4 ohms in parallel with 4 ohms = 2 ohms.
Your amp will deliver 200 watts into a 4-ohm load. If the load is less(2-ohms) then you run the risk of blowing out your amplifier, and it would probably go into self protection mode and shut down.

 
When you bridge an amp the minimum impedance is doubled. That means that if an amp is stable into 4 ohms in mono
then it should be able to drive a 2 ohm load in stereo. You should be able to connect each voice coil to one channel of the amp safely. The woofer would be getting 400 watts total. This is better than hooking the voice coils in series since that will reduce the damping factor of the amp. That will reduce the control over the woofer that the amp has leading to looser bass.
 
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