# Why are most car audio speakers 4ohm, and home audio 8ohm?



## BowDown (Sep 24, 2009)

What's the deal?


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## ErinH (Feb 14, 2007)

car audio guys want to see higher power ratings. iow: marketing


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## cbrei1023 (Dec 2, 2008)

I read somewhere once that more resistance = more clarity but also more power consumption. From this i deducted that while in a car you are running off of 12V and while in a home 120V so 8 ohm drivers would be easier to power. Don't know if its right but its what ive always firgured.


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## kyheng (Jan 31, 2007)

^That's the good point of having marketing gimmick.........


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## chad (Jun 30, 2005)

bikinpunk said:


> car audio guys want to see higher power ratings. iow: marketing


Well kinda.... 

In order to make the same power at 8 ohms you need twice the voltage. When the 4 ohm standard was adopted switching FET technology was fairly in it's infancy and it was rough job to have twice the voltage on the older amps. current was no issue, breakdown voltage in somewhat affordable FETs were a big deal. as were transformers to get that multiplier.


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## Candisa (Sep 15, 2007)

8ohm has some advantages over 4ohm sound quality wise, but in a car, with only a 12-14V power supply, it's easier to power 4ohm speakers (less rail-voltage needed to have the same power compared to 8ohm loads).

Isabelle


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## sqshoestring (Jun 19, 2007)

Yes, you have low voltage and plenty of amperage in a car, just opposite the home. When you lower ohm load to an amp, you need less voltage from it but more amperage flows through it. That is why car amps get hot (amperage makes heat) and home amps don't and can be built lighter for the power because of it (for class AB amps). It is more more efficient to use higher ohm load and higher voltage, easier on the equipment, but it used to be harder to multiply 12v up very high. Today mosfets are way better and can run much faster, amp power supplies get smaller, many old 80s amps have no mosfets at all. A regular transistor they use can not switch like a mosfet. Current amp PS switch much faster like 80Khz compared to your 60Hz home current. This allows them to be smaller, and the mosfets handle a lot of power each.


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