4 ohm vs 8 ohm advantages - AVS Forum
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post #1 of 14 Old 03-20-2010, 03:03 PM - Thread Starter
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lets assume both woofers or mids, or tweets are of the same company, but one in 4ohm and the other, 8ohm. what is the advantage of each? I know the 4ohm can take twice the power but at what cost?
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post #2 of 14 Old 03-20-2010, 03:30 PM
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No way to tell. The wire on the 8 ohm would probably be either thinner in which case it probably handles a tad less power, or perhaps its the same gauge just twice a long or thick and it handles more power or somewhere in between - Ohms alone don't really tell you much, gotta look at the entire package.

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post #3 of 14 Old 03-20-2010, 03:33 PM
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datranz,

that's not quite how it works.

the amplifier provides a voltage.

the lower resistance of the 4 ohm driver allows more current to flow through it.

this draws more power out of your amplifier and flows more power through the speaker.

if both your amplifier and speaker can take the increase in current, then you will get more spl out of your speaker.

many pro-audio amplifiers do not like to be bridged into a load less than 4ohms, so that is why you won't see many subwoofers with a less than 4 ohms rating that are meant for home or pro-use.

also, two 8 ohm drivers in parallel give a 4 ohm load, so if you want to parallel two drivers, the 8 ohm option may be the better choice.

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post #4 of 14 Old 03-20-2010, 05:25 PM
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Quote:
Originally Posted by datranz View Post

lets assume both woofers or mids, or tweets are of the same company, but one in 4ohm and the other, 8ohm. what is the advantage of each? I know the 4ohm can take twice the power but at what cost?

Assuming all other things are equal-the 4 ohm cannot take twice the power. It will produce a louder SPL for the same given input voltage-but the max output will be the same.

Let's say a 8 ohm loudspeaker will produce 100dB with a 2.83V input signal. Then the 4 ohm would produce 103dB with the same input voltage.

The 8 ohm would be pulling 1 watt and the 4 ohm would be pulling 2 watts.

But if the power handling is 100 watts, then the max SPL would be 120dB in either case.

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post #5 of 14 Old 03-21-2010, 05:58 AM
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Heh, years back I thought that a speaker of lower impedence (4 ohms vs 8 ohms) would consequently create less heat in the voice coil.

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post #6 of 14 Old 03-21-2010, 07:11 AM
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I picked the TD-15M 4 ohms for my build for the extra amplifier headroom. One difference would be the need for a thicker speaker cable using 4 ohm due to doubling the current?

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post #7 of 14 Old 03-21-2010, 07:57 AM
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Quote:
Originally Posted by DL86 View Post

I picked the TD-15M 4 ohms for my build for the extra amplifier headroom. One difference would be the need for a thicker speaker cable using 4 ohm due to doubling the current?

I use Roger Russel's guide to determine the gauge of speaker wire.

http://www.roger-russell.com/wire/wire.htm

scroll down to see the chart.

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post #8 of 14 Old 03-21-2010, 08:24 AM
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Power (Volts x Amps = Watts) dictates the gauge of the wire, not current alone. If you have an 8-ohm, 250 watt speaker, you would use the same cable for a 4-ohm, 250 watt speaker.

The main advantage of a 4 ohm speaker is that vs an 8 ohm it requires half the voltage swing for a given output power. Semiconductors with high current ratings are more reliable and cheaper to make than ones with high voltage ratings, that's why high power speakers are found in 4 ohm and 2 ohm versions only.

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post #9 of 14 Old 03-21-2010, 10:29 AM
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"that's why high power speakers are found in 4 ohm and 2 ohm versions only"

? most high power speakers that i have seen are 8ohm nominal.

are you talking about car audio subwoofers?

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post #10 of 14 Old 03-21-2010, 11:27 AM
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Quote:
Originally Posted by Th3_uN1Qu3 View Post

Power (Volts x Amps = Watts) dictates the gauge of the wire, not current alone. If you have an 8-ohm, 250 watt speaker, you would use the same cable for a 4-ohm, 250 watt speaker.

The main advantage of a 4 ohm speaker is that vs an 8 ohm it requires half the voltage swing for a given output power. Semiconductors with high current ratings are more reliable and cheaper to make than ones with high voltage ratings, that's why high power speakers are found in 4 ohm and 2 ohm versions only.

That funny-I have NEVER seen a loudspeaker cable rated for wattage. Maybe you can point out some?

If you want to keep everything equal-you DO need a larger gauge wire for a lower impedance load. That is because for an equal wattage-more current will be flowing throught he cable attached to the lower impedance load.

That extra current will result in more loss of signal AND a lower damping factor on the system.

Having a higher impedance is evidenced by several different types of systems. In audio the standard "70V" in which you hook a bunch of high impedance loudspeakers together. You don't have the losses across normal cable as you would using lower impedance loudspeakers.

Also in AC power distribution. By going to higher voltages and less current-the power company has less loss across the cable.

Also a 4 ohm DOES NOT require half the voltage swing. It requires 70.7% of the voltage that an 8 ohm loudspeaker does-for the same wattage.

For 100 watts a 4 ohm driver requires 20V. For an 8 ohm and 100 watts it is 28.28-NOT 40 volts.

Double the voltage is 6dB more-not 3.

Voltage (and distance) is 20 log x1/x2 while wattage is 10 log x1/x2.

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post #11 of 14 Old 06-02-2014, 12:29 PM
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After reviewing this discussion, I've come to the conclusion that we could all use a refresher course in elementary circuitry.tongue.gif
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post #12 of 14 Old 06-02-2014, 02:01 PM
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Being though the thread is over four years old, i think people have learned. Good job searching though and welcome to avs. biggrin.gif

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post #13 of 14 Old 10-10-2014, 12:53 PM
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most car audio amps rely on 0v to12v output swing to the speakers
using basic DC Power formula, 2 ohm speakers should give 72 watts output power, 4 ohm -> 36 watts, 8 ohm -> 18 watts, P = V^2 / R -> P = 144 / R
increasing volume knob will cause audio output clipping with 8 ohm speakers much sooner than 2 ohm speakers
if using car audio amp that has an internal DC to DC power supply to create higher amp voltages then clipping should not be a problem with any ohm speakers
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post #14 of 14 Old 10-10-2014, 01:39 PM
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I would have bet a years salary that the person who bumped a 4 month old post had a post count of less than 2 without even looking.

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