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Old 11th September 2011, 12:46 AM   #1
epilot is offline epilot  United States
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Default 4 ohms/ 8 ohms speaker

Hello guys,

Just want to see what is the difference between a 4 ohms speaker and a 8 ohms speaker other than the double current draw for the 4 ohms speaker than the 8 ohms one?

What about the loudness? Is the sound loudness is much higher when using a 4 ohms speaker instead of a 8 ohms? If not why use a 4 ohms speaker which draws a double current than a 8 ohms one?

Thanks a bunch
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Old 11th September 2011, 02:04 AM   #2
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A 4 ohm speaker takes twice as much current for the same voltage so the amplifier must supply a lower voltage but twice the current.

For an 8 ohm speaker it needs more volts but half the current to get its rated output.
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Old 11th September 2011, 06:56 PM   #3
AndrewT is offline AndrewT  Scotland
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A 4ohm speaker should have the same efficiency as an 8ohm version of that speaker.
Both should have a sensitivity of XdB/W when measured by the same method.

There will be slight differences in the weights of the Voice Coils. This will have a slight effect on the relative efficiencies.

PA systems where dB is important to the audience, require dB more than almost other parameter bar intelligibility. Some installers forget this requirement.

To get big dBs it helps to use lower impedance speakers or to couple pairs of 8ohms speakers in parallel for more SPL.

I see no sensible reason to use 1, 2, 4, 6ohms drivers in any domestic listening speaker.
The 4ohms to 8ohms type should never be allowed, but that is a cost cutting exercise that the manufacturers jumped on. The combination of a 4ohm mid/bass and 8ohm treble driver allows the speaker to give a more balanced frequency response, without spending the appropriate costs to make a "good" speaker that will be suitable for 8ohm capable amplifiers.
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Old 12th September 2011, 02:05 AM   #4
epilot is offline epilot  United States
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Thanks for all inputs,

I just want to see what is difference between a 4 ohms and a 8 ohms speaker while using them on the same amplifier without changing any other thing (i.e the power supply voltage and so on)?
I am eager to see what is the difference regarding the output SOUND?
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Old 13th September 2011, 07:47 PM   #5
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Assuming you find two speakers that are absolutely equal except for the impedance you get
  • 3 dB more SPL for the same output voltage.
  • the same SPL for the same output power.
  • the same maximum SPL.
  • higher amplifier distortion for the same SPL.
  • double the heat dissipation for the same rail voltage.
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