4 ohms/ 8 ohms speaker

[dr.power]

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

 

[KeepItSimpleStupid]

The amp must be capable of driving 4 ohms. The amp is generally designed to specs such as 100 w/ch into 8 ohms both channels driven. It also could have specs for 4 ohms and sometimes even 2 ohms.

With R constant, you can see that P = I^2*R and I can limit the power output. P = (V^2)/R and in this case V^2 can limit the power. In reality, the smaller of the 2 limits power. The speaker doesn't have a constant Z of 8 or 4 ohms or whatever, so they may be designed for 6 ohms, but only for short periods.

One advantage in a car is because of the 12 V power supply with a huge current available. In bridge mode, you can effectively operate from a + and - 12 V supply, thus lowering the speaker Z has an advantage.

 

[Sceadwian]

It's more about amplifier design than anything inherently better about either type.
http://www.rocketroberts.com/techart/spkr.htm

Not just the large currents available KISS, but the low voltages. Home audio can easily use higher voltages so it's not problem which is why 8ohm speakers are more prevalent in home theater, with a car you're absolutely hard limited to 12V for a single channel and 24volt for bridged, home voltages could be anything you wanted.

 

[KeepItSimpleStupid]

Not just the large currents available KISS, but the low voltages

I basically said that I or V limits the power. V typically is the power supply and I can be the output devices or the power supply. In automotive, you essentially have a huge amount of current available to you at 12V or 24V in bridged mode without any fancy DC-DC converters, thus it's cheaper to use a lower Z speaker than to make an expensive DC-DC converter.

We can estimate the power using +-24V with 2 diode drops or 22.4 V p-p.

 

[Sceadwian]

A FET driver should hit closer to the rails. Nominal car voltage is 13.8 volts from the alternator, lightly loaded. That's why bass/peak hits in a car especially with large capacitors can be rated for so much power. The estimations work good for RMS power, but peak power does actually mean something.

 

[dr.power]

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?

 

[Sceadwian]

Depends on the amplifier, it has nothing to do with the speakers being 4 or 8 ohm just on the amplifiers design to drive it. Using 4 ohm speakers on an amplifier not designed for them will result in a burned out amplifier.

 

[carbonzit]

Let's put it this way: the difference in sound betwixt a 4-ohm and an 8-ohm speaker tested on the same amplifier is approximately equivalent to the difference in sound between using regular connecting cables and gold-plated ones.

In other words, pretty close to nada.

 

[dr.power]

Let's put it this way: the difference in sound betwixt a 4-ohm and an 8-ohm speaker tested on the same amplifier is approximately equivalent to the difference in sound between using regular connecting cables and gold-plated ones.

In other words, pretty close to nada.

What do you mean carbonzit?
If there is no difference between a 4 ohms speaker and an 8 ohms one regarding output sound loudness, then why using a lower impedance speaker and let it to draw more current than a higher impedance speaker?

 

[carbonzit]

What do you mean carbonzit?
If there is no difference between a 4 ohms speaker and an 8 ohms one regarding output sound loudness, then why using a lower impedance speaker and let it to draw more current than a higher impedance speaker?

Why, indeed? I think you just answered your own question there.

(And in English we say "why use a lower impedance speaker".)

 

[BrownOut]

What do you mean carbonzit?
If there is no difference between a 4 ohms speaker and an 8 ohms one regarding output sound loudness, then why using a lower impedance speaker and let it to draw more current than a higher impedance speaker?

Because an amplifier might not have enough output voltage to get the desired output power. For example, for a 12V system, the maximum output voltage is 12VP-P. So, for an 8-ohm speaker, the max P-P wattage is only (12)^2/8 = 18W. But for a 4 ohm speaker, we have (12)^2/4 = 36W. That's a nice gain. For other systems, you might have higher output voltage, so an 8 ohm speaker would be preferable.

 

[dr.power]

Thanks guys,
But I said I would like to see the effect of 4 ohms speaker's LOUDNESS than a 8 ohms one and vice versa when the amplifier specification like supply voltage are held constant for both loads.
?

 

[Nigel Goodwin]

Thanks guys,
But I said I would like to see the effect of 4 ohms speaker's LOUDNESS than a 8 ohms one and vice versa when the amplifier specification like supply voltage are held constant for both loads.
?

Assuming identical speakers in identical enclosures it will be noticably louder - actually giving twice the power.

While twice the power is supposed to be the minimum change you can notice, it certainly makes a BIG difference in practice.

As others have mentioned, it's all about available supply rails.