[flyte3333]

Hi all

Something I've never really understood and I was hoping someone can give a simple explanation (if one exists).

Why is that with speakers, 4 ohm speakers are considered harder to drive than 8 ohm speakers, i.e. with speakers, lower impedance is harder to drive

But with headphones 600 ohm headphones are considered harder to drive than 32 ohm headphones, i.e. with headphones, lower impedance is easier to drive

So why is it reversed between speakers and headphones?

Many thanks in advance

 

[flyte3333]

I know there are smart cookies out there that can explain this

 

[NorCal]

Why is that with speakers, 4 ohm speakers are considered harder to drive than 8 ohm speakers, i.e. with speakers, lower impedance is harder to drive

Most speaker amps will provide 2x the power to 4 ohms compared to 8 ohms, so to me, that's easier to drive.

The problem can be if the amp will fry when it sees a 2 ohm load, and you have two sets of 4 ohm speakers running in parallel, (like with an A speakers + B speakers switch). Many modern amps have protection circuits though.

 

[SilverEars]

Power is current times voltage. Speakers require much more power, and with such small ohmage, just means much much more current the amp has to supply to reach the required power. The lower the ohmage, more current required, which is taxing on the amp as scale of current passing through the amp is quite high.

So, speakers are not easier to drive, headphones are. Just compare the power requirements to drive a speaker to headphones.

Ohamge doesn't directly correlate to drivability. You can have high ohmage and require minimal power to reach 90dB. HE-6 is 50ohms, but 83dB/mW and ma6be even lower in reality, and people drive it off speaker taps. It's the hardest to drive headphone, but much lower than the Sennheisers in impedance.

 

[flyte3333]

The lower the ohmage, more current required

This part I get but the same applies to headphones, no?

Why then are 32ohm nominal impedance headphones considered easier to drive than 600ohm nominal impedance headphones? Here the higher ohmage headphones is considered harder to drive but with speakers the lower ohmage are considered harder to drive. It's reversed, in terms of higher/lower ohmage and easier/harder to drive.

I'm not understanding something obvious.

 

[flyte3333]

Ohamge doesn't directly correlate to drivability. You can have high ohmage and require minimal power to reach 90dB. HE-6 is 50ohms, but 83dB/mW and ma6be even lower in reality, and people drive it off speaker taps. It's the hardest to drive headphone, but much lower than the Sennheisers in impedance.

Fair point. I guess too often I read reviews that do link ohmage directly with drivability (both speakers and headphones) without mention of sensitivity/efficiency.

Seeing it written so often has probably shaped my misunderstanding a little. I see sensitivity/efficiency specs published more with speakers than headphones, so that doesn't help either.

 

[SilverEars]

This part I get but the same applies to headphones, no?

Why then are 32ohm nominal impedance headphones considered easier to drive than 600ohm nominal impedance headphones? Here the higher ohmage headphones is considered harder to drive but with speakers the lower ohmage are considered harder to drive. It's reversed, in terms of higher/lower ohmage and easier/harder to drive.

I'm not understanding something obvious.

Ultimately, depends on the efficiency of the headphone in dB/mW. How much power you put in, and as a result, how loud the driver outputs.

600 ohm may need much less power than 50ohms to get to the equivalent loudness, and between such disparity in ohmage, it's the level of current that differs.

 

[SilverEars]

Fair point. I guess too often I read reviews that do link ohmage directly with drivability (both speakers and headphones) without mention of sensitivity/efficiency.

Seeing it written so often has probably shaped my misunderstanding a little. I see sensitivity/efficiency specs published more with speakers than headphones, so that doesn't help either.

They probably just correlate bigger, the harder, which isn't true at all.

 

[flyte3333]

They probably just correlate bigger, the harder, which isn't true at all.

Yep for headphones review often correlate the bigger, the harder. But for speakers, the lower the harder.

But at least it's easier to find sensitivity/efficiency specs for speakers (usually), to get a better picture of drivability. I've found it less easy to find sensitivity specs for headphones unless you dig and someone has measured it. Or you're very lucky and the manufacturer has published it.

 

[SilverEars]

Just look at voltage being proportional to ohms, and current being inversely proportional to ohms and power is multiple of current and voltage.

All you need is two gradeschool level equations.

V=i × r

P = i × v

 

[flyte3333]

Just look at voltage being proportional to ohms, and current being inversely proportional to ohms and power is multiple of current and voltage.

All you need is two gradeschool level equations.

V=i × r

P = i × v

Of course but like you said, you really need the sensitivity/efficiency specs because these equations don't tell you the complete picture on drivability on their own.

 

[SilverEars]

Of course but like you said yourself, you really need the sensitivity/efficiency specs because these equations don't tell you the complete picture on drivability on their own.

But, these equations twlls you the relationships, which is fundamental.

 

[SilverEars]

For speakers, this equatiin should enlighten you.

p = i^2/r

 

[flyte3333]

But, these equations twlls you the relationships, which is fundamental.

Agreed and we are going in circles but I think the root cause of my misunderstanding is that, for so long in reviews I've read that for speakers lower ohmage means harder to drive and for headphones higher ohmage means harder to drive. This misunderstanding lead me to ask why is this generalisation reversed between headphones and speakes (in reviews anyway).

If one believes the above (like I've seen in so many reviews over the years) then the fundamental laws/equations start to become confusing - hence my opening post

But what's often missing with headphones data (I find) is efficiency/sensitivity. That helps to understand drivability more, just like is often provided with speakers.

 

[flyte3333]

For speakers, this equatiin should enlighten you.

p = i^2/r

I'm relatively new to headphones, so this formula made sense a long time ago to me, when I was only using speakers.

The confusion only started when I started getting into headphones and the ohmage/drivability was reversed in reviews I was reading - higher ohmage, harder to drive headphones. Hence my opening post asking for help hehe