[punkaroo]

Folks!

I've been on this forum for years and never thought to spend time in this subforum! This has been a great resource and I've done a lot of reading. So, thank you for existing!

I'm technical with computers but much of what "audiophiles" discuss goes right over my head. This question is one that's bothered me for a LONG LONG TIME and here it is:

Folks will say stuff like:

"Orthodynamics/planars/insert-type-of-can-here are INEFFICIENT!!!! They need a strong/powerful amp to sound their absolute best!"

And then they'll even start suggesting hooking up said types of headphones to speaker terminals on vintage receivers or similar suggestions.

Can you please explain it to me as if I was 4 years old? Pictures are great too!

Seriously though, thank you in advance all.

 

[dazzerfong]

Ignoring the subjective aspects of source mixing and going straight to electrical engineering, it means low sensitivity. Ignore impedance for now as has nothing to do with 'efficiency': impedance only affects the ratio between current and voltage (which means something later in this explanation).

Efficiency is (usually*) rated in db/mW, or how loud it gets if you put in a certain amount of power. For most portable earphones/headphones, that number is usually greater than 100 dB, which means most of the time your source (laptop, amp, phone, etc.) will require less than 1 mW to actually power the headphones/earphones.

Then you have something like the Hifiman HE-6, which has a sensitivity of 83.5 dB. To get it to the some relative loudness as portable earphones/headphones, you need 100x the power. That's inefficient. Problem with inefficiency is that if your amp is 'maxed out', you'll get clipping which results in massively increased distortion.

You might be thinking '83.5 dB is already pretty loud! 1 mW isn't that much!', the problem is that it needs both higher voltage and current. Headphone amps are usually high voltage but low current: thus why the 'need' for speaker amps.

Good thing is that most things these days aren't nowhere near as inefficient. If something has a high impedance (like the Sennheiser HD-600/650), that means that it needs a lot more voltage than current compared to a low impedance headphone. Power, however, still remains the same.

* Sometimes it's in dB/V, which means how loud it'll get with respects to voltage. As voltage, power and current are all tangentially related by impedance, (V = IR), it doesn't really make much of a difference but just annoying to see because you need to do some maths to convert it. Looking at you Sennheiser!