Good resource for understanding what makes headphones hard to drive?

[Blake Klondike]

I am sure this has been covered dozens of times on ASR, but what exactly makes headphones hard to drive? I listened to HD800s today through Oppo HA-2 and Fiio Q-5, and neither had enough power to drive them, even with hi-gain turned on. Does listening with anemic power have an effect on the sound quality or just volume? Thanks!

 

[solderdude]

what exactly makes headphones hard to drive?

There are only a handful of headphones that are 'hard to drive'.
There are a lot of headphones that are said to be hard to drive but in reality aren't.
It's just that some headphones require a higher maximum output voltage swing (gain related) than others.
Usually these are higher impedance headphones (> 150 Ohm)
These headphones have a low dB/V efficiency but because of their high impedance may well have a high dB/mW efficiency.
They thus require a higher voltage (and gain) to play loud and still sound good.

When an amp does not have enough gain or a too low max. output voltage for a particular headphone it will not go as loud as the owner wants or starts to sound less nice at too low levels.
This is the point where folks claim they are hard to drive.
They are not, they are just not using a suitable amp.

Then there are low impedance headphones which usually have a high dB/V efficiency, and thus require very little voltage to be driven quite loud.
Still here too there are some (usually inefficient planars) that have a low dB/mW efficiency and require the used amp to provide more current than what a device like a phone or dongle can provide.

When an amp is limited in their max output current capabilities for a particular headphone it will not go as loud as the owner wants or starts to sound less nice at too low levels.
This is the point where folks claim they are hard to drive.
They are not, they are just not using a suitable amp.

So whenever it appears or is said a headphone is hard to drive they are just using an amp that is not suited to drive those headphones.

Basically when you have a high impedance headphone your amp has to have a high power output rating at 300 Ohm.
With 'high' I mean > 100mW
When you have a low impedance headphone you need to look for an amplifier that has a high power output rating at 32 Ohm.
High can be >200mW (for some 20mW is already too high, these have a high dB/mW rating) to 2W or 3W (low dB/mW rating but high power rating)

So when you buy an amp that has a high power rating in 32 Ohm (and low gain option) and a high power rating (and higher gain option) you can drive any headphone you like.

This is where this table comes in handy when you want a certain (over- or on-ear) headphone and/or an amplifier and you want to find out if you can drive it properly.

 

[Blake Klondike]

There are only a handful of headphones that are 'hard to drive'.
There are a lot of headphones that are said to be hard to drive but in reality aren't.
It's just that some headphones require a higher maximum output voltage swing (gain related) than others.
Usually these are higher impedance headphones (> 150 Ohm)
These headphones have a low dB/V efficiency but because of their high impedance may well have a high dB/mW efficiency.
They thus require a higher voltage (and gain) to play loud and still sound good.

When an amp does not have enough gain or a too low max. output voltage for a particular headphone it will not go as loud as the owner wants or starts to sound less nice at too low levels.
This is the point where folks claim they are hard to drive.
They are not, they are just not using a suitable amp.

Then there are low impedance headphones which usually have a high dB/V efficiency, and thus require very little voltage to be driven quite loud.
Still here too there are some (usually inefficient planars) that have a low dB/mW efficiency and require the used amp to provide more current than what a device like a phone or dongle can provide.

When an amp is limited in their max output current capabilities for a particular headphone it will not go as loud as the owner wants or starts to sound less nice at too low levels.
This is the point where folks claim they are hard to drive.
They are not, they are just not using a suitable amp.

So whenever it appears or is said a headphone is hard to drive they are just using an amp that is not suited to drive those headphones.

Basically when you have a high impedance headphone your amp has to have a high power output rating at 300 Ohm.
With 'high' I mean > 100mW
When you have a low impedance headphone you need to look for an amplifier that has a high power output rating at 32 Ohm.
High can be >200mW (for some 20mW is already too high, these have a high dB/mW rating) to 2W or 3W (low dB/mW rating but high power rating)

So when you buy an amp that has a high power rating in 32 Ohm (and low gain option) and a high power rating (and higher gain option) you can drive any headphone you like.

This is where this table comes in handy when you want a certain (over- or on-ear) headphone and/or an amplifier and you want to find out if you can drive it properly.

Thanks so much! So what are the meaningful specs for the HD800 to match with an amp?

 

[solderdude]

Look at the HD800 and the 120dB values for power (in W). This will give you the minimum required power level of the amp.
With 120dB peaks you can play impressively loud at levels you can only endure for short moments.
The 105dB values (in mW) will give you the minimum required power levels for an amp if you want to play comfortable loud.

In the required voltage data you can see the required voltages to reach those levels.
Combined with knowledge of the DAC output you can calculate the needed gain.

So for HD800 to reach impressive levels and never run out of 'steam' in all circumstances your amp needs to reach 160mW (in 300 Ohm) and 5V
When your DAC can reach 2V you thus need about 2.5x gain (+8dB)
To reach comfortable loud levels you need merely 5 to 10mW in 300 Ohm and 1.5V (just over what a dongle can deliver) and have enough gain with 1x (0dB) gain setting.

This changes dramatically when you start using digital EQ (which is essential with HD800 IMO) in which case the gain needs to be 4 to 10dB higher.
This is something most folks do not realize and believe +6dB or +9dB gain settings are enough.
They end up with gear that cannot drive their headphones to full potential when using digital EQ.

 

[Blake Klondike]

This changes dramatically when you start using digital EQ (which is essential with HD800 IMO) in which case the gain needs to be 4 to 10dB higher.
This is something most folks do not realize and believe +6dB or +9dB gain settings are enough.
They end up with gear that cannot drive their headphones to full potential when using digital EQ.

Yes-- this was exactly my experience! Now the search begins for a portable DAC that measures well, and is suitable for the HD800s.